self-hosted/postgis
self-hosted/postgis
1
0
Fork 0
mirror of https://git.osgeo.org/gitea/postgis/postgis synced 2024-10-24 09:02:37 +00:00
Code Issues Packages Projects Releases Wiki Activity
postgis/doc/postgis.xml
Sandro Santilli 43f510b410 Updated documentation for X,Y,M and Z 
git-svn-id: http://svn.osgeo.org/postgis/trunk@2095 b70326c6-7e19-0410-871a-916f4a2858ee
2005-11-29 09:00:00 +00:00

5576 lines
187 KiB
XML
Raw Blame History

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
<book>
<title>PostGIS Manual</title>
<bookinfo>
<editor>
<firstname>Paul</firstname>
<surname>Ramsey</surname>
<affiliation>
<orgname><ulink url="http://www.refractions.net">Refractions Research
Inc</ulink></orgname>
<address>
<street>Suite 400, 1207 Douglas Street</street>
<city>Victoria</city>
<state>British Columbia</state>
<country>Canada</country>
<email>pramsey@refractions.net</email>
</address>
</affiliation>
</editor>
<abstract>
<para>PostGIS is an extension to the PostgreSQL object-relational
database system which allows GIS (Geographic Information Systems)
objects to be stored in the database. PostGIS includes support for
GiST-based R-Tree spatial indexes, and functions for analysis and
processing of GIS objects.</para>
</abstract>
</bookinfo>
<chapter>
<title>Introduction</title>
<para>PostGIS is developed by Refractions Research Inc, as a spatial
database technology research project. Refractions is a GIS and database
consulting company in Victoria, British Columbia, Canada, specializing in
data integration and custom software development. We plan on supporting
and developing PostGIS to support a range of important GIS functionality,
including full OpenGIS support, advanced topological constructs
(coverages, surfaces, networks), desktop user interface tools for viewing
and editing GIS data, and web-based access tools.</para>
<sect1>
<title>Credits</title>
<variablelist>
<varlistentry>
<term>Sandro Santilli &lt;strk@refractions.net&gt;</term>
<listitem>
<para>Coordinates all bug fixing and maintainance effort,
integration of new GEOS functionality, and new function
enhancements.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Chris Hodgson &lt;chodgson@refractions.net&gt;</term>
<listitem>
<para>Maintains new functions and the 7.2 index bindings.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Paul Ramsey &lt;pramsey@refractions.net&gt;</term>
<listitem>
<para>Maintains the JDBC objects and keeps track of the
documentation and packaging.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Jeff Lounsbury &lt;jeffloun@refractions.net&gt;</term>
<listitem>
<para>Original development of the Shape file loader/dumper.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Dave Blasby &lt;dblasby@gmail.com&gt;</term>
<listitem>
<para>The original developer of PostGIS. Dave wrote the server
side objects, index bindings, and many of the server side
analytical functions.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Other contributors</term>
<listitem>
<para>
In alphabetical order:
Alex Bodnaru, Bernhard Reiter, Bruno Wolff III,
Carl Anderson, David Skea, David Techer,
IIDA Tetsushi, Geographic Data BC, Gerald Fenoy,
Gino Lucrezi, Klaus Foerster, Kris Jurka, Mark Cave-Ayland,
Mark Sondheim, Markus Schaber, Michael Fuhr, Nikita Shulga,
Norman Vine, Olivier Courtin, Ralph Mason, Steffen Macke.
</para>
</listitem>
</varlistentry>
</variablelist>
</sect1>
<sect1>
<title>More Information</title>
<itemizedlist>
<listitem>
<para>The latest software, documentation and news items are
available at the PostGIS web site, <ulink
url="http://postgis.refractions.net">http://postgis.refractions.net</ulink>.</para>
</listitem>
<listitem>
<para>More information about the GEOS geometry operations library is
available at<ulink url="http://geos.refractions.net">
http://geos.refractions.net</ulink>.</para>
</listitem>
<listitem>
<para>More information about the Proj4 reprojection library is
available at <ulink
url="http://www.remotesensing.org/proj">http://www.remotesensing.org/proj</ulink>.</para>
</listitem>
<listitem>
<para>More information about the PostgreSQL database server is
available at the PostgreSQL main site <ulink
url="http://www.postgresql.org">http://www.postgresql.org</ulink>.</para>
</listitem>
<listitem>
<para>More information about GiST indexing is available at the
PostgreSQL GiST development site, <ulink
url="http://www.sai.msu.su/~megera/postgres/gist">http://www.sai.msu.su/~megera/postgres/gist</ulink>.</para>
</listitem>
<listitem>
<para>More information about Mapserver internet map server is
available at <ulink
url="http://mapserver.gis.umn.edu/">http://mapserver.gis.umn.edu</ulink>.</para>
</listitem>
<listitem>
<para>The "<ulink
url="http://www.opengis.org/docs/99-049.pdf">Simple Features
for Specification for SQL</ulink>" is available at the OpenGIS
Consortium web site: <ulink
url="http://www.opengis.org">http://www.opengis.org</ulink>.</para>
</listitem>
</itemizedlist>
</sect1>
</chapter>
<chapter>
<title>Installation</title>
<sect1>
<title>Requirements</title>
<para>PostGIS has the following requirements for building and
usage:</para>
<itemizedlist>
<listitem>
<para>A complete configured and built PostgreSQL source code tree.
PostGIS uses definitions from the PostgreSQL configure/build process
to conform to the particular platform you are building on.
PostgreSQL is available from <ulink
url="http://www.postgresql.org">http://www.postgresql.org</ulink>.</para>
</listitem>
<listitem>
<para>GNU C compiler (<filename>gcc</filename>). Some other ANSI C
compilers can be used to compile PostGIS, but we find far fewer
problems when compiling with <filename>gcc</filename>.</para>
</listitem>
<listitem>
<para>GNU Make (<filename>gmake</filename> or
<filename>make</filename>). For many systems, GNU
<filename>make</filename> is the default version of make. Check the
version by invoking <filename>make -v</filename>. Other versions of
<filename>make</filename> may not process the PostGIS
<filename>Makefile</filename> properly.</para>
</listitem>
<listitem>
<para>(Recommended) Proj4 reprojection library. The Proj4 library is
used to provide coordinate reprojection support within PostGIS.
Proj4 is available for download from <ulink
url="http://www.remotesensing.org/proj">http://www.remotesensing.org/proj</ulink>.</para>
</listitem>
<listitem>
<para>(Recommended) GEOS geometry library. The GEOS library is used
to provide geometry tests (Touches(), Contains(), Intersects()) and
operations (Buffer(), GeomUnion(), Difference()) within PostGIS.
GEOS is available for download from <ulink
url="http://geos.refractions.net">http://geos.refractions.net</ulink>.</para>
</listitem>
</itemizedlist>
</sect1>
<sect1 id="PGInstall">
<title>PostGIS</title>
<para>The PostGIS module is a extension to the PostgreSQL backend
server. As such, PostGIS @@LAST_RELEASE_VERSION@@
<emphasis>requires</emphasis> a full copy of the PostgreSQL source tree
in order to compile. The PostgreSQL source code is available at <ulink
url="http://www.postgresql.org">http://www.postgresql.org</ulink>.</para>
<para>PostGIS @@LAST_RELEASE_VERSION@@ can be built against PostgreSQL
versions 7.2.0 to 7.4.x. Earlier versions of PostgreSQL are
<emphasis>not</emphasis> supported.</para>
<orderedlist>
<listitem>
<para>Before you can compile the PostGIS server modules, you must
compile and install the PostgreSQL package.</para>
<note>
<para>If you plan to use GEOS functionality you might need to
explicitly link PostgreSQL against the standard C++
library:</para>
<programlisting>LDFLAGS=-lstdc++ ./configure [YOUR OPTIONS HERE]</programlisting>
<para>This is a workaround for bogus C++ exceptions interaction
with older development tools. If you experience weird problems
(backend unexpectedly closed or similar things) try this trick.
This will require recompiling your PostgreSQL from scratch, of
course.</para>
</note>
</listitem>
<listitem>
<para>Retrieve the PostGIS source archive from <ulink
url="http://postgis.refractions.net/postgis-@@LAST_RELEASE_VERSION@@.tar.gz">http://postgis.refractions.net/postgis-@@LAST_RELEASE_VERSION@@.tar.gz</ulink>.
Uncompress and untar the archive in the "contrib" directory of the
PostgreSQL source tree.</para>
<programlisting># cd [postgresql source tree]/contrib
# gzip -d -c postgis-@@LAST_RELEASE_VERSION@@.tar.gz | tar xvf -</programlisting>
</listitem>
<listitem>
<para>Once your PostgreSQL installation is up-to-date, enter the
"postgis" directory, and edit the
<filename>Makefile.config</filename> file.</para>
<itemizedlist>
<listitem>
<para>If want support for coordinate reprojection you must have
the Proj4 library installed, set the <varname>USE_PROJ</varname>
variable to <emphasis>1</emphasis>, and adjust the
<varname>PROJ_DIR</varname> variable to point to your Proj4
installation directory.</para>
</listitem>
<listitem>
<para>If want to use GEOS functionality you must have the GEOS
library installed, set the <varname>USE_GEOS</varname> variable
to <emphasis>1</emphasis>, and adjust the
<varname>GEOS_DIR</varname> variable to point to your GEOS
installation directory.</para>
</listitem>
</itemizedlist>
</listitem>
<listitem>
<para>Run the compile and install commands.</para>
<programlisting># make
# make install</programlisting>
<para>All files are installed relative to the PostgreSQL install
directory, <filename>[prefix]</filename>.</para>
<itemizedlist>
<listitem>
<para>Libraries are installed
<filename>[prefix]/lib/contrib</filename>.</para>
</listitem>
<listitem>
<para>Important support files such as
<filename>lwpostgis.sql</filename> are installed in
<filename>[prefix]/share/contrib</filename>.</para>
</listitem>
<listitem>
<para>Loader and dumber binaries are installed in
<filename>[prefix]/bin</filename>.</para>
</listitem>
</itemizedlist>
</listitem>
<listitem>
<para>PostGIS requires the PL/pgSQL procedural language extension.
Before loading the <filename>lwpostgis.sql</filename> file, you must
first enable PL/pgSQL. You should use the
<filename>createlang</filename> command. The PostgreSQL
Programmer's Guide has the details if you want to this manually for
some reason.</para>
<programlisting># createlang plpgsql [yourdatabase]</programlisting>
</listitem>
<listitem>
<para>Now load the PostGIS object and function definitions into your
database by loading the <filename>lwpostgis.sql</filename> definitions
file.</para>
<programlisting># psql -d [yourdatabase] -f lwpostgis.sql</programlisting>
<para>The PostGIS server extensions are now loaded and ready to
use.</para>
</listitem>
<listitem>
<para>For a complete set of EPSG coordinate system definition
identifiers, you can also load the
<filename>spatial_ref_sys.sql</filename> definitions file and
populate the <varname>SPATIAL_REF_SYS</varname> table.</para>
<programlisting># psql -d [yourdatabase] -f spatial_ref_sys.sql</programlisting>
</listitem>
</orderedlist>
<sect2 id="upgrading">
<title>Upgrading</title>
<para>
Upgrading PostGIS can be tricky, because it is composed by both a shared
library and a set of definitions that are stored in the host database.
</para>
<para>
When the set of definitions changes (new objects, or procedural language
functions modifications) it is not always easy to have them replace the
old ones. Having a mismatch between definitions and implementations can
bring to an unstable or unsable system.
</para>
<para>
Since postgis version 0.9.0 You can check your installation state
using <link linkend="postgis_full_version">postgis_full_version()</link>.
The function will warn you with a "need proc upgrade" message if a mismatch
is found.
</para>
<para>
Before attempting to upgrade postgis, it is always worth to backup
your data. If you use the -Fc flag to pg_dump you will always be able
to restore the dump with an HARD UPGRADE.
</para>
<sect3 id="hard_upgrade">
<title>Hard upgrade</title>
<para>
By HARD UPGRADE we intend full dump/reload of postgis-enabled databases.
You need an HARD UPGRADE when postgis objects' internal storage
changes or when SOFT UPGRADE is not possible.
The <link linkend="release_notes">Release Notes</link> appendix reports for each version wheter you need a
dump/reload (HARD UPGRADE) to upgrade.
</para>
<para>
PostGIS provides an utility script to restore a dump
produced with the pg_dump -Fc command. It is experimental so redirecting
its output to a file will help in case of problems. The procedure is
as follow:
</para>
<programlisting>
# Create a "custom-format" dump of the database you want
# to upgrade (let's call it "olddb")
$ pg_dump -Fc olddb &gt; olddb.dump
# Restore the dump contextually upgrading postgis into
# a new database. The new database doesn't have to exist.
# Let's call it "newdb"
$ sh utils/postgis_restore.pl lwpostgis.sql newdb olddb.dump &gt; restore.log
# Check that all restored dump objects really had to be restored from dump
# and do not conflict with the ones defined in lwpostgis.sql
$ grep ^KEEPING restore.log | less
# If upgrading from PostgreSQL &lt; 7.5 to &gt;= 7.5 you might want to
# drop the attrelid, varattnum and stats columns in the geometry_columns
# table, which are no-more needed. Keeping them won't hurt.
# !!! DROPPING THEM WHEN REALLY NEEDED WILL DO HURT !!!!
$ psql newdb -c "ALTER TABLE geometry_columns DROP attrelid"
$ psql newdb -c "ALTER TABLE geometry_columns DROP varattnum"
$ psql newdb -c "ALTER TABLE geometry_columns DROP stats"
# spatial_ref_sys table is restore from the dump, to ensure your custom
# additions are kept, but the distributed one might contain modification
# so you should backup your entries, drop the table and source the new one.
# If you did make additions we assume you know how to backup them before
# upgrading the table. Replace of it with the new one is done like this:
$ psql newdb
newdb=&gt; delete from spatial_ref_sys;
DROP
newdb=&gt; \i spatial_ref_sys.sql
</programlisting>
</sect3>
<sect3 id="soft_upgrade">
<title>Soft upgrade</title>
<para>
By SOFT UPGRADE we intend a live replacement of objects definitions.
This is only possible in certain circumstances as not all objects
are replaceable in a live system.
</para>
<para>
To know wheter a SOFT UPGRADE should work for you refer to your new
version section in the <link linkend="release_notes">Release Notes</link>
appendix of this manual.
</para>
<para>
The <link linkend="postgis_full_version">postgis_full_version()</link>
function will also show you current state
and by that you should be able to find out wheter or not SOFT UPGRADE
will be possible. You should look at the DBPROC and RELPROC values.
DBPROC are the procedures stored in the database, RELPROC are the
procedures expected by the shared library (RELeased PROCedures).
Their values represent SCRIPTS versions. If they don't match the
function will warn you with a message: "needs proc upgrade".
</para>
<para>
Soft (proc) upgrade will only be possible when the DBPROC and RELPROC
versions share MAJOR and MINOR numbers. If this is the case you can
try to use the utils/postgis_proc_upgrade.pl script. Note that the
script will check for this itself so you should be safe attempting
w/out checking it manually. Here is how you do:
</para>
<programlisting>
$ make install # DON'T DO IT IF WITHOUT BACKING UP YOUR DATA !
$ utils/postgis_proc_upgrade.pl lwpostgis.sql | psql &lt;db&gt;
</programlisting>
</sect3>
<sect3 id="hack_upgrade">
<title>Old method</title>
<para>
Following is the "old" procedure description. IT SHOULD BE AVOIDED if possible,
as it will leave in the database many spurious functions. It is kept in this document
as a "backup" in case HARD UPGRADE or SOFT UPGRADE won't work for you:
</para>
<programlisting>
pg_dump -t "*" -f dumpfile.sql yourdatabase
dropdb yourdatabase
createdb yourdatabase
createlang plpgsql yourdatabase
psql -f lwpostgis.sql -d yourdatabase
psql -f dumpfile.sql -d yourdatabase
vacuumdb -z yourdatabase
</programlisting>
</sect3>
</sect2>
<sect2>
<title>Common Problems</title>
<para>There are several things to check when your installation or
upgrade doesn't go as you expected.</para>
<orderedlist>
<listitem>
<para>It is easiest if you untar the PostGIS distribution into the
contrib directory under the PostgreSQL source tree. However, if
this is not possible for some reason, you can set the
<varname>PGSQL_SRC</varname> environment variable to the path to
the PostgreSQL source directory. This will allow you to compile
PostGIS, but the <command>make install</command> may not work, so
be prepared to copy the PostGIS library and executable files to
the appropriate locations yourself.</para>
</listitem>
<listitem>
<para>Check that you you have installed PostgreSQL 7.2 or newer,
and that you are compiling against the same version of the
PostgreSQL source as the version of PostgreSQL that is running.
Mix-ups can occur when your (Linux) distrubution has already
installed PostgreSQL, or you have otherwise installed PostgreSQL
before and forgotten about it. PostGIS will only work with
PostgreSQL 7.2 or newer, and strange, unexpected error messages
will result if you use an older version. To check the version of
PostgreSQL which is running, connect to the database using psql
and run this query:</para>
<programlisting>SELECT version();</programlisting>
<para>If you are running an RPM based distribution, you can check
for the existence of pre-installed packages using the
<command>rpm</command> command as follows: <command>rpm -qa | grep
postgresql</command></para>
</listitem>
</orderedlist>
<para>Also check that you have made any necessary changes to the top
of the Makefile.config. This includes:</para>
<orderedlist>
<listitem>
<para>If you want to be able to do coordinate reprojections, you
must install the Proj4 library on your system, set the
<varname>USE_PROJ</varname> variable to 1 and the
<varname>PROJ_DIR</varname> to your installation prefix in the
Makefile.config.</para>
</listitem>
<listitem>
<para>If you want to be able to use GEOS functions you must
install the GEOS library on your system, and set the
<varname>USE_GEOS</varname> to 1 and the
<varname>GEOS_DIR</varname> to your installation prefix in the
Makefile.config</para>
</listitem>
</orderedlist>
</sect2>
</sect1>
<sect1>
<title>JDBC</title>
<para>The JDBC extensions provide Java objects corresponding to the
internal PostGIS types. These objects can be used to write Java clients
which query the PostGIS database and draw or do calculations on the GIS
data in PostGIS.</para>
<orderedlist>
<listitem>
<para>Enter the <filename>jdbc</filename> sub-directory of the
PostGIS distribution.</para>
</listitem>
<listitem>
<para>Edit the <filename>Makefile</filename> to provide the correct
paths of your java compiler (<varname>JAVAC</varname>) and
interpreter (<varname>JAVA</varname>).</para>
</listitem>
<listitem>
<para>Run the <filename>make</filename> command. Copy the
<filename>postgis.jar</filename> file to wherever you keep your java
libraries.</para>
</listitem>
</orderedlist>
</sect1>
<sect1>
<title>Loader/Dumper</title>
<para>The data loader and dumper are built and installed automatically
as part of the PostGIS build. To build and install them manually:</para>
<programlisting># cd postgis-@@LAST_RELEASE_VERSION@@/loader
# make
# make install</programlisting>
<para>The loader is called <filename>shp2pgsql</filename> and converts
ESRI Shape files into SQL suitable for loading in PostGIS/PostgreSQL.
The dumper is called <filename>pgsql2shp</filename> and converts PostGIS
tables (or queries) into ESRI Shape files.</para>
</sect1>
</chapter>
<chapter>
<title>Frequently Asked Questions</title>
<qandaset>
<qandaentry>
<question>
<para>What kind of geometric objects can I store?</para>
</question>
<answer>
<para>You can store point, line, polygon, multipoint, multiline,
multipolygon, and geometrycollections. These are specified in the
Open GIS Well Known Text Format (with XYZ,XYM,XYZM extentions).</para>
</answer>
</qandaentry>
<qandaentry>
<question>
<para>How do I insert a GIS object into the database?</para>
</question>
<answer>
<para>First, you need to create a table with a column of type
"geometry" to hold your GIS data. Connect to your database with
<filename>psql</filename> and try the following SQL:</para>
<programlisting>CREATE TABLE gtest ( ID int4, NAME varchar(20) );
SELECT AddGeometryColumn('', 'gtest','geom',-1,'LINESTRING',2);</programlisting>
<para>If the geometry column addition fails, you probably have not
loaded the PostGIS functions and objects into this database. See the
<link linkend="PGInstall">installation instructions</link>.</para>
<para>Then, you can insert a geometry into the table using a SQL
insert statement. The GIS object itself is formatted using the
OpenGIS Consortium "well-known text" format:</para>
<programlisting>INSERT INTO gtest (ID, NAME, GEOM) VALUES (1, 'First Geometry', GeomFromText('LINESTRING(2 3,4 5,6 5,7 8)', -1));</programlisting>
<para>For more information about other GIS objects, see the <link
linkend="RefObject">object reference</link>.</para>
<para>To view your GIS data in the table:</para>
<programlisting>SELECT id, name, AsText(geom) AS geom FROM gtest;</programlisting>
<para>The return value should look something like this:</para>
<programlisting> id | name | geom
----+----------------+-----------------------------
1 | First Geometry | LINESTRING(2 3,4 5,6 5,7 8)
(1 row)</programlisting>
</answer>
</qandaentry>
<qandaentry>
<question>
<para>How do I construct a spatial query?</para>
</question>
<answer>
<para>The same way you construct any other database query, as an SQL
combination of return values, functions, and boolean tests.</para>
<para>For spatial queries, there are two issues that are important
to keep in mind while constructing your query: is there a spatial
index you can make use of; and, are you doing expensive calculations
on a large number of geometries.</para>
<para>In general, you will want to use the "intersects operator"
(&amp;&amp;) which tests whether the bounding boxes of features
intersect. The reason the &amp;&amp; operator is useful is because
if a spatial index is available to speed up the test, the &amp;&amp;
operator will make use of this. This can make queries much much
faster.</para>
<para>You will also make use of spatial functions, such as
Distance(), Intersects(), Contains() and Within(), among others, to
narrow down the results of your search. Most spatial queries include
both an indexed test and a spatial function test. The index test
serves to limit the number of return tuples to only tuples that
<emphasis>might</emphasis> meet the condition of interest. The
spatial functions are then use to test the condition exactly.</para>
<programlisting>SELECT id, the_geom FROM thetable
WHERE
the_geom &amp;&amp; 'POLYGON((0 0, 0 10, 10 10, 10 0, 0 0))'
AND
Contains(the_geom,'POLYGON((0 0, 0 10, 10 10, 10 0, 0 0))';</programlisting>
</answer>
</qandaentry>
<qandaentry>
<question>
<para>How do I speed up spatial queries on large tables?</para>
</question>
<answer>
<para>Fast queries on large tables is the <emphasis>raison
d'etre</emphasis> of spatial databases (along with transaction
support) so having a good index is important.</para>
<para>To build a spatial index on a table with a
<varname>geometry</varname> column, use the "CREATE INDEX" function
as follows:</para>
<programlisting>CREATE INDEX [indexname] ON [tablename]
USING GIST ( [geometrycolumn] );</programlisting>
<para>The "USING GIST" option tells the server to use a GiST
(Generalized Search Tree) index.</para>
<note>
<para>
GiST indexes are assumed to be lossy.
Lossy indexes uses a proxy object (in the spatial case,
a bounding box) for building the index.</para>
</note>
<para>You should also ensure that the PostgreSQL query planner has
enough information about your index to make rational decisions about
when to use it. To do this, you have to "gather statistics" on your
geometry tables.</para>
<para>For PostgreSQL 8.0.x and greater, just run the <command>VACUUM
ANALYZE</command> command.</para>
<para>For PostgreSQL 7.4.x and below, run the <command>SELECT
UPDATE_GEOMETRY_STATS()</command> command.</para>
</answer>
</qandaentry>
<qandaentry>
<question>
<para>Why aren't PostgreSQL R-Tree indexes supported?</para>
</question>
<answer>
<para>Early versions of PostGIS used the PostgreSQL R-Tree indexes.
However, PostgreSQL R-Trees have been completely discarded since
version 0.6, and spatial indexing is provided with an
R-Tree-over-GiST scheme.</para>
<para>Our tests have shown search speed for native R-Tree and GiST
to be comparable. Native PostgreSQL R-Trees have two limitations
which make them undesirable for use with GIS features (note that
these limitations are due to the current PostgreSQL native R-Tree
implementation, not the R-Tree concept in general):</para>
<itemizedlist>
<listitem>
<para>R-Tree indexes in PostgreSQL cannot handle features which
are larger than 8K in size. GiST indexes can, using the "lossy"
trick of substituting the bounding box for the feature
itself.</para>
</listitem>
<listitem>
<para>R-Tree indexes in PostgreSQL are not "null safe", so
building an index on a geometry column which contains null
geometries will fail.</para>
</listitem>
</itemizedlist>
</answer>
</qandaentry>
<qandaentry>
<question>
<para>Why should I use the <varname>AddGeometryColumn()</varname>
function and all the other OpenGIS stuff?</para>
</question>
<answer>
<para>If you do not want to use the OpenGIS support functions, you
do not have to. Simply create tables as in older versions, defining
your geometry columns in the CREATE statement. All your geometries
will have SRIDs of -1, and the OpenGIS meta-data tables will
<emphasis>not</emphasis> be filled in properly. However, this will
cause most applications based on PostGIS to fail, and it is
generally suggested that you do use
<varname>AddGeometryColumn()</varname> to create geometry
tables.</para>
<para>Mapserver is one application which makes use of the
<varname>geometry_columns</varname> meta-data. Specifically,
Mapserver can use the SRID of the geometry column to do on-the-fly
reprojection of features into the correct map projection.</para>
</answer>
</qandaentry>
<qandaentry>
<question>
<para>What is the best way to find all objects within a radius of
another object?</para>
</question>
<answer>
<para>To use the database most efficiently, it is best to do radius
queries which combine the radius test with a bounding box test: the
bounding box test uses the spatial index, giving fast access to a
subset of data which the radius test is then applied to.</para>
<para>The <varname>Expand()</varname> function is a handy way of
enlarging a bounding box to allow an index search of a region of
interest. The combination of a fast access index clause and a slower
accurate distance test provides the best combination of speed and
precision for this query.</para>
<para>For example, to find all objects with 100 meters of POINT(1000
1000) the following query would work well:</para>
<programlisting>SELECT *
FROM GEOTABLE
WHERE
GEOCOLUMN &amp;&amp; Expand(GeomFromText('POINT(1000 1000)',-1),100)
AND
Distance(GeomFromText('POINT(1000 1000)',-1),GEOCOLUMN) &lt; 100;</programlisting>
</answer>
</qandaentry>
<qandaentry>
<question>
<para>How do I perform a coordinate reprojection as part of a
query?</para>
</question>
<answer>
<para>To perform a reprojection, both the source and destination
coordinate systems must be defined in the SPATIAL_REF_SYS table, and
the geometries being reprojected must already have an SRID set on
them. Once that is done, a reprojection is as simple as referring to
the desired destination SRID.</para>
<programlisting>SELECT Transform(GEOM,4269) FROM GEOTABLE;</programlisting>
</answer>
</qandaentry>
</qandaset>
</chapter>
<chapter>
<title>Using PostGIS</title>
<sect1 id="RefObject">
<title>GIS Objects</title>
<para>The GIS objects supported by PostGIS are a superset of
the "Simple Features" defined by the OpenGIS Consortium (OGC).
As of version 0.9, PostGIS supports all the objects and functions
specified in the OGC "Simple Features for SQL" specification.</para>
<para>PostGIS extends the standard with support for 3DZ,3DM and 4D
coordinates.</para>
<sect2>
<title>OpenGIS WKB and WKT</title>
<para>The OpenGIS specification defines two standard ways of
expressing spatial objects: the Well-Known Text (WKT) form and
the Well-Known Binary (WKB) form. Both WKT and WKB include
information about the type of the object and the
coordinates which form the object.</para>
<para>Examples of the text representations (WKT) of the spatial
objects of the features are as follows:</para>
<itemizedlist>
<listitem>
<para>POINT(0 0)</para>
</listitem>
<listitem>
<para>LINESTRING(0 0,1 1,1 2)</para>
</listitem>
<listitem>
<para>POLYGON((0 0,4 0,4 4,0 4,0 0),(1 1, 2 1, 2 2, 1 2,1 1))</para>
</listitem>
<listitem>
<para>MULTIPOINT(0 0,1 2)</para>
</listitem>
<listitem>
<para>MULTILINESTRING((0 0,1 1,1 2),(2 3,3 2,5 4))</para>
</listitem>
<listitem>
<para>MULTIPOLYGON(((0 0,4 0,4 4,0 4,0 0),(1 1,2 1,2 2,1 2,1 1)),
((-1 -1,-1 -2,-2 -2,-2 -1,-1 -1)))</para>
</listitem>
<listitem>
<para>GEOMETRYCOLLECTION(POINT(2 3),LINESTRING((2 3,3 4)))</para>
</listitem>
</itemizedlist>
<para>The OpenGIS specification also requires that the
internal storage format of spatial objects include a spatial
referencing system identifier (SRID). The SRID is required when
creating spatial objects for insertion into the database.</para>
<para>
Input/Output of these formats are available using the following
interfaces:
</para>
<programlisting>
bytea WKB = asBinary(geometry);
text WKT = asText(geometry);
geometry = GeomFromWKB(bytea WKB, SRID);
geometry = GeometryFromText(text WKT, SRID);
</programlisting>
<para> For example, a valid insert statement to create and insert an OGC spatial object would be:</para>
<programlisting>
INSERT INTO SPATIALTABLE (
THE_GEOM,
THE_NAME
)
VALUES (
GeomFromText('POINT(-126.4 45.32)', 312),
'A Place'
)</programlisting>
</sect2>
<sect2>
<title>PostGIS EWKB, EWKT and Canonical Forms</title>
<para>
OGC formats only support 2d geometries, and the associated SRID
is *never* embedded in the input/output representations.
</para>
<para>
Postgis extended formats are currently superset of OGC one (every
valid WKB/WKT is a valid EWKB/EWKT) but this might vary in the
future, specifically if OGC comes out with a new format conflicting
with our extensions. Thus you SHOULD NOT rely on this feature!
</para>
<para>
Postgis EWKB/EWKT add 3dm,3dz,4d coordinates support and embedded
SRID information.
</para>
<para>Examples of the text representations (EWKT) of the
extended spatial objects of the features are as follows:</para>
<itemizedlist>
<listitem>
<para>POINT(0 0 0) -- XYZ</para>
</listitem>
<listitem>
<para>SRID=32632;POINT(0 0) -- XY with SRID</para>
</listitem>
<listitem>
<para>POINTM(0 0 0) -- XYM</para>
</listitem>
<listitem>
<para>POINT(0 0 0 0) -- XYZM</para>
</listitem>
<listitem>
<para>SRID=4326;MULTIPOINTM(0 0 0,1 2 1) -- XYM with SRID</para>
</listitem>
<listitem>
<para>MULTILINESTRING((0 0 0,1 1 0,1 2 1),(2 3 1,3 2 1,5 4
1))</para>
</listitem>
<listitem>
<para>POLYGON((0 0 0,4 0 0,4 4 0,0 4 0,0 0 0),(1 1 0,2 1 0,2 2 0,1 2
0,1 1 0))</para>
</listitem>
<listitem>
<para>MULTIPOLYGON(((0 0 0,4 0 0,4 4 0,0 4 0,0 0 0),(1 1 0,2 1 0,2 2
0,1 2 0,1 1 0)),((-1 -1 0,-1 -2 0,-2 -2 0,-2 -1 0,-1 -1 0)))</para>
</listitem>
<listitem>
<para>GEOMETRYCOLLECTIONM(POINTM(2 3 9),LINESTRINGM((2 3 4,3 4
5)))</para>
</listitem>
</itemizedlist>
<para>
Input/Output of these formats are available using the following
interfaces:
</para>
<programlisting>
bytea EWKB = asEWKB(geometry);
text EWKT = asEWKT(geometry);
geometry = GeomFromEWKB(bytea EWKB);
geometry = GeomFromEWKT(text EWKT);
</programlisting>
<para>
For example, a valid insert statement to create and insert a PostGIS spatial object would be:
</para>
<programlisting>
INSERT INTO SPATIALTABLE (
THE_GEOM,
THE_NAME
)
VALUES (
GeomFromEWKT('SRID=312;POINTM(-126.4 45.32 15)'),
'A Place'
)</programlisting>
<para>
The "canonical forms" of a PostgreSQL type are the representations
you get with a simple query (without any function call) and the one
which is guaranteed to be accepted with a simple insert, update or
copy. For the postgis 'geometry' type these are:
<programlisting>
- Output -
binary: EWKB
ascii: HEXEWKB (EWKB in hex form)
- Input -
binary: EWKB
ascii: HEXEWKB|EWKT
</programlisting>
</para>
<para>
For example this statement reads EWKT and returns HEXEWKB in the
process of canonical ascii input/output:
</para>
<programlisting>
=# SELECT 'SRID=4;POINT(0 0)'::geometry;
geometry
----------------------------------------------------
01010000200400000000000000000000000000000000000000
(1 row)
</programlisting>
</sect2>
</sect1>
<sect1>
<title>Using OpenGIS Standards</title>
<para>The OpenGIS "Simple Features Specification for SQL" defines
standard GIS object types, the functions required to manipulate them,
and a set of meta-data tables. In order to ensure that meta-data remain
consistent, operations such as creating and removing a spatial column
are carried out through special procedures defined by OpenGIS.</para>
<para>There are two OpenGIS meta-data tables:
<varname>SPATIAL_REF_SYS</varname> and
<varname>GEOMETRY_COLUMNS</varname>. The
<varname>SPATIAL_REF_SYS</varname> table holds the numeric IDs and
textual descriptions of coordinate systems used in the spatial
database.</para>
<sect2>
<title>The SPATIAL_REF_SYS Table</title>
<para>The <varname>SPATIAL_REF_SYS</varname> table definition is as
follows:</para>
<programlisting>CREATE TABLE SPATIAL_REF_SYS (
SRID INTEGER NOT NULL PRIMARY KEY,
AUTH_NAME VARCHAR(256),
AUTH_SRID INTEGER,
SRTEXT VARCHAR(2048),
PROJ4TEXT VARCHAR(2048)
)</programlisting>
<para>The <varname>SPATIAL_REF_SYS</varname> columns are as
follows:</para>
<variablelist>
<varlistentry>
<term>SRID</term>
<listitem>
<para>An integer value that uniquely identifies the Spatial
Referencing System (SRS) within the database.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>AUTH_NAME</term>
<listitem>
<para>The name of the standard or standards body that is being
cited for this reference system. For example, "EPSG" would be a
valid <varname>AUTH_NAME</varname>.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>AUTH_SRID</term>
<listitem>
<para>The ID of the Spatial Reference System as defined by the
Authority cited in the <varname>AUTH_NAME</varname>. In the case
of EPSG, this is where the EPSG projection code would go.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>SRTEXT</term>
<listitem>
<para>The Well-Known Text representation of the Spatial
Reference System. An example of a WKT SRS representation
is:</para>
<programlisting>PROJCS["NAD83 / UTM Zone 10N",
GEOGCS["NAD83",
DATUM["North_American_Datum_1983",
SPHEROID["GRS 1980",6378137,298.257222101]
],
PRIMEM["Greenwich",0],
UNIT["degree",0.0174532925199433]
],
PROJECTION["Transverse_Mercator"],
PARAMETER["latitude_of_origin",0],
PARAMETER["central_meridian",-123],
PARAMETER["scale_factor",0.9996],
PARAMETER["false_easting",500000],
PARAMETER["false_northing",0],
UNIT["metre",1]
]</programlisting>
<para>For a listing of EPSG projection codes and their
corresponding WKT representations, see <ulink
url="http://www.opengis.org/techno/interop/EPSG2WKT.TXT">http://www.opengis.org/techno/interop/EPSG2WKT.TXT</ulink>.
For a discussion of WKT in general, see the OpenGIS "Coordinate
Transformation Services Implementation Specification" at <ulink
url="http://www.opengis.org/techno/specs.htm">http://www.opengis.org/techno/specs.htm</ulink>.
For information on the European Petroleum Survey Group (EPSG)
and their database of spatial reference systems, see <ulink
url="http://epsg.org">http://epsg.org</ulink>.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>PROJ4TEXT</term>
<listitem>
<para>PostGIS uses the Proj4 library to provide coordinate
transformation capabilities. The <varname>PROJ4TEXT</varname>
column contains the Proj4 coordinate definition string for a
particular SRID. For example:</para>
<programlisting>+proj=utm +zone=10 +ellps=clrk66 +datum=NAD27 +units=m</programlisting>
<para>For more information about, see the Proj4 web site at
<ulink
url="http://www.remotesensing.org/proj">http://www.remotesensing.org/proj</ulink>.
The <filename>spatial_ref_sys.sql</filename> file contains both
<varname>SRTEXT</varname> and <varname>PROJ4TEXT</varname>
definitions for all EPSG projections.</para>
</listitem>
</varlistentry>
</variablelist>
</sect2>
<sect2>
<title>The GEOMETRY_COLUMNS Table</title>
<para>The <varname>GEOMETRY_COLUMNS</varname> table definition is as
follows:</para>
<programlisting>CREATE TABLE GEOMETRY_COLUMNS (
F_TABLE_CATALOG VARCHAR(256) NOT NULL,
F_TABLE_SCHEMA VARCHAR(256) NOT NULL,
F_TABLE_NAME VARCHAR(256) NOT NULL,
F_GEOMETRY_COLUMN VARCHAR(256) NOT NULL,
COORD_DIMENSION INTEGER NOT NULL,
SRID INTEGER NOT NULL,
TYPE VARCHAR(30) NOT NULL
)</programlisting>
<para>The columns are as follows:</para>
<variablelist>
<varlistentry>
<term>F_TABLE_CATALOG, F_TABLE_SCHEMA, F_TABLE_NAME</term>
<listitem>
<para>The fully qualified name of the feature table containing
the geometry column. Note that the terms "catalog" and "schema"
are Oracle-ish. There is not PostgreSQL analogue of "catalog" so
that column is left blank -- for "schema" the PostgreSQL schema
name is used (<varname>public</varname> is the default).</para>
</listitem>
</varlistentry>
<varlistentry>
<term>F_GEOMETRY_COLUMN</term>
<listitem>
<para>The name of the geometry column in the feature
table.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>COORD_DIMENSION</term>
<listitem>
<para>The spatial dimension (2, 3 or 4 dimensional) of the
column.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>SRID</term>
<listitem>
<para>The ID of the spatial reference system used for the
coordinate geometry in this table. It is a foreign key reference
to the <varname>SPATIAL_REF_SYS</varname>.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>TYPE</term>
<listitem>
<para>The type of the spatial object. To restrict the spatial
column to a single type, use one of: POINT, LINESTRING, POLYGON,
MULTIPOINT, MULTILINESTRING, MULTIPOLYGON, GEOMETRYCOLLECTION or
corresponding XYM versions POINTM, LINESTRINGM, POLYGONM,
MULTIPOINTM, MULTILINESTRINGM, MULTIPOLYGONM, GEOMETRYCOLLECTIONM.
For heterogeneous (mixed-type) collections, you can use
"GEOMETRY" as the type.</para>
<note>
<para>This attribute is (probably) not part of the OpenGIS
specification, but is required for ensuring type
homogeneity.</para>
</note>
</listitem>
</varlistentry>
</variablelist>
</sect2>
<sect2>
<title>Creating a Spatial Table</title>
<para>Creating a table with spatial data is done in two stages:</para>
<itemizedlist>
<listitem>
<para>Create a normal non-spatial table.</para>
<para>For example: <command>CREATE TABLE ROADS_GEOM ( ID int4,
NAME varchar(25) )</command></para>
</listitem>
<listitem>
<para>Add a spatial column to the table using the OpenGIS
"AddGeometryColumn" function.</para>
<para>The syntax is:
<programlisting>AddGeometryColumn(&lt;schema_name&gt;, &lt;table_name&gt;,
&lt;column_name&gt;, &lt;srid&gt;, &lt;type&gt;,
&lt;dimension&gt;)</programlisting>
Or, using current schema:
<programlisting>AddGeometryColumn(&lt;table_name&gt;,
&lt;column_name&gt;, &lt;srid&gt;, &lt;type&gt;,
&lt;dimension&gt;)</programlisting>
</para>
<para>Example1: <command>SELECT AddGeometryColumn('public',
'roads_geom', 'geom', 423, 'LINESTRING', 2)</command></para>
<para>Example2: <command>SELECT AddGeometryColumn(
'roads_geom', 'geom', 423, 'LINESTRING', 2)</command></para>
</listitem>
</itemizedlist>
<para>Here is an example of SQL used to create a table and add a
spatial column (assuming that an SRID of 128
exists already):</para>
<programlisting>CREATE TABLE parks ( PARK_ID int4, PARK_NAME varchar(128), PARK_DATE date, PARK_TYPE varchar(2) );
SELECT AddGeometryColumn('parks', 'park_geom', 128, 'MULTIPOLYGON', 2 );</programlisting>
<para>Here is another example, using the generic "geometry" type and
the undefined SRID value of -1:</para>
<programlisting>CREATE TABLE roads ( ROAD_ID int4, ROAD_NAME varchar(128) );
SELECT AddGeometryColumn( 'roads', 'roads_geom', -1, 'GEOMETRY', 3 );</programlisting>
</sect2>
<sect2>
<title>Ensuring OpenGIS compliancy of geometries</title>
<para>Most of the functions implemented by the GEOS library
rely on the assumption that your geometries are valid
as specified by the OpenGIS Simple Feature Specification.
To check validity of geometries you can use the
<link linkend="IsValid">IsValid()</link> function:</para>
<programlisting>gisdb=# select isvalid('LINESTRING(0 0, 1 1)'), isvalid('LINESTRING(0 0,0 0)');
isvalid | isvalid
---------+---------
t | f</programlisting>
<para>By default, PostGIS does not apply this validity check on geometry input, because
testing for validity needs lots of CPU time for complex geometries, especially polygons.
If you do not trust your data sources, you can manually enforce such a check to your tables
by adding a check constraint:</para>
<programlisting>ALTER TABLE mytable ADD CONSTRAINT geometry_valid_check CHECK (isvalid(the_geom));</programlisting>
<para>If you encounter any strange error messages such as "GEOS Intersection() threw an
error!" or "JTS Intersection() threw an error!" when calling PostGIS functions with valid
input geometries, you likely found an error in either PostGIS or one of the libraries it
uses, and you should contact the PostGIS developers. The same is true if a PostGIS function returns
an invalid geometry for valid input.</para>
<note>
<para>
Strictly compliant OGC geometries cannot have Z or M values.
The <link linkend="IsValid">IsValid()</link> function won't
consider higher dimensioned geometries invalid! Invocations
of <link linkend="AddGeometryColumn">AddGeometryColumn()</link>
will add a constraint checking geometry dimensions, so it is
enough to specify 2 there.
</para>
</note>
</sect2>
</sect1>
<sect1>
<title>Loading GIS Data</title>
<para>Once you have created a spatial table, you are ready to upload GIS
data to the database. Currently, there are two ways to get data into a
PostGIS/PostgreSQL database: using formatted SQL statements or using the
Shape file loader/dumper.</para>
<sect2>
<title>Using SQL</title>
<para>If you can convert your data to a text representation, then
using formatted SQL might be the easiest way to get your data into
PostGIS. As with Oracle and other SQL databases, data can be bulk
loaded by piping a large text file full of SQL "INSERT" statements
into the SQL terminal monitor.</para>
<para>A data upload file (<filename>roads.sql</filename> for example)
might look like this:</para>
<programlisting>BEGIN;
INSERT INTO ROADS_GEOM (ID,GEOM,NAME ) VALUES (1,GeomFromText('LINESTRING(191232 243118,191108 243242)',-1),'Jeff Rd');
INSERT INTO ROADS_GEOM (ID,GEOM,NAME ) VALUES (2,GeomFromText('LINESTRING(189141 244158,189265 244817)',-1),'Geordie Rd');
INSERT INTO ROADS_GEOM (ID,GEOM,NAME ) VALUES (3,GeomFromText('LINESTRING(192783 228138,192612 229814)',-1),'Paul St');
INSERT INTO ROADS_GEOM (ID,GEOM,NAME ) VALUES (4,GeomFromText('LINESTRING(189412 252431,189631 259122)',-1),'Graeme Ave');
INSERT INTO ROADS_GEOM (ID,GEOM,NAME ) VALUES (5,GeomFromText('LINESTRING(190131 224148,190871 228134)',-1),'Phil Tce');
INSERT INTO ROADS_GEOM (ID,GEOM,NAME ) VALUES (6,GeomFromText('LINESTRING(198231 263418,198213 268322)',-1),'Dave Cres');
COMMIT;</programlisting>
<para>The data file can be piped into PostgreSQL very easily using the
"psql" SQL terminal monitor:</para>
<programlisting>psql -d [database] -f roads.sql</programlisting>
</sect2>
<sect2>
<title>Using the Loader</title>
<para>The <filename>shp2pgsql</filename> data loader converts ESRI
Shape files into SQL suitable for insertion into a PostGIS/PostgreSQL
database. The loader has several operating modes distinguished by
command line flags:</para>
<variablelist>
<varlistentry>
<term>-d</term>
<listitem>
<para>Drops the database table before creating a new table with
the data in the Shape file.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>-a</term>
<listitem>
<para>Appends data from the Shape file into the database table.
Note that to use this option to load multiple files, the files
must have the same attributes and same data types.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>-c</term>
<listitem>
<para>Creates a new table and populates it from the Shape file.
<emphasis>This is the default mode.</emphasis></para>
</listitem>
</varlistentry>
<varlistentry>
<term>-p</term>
<listitem>
<para>Only produces the table creation SQL code, without adding
any actual data. This can be used if you need to completely
separate the table creation and data loading steps.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>-D</term>
<listitem>
<para>Use the PostgreSQL "dump" format for the output data. This
can be combined with -a, -c and -d. It is much faster to load
than the default "insert" SQL format. Use this for very large data
sets.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>-s &lt;SRID&gt;</term>
<listitem>
<para>Creates and populates the geometry tables with the
specified SRID.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>-k</term>
<listitem>
<para>Keep idendifiers case (column, schema and attributes). Note that attributes in Shapefile are all UPPERCASE.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>-i</term>
<listitem>
<para>Coerce all integers to standard 32-bit integers, do not
create 64-bit bigints, even if the DBF header signature appears
to warrant it.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>-I</term>
<listitem>
<para>Create a GiST index on the geometry column.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>-w</term>
<listitem>
<para>
Output WKT format, for use with older (0.x) versions of PostGIS.
Note that this will introduce coordinate drifts and will drop M
values from shapefiles.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>-W &lt;encoding&gt;</term>
<listitem>
<para>
Specify encoding of the input data (dbf file).
When used, all attributes of the dbf are converted from the specified
encoding to UTF8. The resulting SQL output will contain a <code>SET
CLIENT_ENCODING to UTF8</code> command, so that the backend will be able
to reconvert from UTF8 to whatever encoding the database is configured
to use internally.
</para>
</listitem>
</varlistentry>
</variablelist>
<para>Note that -a, -c, -d and -p are mutually exclusive.</para>
<para>An example session using the loader to create an input file and
uploading it might look like this:</para>
<programlisting># shp2pgsql shaperoads myschema.roadstable &gt; roads.sql
# psql -d roadsdb -f roads.sql</programlisting>
<para>A conversion and upload can be done all in one step using UNIX
pipes:</para>
<programlisting># shp2pgsql shaperoads myschema.roadstable | psql -d roadsdb</programlisting>
</sect2>
</sect1>
<sect1>
<title>Retrieving GIS Data</title>
<para>Data can be extracted from the database using either SQL or the
Shape file loader/dumper. In the section on SQL we will discuss some of
the operators available to do comparisons and queries on spatial
tables.</para>
<sect2>
<title>Using SQL</title>
<para>The most straightforward means of pulling data out of the
database is to use a SQL select query and dump the resulting columns
into a parsable text file:</para>
<programlisting>db=# SELECT id, AsText(geom) AS geom, name FROM ROADS_GEOM;
id | geom | name
---+-----------------------------------------+-----------
1 | LINESTRING(191232 243118,191108 243242) | Jeff Rd
2 | LINESTRING(189141 244158,189265 244817) | Geordie Rd
3 | LINESTRING(192783 228138,192612 229814) | Paul St
4 | LINESTRING(189412 252431,189631 259122) | Graeme Ave
5 | LINESTRING(190131 224148,190871 228134) | Phil Tce
6 | LINESTRING(198231 263418,198213 268322) | Dave Cres
7 | LINESTRING(218421 284121,224123 241231) | Chris Way
(6 rows)</programlisting>
<para>However, there will be times when some kind of restriction is
necessary to cut down the number of fields returned. In the case of
attribute-based restrictions, just use the same SQL syntax as normal
with a non-spatial table. In the case of spatial restrictions, the
following operators are available/useful:</para>
<variablelist>
<varlistentry>
<term>&amp;&amp;</term>
<listitem>
<para>This operator tells whether the bounding box of one
geometry intersects the bounding box of another.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>~=</term>
<listitem>
<para>This operators tests whether two geometries are
geometrically identical. For example, if 'POLYGON((0 0,1 1,1 0,0
0))' is the same as 'POLYGON((0 0,1 1,1 0,0 0))' (it is).</para>
</listitem>
</varlistentry>
<varlistentry>
<term>=</term>
<listitem>
<para>This operator is a little more naive, it only tests
whether the bounding boxes of to geometries are the same.</para>
</listitem>
</varlistentry>
</variablelist>
<para>Next, you can use these operators in queries. Note that when
specifying geometries and boxes on the SQL command line, you must
explicitly turn the string representations into geometries by using
the "GeomFromText()" function. So, for example:</para>
<programlisting>SELECT
ID, NAME
FROM ROADS_GEOM
WHERE
GEOM ~= GeomFromText('LINESTRING(191232 243118,191108 243242)',-1);</programlisting>
<para>The above query would return the single record from the
"ROADS_GEOM" table in which the geometry was equal to that
value.</para>
<para>When using the "&amp;&amp;" operator, you can specify either a
BOX3D as the comparison feature or a GEOMETRY. When you specify a
GEOMETRY, however, its bounding box will be used for the
comparison.</para>
<programlisting>SELECT
ID, NAME
FROM ROADS_GEOM
WHERE
GEOM &amp;&amp; GeomFromText('POLYGON((191232 243117,191232 243119,191234 243117,191232 243117))',-1);</programlisting>
<para>The above query will use the bounding box of the polygon for
comparison purposes.</para>
<para>The most common spatial query will probably be a "frame-based"
query, used by client software, like data browsers and web mappers, to
grab a "map frame" worth of data for display. Using a "BOX3D" object
for the frame, such a query looks like this:</para>
<programlisting>SELECT
AsText(GEOM) AS GEOM
FROM ROADS_GEOM
WHERE
GEOM &amp;&amp; SetSRID('BOX3D(191232 243117,191232 243119)'::box3d,-1);</programlisting>
<para>Note the use of the SRID, to specify the projection of the
BOX3D. The value -1 is used to indicate no specified SRID.</para>
</sect2>
<sect2>
<title>Using the Dumper</title>
<para>The <filename>pgsql2shp</filename> table dumper connects
directly to the database and converts a table (possibly defined by
a query) into a shape file. The
basic syntax is:</para>
<programlisting>pgsql2shp [&lt;options&gt;] &lt;database&gt; [&lt;schema&gt;.]&lt;table&gt;</programlisting>
<programlisting>pgsql2shp [&lt;options&gt;] &lt;database&gt; &lt;query&gt;</programlisting>
<para>The commandline options are:</para>
<variablelist>
<varlistentry>
<term>-f &lt;filename&gt;</term>
<listitem>
<para>Write the output to a particular filename.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>-h &lt;host&gt;</term>
<listitem>
<para>The database host to connect to.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>-p &lt;port&gt;</term>
<listitem>
<para>The port to connect to on the database host.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>-P &lt;password&gt;</term>
<listitem>
<para>The password to use when connecting to the
database.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>-u &lt;user&gt;</term>
<listitem>
<para>The username to use when connecting to the
database.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>-g &lt;geometry column&gt;</term>
<listitem>
<para>In the case of tables with multiple geometry columns, the
geometry column to use when writing the shape file.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>-b</term>
<listitem>
<para>Use a binary cursor. This will make the operation faster,
but will not work if any NON-geometry attribute in the table
lacks a cast to text.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>-r</term>
<listitem>
<para>Raw mode. Do not drop the <varname>gid</varname> field, or
escape column names.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>-d</term>
<listitem>
<para>For backward compatibility: write a 3-dimensional shape
file when dumping from old (pre-1.0.0) postgis databases (the
default is to write a 2-dimensional shape file in that case).
Starting from postgis-1.0.0+, dimensions are fully encoded.
</para>
</listitem>
</varlistentry>
</variablelist>
</sect2>
</sect1>
<sect1>
<title>Building Indexes</title>
<para>Indexes are what make using a spatial database for large data sets
possible. Without indexing, any search for a feature would require a
"sequential scan" of every record in the database. Indexing speeds up
searching by organizing the data into a search tree which can be quickly
traversed to find a particular record. PostgreSQL supports three kinds
of indexes by default: B-Tree indexes, R-Tree indexes, and GiST
indexes.</para>
<itemizedlist>
<listitem>
<para>B-Trees are used for data which can be sorted along one axis;
for example, numbers, letters, dates. GIS data cannot be rationally
sorted along one axis (which is greater, (0,0) or (0,1) or (1,0)?)
so B-Tree indexing is of no use for us.</para>
</listitem>
<listitem>
<para>R-Trees break up data into rectangles, and sub-rectangles, and
sub-sub rectangles, etc. R-Trees are used by some spatial databases
to index GIS data, but the PostgreSQL R-Tree implementation is not
as robust as the GiST implementation.</para>
</listitem>
<listitem>
<para>GiST (Generalized Search Trees) indexes break up data into
"things to one side", "things which overlap", "things which are
inside" and can be used on a wide range of data-types, including GIS
data. PostGIS uses an R-Tree index implemented on top of GiST to
index GIS data.</para>
</listitem>
</itemizedlist>
<sect2>
<title>GiST Indexes</title>
<para>GiST stands for "Generalized Search Tree" and is a generic form
of indexing. In addition to GIS indexing, GiST is used to speed up
searches on all kinds of irregular data structures (integer arrays,
spectral data, etc) which are not amenable to normal B-Tree
indexing.</para>
<para>Once a GIS data table exceeds a few thousand rows, you will want
to build an index to speed up spatial searches of the data (unless all
your searches are based on attributes, in which case you'll want to
build a normal index on the attribute fields).</para>
<para>The syntax for building a GiST index on a "geometry" column is
as follows:</para>
<para><programlisting>CREATE INDEX [indexname] ON [tablename]
USING GIST ( [geometryfield] GIST_GEOMETRY_OPS ); </programlisting></para>
<para>Building a spatial index is a computationally intensive
exercise: on tables of around 1 million rows, on a 300MHz Solaris
machine, we have found building a GiST index takes about 1 hour. After
building an index, it is important to force PostgreSQL to collect
table statistics, which are used to optimize query plans:</para>
<para><programlisting>VACUUM ANALYZE [table_name] [column_name];
-- This is only needed for PostgreSQL 7.4 installations and below
SELECT UPDATE_GEOMETRY_STATS([table_name], [column_name]);</programlisting></para>
<para>GiST indexes have two advantages over R-Tree indexes in
PostgreSQL. Firstly, GiST indexes are "null safe", meaning they can
index columns which include null values. Secondly, GiST indexes
support the concept of "lossiness" which is important when dealing
with GIS objects larger than the PostgreSQL 8K page size. Lossiness
allows PostgreSQL to store only the "important" part of an object in
an index -- in the case of GIS objects, just the bounding box. GIS
objects larger than 8K will cause R-Tree indexes to fail in the
process of being built.</para>
</sect2>
<sect2>
<title>Using Indexes</title>
<para>Ordinarily, indexes invisibly speed up data access: once the
index is built, the query planner transparently decides when to use
index information to speed up a query plan. Unfortunately, the
PostgreSQL query planner does not optimize the use of GiST indexes
well, so sometimes searches which should use a spatial index instead
default to a sequence scan of the whole table.</para>
<para>If you find your spatial indexes are not being used (or your
attribute indexes, for that matter) there are a couple things you can
do:</para>
<itemizedlist>
<listitem>
<para>Firstly, make sure statistics are gathered about the number
and distributions of values in a table, to provide the query
planner with better information to make decisions around index
usage. For PostgreSQL 7.4 installations and below this is done by
running <command>update_geometry_stats([table_name,
column_name])</command> (compute distribution) and <command>VACUUM
ANALYZE [table_name] [column_name]</command> (compute number of
values). Starting with PostgreSQL 8.0 running <command>VACUUM
ANALYZE</command> will do both operations. You should regularly
vacuum your databases anyways -- many PostgreSQL DBAs have
<command>VACUUM</command> run as an off-peak cron job on a regular
basis.</para>
</listitem>
<listitem>
<para>If vacuuming does not work, you can force the planner to use
the index information by using the <command>SET
ENABLE_SEQSCAN=OFF</command> command. You should only use this
command sparingly, and only on spatially indexed queries:
generally speaking, the planner knows better than you do about
when to use normal B-Tree indexes. Once you have run your query,
you should consider setting <varname>ENABLE_SEQSCAN</varname> back
on, so that other queries will utilize the planner as
normal.</para>
<note>
<para>As of version 0.6, it should not be necessary to force the
planner to use the index with
<varname>ENABLE_SEQSCAN</varname>.</para>
</note>
</listitem>
<listitem>
<para>If you find the planner wrong about the cost of sequencial
vs index scans try reducing the value of random_page_cost in
postgresql.conf or using SET random_page_cost=#. Default value for
the parameter is 4, try setting it to 1 or 2. Decrementing the
value makes the planner more inclined of using Index scans.</para>
</listitem>
</itemizedlist>
</sect2>
</sect1>
<sect1>
<title>Complex Queries</title>
<para>The <emphasis>raison d'etre</emphasis> of spatial database
functionality is performing queries inside the database which would
ordinarily require desktop GIS functionality. Using PostGIS effectively
requires knowing what spatial functions are available, and ensuring that
appropriate indexes are in place to provide good performance.</para>
<sect2>
<title>Taking Advantage of Indexes</title>
<para>When constructing a query it is important to remember that only
the bounding-box-based operators such as &amp;&amp; can take advatage
of the GiST spatial index. Functions such as
<varname>distance()</varname> cannot use the index to optimize their
operation. For example, the following query would be quite slow on a
large table:</para>
<programlisting>SELECT the_geom FROM geom_table
WHERE distance( the_geom, GeomFromText( 'POINT(100000 200000)', -1 ) ) &lt; 100</programlisting>
<para>This query is selecting all the geometries in geom_table which
are within 100 units of the point (100000, 200000). It will be slow
because it is calculating the distance between each point in the table
and our specified point, ie. one <varname>distance()</varname>
calculation for each row in the table. We can avoid this by using the
&amp;&amp; operator to reduce the number of distance calculations
required:</para>
<programlisting>SELECT the_geom FROM geom_table
WHERE the_geom &amp;&amp; 'BOX3D(90900 190900, 100100 200100)'::box3d
AND distance( the_geom, GeomFromText( 'POINT(100000 200000)', -1 ) ) &lt; 100</programlisting>
<para>This query selects the same geometries, but it does it in a more
efficient way. Assuming there is a GiST index on the_geom, the query
planner will recognize that it can use the index to reduce the number
of rows before calculating the result of the
<varname>distance()</varname> function. Notice that the
<varname>BOX3D</varname> geometry which is used in the &amp;&amp;
operation is a 200 unit square box centered on the original point -
this is our "query box". The &amp;&amp; operator uses the index to
quickly reduce the result set down to only those geometries which have
bounding boxes that overlap the "query box". Assuming that our query
box is much smaller than the extents of the entire geometry table,
this will drastically reduce the number of distance calculations that
need to be done.</para>
</sect2>
<sect2>
<title>Examples of Spatial SQL</title>
<para>The examples in this section will make use of two tables, a
table of linear roads, and a table of polygonal municipality
boundaries. The table definitions for the <varname>bc_roads</varname>
table is:</para>
<programlisting> Column | Type | Description
------------+-------------------+-------------------
gid | integer | Unique ID
name | character varying | Road Name
the_geom | geometry | Location Geometry (Linestring)</programlisting>
<para>The table definition for the <varname>bc_municipality</varname>
table is:</para>
<programlisting> Column | Type | Description
-----------+-------------------+-------------------
gid | integer | Unique ID
code | integer | Unique ID
name | character varying | City / Town Name
the_geom | geometry | Location Geometry (Polygon)</programlisting>
<qandaset>
<qandadiv>
<qandaentry>
<question>
<para>What is the total length of all roads, expressed in
kilometers?</para>
</question>
<answer>
<para>You can answer this question with a very simple piece of
SQL:</para>
<programlisting>postgis=# SELECT sum(length(the_geom))/1000 AS km_roads FROM bc_roads;
km_roads
------------------
70842.1243039643
(1 row)</programlisting>
</answer>
</qandaentry>
<qandaentry>
<question>
<para>How large is the city of Prince George, in
hectares?</para>
</question>
<answer>
<para>This query combines an attribute condition (on the
municipality name) with a spatial calculation (of the
area):</para>
<programlisting>postgis=# SELECT area(the_geom)/10000 AS hectares FROM bc_municipality
WHERE name = 'PRINCE GEORGE';
hectares
------------------
32657.9103824927
(1 row) </programlisting>
</answer>
</qandaentry>
<qandaentry>
<question>
<para>What is the largest municipality in the province, by
area?</para>
</question>
<answer>
<para>This query brings a spatial measurement into the query
condition. There are several ways of approaching this problem,
but the most efficient is below:</para>
<programlisting>postgis=# SELECT name, area(the_geom)/10000 AS hectares
FROM bc_municipality
ORDER BY hectares DESC
LIMIT 1;
name | hectares
---------------+-----------------
TUMBLER RIDGE | 155020.02556131
(1 row)</programlisting>
<para>Note that in order to answer this query we have to
calculate the area of every polygon. If we were doing this a
lot it would make sense to add an area column to the table
that we could separately index for performance. By ordering
the results in a descending direction, and them using the
PostgreSQL "LIMIT" command we can easily pick off the largest
value without using an aggregate function like max().</para>
</answer>
</qandaentry>
<qandaentry>
<question>
<para>What is the length of roads fully contained within each
municipality?</para>
</question>
<answer>
<para>This is an example of a "spatial join", because we are
bringing together data from two tables (doing a join) but
using a spatial interaction condition ("contained") as the
join condition rather than the usual relational approach of
joining on a common key:</para>
<programlisting>postgis=# SELECT m.name, sum(length(r.the_geom))/1000 as roads_km
FROM bc_roads AS r,bc_municipality AS m
WHERE r.the_geom &amp;&amp; m.the_geom
AND contains(m.the_geom,r.the_geom)
GROUP BY m.name
ORDER BY roads_km;
name | roads_km
----------------------------+------------------
SURREY | 1539.47553551242
VANCOUVER | 1450.33093486576
LANGLEY DISTRICT | 833.793392535662
BURNABY | 773.769091404338
PRINCE GEORGE | 694.37554369147
...</programlisting>
<para>This query takes a while, because every road in the
table is summarized into the final result (about 250K roads
for our particular example table). For smaller overlays
(several thousand records on several hundred) the response can
be very fast.</para>
</answer>
</qandaentry>
<qandaentry>
<question>
<para>Create a new table with all the roads within the city of
Prince George.</para>
</question>
<answer>
<para>This is an example of an "overlay", which takes in two
tables and outputs a new table that consists of spatially
clipped or cut resultants. Unlike the "spatial join"
demonstrated above, this query actually creates new
geometries. An overlay is like a turbo-charged spatial join,
and is useful for more exact analysis work:</para>
<programlisting>postgis=# CREATE TABLE pg_roads as
SELECT intersection(r.the_geom, m.the_geom) AS intersection_geom,
length(r.the_geom) AS rd_orig_length,
r.*
FROM bc_roads AS r, bc_municipality AS m
WHERE r.the_geom &amp;&amp; m.the_geom
AND intersects(r.the_geom, m.the_geom)
AND m.name = 'PRINCE GEORGE';</programlisting>
</answer>
</qandaentry>
<qandaentry>
<question>
<para>What is the length in kilometers of "Douglas St" in
Victoria?</para>
</question>
<answer>
<programlisting>postgis=# SELECT sum(length(r.the_geom))/1000 AS kilometers
FROM bc_roads r, bc_municipality m
WHERE r.the_geom &amp;&amp; m.the_geom
AND r.name = 'Douglas St'
AND m.name = 'VICTORIA';
kilometers
------------------
4.89151904172838
(1 row)</programlisting>
</answer>
</qandaentry>
<qandaentry>
<question>
<para>What is the largest municipality polygon that has a
hole?</para>
</question>
<answer>
<programlisting>postgis=# SELECT gid, name, area(the_geom) AS area
FROM bc_municipality
WHERE nrings(the_geom) &gt; 1
ORDER BY area DESC LIMIT 1;
gid | name | area
-----+--------------+------------------
12 | SPALLUMCHEEN | 257374619.430216
(1 row)</programlisting>
</answer>
</qandaentry>
</qandadiv>
</qandaset>
</sect2>
</sect1>
<sect1>
<title>Using Mapserver</title>
<para>The Minnesota Mapserver is an internet web-mapping server which
conforms to the OpenGIS Web Mapping Server specification.</para>
<itemizedlist>
<listitem>
<para>The Mapserver homepage is at <ulink
url="http://mapserver.gis.umn.edu">http://mapserver.gis.umn.edu</ulink>.</para>
</listitem>
<listitem>
<para>The OpenGIS Web Map Specification is at <ulink
url="http://www.opengis.org/techno/specs/01-047r2.pdf">http://www.opengis.org/techno/specs/01-047r2.pdf</ulink>.</para>
</listitem>
</itemizedlist>
<sect2>
<title>Basic Usage</title>
<para>To use PostGIS with Mapserver, you will need to know about how
to configure Mapserver, which is beyond the scope of this
documentation. This section will cover specific PostGIS issues and
configuration details.</para>
<para>To use PostGIS with Mapserver, you will need:</para>
<itemizedlist>
<listitem>
<para>Version 0.6 or newer of PostGIS.</para>
</listitem>
<listitem>
<para>Version 3.5 or newer of Mapserver.</para>
</listitem>
</itemizedlist>
<para>Mapserver accesses PostGIS/PostgreSQL data like any other
PostgreSQL client -- using <filename>libpq</filename>. This means that
Mapserver can be installed on any machine with network access to the
PostGIS server, as long as the system has the
<filename>libpq</filename> PostgreSQL client libraries.</para>
<orderedlist>
<listitem>
<para>Compile and install Mapserver, with whatever options you
desire, including the "--with-postgis" configuration
option.</para>
</listitem>
<listitem>
<para>In your Mapserver map file, add a PostGIS layer. For
example:</para>
<programlisting>LAYER
CONNECTIONTYPE postgis
NAME "widehighways"
# Connect to a remote spatial database
CONNECTION "user=dbuser dbname=gisdatabase host=bigserver"
# Get the lines from the 'geom' column of the 'roads' table
DATA "geom from roads"
STATUS ON
TYPE LINE
# Of the lines in the extents, only render the wide highways
FILTER "type = 'highway' and numlanes &gt;= 4"
CLASS
# Make the superhighways brighter and 2 pixels wide
EXPRESSION ([numlanes] &gt;= 6)
COLOR 255 22 22
SYMBOL "solid"
SIZE 2
END
CLASS
# All the rest are darker and only 1 pixel wide
EXPRESSION ([numlanes] &lt; 6)
COLOR 205 92 82
END
END</programlisting>
<para>In the example above, the PostGIS-specific directives are as
follows:</para>
<variablelist>
<varlistentry>
<term>CONNECTIONTYPE</term>
<listitem>
<para>For PostGIS layers, this is always "postgis".</para>
</listitem>
</varlistentry>
<varlistentry>
<term>CONNECTION</term>
<listitem>
<para>The database connection is governed by the a
'connection string' which is a standard set of keys and
values like this (with the default values in
&lt;&gt;):</para>
<para>user=&lt;username&gt; password=&lt;password&gt;
dbname=&lt;username&gt; hostname=&lt;server&gt;
port=&lt;5432&gt;</para>
<para>An empty connection string is still valid, and any of
the key/value pairs can be omitted. At a minimum you will
generally supply the database name and username to connect
with.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>DATA</term>
<listitem>
<para>The form of this parameter is "&lt;column&gt; from
&lt;tablename&gt;" where the column is the spatial column to
be rendered to the map.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>FILTER</term>
<listitem>
<para>The filter must be a valid SQL string corresponding to
the logic normally following the "WHERE" keyword in a SQL
query. So, for example, to render only roads with 6 or more
lanes, use a filter of "num_lanes &gt;= 6".</para>
</listitem>
</varlistentry>
</variablelist>
</listitem>
<listitem>
<para>In your spatial database, ensure you have spatial (GiST)
indexes built for any the layers you will be drawing.</para>
<programlisting>CREATE INDEX [indexname]
ON [tablename]
USING GIST ( [geometrycolumn] GIST_GEOMETRY_OPS );</programlisting>
</listitem>
<listitem>
<para>If you will be querying your layers using Mapserver you will
also need an "oid index".</para>
<para>Mapserver requires unique identifiers for each spatial
record when doing queries, and the PostGIS module of Mapserver
uses the PostgreSQL <varname>oid</varname> value to provide these
unique identifiers. A side-effect of this is that in order to do
fast random access of records during queries, an index on the
<varname>oid</varname> is needed.</para>
<para>To build an "oid index", use the following SQL:</para>
<programlisting>CREATE INDEX [indexname] ON [tablename] ( oid );</programlisting>
</listitem>
</orderedlist>
</sect2>
<sect2>
<title>Frequently Asked Questions</title>
<qandaset>
<qandadiv>
<qandaentry>
<question>
<para>When I use an <varname>EXPRESSION</varname> in my map
file, the condition never returns as true, even though I know
the values exist in my table.</para>
</question>
<answer>
<para>Unlike shape files, PostGIS field names have to be
referenced in EXPRESSIONS using <emphasis>lower
case</emphasis>.</para>
<programlisting>EXPRESSION ([numlanes] &gt;= 6)</programlisting>
</answer>
</qandaentry>
<qandaentry>
<question>
<para>The FILTER I use for my Shape files is not working for
my PostGIS table of the same data.</para>
</question>
<answer>
<para>Unlike shape files, filters for PostGIS layers use SQL
syntax (they are appended to the SQL statement the PostGIS
connector generates for drawing layers in Mapserver).</para>
<programlisting>FILTER "type = 'highway' and numlanes &gt;= 4"</programlisting>
</answer>
</qandaentry>
<qandaentry>
<question>
<para>My PostGIS layer draws much slower than my Shape file
layer, is this normal?</para>
</question>
<answer>
<para>In general, expect PostGIS layers to be 10% slower than
equivalent Shape files layers, due to the extra overhead
involved in database connections, data transformations and
data transit between the database and Mapserver.</para>
<para>If you are finding substantial draw performance
problems, it is likely that you have not build a spatial index
on your table.</para>
<programlisting>postgis# CREATE INDEX geotable_gix ON geotable USING GIST ( geocolumn );
postgis# SELECT update_geometry_stats(); -- For PGSQL &lt; 8.0
postgis# VACUUM ANALYZE; -- For PGSQL &gt;= 8.0</programlisting>
</answer>
</qandaentry>
<qandaentry>
<question>
<para>My PostGIS layer draws fine, but queries are really
slow. What is wrong?</para>
</question>
<answer>
<para>For queries to be fast, you must have a unique key for
your spatial table and you must have an index on that unique
key.</para>
<para>You can specify what unique key for mapserver to use
with the <varname>USING UNIQUE</varname> clause in your
<varname>DATA</varname> line:</para>
<programlisting>DATA "the_geom FROM geotable USING UNIQUE gid"</programlisting>
<para>If your table does not have an explicit unique column,
you can "fake" a unique column by using the PostgreSQL row
"oid" for your unique column. "oid" is the default unique
column if you do not declare one, so enhancing your query
speed is a matter of building an index on your spatial table
oid value.</para>
<programlisting>postgis# CREATE INDEX geotable_oid_idx ON geotable (oid);</programlisting>
</answer>
</qandaentry>
</qandadiv>
</qandaset>
</sect2>
<sect2>
<title>Advanced Usage</title>
<para>The <varname>USING</varname> pseudo-SQL clause is used to add
some information to help mapserver understand the results of more
complex queries. More specifically, when either a view or a subselect
is used as the source table (the thing to the right of "FROM" in a
<varname>DATA</varname> definition) it is more difficult for mapserver
to automatically determine a unique identifier for each row and also
the SRID for the table. The <varname>USING</varname> clause can
provide mapserver with these two pieces of information as
follows:</para>
<programlisting>DATA "the_geom FROM (SELECT table1.the_geom AS the_geom, table1.oid AS oid, table2.data AS data
FROM table1 LEFT JOIN table2 ON table1.id = table2.id) AS new_table USING UNIQUE oid USING SRID=-1"</programlisting>
<variablelist>
<varlistentry>
<term>USING UNIQUE &lt;uniqueid&gt;</term>
<listitem>
<para>Mapserver requires a unique id for each row in order to
identify the row when doing map queries. Normally, it would use
the oid as the unique identifier, but views and subselects don't
automatically have an oid column. If you want to use Mapserver's
query functionality, you need to add a unique column to your
view or subselect, and declare it with <varname>USING
UNIQUE</varname>. For example, you could explicitly select one
of the table's oid values for this purpose, or any other column
which is guaranteed to be unique for the result set.</para>
<para>The <varname>USING</varname> statement can also be useful
even for simple <varname>DATA</varname> statements, if you are
doing map queries. It was previously recommended to add an index
on the oid column of tables used in query-able layers, in order
to speed up the performance of map queries. However, with the
<varname>USING</varname> clause, it is possible to tell
mapserver to use your table's primary key as the identifier for
map queries, and then it is no longer necessary to have an
additional index.</para>
<note>
<para>"Querying a Map" is the action of clicking on a map to
ask for information about the map features in that location.
Don't confuse "map queries" with the SQL query in a
<varname>DATA</varname> definition.</para>
</note>
</listitem>
</varlistentry>
<varlistentry>
<term>USING SRID=&lt;srid&gt;</term>
<listitem>
<para>PostGIS needs to know which spatial referencing system is
being used by the geometries in order to return the correct data
back to mapserver. Normally it is possible to find this
information in the "geometry_columns" table in the PostGIS
database, however, this is not possible for tables which are
created on the fly such as subselects and views. So the
<varname>USING SRID=</varname> option allows the correct SRID to
be specified in the <varname>DATA</varname> definition.</para>
</listitem>
</varlistentry>
</variablelist>
<warning>
<para>The parser for Mapserver PostGIS layers is fairly primitive,
and is case sensitive in a few areas. Be careful to ensure that all
SQL keywords and all your <varname>USING</varname> clauses are in
upper case, and that your <varname>USING UNIQUE</varname> clause
precedes your <varname>USING SRID</varname> clause.</para>
</warning>
</sect2>
<sect2>
<title>Examples</title>
<para>Lets start with a simple example and work our way up. Consider
the following Mapserver layer definition:</para>
<programlisting>LAYER
CONNECTIONTYPE postgis
NAME "roads"
CONNECTION "user=theuser password=thepass dbname=thedb host=theserver"
DATA "the_geom FROM roads"
STATUS ON
TYPE LINE
CLASS
COLOR 0 0 0
END
END</programlisting>
<para>This layer will display all the road geometries in the roads
table as black lines.</para>
<para>Now lets say we want to show only the highways until we get
zoomed in to at least a 1:100000 scale - the next two layers will
acheive this effect:</para>
<programlisting>LAYER
CONNECTION "user=theuser password=thepass dbname=thedb host=theserver"
DATA "the_geom FROM roads"
MINSCALE 100000
STATUS ON
TYPE LINE
FILTER "road_type = 'highway'"
CLASS
COLOR 0 0 0
END
END
LAYER
CONNECTION "user=theuser password=thepass dbname=thedb host=theserver"
DATA "the_geom FROM roads"
MAXSCALE 100000
STATUS ON
TYPE LINE
CLASSITEM road_type
CLASS
EXPRESSION "highway"
SIZE 2
COLOR 255 0 0
END
CLASS
COLOR 0 0 0
END
END</programlisting>
<para>The first layer is used when the scale is greater than 1:100000,
and displays only the roads of type "highway" as black lines. The
<varname>FILTER</varname> option causes only roads of type "highway"
to be displayed.</para>
<para>The second layer is used when the scale is less than 1:100000,
and will display highways as double-thick red lines, and other roads
as regular black lines.</para>
<para>So, we have done a couple of interesting things using only
mapserver functionality, but our <varname>DATA</varname> SQL statement
has remained simple. Suppose that the name of the road is stored in
another table (for whatever reason) and we need to do a join to get it
and label our roads.</para>
<programlisting>LAYER
CONNECTION "user=theuser password=thepass dbname=thedb host=theserver"
DATA "the_geom FROM (SELECT roads.oid AS oid, roads.the_geom AS the_geom, road_names.name as name
FROM roads LEFT JOIN road_names ON roads.road_name_id = road_names.road_name_id) AS named_roads
USING UNIQUE oid USING SRID=-1"
MAXSCALE 20000
STATUS ON
TYPE ANNOTATION
LABELITEM name
CLASS
LABEL
ANGLE auto
SIZE 8
COLOR 0 192 0
TYPE truetype
FONT arial
END
END
END</programlisting>
<para>This annotation layer adds green labels to all the roads when
the scale gets down to 1:20000 or less. It also demonstrates how to
use an SQL join in a <varname>DATA</varname> definition.</para>
</sect2>
</sect1>
<sect1>
<title>Java Clients (JDBC)</title>
<para>Java clients can access PostGIS "geometry" objects in the
PostgreSQL database either directly as text representations or using the
JDBC extension objects bundled with PostGIS. In order to use the
extension objects, the "postgis.jar" file must be in your CLASSPATH
along with the "postgresql.jar" JDBC driver package.</para>
<programlisting>import java.sql.*;
import java.util.*;
import java.lang.*;
import org.postgis.*;
public class JavaGIS {
public static void main(String[] args)
{
java.sql.Connection conn;
try
{
/*
* Load the JDBC driver and establish a connection.
*/
Class.forName("org.postgresql.Driver");
String url = "jdbc:postgresql://localhost:5432/database";
conn = DriverManager.getConnection(url, "postgres", "");
/*
* Add the geometry types to the connection. Note that you
* must cast the connection to the pgsql-specific connection * implementation before calling the addDataType() method.
*/
((org.postgresql.Connection)conn).addDataType("geometry","org.postgis.PGgeometry");
((org.postgresql.Connection)conn).addDataType("box3d","org.postgis.PGbox3d");
/*
* Create a statement and execute a select query.
*/
Statement s = conn.createStatement();
ResultSet r = s.executeQuery("select AsText(geom) as geom,id from geomtable");
while( r.next() )
{
/*
* Retrieve the geometry as an object then cast it to the geometry type.
* Print things out.
*/
PGgeometry geom = (PGgeometry)r.getObject(1);
int id = r.getInt(2);
System.out.println("Row " + id + ":");
System.out.println(geom.toString());
}
s.close();
conn.close();
}
catch( Exception e )
{
e.printStackTrace();
}
}
}</programlisting>
<para>The "PGgeometry" object is a wrapper object which contains a
specific topological geometry object (subclasses of the abstract class
"Geometry") depending on the type: Point, LineString, Polygon,
MultiPoint, MultiLineString, MultiPolygon.</para>
<programlisting>PGgeometry geom = (PGgeometry)r.getObject(1);
if( geom.getType() = Geometry.POLYGON )
{
Polygon pl = (Polygon)geom.getGeometry();
for( int r = 0; r &lt; pl.numRings(); r++ )
{
LinearRing rng = pl.getRing(r);
System.out.println("Ring: " + r);
for( int p = 0; p &lt; rng.numPoints(); p++ )
{
Point pt = rng.getPoint(p);
System.out.println("Point: " + p);
System.out.println(pt.toString());
}
}
}</programlisting>
<para>The JavaDoc for the extension objects provides a reference for the
various data accessor functions in the geometric objects.</para>
</sect1>
<sect1>
<title>C Clients (libpq)</title>
<para>...</para>
<sect2>
<title>Text Cursors</title>
<para>...</para>
</sect2>
<sect2>
<title>Binary Cursors</title>
<para>...</para>
</sect2>
</sect1>
</chapter>
<chapter> <title>Performance tips</title>
<sect1> <title>Small tables of large geometries</title>
<sect2><title>Problem description</title>
<para>
Current PostgreSQL versions (including 8.0) suffer from a query
optimizer weakness regarding TOAST tables. TOAST tables are a kind of
"extension room" used to store large (in the sense of data size) values
that do not fit into normal data pages (like long texts, images or
complex geometries with lots of vertices), see
http://www.postgresql.org/docs/8.0/static/storage-toast.html for more
information).
</para>
<para>
The problem appears if you happen to have a table with rather large
geometries, but not too much rows of them (like a table containing the
boundaries of all european countries in high resolution). Then the table
itsself is small, but it uses lots of TOAST space. In our example case,
the table itsself had about 80 rows and used only 3 data pages, but the
TOAST table used 8225 pages.
</para>
<para>
Now issue a query where you use the geometry operator &amp;&amp; to search for a
bounding box that matches only very few of those rows. Now the query
optimizer sees that the table has only 3 pages and 80 rows. He estimates
that a sequential scan on such a small table is much faster than using
an index. And so he decides to ignore the GIST index. Usually, this
estimation is correct. But in our case, the &amp;&amp; operator has to fetch
every geometry from disk to compare the bounding boxes, thus reading all
TOAST pages, too.
</para>
<para>
To see whether your suffer from this bug, use the "EXPLAIN ANALYZE"
postgresql command. For more information and the technical details, you
can read the thread on the postgres performance mailing list:
http://archives.postgresql.org/pgsql-performance/2005-02/msg00030.php
</para>
</sect2>
<sect2><title>Workarounds</title>
<para>
The PostgreSQL people are trying to solve this issue by making the query
estimation TOAST-aware. For now, here are two workarounds:
</para>
<para>
The first workaround is to force the query planner to use the index.
Send "SET enable_seqscan TO off;" to the server before issuing the
query. This basically forces the query planner to avoid sequential scans
whenever possible. So it uses the GIST index as usual. But this flag has
to be set on every connection, and it causes the query planner to make
misestimations in other cases, so you should "SET enable_seqscan TO on;"
after the query.
</para>
<para>
The second workaround is to make the sequential scan as fast as the
query planner thinks. This can be achieved by creating an additional
column that "caches" the bbox, and matching against this. In our
example, the commands are like:
</para>
<programlisting>
SELECT addGeometryColumn('myschema','mytable','bbox','4326','GEOMETRY','2');
UPDATE mytable set bbox = Envelope(Force_2d(the_geom));
</programlisting>
<para>
Now change your query to use the &amp;&amp; operator against bbox instead of
geom_column, like:
</para>
<programlisting>
SELECT geom_column FROM mytable WHERE bbox &amp;&amp; SetSrid('BOX3D(0 0,1 1)'::box3d,4326);
</programlisting>
<para>
Of yourse, if you change or add rows to mytable, you have to keep the
bbox "in sync". The most transparent way to do this would be triggers,
but you also can modify your application to keep the bbox column current
or run the UPDATE query above after every modification.
</para>
</sect2>
</sect1>
<sect1> <title>CLUSTERing on geometry indices</title>
<para>
For tables that are mostly read-only, and where a single index is used for the
majority of queries, PostgreSQL offers the CLUSTER command. This command
physically reorders all the data rows in the same order as the index criteria,
yielding two performance advantages: First, for index range scans, the number of
seeks on the data table is drastically reduced. Second, if your working set
concentrates to some small intervals on the indices, you have a more efficient
caching because the data rows are spread along fewer data pages. (Feel invited
to read the CLUSTER command documentation from the PostgreSQL manual at this
point.)
</para>
<para>
However, currently PostgreSQL does not allow clustering on PostGIS GIST indices
because GIST indices simply ignores NULL values, you get an error message like:
</para>
<programlisting>
lwgeom=# CLUSTER my_geom_index ON my_table;
ERROR: cannot cluster when index access method does not handle null values
HINT: You may be able to work around this by marking column "the_geom" NOT NULL.
</programlisting>
<para>
As the HINT message tells you, one can work around this deficiency by adding a
"not null" constraint to the table:
</para>
<programlisting>
lwgeom=# ALTER TABLE my_table ALTER COLUMN the_geom SET not null;
ALTER TABLE
</programlisting>
<para>
Of course, this will not work if you in fact need NULL values in your geometry
column. Additionally, you must use the above method to add the constraint, using
a CHECK constraint like "ALTER TABLE blubb ADD CHECK (geometry is not null);" will
not work.
</para>
</sect1>
<sect1><title>Avoiding dimension conversion</title>
<para>
Sometimes, you happen to have 3D or 4D data in your table, but always access
it using OpenGIS compliant asText() or asBinary() functions that only output
2D geometries. They do this by internally calling the force_2d() function,
which introduces a significant overhead for large geometries. To avoid this
overhead, it may be feasible to pre-drop those additional dimensions once and
forever:
</para>
<programlisting>
UPDATE mytable SET the_geom = force_2d(the_geom);
VACUUM FULL ANALYZE mytable;
</programlisting>
<para>
Note that if you added your geometry column using AddGeometryColumn()
there'll be a constraint on geometry dimension.
To bypass it you will need to drop the constraint.
Remember to update the entry in the geometry_columns table and
recreate the constraint afterwards.
</para>
<para>
In case of large tables, it may be wise to divide this UPDATE into smaller portions
by constraining the UPDATE to a part of the table via a WHERE clause and your
primary key or another feasible criteria, and running a simple "VACUUM;" between
your UPDATEs. This drastically reduces the need for temporary disk space.
Additionally, if you have mixed dimension geometries, restricting the UPDATE by "WHERE
dimension(the_geom)>2" skips re-writing of geometries that already are in 2D.
</para>
</sect1>
</chapter>
<chapter>
<title>PostGIS Reference</title>
<para>The functions given below are the ones which a user of PostGIS is
likely to need. There are other functions which are required support
functions to the PostGIS objects which are not of use to a general
user.</para>
<sect1>
<title>OpenGIS Functions</title>
<sect2>
<title>Management Functions</title>
<variablelist>
<varlistentry id="AddGeometryColumn">
<term>AddGeometryColumn(varchar, varchar, varchar, integer,
varchar, integer)</term>
<listitem>
<para>Syntax: AddGeometryColumn(&lt;schema_name&gt;,
&lt;table_name&gt;, &lt;column_name&gt;, &lt;srid&gt;,
&lt;type&gt;, &lt;dimension&gt;). Adds a geometry column to an
existing table of attributes. The <varname>schema_name</varname>
is the name of the table schema (unused for pre-schema
PostgreSQL installations). The <varname>srid</varname> must be
an integer value reference to an entry in the SPATIAL_REF_SYS
table. The <varname>type</varname> must be an uppercase string
corresponding to the geometry type, eg, 'POLYGON' or
'MULTILINESTRING'.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>DropGeometryColumn(varchar, varchar, varchar)</term>
<listitem>
<para>Syntax: DropGeometryColumn(&lt;schema_name&gt;,
&lt;table_name&gt;, &lt;column_name&gt;). Remove a geometry
column from a spatial table. Note that schema_name will need to
match the f_schema_name field of the table's row in the
geometry_columns table.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>SetSRID(geometry, integer)</term>
<listitem>
<para>Set the SRID on a geometry to a particular integer value.
Useful in constructing bounding boxes for queries.</para>
</listitem>
</varlistentry>
</variablelist>
</sect2>
<sect2>
<title>Geometry Relationship Functions</title>
<variablelist>
<varlistentry>
<term>Distance(geometry, geometry)</term>
<listitem>
<para>Return the cartesian distance between two geometries in
projected units.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Equals(geometry, geometry)</term>
<listitem>
<para>Returns 1 (TRUE) if the given Geometries are
"spatially equal". Use this for a 'better' answer than '='.
equals('LINESTRING(0 0, 10 10)','LINESTRING(0 0, 5 5, 10 10)')
is true.</para>
<para>Performed by the GEOS module</para>
<para>OGC SPEC s2.1.1.2</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Disjoint(geometry, geometry)</term>
<listitem>
<para>Returns 1 (TRUE) if the Geometries are "spatially disjoint".
</para>
<para>Performed by the GEOS module</para>
<para>Do not call with a GeometryCollection as an
argument</para>
<para>NOTE: this is the "allowable" version that returns a
boolean, not an integer.</para>
<para>OGC SPEC s2.1.1.2 //s2.1.13.3 - a.Relate(b,
'FF*FF****')</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Intersects(geometry, geometry)</term>
<listitem>
<para>Returns 1 (TRUE) if the Geometries "spatially intersect".
</para>
<para>Performed by the GEOS module</para>
<para>Do not call with a GeometryCollection as an
argument</para>
<para>NOTE: this is the "allowable" version that returns a
boolean, not an integer.</para>
<para>OGC SPEC s2.1.1.2 //s2.1.13.3 - Intersects(g1, g2 ) --&gt;
Not (Disjoint(g1, g2 ))</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Touches(geometry, geometry)</term>
<listitem>
<para>Returns 1 (TRUE) if the Geometries "spatially touch".
</para>
<para>Performed by the GEOS module</para>
<para>Do not call with a GeometryCollection as an
argument</para>
<para>NOTE: this is the "allowable" version that returns a
boolean, not an integer.</para>
<para>OGC SPEC s2.1.1.2 // s2.1.13.3- a.Touches(b) -&gt; (I(a)
intersection I(b) = {empty set} ) and (a intersection b) not
empty</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Crosses(geometry, geometry)</term>
<listitem>
<para>Returns 1 (TRUE) if the Geometries "spatially cross".
</para>
<para>Performed by the GEOS module</para>
<para>Do not call with a GeometryCollection as an
argument</para>
<para>NOTE: this is the "allowable" version that returns a
boolean, not an integer.</para>
<para>OGC SPEC s2.1.1.2 // s2.1.13.3 - a.Relate(b,
'T*T******')</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Within(geometry A, geometry B)</term>
<listitem>
<para>Returns 1 (TRUE) if Geometry A is "spatially within"
Geometry B.</para>
<para>Performed by the GEOS module</para>
<para>Do not call with a GeometryCollection as an
argument</para>
<para>NOTE: this is the "allowable" version that returns a
boolean, not an integer.</para>
<para>OGC SPEC s2.1.1.2 // s2.1.13.3 - a.Relate(b,
'T*F**F***')</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Overlaps(geometry, geometry)</term>
<listitem>
<para>Returns 1 (TRUE) if the Geometries "spatially
overlap".</para>
<para>Performed by the GEOS module</para>
<para>Do not call with a GeometryCollection as an
argument</para>
<para>NOTE: this is the "allowable" version that returns a
boolean, not an integer.</para>
<para>OGC SPEC s2.1.1.2 // s2.1.13.3</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Contains(geometry A, geometry B)</term>
<listitem>
<para>Returns 1 (TRUE) if Geometry A "spatially contains"
Geometry B.</para>
<para>Performed by the GEOS module</para>
<para>Do not call with a GeometryCollection as an
argument</para>
<para>NOTE: this is the "allowable" version that returns a
boolean, not an integer.</para>
<para>OGC SPEC s2.1.1.2 // s2.1.13.3 - same as
within(geometry B, geometry A)</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Intersects(geometry, geometry)</term>
<listitem>
<para>Returns 1 (TRUE) if the Geometries "spatially
intersect".</para>
<para>Performed by the GEOS module</para>
<para>Do not call with a GeometryCollection as an
argument</para>
<para>NOTE: this is the "allowable" version that returns a
boolean, not an integer.</para>
<para>OGC SPEC s2.1.1.2 // s2.1.13.3 - NOT
disjoint(geometry, geometry)</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Relate(geometry, geometry, intersectionPatternMatrix)</term>
<listitem>
<para>Returns 1 (TRUE) if this Geometry is spatially related to
anotherGeometry, by testing for intersections between the
Interior, Boundary and Exterior of the two geometries as
specified by the values in the intersectionPatternMatrix.</para>
<para>Performed by the GEOS module</para>
<para>Do not call with a GeometryCollection as an
argument</para>
<para>NOTE: this is the "allowable" version that returns a
boolean, not an integer.</para>
<para>OGC SPEC s2.1.1.2 // s2.1.13.3</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Relate(geometry, geometry)</term>
<listitem>
<para>returns the DE-9IM (dimensionally extended
nine-intersection matrix)</para>
<para>Performed by the GEOS module</para>
<para>Do not call with a GeometryCollection as an
argument</para>
<para>not in OGC spec, but implied. see s2.1.13.2</para>
</listitem>
</varlistentry>
</variablelist>
</sect2>
<sect2>
<title>Geometry Processing Functions</title>
<variablelist>
<varlistentry>
<term>Centroid(geometry)</term>
<listitem>
<para>Returns the centroid of the geometry as a point.</para>
<para>Computation will be more accurate if performed by the GEOS
module (enabled at compile time).</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Area(geometry)</term>
<listitem>
<para>Returns the area of the geometry if it is a polygon or
multi-polygon. </para>
</listitem>
</varlistentry>
<varlistentry>
<term>Length(geometry)</term>
<listitem>
<para>The length of this Curve in its associated spatial
reference.</para>
<para>synonym for length2d()</para>
<para>OGC SPEC 2.1.5.1</para>
</listitem>
</varlistentry>
<varlistentry>
<term>PointOnSurface(geometry)</term>
<listitem>
<para>Return a Point guaranteed to lie on the surface</para>
<para>Implemented using GEOS</para>
<para>OGC SPEC 3.2.14.2 and 3.2.18.2 -</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Boundary(geometry)</term>
<listitem>
<para>Returns the closure of the combinatorial boundary of this
Geometry. The combinatorial boundary is defined as described in
section 3.12.3.2 of the OGC SPEC. Because the result of this
function is a closure, and hence topologically closed, the
resulting boundary can be represented using representational
geometry primitives as discussed in the OGC SPEC, section
3.12.2.</para>
<para>Performed by the GEOS module</para>
<para>OGC SPEC s2.1.1.1</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Buffer(geometry, double, [integer])</term>
<listitem>
<para>Returns a geometry that represents all points whose
distance from this Geometry is less than or equal to distance.
Calculations are in the Spatial Reference System of this
Geometry. The optional third parameter sets the
number of segment used to approximate a quarter circle
(defaults to 8).</para>
<para>Performed by the GEOS module</para>
<para>Do not call with a GeometryCollection as an
argument</para>
<para>OGC SPEC s2.1.1.3</para>
</listitem>
</varlistentry>
<varlistentry>
<term>ConvexHull(geometry)</term>
<listitem>
<para>Returns a geometry that represents the convex hull of this
Geometry.</para>
<para>Performed by the GEOS module</para>
<para>OGC SPEC s2.1.1.3</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Intersection(geometry, geometry)</term>
<listitem>
<para>Returns a geometry that represents the point set
intersection of the Geometies.</para>
<para>Performed by the GEOS module</para>
<para>Do not call with a GeometryCollection as an
argument</para>
<para>OGC SPEC s2.1.1.3</para>
</listitem>
</varlistentry>
<varlistentry>
<term>SymDifference(geometry A, geometry B)</term>
<listitem>
<para>Returns a geometry that represents the point set symmetric
difference of Geometry A with Geometry B.</para>
<para>Performed by the GEOS module</para>
<para>Do not call with a GeometryCollection as an
argument</para>
<para>OGC SPEC s2.1.1.3</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Difference(geometry A, geometry B)</term>
<listitem>
<para>Returns a geometry that represents the point set symmetric
difference of Geometry A with Geometry B.</para>
<para>Performed by the GEOS module</para>
<para>Do not call with a GeometryCollection as an
argument</para>
<para>OGC SPEC s2.1.1.3</para>
</listitem>
</varlistentry>
<varlistentry>
<term>GeomUnion(geometry, geometry)</term>
<listitem>
<para>Returns a geometry that represents the point set union of
the Geometries.</para>
<para>Performed by the GEOS module</para>
<para>Do not call with a GeometryCollection as an
argument</para>
<para>NOTE: this is renamed from "union" because union is an SQL
reserved word</para>
<para>OGC SPEC s2.1.1.3</para>
</listitem>
</varlistentry>
<varlistentry>
<term>GeomUnion(geometry set)</term>
<listitem>
<para>Returns a geometry that represents the point set union of
this all Geometries in given set.</para>
<para>Performed by the GEOS module</para>
<para>Do not call with a GeometryCollection in the argument
set</para>
<para>Not explicitly defined in OGC SPEC</para>
</listitem>
</varlistentry>
<varlistentry>
<term>MemGeomUnion(geometry set)</term>
<listitem>
<para>Same as the above, only memory-friendly (uses less memory
and more processor time).</para>
</listitem>
</varlistentry>
</variablelist>
</sect2>
<sect2>
<title>Geometry Accessors</title>
<variablelist>
<varlistentry>
<term>AsText(geometry)</term>
<listitem>
<para>Return the Well-Known Text representation of the geometry.
For example: POLYGON(0 0,0 1,1 1,1 0,0 0)</para>
<para>OGC SPEC s2.1.1.1</para>
</listitem>
</varlistentry>
<varlistentry>
<term>AsBinary(geometry)</term>
<listitem>
<para>Returns the geometry in the OGC "well-known-binary"
format, using the endian encoding of the server on which the
database is running. This is useful in binary cursors to pull
data out of the database without converting it to a string
representation.</para>
<para>OGC SPEC s2.1.1.1 - also see
asBinary(&lt;geometry&gt;,'XDR') and
asBinary(&lt;geometry&gt;,'NDR')</para>
</listitem>
</varlistentry>
<varlistentry>
<term>SRID(geometry)</term>
<listitem>
<para>Returns the integer SRID number of the spatial reference
system of the geometry.</para>
<para>OGC SPEC s2.1.1.1</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Dimension(geometry)</term>
<listitem>
<para>The inherent dimension of this Geometry object, which must
be less than or equal to the coordinate dimension. OGC SPEC
s2.1.1.1 - returns 0 for points, 1 for lines, 2 for polygons,
and the largest dimension of the components of a
GEOMETRYCOLLECTION.</para>
<programlisting>select dimension('GEOMETRYCOLLECTION(LINESTRING(1 1,0 0),POINT(0 0)');
dimension
-----------
1</programlisting>
</listitem>
</varlistentry>
<varlistentry>
<term>Envelope(geometry)</term>
<listitem>
<para>Returns a POLYGON representing the bounding box of the
geometry.</para>
<para>OGC SPEC s2.1.1.1 - The minimum bounding box for this
Geometry, returned as a Geometry. The polygon is defined by the
corner points of the bounding box ((MINX, MINY), (MAXX, MINY),
(MAXX, MAXY), (MINX, MAXY), (MINX, MINY)).</para>
<para>NOTE:PostGIS will add a Zmin/Zmax coordinate as
well.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>IsEmpty(geometry)</term>
<listitem>
<para>Returns 1 (TRUE) if this Geometry is the empty geometry .
If true, then this Geometry represents the empty point set -
i.e. GEOMETRYCOLLECTION(EMPTY).</para>
<para>OGC SPEC s2.1.1.1</para>
</listitem>
</varlistentry>
<varlistentry id="IsSimple">
<term>IsSimple(geometry)</term>
<listitem>
<para>Returns 1 (TRUE) if this Geometry has no anomalous
geometric points, such as self intersection or self
tangency.</para>
<para>Performed by the GEOS module</para>
<para>OGC SPEC s2.1.1.1</para>
</listitem>
</varlistentry>
<varlistentry id="IsClosed">
<term>IsClosed(geometry)</term>
<listitem>
<para>Returns true of the geometry start and end points are
coincident.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>IsRing(geometry)</term>
<listitem>
<para>Returns 1 (TRUE) if this Curve is closed (StartPoint ( ) =
EndPoint ( )) and this Curve is simple (does not pass through
the same point more than once).</para>
<para>performed by GEOS</para>
<para>OGC spec 2.1.5.1</para>
</listitem>
</varlistentry>
<varlistentry>
<term>NumGeometries(geometry)</term>
<listitem>
<para>If geometry is a GEOMETRYCOLLECTION (or MULTI*) return the
number of geometries, otherwise return NULL.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>GeometryN(geometry,int)</term>
<listitem>
<para>Return the N'th geometry if the geometry is a
GEOMETRYCOLLECTION, MULTIPOINT, MULTILINESTRING or MULTIPOLYGON.
Otherwise, return NULL.</para>
<note> <para>
Index is 1-based as for OGC specs since version 0.8.0.
Previous versions implemented this as 0-based instead.
</para></note>
</listitem>
</varlistentry>
<varlistentry>
<term>NumPoints(geometry)</term>
<listitem>
<para>Find and return the number of points in the first
linestring in the geometry. Return NULL if there is no
linestring in the geometry.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>PointN(geometry,integer)</term>
<listitem>
<para>Return the N'th point in the first linestring in the
geometry. Return NULL if there is no linestring in the
geometry.</para>
<note> <para>
Index is 1-based as for OGC specs since version 0.8.0.
Previous versions implemented this as 0-based instead.
</para></note>
</listitem>
</varlistentry>
<varlistentry>
<term>ExteriorRing(geometry)</term>
<listitem>
<para>Return the exterior ring of the polygon geometry.
Return NULL if the geometry is not a polygon.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>NumInteriorRings(geometry)</term>
<listitem>
<para>Return the number of interior rings of the first polygon
in the geometry. Return NULL if there is no polygon in the
geometry.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>InteriorRingN(geometry,integer)</term>
<listitem>
<para>Return the N'th interior ring of the polygon geometry.
Return NULL if the geometry is not a polygon or the given
N is out of range.</para>
<note> <para>
Index is 1-based as for OGC specs since version 0.8.0.
Previous versions implemented this as 0-based instead.
</para></note>
</listitem>
</varlistentry>
<varlistentry>
<term>EndPoint(geometry)</term>
<listitem>
<para>Returns the last point of the LineString geometry as a point.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>StartPoint(geometry)</term>
<listitem>
<para>Returns the first point of the LineString geometry as a point.</para>
</listitem>
</varlistentry>
<varlistentry id="GeometryType">
<term>GeometryType(geometry)</term>
<listitem>
<para>Returns the type of the geometry as a string. Eg:
'LINESTRING', 'POLYGON', 'MULTIPOINT', etc.</para>
<para>OGC SPEC s2.1.1.1 - Returns the name of the instantiable
subtype of Geometry of which this Geometry instance is a member.
The name of the instantiable subtype of Geometry is returned as
a string.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>X(geometry)</term>
<listitem>
<para>Return the X coordinate of the point.
Input must be a point.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Y(geometry)</term>
<listitem>
<para>Return the Y coordinate of the point.
Input must be a point.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Z(geometry)</term>
<listitem>
<para>Return the Z coordinate of the point,
or NULL if not available.
Input must be a point.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>M(geometry)</term>
<listitem>
<para>Return the M coordinate of the point,
or NULL if not available.
Input must be a point.</para>
<note><para>This is not (yet) part of the OGC spec,
but is listed here to complete the point coordinate
extractor function list.</para></note>
</listitem>
</varlistentry>
</variablelist>
</sect2>
<sect2>
<title>Geometry Constructors</title>
<variablelist>
<varlistentry>
<term>GeomFromText(text,[&lt;srid&gt;])</term>
<listitem>
<para>Makes a Geometry from WKT with the given SRID.</para>
<para>OGC SPEC 3.2.6.2 - option SRID is from the conformance
suite</para>
</listitem>
</varlistentry>
<varlistentry>
<term>PointFromText(text,[&lt;srid&gt;])</term>
<listitem>
<para>Makes a Geometry from WKT with the given SRID. If SRID is
not give, it defaults to -1.</para>
<para>OGC SPEC 3.2.6.2 - option SRID is from the conformance
suite</para>
<para>Throws an error if the WKT is not a Point</para>
</listitem>
</varlistentry>
<varlistentry>
<term>LineFromText(text,[&lt;srid&gt;])</term>
<listitem>
<para>Makes a Geometry from WKT with the given SRID. If SRID is
not give, it defaults to -1.</para>
<para>OGC SPEC 3.2.6.2 - option SRID is from the conformance
suite</para>
<para>Throws an error if the WKT is not a Line</para>
</listitem>
</varlistentry>
<varlistentry>
<term>LinestringFromText(text,[&lt;srid&gt;])</term>
<listitem>
<para>Makes a Geometry from WKT with the given SRID. If SRID is
not give, it defaults to -1.</para>
<para>from the conformance suite</para>
<para>Throws an error if the WKT is not a Line</para>
</listitem>
</varlistentry>
<varlistentry>
<term>PolyFromText(text,[&lt;srid&gt;])</term>
<listitem>
<para>Makes a Geometry from WKT with the given SRID. If SRID is
not give, it defaults to -1.</para>
<para>OGC SPEC 3.2.6.2 - option SRID is from the conformance
suite</para>
<para>Throws an error if the WKT is not a Polygon</para>
</listitem>
</varlistentry>
<varlistentry>
<term>PolygonFromText(text,[&lt;srid&gt;])</term>
<listitem>
<para>Makes a Geometry from WKT with the given SRID. If SRID is
not give, it defaults to -1.</para>
<para>from the conformance suite</para>
<para>Throws an error if the WKT is not a Polygon</para>
</listitem>
</varlistentry>
<varlistentry>
<term>MPointFromText(text,[&lt;srid&gt;])</term>
<listitem>
<para>Makes a Geometry from WKT with the given SRID. If SRID is
not give, it defaults to -1.</para>
<para>OGC SPEC 3.2.6.2 - option SRID is from the conformance
suite</para>
<para>Throws an error if the WKT is not a MULTIPOINT</para>
</listitem>
</varlistentry>
<varlistentry>
<term>MLineFromText(text,[&lt;srid&gt;])</term>
<listitem>
<para>Makes a Geometry from WKT with the given SRID. If SRID is
not give, it defaults to -1.</para>
<para>OGC SPEC 3.2.6.2 - option SRID is from the conformance
suite</para>
<para>Throws an error if the WKT is not a MULTILINESTRING</para>
</listitem>
</varlistentry>
<varlistentry>
<term>MPolyFromText(text,[&lt;srid&gt;])</term>
<listitem>
<para>Makes a Geometry from WKT with the given SRID. If SRID is
not give, it defaults to -1.</para>
<para>OGC SPEC 3.2.6.2 - option SRID is from the conformance
suite</para>
<para>Throws an error if the WKT is not a MULTIPOLYGON</para>
</listitem>
</varlistentry>
<varlistentry>
<term>GeomCollFromText(text,[&lt;srid&gt;])</term>
<listitem>
<para>Makes a Geometry from WKT with the given SRID. If SRID is
not give, it defaults to -1.</para>
<para>OGC SPEC 3.2.6.2 - option SRID is from the conformance
suite</para>
<para>Throws an error if the WKT is not a
GEOMETRYCOLLECTION</para>
</listitem>
</varlistentry>
<varlistentry>
<term>GeomFromWKB(bytea,[&lt;srid&gt;])</term>
<listitem>
<para>Makes a Geometry from WKB with the given SRID. If SRID is
not give, it defaults to -1.</para>
<para>OGC SPEC 3.2.6.2 - option SRID is from the conformance
suite</para>
</listitem>
</varlistentry>
<varlistentry>
<term>GeomFromWKB(bytea,[&lt;srid&gt;])</term>
<listitem>
<para>Makes a Geometry from WKB with the given SRID. If SRID is
not give, it defaults to -1.</para>
<para>OGC SPEC 3.2.7.2 - option SRID is from the conformance
suite</para>
</listitem>
</varlistentry>
<varlistentry>
<term>PointFromWKB(bytea,[&lt;srid&gt;])</term>
<listitem>
<para>Makes a Geometry from WKB with the given SRID. If SRID is
not give, it defaults to -1.</para>
<para>OGC SPEC 3.2.7.2 - option SRID is from the conformance
suite</para>
<para>throws an error if WKB is not a POINT</para>
</listitem>
</varlistentry>
<varlistentry>
<term>LineFromWKB(bytea,[&lt;srid&gt;])</term>
<listitem>
<para>Makes a Geometry from WKB with the given SRID. If SRID is
not give, it defaults to -1.</para>
<para>OGC SPEC 3.2.7.2 - option SRID is from the conformance
suite</para>
<para>throws an error if WKB is not a LINESTRING</para>
</listitem>
</varlistentry>
<varlistentry>
<term>LinestringFromWKB(bytea,[&lt;srid&gt;])</term>
<listitem>
<para>Makes a Geometry from WKB with the given SRID. If SRID is
not give, it defaults to -1.</para>
<para>from the conformance suite</para>
<para>throws an error if WKB is not a LINESTRING</para>
</listitem>
</varlistentry>
<varlistentry>
<term>PolyFromWKB(bytea,[&lt;srid&gt;])</term>
<listitem>
<para>Makes a Geometry from WKB with the given SRID. If SRID is
not give, it defaults to -1.</para>
<para>OGC SPEC 3.2.7.2 - option SRID is from the conformance
suite</para>
<para>throws an error if WKB is not a POLYGON</para>
</listitem>
</varlistentry>
<varlistentry>
<term>PolygonFromWKB(bytea,[&lt;srid&gt;])</term>
<listitem>
<para>Makes a Geometry from WKB with the given SRID. If SRID is
not give, it defaults to -1.</para>
<para>from the conformance suite</para>
<para>throws an error if WKB is not a POLYGON</para>
</listitem>
</varlistentry>
<varlistentry>
<term>MPointFromWKB(bytea,[&lt;srid&gt;])</term>
<listitem>
<para>Makes a Geometry from WKB with the given SRID. If SRID is
not give, it defaults to -1.</para>
<para>OGC SPEC 3.2.7.2 - option SRID is from the conformance
suite</para>
<para>throws an error if WKB is not a MULTIPOINT</para>
</listitem>
</varlistentry>
<varlistentry>
<term>MLineFromWKB(bytea,[&lt;srid&gt;])</term>
<listitem>
<para>Makes a Geometry from WKB with the given SRID. If SRID is
not give, it defaults to -1.</para>
<para>OGC SPEC 3.2.7.2 - option SRID is from the conformance
suite</para>
<para>throws an error if WKB is not a MULTILINESTRING</para>
</listitem>
</varlistentry>
<varlistentry>
<term>MPolyFromWKB(bytea,[&lt;srid&gt;])</term>
<listitem>
<para>Makes a Geometry from WKB with the given SRID. If SRID is
not give, it defaults to -1.</para>
<para>OGC SPEC 3.2.7.2 - option SRID is from the conformance
suite</para>
<para>throws an error if WKB is not a MULTIPOLYGON</para>
</listitem>
</varlistentry>
<varlistentry>
<term>GeomCollFromWKB(bytea,[&lt;srid&gt;])</term>
<listitem>
<para>Makes a Geometry from WKB with the given SRID. If SRID is
not give, it defaults to -1.</para>
<para>OGC SPEC 3.2.7.2 - option SRID is from the conformance
suite</para>
<para>throws an error if WKB is not a GEOMETRYCOLLECTION</para>
</listitem>
</varlistentry>
</variablelist>
</sect2>
</sect1>
<sect1>
<title>Postgis Extensions</title>
<sect2>
<title>Management Functions</title>
<variablelist>
<varlistentry>
<term>DropGeometryTable([&lt;schema_name&gt;],
&lt;table_name&gt;)</term>
<listitem>
<para>Drops a table and all its references in geometry_columns.
Note: uses current_schema() on schema-aware pgsql installations if
schema is not provided.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>UpdateGeometrySRID([&lt;schema_name&gt;],
&lt;table_name&gt;, &lt;column_name&gt;, &lt;srid&gt;)</term>
<listitem>
<para>Update the SRID of all features in a geometry column updating constraints and reference in geometry_columns.
Note: uses current_schema() on schema-aware pgsql installations if schema is not provided.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>update_geometry_stats([&lt;table_name&gt;,
&lt;column_name&gt;])</term>
<listitem>
<para>Update statistics about spatial tables for use by the query
planner. You will also need to run "VACUUM ANALYZE [table_name]
[column_name]" for the statistics gathering process to be
complete. NOTE: starting with PostgreSQL 8.0 statistics gathering
is automatically performed running "VACUUM ANALYZE".</para>
</listitem>
</varlistentry>
<varlistentry>
<term>postgis_version()</term>
<listitem>
<para>Returns the version number of the PostGIS functions
installed in this database (deprecated, use postgis_full_version()
instead).</para>
</listitem>
</varlistentry>
<varlistentry>
<term>postgis_lib_version()</term>
<listitem>
<para>Returns the version number of the PostGIS library.</para>
<para>
Availability: 0.9.0
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>postgis_lib_build_date()</term>
<listitem>
<para>Returns build date of the PostGIS library.</para>
<para>
Availability: 1.0.0RC1
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>postgis_script_build_date()</term>
<listitem>
<para>Returns build date of the PostGIS scripts.</para>
<para>
Availability: 1.0.0RC1
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>postgis_scripts_installed()</term>
<listitem>
<para>Returns the version number of the lwpostgis.sql script
installed in this database.</para>
<para>
Availability: 0.9.0
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>postgis_scripts_released()</term>
<listitem>
<para>Returns the version number of the lwpostgis.sql script
released with the installed postgis lib.</para>
<para>
Availability: 0.9.0
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>postgis_geos_version()</term>
<listitem>
<para>Returns the version number of the GEOS library, or NULL if
GEOS support is not enabled.</para>
<para>
Availability: 0.9.0
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>postgis_jts_version()</term>
<listitem>
<para>Returns the version number of the JTS library, or NULL if
JTS support is not enabled.</para>
<para>
Availability: 1.1.0
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>postgis_proj_version()</term>
<listitem>
<para>Returns the version number of the PROJ4 library, or NULL if
PROJ4 support is not enabled.</para>
<para>
Availability: 0.9.0
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>postgis_uses_stats()</term>
<listitem>
<para>Returns true if STATS usage has been enabled, false
otherwise.</para>
<para>
Availability: 0.9.0
</para>
</listitem>
</varlistentry>
<varlistentry id="postgis_full_version">
<term>postgis_full_version()</term>
<listitem>
<para>Reports full postgis version and build configuration
infos.</para>
<para>Availability: 0.9.0</para>
</listitem>
</varlistentry>
</variablelist>
</sect2>
<sect2>
<title>Operators</title>
<variablelist>
<varlistentry>
<term>A &amp;&lt; B</term>
<listitem>
<para>The "&amp;&lt;" operator returns true if A's bounding box
overlaps or is to the left of B's bounding box.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>A &amp;&gt; B</term>
<listitem>
<para>The "&amp;&gt;" operator returns true if A's bounding box
overlaps or is to the right of B's bounding box.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>A &lt;&lt; B</term>
<listitem>
<para>The "&lt;&lt;" operator returns true if A's bounding box is
strictly to the left of B's bounding box.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>A &gt;&gt; B</term>
<listitem>
<para>The "&gt;&gt;" operator returns true if A's bounding box is
strictly to the right of B's bounding box.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>A &amp;&lt;| B</term>
<listitem>
<para>The "&amp;&lt;|" operator returns true if A's bounding box
overlaps or is below B's bounding box.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>A |&amp;&gt; B</term>
<listitem>
<para>The "|&amp;&gt;" operator returns true if A's bounding box
overlaps or is above B's bounding box.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>A &lt;&lt;| B</term>
<listitem>
<para>The "&lt;&lt;|" operator returns true if A's bounding box is
strictly below B's bounding box.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>A |&gt;&gt; B</term>
<listitem>
<para>The "|&gt;&gt;" operator returns true if A's bounding box is
strictly above B's bounding box.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>A ~= B</term>
<listitem>
<para>The "~=" operator is the "same as" operator. It tests actual
geometric equality of two features. So if A and B are the same
feature, vertex-by-vertex, the operator returns true.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>A @ B</term>
<listitem>
<para>The "@" operator returns true if A's bounding box is
completely contained by B's bounding box.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>A ~ B</term>
<listitem>
<para>The "~" operator returns true if A's bounding box completely
contains B's bounding box.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>A &amp;&amp; B</term>
<listitem>
<para>The "&amp;&amp;" operator is the "overlaps" operator. If A's
bounding boux overlaps B's bounding box the operator returns
true.</para>
</listitem>
</varlistentry>
</variablelist>
</sect2>
<sect2>
<title>Measurement Functions</title>
<variablelist>
<varlistentry>
<term>area2d(geometry)</term>
<listitem>
<para>Returns the area of the geometry if it is a polygon or
multi-polygon.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>distance_sphere(point, point)</term>
<listitem>
<para>Returns linear distance in meters between two lat/lon
points. Uses a spherical earth and radius of 6370986 meters.
Faster than <link linkend="distance_spheroid">distance_spheroid()</link>, but
less accurate.
Only implemented for points.</para>
</listitem>
</varlistentry>
<varlistentry id="distance_spheroid">
<term>distance_spheroid(point, point, spheroid)</term>
<listitem>
<para>Returns linear distance between two lat/lon points given a
particular spheroid. See the explanation of spheroids given for
<link linkend="length_spheroid">length_spheroid()</link>.
Currently only implemented for points.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>length2d(geometry)</term>
<listitem>
<para>Returns the 2-dimensional length of the geometry if it is a
linestring or multi-linestring.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>length3d(geometry)</term>
<listitem>
<para>Returns the 3-dimensional length of the geometry if it is a
linestring or multi-linestring.</para>
</listitem>
</varlistentry>
<varlistentry id="length_spheroid">
<term>length_spheroid(geometry,spheroid)</term>
<listitem>
<para>Calculates the length of of a geometry on an elipsoid. This
is useful if the coordinates of the geometry are in
latitude/longitude and a length is desired without reprojection.
The elipsoid is a separate database type and can be constructed as
follows:</para>
<literallayout>SPHEROID[&lt;NAME&gt;,&lt;SEMI-MAJOR AXIS&gt;,&lt;INVERSE FLATTENING&gt;]</literallayout>
<para>Eg:</para>
<literallayout>SPHEROID["GRS_1980",6378137,298.257222101]</literallayout>
<para>An example calculation might look like this:</para>
<literallayout>SELECT
length_spheroid(
geometry_column,
'SPHEROID["GRS_1980",6378137,298.257222101]'
)
FROM geometry_table;</literallayout>
</listitem>
</varlistentry>
<varlistentry>
<term>length3d_spheroid(geometry,spheroid)</term>
<listitem>
<para>Calculates the length of of a geometry on an elipsoid,
taking the elevation into account. This is just like
length_spheroid except vertical coordinates (expressed in the same
units as the spheroid axes) are used to calculate the extra
distance vertical displacement adds.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>distance(geometry, geometry)</term>
<listitem>
<para>Returns the smaller distance between two geometries.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>max_distance(linestring,linestring)</term>
<listitem>
<para>Returns the largest distance between two line
strings.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>perimeter(geometry)</term>
<listitem>
<para>Returns the 2-dimensional perimeter of the geometry, if it
is a polygon or multi-polygon.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>perimeter2d(geometry)</term>
<listitem>
<para>Returns the 2-dimensional perimeter of the geometry, if it
is a polygon or multi-polygon.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>perimeter3d(geometry)</term>
<listitem>
<para>Returns the 3-dimensional perimeter of the geometry, if it
is a polygon or multi-polygon.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>azimuth(geometry, geometry)</term>
<listitem>
<para>
Returns the azimuth of the segment defined by the given Point
geometries, or NULL if the two points are coincident.
Return value is in radians.
</para>
<para>
Availability: 1.1.0
</para>
</listitem>
</varlistentry>
</variablelist>
</sect2>
<sect2>
<title>Geometry Outputs</title>
<variablelist>
<varlistentry>
<term>AsBinary(geometry,{'NDR'|'XDR'})</term>
<listitem>
<para>Returns the geometry in the OGC "well-known-binary" format as a bytea, using little-endian (NDR) or big-endian (XDR) encoding. This is useful in binary cursors to pull data out of the database without converting it to a string representation.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>AsEWKT(geometry)</term>
<listitem>
<para>Returns a Geometry in EWKT format (as text).</para>
</listitem>
</varlistentry>
<varlistentry>
<term>AsEWKB(geometry, {'NDR'|'XDR'})</term>
<listitem>
<para>Returns a Geometry in EWKB format (as bytea) using either little-endian (NDR) or big-endian (XDR) encoding.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>AsSVG(geometry, [rel], [precision])</term>
<listitem>
<para>Return the geometry as an SVG path data. Use 1 as second argument to have the path data implemented in terms of relative moves, the default (or 0) uses absolute moves. Third argument may be used to reduce the maximum number of decimal digits used in output (defaults to 15). Point geometries will be rendered as cx/cy when 'rel' arg is 0, x/y when 'rel' is 1.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>AsGML(geometry, [precision])</term>
<listitem>
<para>Return the geometry as a GML element. Second argument may be used to reduce the maximum number of significant digits used in output (defaults to 15).</para>
</listitem>
</varlistentry>
</variablelist>
</sect2>
<sect2>
<title>Geometry Constructors</title>
<variablelist>
<varlistentry>
<term>GeomFromEWKT(text)</term>
<listitem>
<para>Makes a Geometry from EWKT.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>GeomFromEWKB(bytea)</term>
<listitem>
<para>Makes a Geometry from EWKB.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>MakePoint(&lt;x&gt;, &lt;y&gt;, [&lt;z&gt;], [&lt;m&gt;])</term>
<listitem>
<para>Creates a 2d,3dz or 4d point geometry.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>MakePointM(&lt;x&gt;, &lt;y&gt;, &lt;m&gt;)</term>
<listitem>
<para>Creates a 3dm point geometry.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>MakeBox2D(&lt;LL&gt;, &lt;UR&gt;)</term>
<listitem>
<para>Creates a BOX2D defined by the given point geometries.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>MakeBox3D(&lt;LLB&gt;, &lt;URT&gt;)</term>
<listitem>
<para>Creates a BOX3D defined by the given point geometries.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>MakeLine(geometry set)</term>
<listitem>
<para>Creates a Linestring from a set of point geometries.
You might want to use a subselect to order points before
feeding them to this aggregate.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>MakeLine(geometry, geometry)</term>
<listitem>
<para>Creates a Linestring from the two given point
geometries.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>LineFromMultiPoint(multipoint)</term>
<listitem>
<para>Creates a LineString from a MultiPoint geometry.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>MakePolygon(linestring, [linestring[]])</term>
<listitem>
<para>Creates a Polygon formed by the given
shell and array of holes. You can construct
a geometry array using <link linkend="Accum">Accum</link>.
Input geometries must be closed LINESTRINGS (see <link linkend="IsClosed">IsClosed</link> and <link linkend="GeometryType">GeometryType</link>).
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Polygonize(geometry set)</term>
<listitem>
<para>
Aggregate. Creates a GeometryCollection containing
possible polygons formed from the costituent linework
of a set of geometries.
</para>
<para>
Availability: 1.0.0RC1 - requires GEOS >= 2.1.0.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Collect(geometry set)</term>
<listitem>
<para>This function returns a GEOMETRYCOLLECTION or a MULTI object from a set
of geometries. The collect() function is an "aggregate" function
in the terminology of PostgreSQL. That means that it operators on
lists of data, in the same way the sum() and mean() functions do.
For example, "SELECT COLLECT(GEOM) FROM GEOMTABLE GROUP BY
ATTRCOLUMN" will return a separate GEOMETRYCOLLECTION for each
distinct value of ATTRCOLUMN.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Collect(geometry, geometry)</term>
<listitem>
<para>This function returns a geometry being a collection
of two input geometries. Output type can be a MULTI* or
a GEOMETRYCOLLECTION.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Dump(geometry)</term>
<listitem>
<para>This is a set-returning function (SRF).
It returns a set of geometry_dump rows, formed
by a geometry (geom) and an array of integers (path).
When the input geometry is a simple type
(POINT,LINESTRING,POLYGON)
a single record will be returned with an empty
path array and the input geometry as geom.
When the input geometry is a collection or multi
it will return a record for each of the collection
components, and the path will express the position
of the component inside the collection.
</para>
<para>NOTE: this function is not available for
builds against PostgreSQL 7.2.x</para>
</listitem>
</varlistentry>
</variablelist>
</sect2>
<sect2>
<title>Geometry Editors</title>
<variablelist>
<varlistentry id="addbbox">
<term>AddBBOX(geometry)</term>
<listitem>
<para>Add bounding box to the geometry. This would make bounding
box based queries faster, but will increase the size of the
geometry.</para>
</listitem>
</varlistentry>
<varlistentry id="dropbbox">
<term>DropBBOX(geometry)</term>
<listitem>
<para>Drop the bounding box cache from the geometry.
This reduces geometry size, but makes bounding-box based
queries slower.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>AddPoint(linestring, point, [&lt;position&gt;])</term>
<listitem>
<para>Adds a point to a LineString at position &lt;pos&gt;.
Third parameter can be omitted or set to -1 for appending.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Force_collection(geometry)</term>
<listitem>
<para>Converts the geometry into a GEOMETRYCOLLECTION. This is
useful for simplifying the WKB representation.</para>
</listitem>
</varlistentry>
<varlistentry id="force_2d">
<term>Force_2d(geometry)</term>
<listitem>
<para>Forces the geometries into a "2-dimensional mode" so that
all output representations will only have the X and Y coordinates.
This is useful for force OGC-compliant output (since OGC only
specifies 2-D geometries).</para>
</listitem>
</varlistentry>
<varlistentry id="force_3dz">
<term>Force_3dz(geometry)</term>
<term>Force_3d(geometry)</term>
<listitem>
<para>Forces the geometries into XYZ mode.</para>
</listitem>
</varlistentry>
<varlistentry id="force_3dm">
<term>Force_3dm(geometry)</term>
<listitem>
<para>Forces the geometries into XYM mode.</para>
</listitem>
</varlistentry>
<varlistentry id="force_4d">
<term>Force_4d(geometry)</term>
<listitem>
<para>Forces the geometries into XYZM mode.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Multi(geometry)</term>
<listitem>
<para>Returns the geometry as a MULTI* geometry. If the geometry
is already a MULTI*, it is returned unchanged.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Transform(geometry,integer)</term>
<listitem>
<para>Returns a new geometry with its coordinates transformed to
the SRID referenced by the integer parameter. The destination SRID
must exist in the <varname>SPATIAL_REF_SYS</varname> table.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Translate(geometry,float8,float8,float8)</term>
<listitem>
<para>Translates the geometry to a new location using the numeric
parameters as offsets. Ie: translate(geom, X, Y, Z).</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Scale(geometry,float8,float8,float8)</term>
<listitem>
<para>scales the geometry to a new size by multiplying the
ordinates with the parameters. Ie: scale(geom, Xfactor, Yfactor, Zfactor).</para>
<para>
Availability: 1.1.0
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>TransScale(geometry,float8,float8,float8,float8)</term>
<listitem>
<para>First, translates the geometry using the first two floats, then scales it
using the second two floats, working in 2D only. Using
transscale(geom, X, Y, XFactor, YFactor) effectively is an efficient shortcut
for scale(translate(geom,X,Y,0),Xfactor,YFactor,1).</para>
<para>
Availability: 1.1.0
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Reverse(geometry)</term>
<listitem>
<para>Returns the geometry with vertex order reversed.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>ForceRHR(geometry)</term>
<listitem>
<para>Force polygons of the collection to obey Right-Hand-Rule.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Simplify(geometry, tolerance)</term>
<listitem>
<para>Returns a "simplified" version of the given geometry using
the Douglas-Peuker algorithm. Will actually do something only with
(multi)lines and (multi)polygons but you can safely call it with
any kind of geometry. Since simplification occurs on a
object-by-object basis you can also feed a GeometryCollection to
this function. Note that returned geometry might loose its
simplicity (see <link linkend="IsSimple">IsSimple</link>)</para>
</listitem>
</varlistentry>
<varlistentry>
<term>SnapToGrid(geometry, originX, originY, sizeX, sizeY)</term>
<term>SnapToGrid(geometry, sizeX, sizeY)</term>
<term>SnapToGrid(geometry, size)</term>
<listitem>
<para>Snap all points of the input geometry to the grid
defined by its origin and cell size.
Remove consecutive points falling on the same cell,
eventually returning NULL if output points are not
enough to define a geometry of the given type.
Collapsed geometries in a collection are stripped
from it.
Note that returned geometry might loose its
simplicity (see <link linkend="IsSimple">IsSimple</link>).
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Segmentize(geometry, maxlength)</term>
<listitem>
<para>Return a modified [multi]polygon having no ring segment
longer then the given distance. Interpolated points will have Z
and M values (if needed) set to 0. Distance computation is
performed in 2d only.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>LineMerge(geometry)</term>
<listitem>
<para>
Returns a (set of) LineString(s) formed by sewing
togheter costituent linework of input.
</para>
<para>
Availability: 1.1.0 - requires GEOS >= 2.1.0
</para>
</listitem>
</varlistentry>
</variablelist>
</sect2>
<sect2>
<title>Linear Referencing</title>
<variablelist>
<varlistentry>
<term>line_interpolate_point(linestring, proportion)</term>
<listitem>
<para>Interpolates a point along a line. First argument must be a
LINESTRING. Second argument is a float between 0 and 1. Returns a
point.</para>
<para>
Availability: 0.8.2
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>line_substring(linestring, start, end)</term>
<listitem>
<para>
Return a linestring being a substring of the input one starting
and ending at the given fractions of total length. Second
and third arguments are float8 values between 0 and 1.
</para>
<para>
Availability: 1.1.0
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>line_locate_point(linestring, point)</term>
<listitem>
<para>
Returns a float, representing the proportional distance the
point is located along the line.
</para>
<para>
Availability: 1.1.0
</para>
</listitem>
</varlistentry>
</variablelist>
</sect2>
<sect2>
<title>Misc</title>
<variablelist>
<varlistentry>
<term>Summary(geometry)</term>
<listitem>
<para>Returns a text summary of the contents of the geometry.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>box2d(geometry)</term>
<listitem>
<para>Returns a BOX2D representing the maximum extents of the geometry.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>box3d(geometry)</term>
<listitem>
<para>Returns a BOX3D representing the maximum extents of the geometry.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>extent(geometry set)</term>
<listitem>
<para>The extent() function is an "aggregate" function in the terminology of PostgreSQL. That means that it operators on lists of data, in the same way the sum() and mean() functions do. For example, "SELECT EXTENT(GEOM) FROM GEOMTABLE" will return a BOX3D giving the maximum extend of all features in the table. Similarly, "SELECT EXTENT(GEOM) FROM GEOMTABLE GROUP BY CATEGORY" will return one extent result for each category.</para>
</listitem>
</varlistentry>
<varlistentry id="zmflag">
<term>zmflag(geometry)</term>
<listitem>
<para>Returns ZM (dimension semantic) flag of the geometries as a small int. Values are: 0=2d, 1=3dm, 2=3dz, 3=4d. </para>
</listitem>
</varlistentry>
<varlistentry id="hasbbox">
<term>HasBBOX(geometry)</term>
<listitem>
<para>Returns TRUE if the bbox of this geometry is cached, FALSE otherwise. Use <link linkend="addbbox">addBBOX()</link> and <link linkend="dropbbox">dropBBOX()</link> to control caching.</para>
</listitem>
</varlistentry>
<varlistentry id="ndims">
<term>ndims(geometry)</term>
<listitem>
<para>Returns number of dimensions of the geometry as a small int. Values are: 2,3 or 4.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>nrings(geometry)</term>
<listitem>
<para>If the geometry is a polygon or multi-polygon returns the number of rings.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>npoints(geometry)</term>
<listitem>
<para>Returns the number of points in the geometry.</para>
</listitem>
</varlistentry>
<varlistentry id="IsValid">
<term>isvalid(geometry)</term>
<listitem>
<para>returns true if this geometry is valid.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>expand(geometry, float)</term>
<listitem>
<para>This function returns a bounding box expanded in all
directions from the bounding box of the input geometry, by an
amount specified in the second argument. Very useful for
distance() queries, to add an index filter to the query.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>estimated_extent([schema], table, geocolumn)</term>
<listitem>
<para> Return the 'estimated' extent of the given spatial table. The estimated is taken from the geometry column's statistics. The current schema will be used if not specified.</para>
<para>For PostgreSQL&gt;=8.0.0 statistics are gathered by VACUUM ANALYZE and resulting extent will be about 95% of the real one.</para>
<para>For PostgreSQL&lt;8.0.0 statistics are gathered by update_geometry_stats() and resulting extent will be exact.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>find_srid(varchar,varchar,varchar)</term>
<listitem>
<para>The syntax is find_srid(&lt;db/schema&gt;, &lt;table&gt;,
&lt;column&gt;) and the function returns the integer SRID of the
specified column by searching through the GEOMETRY_COLUMNS table.
If the geometry column has not been properly added with the
AddGeometryColumns() function, this function will not work
either.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>mem_size(geometry)</term>
<listitem>
<para>Returns the amount of space (in bytes) the geometry
takes.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>numb_sub_objects(geometry)</term>
<listitem>
<para>Returns the number of objects stored in the geometry. This
is useful for MULTI-geometries and GEOMETRYCOLLECTIONs.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>point_inside_circle(geometry,float,float,float)</term>
<listitem>
<para>The syntax for this functions is
point_inside_circle(&lt;geometry&gt;,&lt;circle_center_x&gt;,&lt;circle_center_y&gt;,&lt;radius&gt;).
Returns the true if the geometry is a point and is inside the
circle. Returns false otherwise.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>xmin(box3d) ymin(box3d) zmin(box3d)</term>
<listitem>
<para>Returns the requested minima of a bounding box.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>xmax(box3d) ymax(box3d) zmax(box3d)</term>
<listitem>
<para>Returns the requested maxima of a bounding box.</para>
</listitem>
</varlistentry>
<varlistentry id="Accum">
<term>Accum(geometry set)</term>
<listitem>
<para>Aggregate. Constructs an array of geometries.</para>
</listitem>
</varlistentry>
</variablelist>
</sect2>
</sect1>
</chapter>
<chapter>
<title>Reporting Bugs</title>
<para>
Reporting bugs effectively is a fundamental way to help PostGIS
development. The most effective bug report is that enabling
PostGIS developers to reproduce it, so it would ideally contain
a script triggering it and every information reguarding the
environment in which it was detected. Good enough info can
be extracted running <code>SELECT postgis_full_version()</code>
[for postgis] and <code>SELECT version()</code> [for postgresql].
</para>
<para>
If you aren't using latest release, it's worth taking a look
at its <ulink
url="http://postgis.refractions.net/CHANGES.txt">release
changelog</ulink> first, to find out if your bug has already been
fixed.
</para>
<para>
Using the <ulink url="http://postgis.refractions.net/bugs/">PostGIS
bug tracker</ulink> will ensure your reports are not discarded, and
will keep you informed on it's handling process. Before reporting
a new bug please query the database to see if it is a known one, and
if it is please add any new information you have about it.
</para>
<para>
You might want to read Simon Tatham's paper about <ulink
url="http://www.chiark.greenend.org.uk/~sgtatham/bugs.html">How
to Report Bugs Effectively</ulink> before filing a new report.
</para>
</chapter>
<appendix id="release_notes">
<title>Release Notes</title>
<sect1>
<title>Release 1.0.5</title>
<para>Release date: 2005/11/25</para>
<para>
Contains memory-alignment fixes in the library, a segfault fix in loader's
handling of UTF8 attributes and a few improvements and cleanups.
</para>
<note><para>
Return code of shp2pgsl changed from previous releases to conform to unix
standards (return 0 on success).
</para></note>
<sect2>
<title>Upgrading</title>
<para>If you are upgrading from
release 1.0.3 or later you <emphasis>DO
NOT</emphasis> need a dump/reload.
</para>
<para>If you are upgrading from
a release <emphasis>between 1.0.0RC6 and
1.0.2</emphasis> (inclusive) and really want
a live upgrade read the <link
linkend="rel_1.0.3_upgrading">upgrade
section</link> of the 1.0.3 release notes
chapter.
</para>
<para>
Upgrade from any release prior to 1.0.0RC6
requires an <link linkend="hard_upgrade">hard
upgrade</link>.
</para>
</sect2>
<sect2>
<title>Library changes</title>
<para>Fixed memory alignment problems</para>
<para>Fixed computation of null values fraction in analyzer</para>
<para>Fixed a small bug in the getPoint4d_p() low-level function</para>
<para>Speedup of serializer functions</para>
<para>Fixed a bug in force_3dm(), force_3dz() and force_4d()</para>
</sect2>
<sect2>
<title>Loader changes</title>
<para>Fixed return code of shp2pgsql</para>
<para>Fixed back-compatibility issue in loader (load of null shapefiles)</para>
<para>Fixed handling of trailing dots in dbf numerical attributes</para>
<para>Segfault fix in shp2pgsql (utf8 encoding)</para>
</sect2>
<sect2>
<title>Other changes</title>
<para>Schema aware postgis_proc_upgrade.pl, support for pgsql 7.2+</para>
<para>New "Reporting Bugs" chapter in manual</para>
</sect2>
</sect1>
<sect1>
<title>Release 1.0.4</title>
<para>Release date: 2005/09/09</para>
<para>
Contains important bug fixes and a few improvements. In particular, it
fixes a memory leak preventing successful build of GiST indexes
for large spatial tables.
</para>
<sect2>
<title>Upgrading</title>
<para>If you are upgrading from
release 1.0.3 you <emphasis>DO
NOT</emphasis> need a dump/reload.
</para>
<para>If you are upgrading from
a release <emphasis>between 1.0.0RC6 and
1.0.2</emphasis> (inclusive) and really want
a live upgrade read the <link
linkend="rel_1.0.3_upgrading">upgrade
section</link> of the 1.0.3 release notes
chapter.
</para>
<para>
Upgrade from any release prior to 1.0.0RC6
requires an <link linkend="hard_upgrade">hard
upgrade</link>.
</para>
</sect2>
<sect2>
<title>Bug fixes</title>
<para>Memory leak plugged in GiST indexing</para>
<para>Segfault fix in transform() handling of proj4 errors</para>
<para>Fixed some proj4 texts in spatial_ref_sys (missing +proj)</para>
<para>Loader: fixed string functions usage, reworked NULL objects check, fixed segfault on MULTILINESTRING input.</para>
<para>Fixed bug in MakeLine dimension handling</para>
<para>Fixed bug in translate() corrupting output bounding box</para>
</sect2>
<sect2>
<title>Improvements</title>
<para>Documentation improvements</para>
<para>More robust selectivity estimator </para>
<para>Minor speedup in distance()</para>
<para>Minor cleanups </para>
<para>GiST indexing cleanup</para>
<para>Looser syntax acceptance in box3d parser</para>
</sect2>
</sect1>
<sect1 id="rel_1.0.3_upgrading">
<title>Release 1.0.3</title>
<para>Release date: 2005/08/08</para>
<para>
Contains some bug fixes - <emphasis>including a severe one affecting
correctness of stored geometries</emphasis> - and a few improvements.
</para>
<sect2>
<title>Upgrading</title>
<para>
Due to a bug in a bounding box computation routine, the upgrade procedure
requires special attention, as bounding boxes cached in the database could
be incorrect.
</para>
<para>
An <link linkend="hard_upgrade">hard upgrade</link> procedure (dump/reload)
will force recomputation of all bounding boxes (not included in dumps).
This is <emphasis>required</emphasis> if upgrading from releases prior
to 1.0.0RC6.
</para>
<para>
If you are upgrading from versions 1.0.0RC6 or up, this release includes a
perl script (utils/rebuild_bbox_caches.pl) to force recomputation of
geometries' bounding boxes and invoke all operations required to propagate
eventual changes in them (geometry statistics update, reindexing).
Invoke the script after a make install (run with no args for syntax help).
Optionally run utils/postgis_proc_upgrade.pl to refresh postgis procedures
and functions signatures (see <link linkend="soft_upgrade">Soft upgrade</link>).
</para>
</sect2>
<sect2>
<title>Bug fixes</title>
<para>Severe bugfix in lwgeom's 2d bounding box computation</para>
<para>Bugfix in WKT (-w) POINT handling in loader</para>
<para>Bugfix in dumper on 64bit machines</para>
<para>Bugfix in dumper handling of user-defined queries </para>
<para>Bugfix in create_undef.pl script</para>
</sect2>
<sect2>
<title>Improvements</title>
<para>Small performance improvement in canonical input function</para>
<para>Minor cleanups in loader</para>
<para>Support for multibyte field names in loader</para>
<para>Improvement in the postgis_restore.pl script</para>
<para>New rebuild_bbox_caches.pl util script</para>
</sect2>
</sect1>
<sect1>
<title>Release 1.0.2</title>
<para>Release date: 2005/07/04</para>
<para>
Contains a few bug fixes and improvements.
</para>
<sect2>
<title>Upgrading</title>
<para>If you are upgrading from
release 1.0.0RC6 or up you <emphasis>DO
NOT</emphasis> need a dump/reload.</para>
<para>Upgrading from older releases
requires a dump/reload.
See the <link
linkend="upgrading">upgrading</link>
chapter for more informations.</para>
</sect2>
<sect2>
<title>Bug fixes</title>
<para>Fault tolerant btree ops</para>
<para>Memory leak plugged in pg_error</para>
<para>Rtree index fix</para>
<para>Cleaner build scripts (avoided mix of CFLAGS and CXXFLAGS)</para>
</sect2>
<sect2>
<title>Improvements</title>
<para>New index creation capabilities in loader (-I switch)</para>
<para>Initial support for postgresql 8.1dev</para>
</sect2>
</sect1>
<sect1>
<title>Release 1.0.1</title>
<para>Release date: 2005/05/24</para>
<para>
Contains a few bug fixes and some improvements.
</para>
<sect2>
<title>Upgrading</title>
<para>If you are upgrading from
release 1.0.0RC6 or up you <emphasis>DO
NOT</emphasis> need a dump/reload.</para>
<para>Upgrading from older releases
requires a dump/reload.
See the <link
linkend="upgrading">upgrading</link>
chapter for more informations.</para>
</sect2>
<sect2>
<title>Library changes</title>
<para>BUGFIX in 3d computation of lenght_spheroid()</para>
<para>BUGFIX in join selectivity estimator</para>
</sect2>
<sect2>
<title>Other changes/additions</title>
<para>BUGFIX in shp2pgql escape functions</para>
<para>better support for concurrent postgis in multiple schemas</para>
<para>documentation fixes</para>
<para>jdbc2: compile with "-target 1.2 -source 1.2" by default</para>
<para>NEW -k switch for pgsql2shp</para>
<para>NEW support for custom createdb options in postgis_restore.pl</para>
<para>BUGFIX in pgsql2shp attribute names unicity enforcement</para>
<para>BUGFIX in Paris projections definitions</para>
<para>postgis_restore.pl cleanups</para>
</sect2>
</sect1>
<sect1>
<title>Release 1.0.0</title>
<para>Release date: 2005/04/19</para>
<para>Final 1.0.0 release.
Contains a few bug fixes, some improvements
in the loader (most notably support for older
postgis versions), and more docs.
</para>
<sect2>
<title>Upgrading</title>
<para>If you are upgrading from
release 1.0.0RC6 you <emphasis>DO
NOT</emphasis> need a dump/reload.</para>
<para>Upgrading from any other precedent
release requires a dump/reload.
See the <link
linkend="upgrading">upgrading</link>
chapter for more informations.</para>
</sect2>
<sect2>
<title>Library changes</title>
<para>BUGFIX in transform() releasing random memory address</para>
<para>BUGFIX in force_3dm() allocating less memory then required</para>
<para>BUGFIX in join selectivity estimator (defaults, leaks, tuplecount, sd)</para>
</sect2>
<sect2>
<title>Other changes/additions</title>
<para>BUGFIX in shp2pgsql escape of values starting with tab or single-quote</para>
<para>NEW manual pages for loader/dumper</para>
<para>NEW shp2pgsql support for old (HWGEOM) postgis versions</para>
<para>NEW -p (prepare) flag for shp2pgsql</para>
<para>NEW manual chapter about OGC compliancy enforcement</para>
<para>NEW autoconf support for JTS lib</para>
<para>BUGFIX in estimator testers (support for LWGEOM and schema parsing)</para>
</sect2>
</sect1>
<sect1>
<title>Release 1.0.0RC6</title>
<para>Release date: 2005/03/30</para>
<para>Sixth release candidate for 1.0.0.
Contains a few bug fixes and cleanups.</para>
<sect2>
<title>Upgrading</title>
<para>You need a dump/reload to upgrade
from precedent releases. See the <link
linkend="upgrading">upgrading</link>
chapter for more informations.</para>
</sect2>
<sect2>
<title>Library changes</title>
<para>BUGFIX in multi()</para>
<para>early return [when noop] from multi()</para>
</sect2>
<sect2>
<title>Scripts changes</title>
<para>dropped {x,y}{min,max}(box2d) functions</para>
</sect2>
<sect2>
<title>Other changes</title>
<para>BUGFIX in postgis_restore.pl scrip</para>
<para>BUGFIX in dumper's 64bit support</para>
</sect2>
</sect1>
<sect1>
<title>Release 1.0.0RC5</title>
<para>Release date: 2005/03/25</para>
<para>Fifth release candidate for 1.0.0.
Contains a few bug fixes and a improvements.</para>
<sect2>
<title>Upgrading</title>
<para>If you are upgrading from
release 1.0.0RC4 you <emphasis>DO
NOT</emphasis> need a dump/reload.</para>
<para>Upgrading from any other precedent
release requires a dump/reload.
See the <link
linkend="upgrading">upgrading</link>
chapter for more informations.</para>
</sect2>
<sect2>
<title>Library changes</title>
<para>BUGFIX (segfaulting) in box3d computation (yes, another!).</para>
<para>BUGFIX (segfaulting) in estimated_extent().</para>
</sect2>
<sect2>
<title>Other changes</title>
<para>Small build scripts and utilities refinements.</para>
<para>Additional performance tips documented.</para>
</sect2>
</sect1>
<sect1>
<title>Release 1.0.0RC4</title>
<para>Release date: 2005/03/18</para>
<para>Fourth release candidate for 1.0.0.
Contains bug fixes and a few improvements.</para>
<sect2>
<title>Upgrading</title>
<para>You need a dump/reload to upgrade
from precedent releases. See the <link
linkend="upgrading">upgrading</link>
chapter for more informations.</para>
</sect2>
<sect2>
<title>Library changes</title>
<para>BUGFIX (segfaulting) in geom_accum().</para>
<para>BUGFIX in 64bit architectures support.</para>
<para>BUGFIX in box3d computation function with collections.</para>
<para>NEW subselects support in selectivity estimator.</para>
<para>Early return from force_collection.</para>
<para>Consistency check fix in SnapToGrid().</para>
<para>Box2d output changed back to 15 significant digits.</para>
</sect2>
<sect2>
<title>Scripts changes</title>
<para>NEW distance_sphere() function.</para>
<para>Changed get_proj4_from_srid implementation to use PL/PGSQL instead of SQL.</para>
</sect2>
<sect2>
<title>Other changes</title>
<para>BUGFIX in loader and dumper handling of MultiLine shapes</para>
<para>BUGFIX in loader, skipping all but first hole of polygons.</para>
<para>jdbc2: code cleanups, Makefile improvements</para>
<para>FLEX and YACC variables set *after* pgsql Makefile.global is included and only if the pgsql *stripped* version evaulates to the empty string</para>
<para>Added already generated parser in release</para>
<para>Build scripts refinements</para>
<para>improved version handling, central Version.config</para>
<para>improvements in postgis_restore.pl</para>
</sect2>
</sect1>
<sect1>
<title>Release 1.0.0RC3</title>
<para>Release date: 2005/02/24</para>
<para>Third release candidate for 1.0.0.
Contains many bug fixes and improvements.</para>
<sect2>
<title>Upgrading</title>
<para>You need a dump/reload to upgrade
from precedent releases. See the <link
linkend="upgrading">upgrading</link>
chapter for more informations.</para>
</sect2>
<sect2>
<title>Library changes</title>
<para>BUGFIX in transform(): missing SRID, better error handling.</para>
<para>BUGFIX in memory alignment handling</para>
<para>BUGFIX in force_collection() causing mapserver connector failures on simple (single) geometry types.</para>
<para>BUGFIX in GeometryFromText() missing to add a bbox cache.</para>
<para>reduced precision of box2d output.</para>
<para>prefixed DEBUG macros with PGIS_ to avoid clash with pgsql one</para>
<para>plugged a leak in GEOS2POSTGIS converter</para>
<para>Reduced memory usage by early releasing query-context palloced one.</para>
</sect2>
<sect2>
<title>Scripts changes</title>
<para>BUGFIX in 72 index bindings.</para>
<para>BUGFIX in probe_geometry_columns() to work with PG72 and support multiple geometry columns in a single table</para>
<para>NEW bool::text cast</para>
<para>Some functions made IMMUTABLE from STABLE, for performance
improvement.</para>
</sect2>
<sect2>
<title>JDBC changes</title>
<para>jdbc2: small patches, box2d/3d tests, revised docs and license.</para>
<para>jdbc2: bug fix and testcase in for pgjdbc 8.0 type autoregistration</para>
<para>jdbc2: Removed use of jdk1.4 only features to enable build with older jdk releases.</para>
<para>jdbc2: Added support for building against pg72jdbc2.jar</para>
<para>jdbc2: updated and cleaned makefile</para>
<para>jdbc2: added BETA support for jts geometry classes</para>
<para>jdbc2: Skip known-to-fail tests against older PostGIS servers.</para>
<para>jdbc2: Fixed handling of measured geometries in EWKT.</para>
</sect2>
<sect2>
<title>Other changes</title>
<para>new performance tips chapter in manual</para>
<para>documentation updates: pgsql72 requirement, lwpostgis.sql</para>
<para>few changes in autoconf </para>
<para>BUILDDATE extraction made more portable</para>
<para>fixed spatial_ref_sys.sql to avoid vacuuming the whole
database.</para>
<para>spatial_ref_sys: changed Paris entries to match the ones
distributed with 0.x.</para>
</sect2>
</sect1>
<sect1>
<title>Release 1.0.0RC2</title>
<para>Release date: 2005/01/26</para>
<para>Second release candidate for 1.0.0
containing bug fixes and a few improvements.</para>
<sect2>
<title>Upgrading</title>
<para>You need a dump/reload to upgrade
from precedent releases. See the <link
linkend="upgrading">upgrading</link>
chapter for more informations.</para>
</sect2>
<sect2>
<title>Library changes</title>
<para>BUGFIX in pointarray box3d computation</para>
<para>BUGFIX in distance_spheroid definition</para>
<para>BUGFIX in transform() missing to update bbox cache</para>
<para>NEW jdbc driver (jdbc2)</para>
<para>GEOMETRYCOLLECTION(EMPTY) syntax support for backward compatibility</para>
<para>Faster binary outputs</para>
<para>Stricter OGC WKB/WKT constructors</para>
</sect2>
<sect2>
<title>Scripts changes</title>
<para>More correct STABLE, IMMUTABLE, STRICT uses in lwpostgis.sql</para>
<para>stricter OGC WKB/WKT constructors</para>
</sect2>
<sect2>
<title>Other changes</title>
<para>Faster and more robust loader (both i18n and not)</para>
<para>Initial autoconf script</para>
</sect2>
</sect1>
<sect1>
<title>Release 1.0.0RC1</title>
<para>Release date: 2005/01/13</para>
<para>This is the first candidate of a
major postgis release, with internal
storage of postgis types redesigned to be smaller
and faster on indexed queries.</para>
<sect2>
<title>Upgrading</title>
<para>You need a dump/reload to upgrade
from precedent releases. See the <link
linkend="upgrading">upgrading</link>
chapter for more informations.</para>
</sect2>
<sect2>
<title>Changes</title>
<para>
Faster canonical input parsing.
</para>
<para>
Lossless canonical output.
</para>
<para>
EWKB Canonical binary IO with PG>73.
</para>
<para>
Support for up to 4d coordinates, providing
lossless shapefile->postgis->shapefile
conversion.
</para>
<para>
New function: UpdateGeometrySRID(), AsGML(),
SnapToGrid(), ForceRHR(), estimated_extent(),
accum().
</para>
<para>
Vertical positioning indexed operators.
</para>
<para>
JOIN selectivity function.
</para>
<para>
More geometry constructors / editors.
</para>
<para>
Postgis extension API.
</para>
<para>
UTF8 support in loader.
</para>
</sect2>
</sect1>
</appendix>
</book>
Reference in a new issue View git blame Copy permalink