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163 lines
5.5 KiB
Plaintext
163 lines
5.5 KiB
Plaintext
PostGIS - Geographic Information Systems Extensions to PostgreSQL
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~~~~~~~ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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VERSION: 0.7.4 (2003/02/12)
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MORE INFORMATION: http://postgis.refractions.net
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INTRODUCTION:
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This distribution contains a module which implements GIS simple
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features, ties the features to rtree indexing, and provides some
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spatial functions for accessing and analyzing geographic data.
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Directory structure:
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./ Core source code, makefiles and install directions.
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./jdbc Extensions to the PostgreSQL JDBC drivers to support
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the GIS objects.
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./doc Documentation on the code, objects and functions
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provided.
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./loader A program to convert ESRI Shape files into SQL text
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suitable for uploading into a PostGIS/PostgreSQL database.
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./examples Small programs which demonstrate ways of accessing
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GIS data.
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INSTALLATION:
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PostGIS is compatible with PostgreSQL 7.1 and above.
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To install the module, move this directory to the "contrib" directory of your
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PostgreSQL source installation. Alternately, edit the "top_buildir" in the
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Makefile and point it at your PostgreSQL source tree. You must have a
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PostgreSQL source tree, and you must have run succesfully built and installed
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it for this to work.
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* PROJ4 SUPPORT:
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The Proj4 reprojection library is required if you want to use the
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transform() function to reproject features within the database.
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Install Proj4 in the default location.
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Edit the postgis Makefile and change the USE_PROJ variable to 1
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and ensure that the PROJ_DIR variable points to your Proj4
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installation location (/usr/local is the default).
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As root run:
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make
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make install
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PostGIS now requires the PL/pgSQL procedural language in order to operate
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correctly. To install PL/pgSQL use the 'createlang' program from the PostgreSQL
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installation. (The PostgreSQL Programmer's Guide has details if you want
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to this manually for some reason.)
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As postgres run:
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createlang plpgsql yourdatabase
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psql -f postgis.sql -d yourdatabase
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Installation should now be complete.
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UPGRADING:
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Upgrading PostGIS can be tricky, because the underlying C libraries which
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support the object types and geometries may have changed between versions.
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To avoid problems when upgrading, you will have to dump all the tables
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in your database, destroy the database, create a new one, add the PL/pgSQL
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language, upload the new postgis.sql file, then upload your database dump:
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pg_dump -t "*" -f dumpfile.sql yourdatabase
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dropdb yourdatabase
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createdb yourdatabase
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createlang plpgsql yourdatabase
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psql -f postgis.sql -d yourdatabase
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psql -f dumpfile.sql -d yourdatabase
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vacuumdb -z yourdatabase
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When upgrading to 0.6+, all your geometries will be created with an SRID
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of -1. To create valid OpenGIS geometries, you will have to create a
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valid SRID in the SPATIAL_REF_SYS table, and then update your geometries
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to reference the SRID with the following SQL (with the appropriate
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substitutions:
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UPDATE <table> SET <geocolumn> = SetSRID(<geocolumn>,<SRID>);
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USAGE:
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Try the following example SQL statements to create non-OpenGIS tables and
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geometries:
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CREATE TABLE geom_test ( gid int4, geom geometry,name varchar(25) );
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INSERT INTO geom_test ( gid, geom, name )
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VALUES ( 1, 'POLYGON((0 0 0,0 5 0,5 5 0,5 0 0,0 0 0))', '3D Square');
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INSERT INTO geom_test ( gid, geom, name )
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VALUES ( 2, 'LINESTRING(1 1 1,5 5 5,7 7 5)', '3D Line' );
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INSERT INTO geom_test ( gid, geom, name )
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VALUES ( 3, 'MULTIPOINT(3 4,8 9)', '2D Aggregate Point' );
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SELECT * from geom_test WHERE geom && 'BOX3D(2 2 0,3 3 0)'::box3d;
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The following SQL creates proper OpenGIS entries in the SPATIAL_REF_SYS
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and GEOMETRY_COLUMNS tables, and ensures that all geometries are created
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with an SRID.
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INSERT INTO SPATIAL_REF_SYS
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( SRID, AUTH_NAME, AUTH_SRID, SRTEXT ) VALUES
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( 1, 'EPSG', 4269,
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'GEOGCS["NAD83",
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DATUM[
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"North_American_Datum_1983",
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SPHEROID[
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"GRS 1980",
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6378137,
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298.257222101
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]
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],
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PRIMEM["Greenwich",0],
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UNIT["degree",0.0174532925199433]]'
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);
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CREATE TABLE geotest (
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id INT4,
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name VARCHAR(32)
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);
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SELECT AddGeometryColumn('db','geotest','geopoint',1,'POINT',2);
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INSERT INTO geotest (id, name, geopoint)
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VALUES (1, 'Olympia', GeometryFromText('POINT(-122.90 46.97)',1));
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INSERT INTO geotest (id, name, geopoint)
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VALUES (2, 'Renton', GeometryFromText('POINT(-122.22 47.50)',1));
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SELECT name,AsText(geopoint) FROM geotest;
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Spatial Indexes:
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PostgreSQL provides support for GiST spatial indexing. The GiST scheme offers
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indexing even on large objects, using a system of "lossy" indexing where
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a large object is proxied by a smaller one in the index. In the case
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of the PostGIS indexing system, all objects are proxied in the index by
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their bounding boxes.
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You can build a GiST index with:
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CREATE INDEX <indexname> ON <tablename>
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USING gist ( <geometryfield> gist_geometry_ops );
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Always run the "VACUUM ANALYZE <tablename>" on your tables after
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creating an index. This gathers statistics which the query planner
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uses to optimize index usage.
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Note that PostgreSQL may occasionally not use the GiST indexes when
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performing searches. If you find your system is not using the
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indexes automatically (use 'EXPLAIN' to see the query plan)
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you can force index use with the command:
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SET ENABLE_SEQSCAN = OFF
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Try doing an EXPLAIN on your query before and after the 'enable_seqscan'
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command to see the different query plans.
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