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261 lines
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261 lines
15 KiB
XML
<?xml version="1.0" encoding="UTF-8"?>
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<chapter id="RT_FAQ">
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<title>PostGIS Raster Frequently Asked Questions</title>
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<qandaset>
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<qandaentry>
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<question>
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<para>Where can I find out more about the PostGIS Raster Project?</para>
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</question>
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<answer>
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<para>Refer to the <ulink url="http://trac.osgeo.org/postgis/wiki/WKTRaster">PostGIS Raster home page</ulink>.</para>
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</answer>
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</qandaentry>
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<qandaentry>
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<question>
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<para>Are there any books or tutorials to get me started with this wonderful invention?</para>
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</question>
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<answer>
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<para>There is a full length beginner tutorial <ulink url="http://trac.osgeo.org/postgis/wiki/WKTRasterTutorial01"> Intersecting vector buffers with large raster coverage using PostGIS Raster</ulink>.
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Jorge has a series of blog articles on PostGIS Raster that demonstrate how to load raster data as well as cross compare to same tasks in Oracle GeoRaster. Check out
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<ulink url="http://gis4free.wordpress.com/category/postgis-raster/">Jorge's PostGIS Raster / Oracle GeoRaster Series</ulink>.
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There is a whole chapter (more than 35 pages of content) dedicated to PostGIS Raster with free code and data downloads at <ulink url="http://www.postgis.us/chapter_13">PostGIS in Action - Raster chapter</ulink>.
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You can <ulink url="http://www.postgis.us/page_buy_book">buy PostGIS in Action</ulink> now from Manning in hard-copy (significant discounts for bulk purchases) or just the E-book format.
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You can also buy from Amazon and various other book distributors. All hard-copy books come with a free coupon to download the E-book version.
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</para>
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<para>Here is a review from a PostGIS Raster user <ulink url="http://fuzzytolerance.info/code/postgis-raster-ftw/">PostGIS raster applied to land classification urban forestry</ulink></para>
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</answer>
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</qandaentry>
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<qandaentry>
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<question>
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<para>How do I install Raster support in my PostGIS database?</para>
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</question>
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<answer>
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<para>The easiest is to download binaries for PostGIS and Raster which are currently available for windows and latest versions of Mac OSX.
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First you need a working PostGIS 1.3.5 or above and be running PostgreSQL 8.3, 8.4, or 9.0. Note in PostGIS 2.0 PostGIS Raster is fully integrated, so it will be compiled when you compile PostGIS.</para>
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<para>Instructions for installing and running under windows are available at <ulink url="http://gis4free.wordpress.com/2011/03/10/how-to-install-and-configure-postgis-raster-on-windows/">How to Install and Configure PostGIS raster on windows</ulink></para>
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<para>
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If you are on windows, you can compile yourself, or use the <ulink
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url="http://www.postgis.org/download/windows/experimental.php#wktraster">pre-compiled
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PostGIS Raster windows binaries</ulink>.
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If you are on Mac OSX Leopard or Snow Leopard, there are binaries available at <ulink url="http://www.kyngchaos.com/software/postgres">Kyng Chaos Mac OSX PostgreSQL/GIS binaries</ulink>.
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</para>
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<para>Then to enable raster support in your database, run the rtpostgis.sql file in your database.</para>
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<para>For other platforms, you generally need to compile yourself. Dependencies are PostGIS and GDAL. For more details about compiling from source, please refer to <ulink url="http://trac.osgeo.org/postgis/wiki/WKTRaster/Documentation01#a2.3-CompilingandInstallingfromSources">Installing PostGIS Raster from source (in prior versions of PostGIS)</ulink></para>
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</answer>
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</qandaentry>
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<qandaentry>
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<question>
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<para>I get error could not load library "C:/Program Files/PostgreSQL/8.4/lib/rtpostgis.dll": The specified module could not be found.
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or could not load library on Linux when trying to run rtpostgis.sql</para>
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</question>
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<answer>
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<para>rtpostgis.so/dll is built with dependency on libgdal.dll/so. Make sure for Windows you have libgdal.dll in the bin folder of your PostgreSQL install.
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For Linux libgdal has to be in your path or bin folder. </para>
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<para>You may also run into different errors if you don't have PostGIS installed in your database. Make sure to install PostGIS first in your
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database before trying to install the raster support.</para>
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</answer>
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</qandaentry>
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<qandaentry>
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<question>
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<para>How do I load Raster data into PostGIS?</para>
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</question>
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<answer>
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<para>Currently you need <ulink url="http://www.gdal.org/">GDAL 1.6+</ulink> though later versions would be better since they have many memory leak fixes, <ulink url="http://www.python.org/download/releases/2.5/">Python 2.5</ulink> with <ulink url="http://pypi.python.org/pypi/GDAL/1.6.1">GDAL 1.6 or higher bindings</ulink>,
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and <ulink url="http://pypi.python.org/pypi/numpy">NumPy</ulink>.</para>
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<para>
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For windows users, installing these components from binary sources is documented in the
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ReadMe.txt packaged with the <ulink
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url="http://www.postgis.org/download/windows/experimental.php#wktraster">Windows
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PostGIS Raster experimental builds</ulink>.</para>
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<para>Once you have a functioning Python with GDAL and NumPy, you can
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use the raster2pgsql.py script packaged with PostGIS Raster.</para>
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<para>Please refer to <ulink url="http://trac.osgeo.org/gdal/wiki/frmts_wtkraster.html">raster2pgsql.py usage</ulink> and <xref linkend="RT_Loading_Rasters" /> for more details.</para>
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</answer>
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</qandaentry>
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<qandaentry>
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<question>
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<para>What kind of raster file formats can I load into my database?</para>
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</question>
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<answer>
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<para>Any that your GDAL library supports. GDAL supported formats are documented <ulink url="http://www.gdal.org/formats_list.html">GDAL File Formats</ulink>.</para>
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<para>Your particular GDAL install may not support all formats. To verify the ones supported by your particular GDAL install, you can use</para>
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<programlisting>gdalinfo --formats</programlisting>
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</answer>
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</qandaentry>
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<qandaentry>
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<question>
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<para>Can I export my PostGIS raster data to other raster formats?</para>
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</question>
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<answer>
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<para>Yes</para>
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<para>GDAL 1.7+ has a PostGIS raster driver, but is only compiled in if you choose to compile with PostgreSQL support. </para>
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<para>The driver currently doesn't support irregularly blocked rasters,
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although you can store irregularly blocked rasters in PostGIS raster data type.</para>
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<para>If you are compiling from source, you need to include in your configure
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<programlisting>--with-pg=path/to/pg_config</programlisting> to enable the driver.
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Refer to <ulink url="http://trac.osgeo.org/gdal/wiki/BuildHints">GDAL Build Hints</ulink> for tips
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on building GDAL against in various OS platforms.
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</para>
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<para>If your version of GDAL is compiled with the PostGIS Raster driver
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you should see PostGIS Raster in list when you do
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<programlisting>gdalinfo --formats</programlisting></para>
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<para>To get a summary about your raster via GDAL use gdalinfo:
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<programlisting>gdalinfo "PG:host=localhost port=5432 dbname='mygisdb' user='postgres' password='whatever' schema='someschema' table=sometable"</programlisting>
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</para>
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<para>To export data to other raster formats,
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use gdal_translate the below will export all data from a table to a PNG file at 10% size.</para>
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<para>Depending on your pixel band types, some translations may not work if the export format does not support that Pixel type.
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For example floating point band types and 32 bit unsigned ints
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will not translate easily to JPG or some others.</para>
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<para>Here is an example simple translation</para>
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<programlisting>gdal_translate -of PNG -outsize 10% 10% "PG:host=localhost dbname='mygisdb' user='postgres' password=whatever' schema='someschema' table=sometable" C:\somefile.png</programlisting>
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<para>You can also use SQL where clauses in your export using the where=... in your driver connection string.
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Below are some using a where clause</para>
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<programlisting>gdal_translate -of PNG -outsize 10% 10% "PG:host=localhost dbname='mygisdb' user='postgres' password=whatever' schema='someschema' table=sometable where="owner='jimmy'" " C:\somefile.png</programlisting>
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<programlisting>gdal_translate -of PNG -outsize 10% 10% "PG:host=localhost dbname='mygisdb' user='postgres' password=whatever' schema='someschema' table=sometable where='ST_Intersects(rast, ST_SetSRID(ST_Point(-71.032,42.3793),4326) )' " C:\intersectregion.png</programlisting>
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<para>To see more examples and syntax refer to <ulink url="http://trac.osgeo.org/gdal/wiki/frmts_wtkraster.html#a3.2-Readingdata">Reading Raster Data of PostGIS Raster section</ulink></para>
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</answer>
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</qandaentry>
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<qandaentry>
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<question><para>Are their binaries of GDAL available already compiled with PostGIS Raster suppport?</para></question>
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<answer>
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<para>Yes. Check out the page <ulink url="http://trac.osgeo.org/gdal/wiki/DownloadingGdalBinaries">GDAL Binaries</ulink> page. Any compiled wiht PostgreSQL
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support should have PostGIS Raster in them. </para>
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<para>We know for sure the following windows binaries have PostGIS Raster built in.</para>
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<para><ulink url="http://fwtools.maptools.org/">FWTools latest stable version for Windows is compiled with Raster support</ulink>.</para>
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<para>PostGIS Raster is undergoing many changes. If you want to get the latest nightly build for Windows -- then check out
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the Tamas Szekeres nightly builds built with Visual Studio which contain GDAL trunk, Python Bindings and MapServer executables and PostGIS Raster driver built-in. Just
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click the SDK bat and run your commands from there. <ulink url="http://vbkto.dyndns.org/sdk/">http://vbkto.dyndns.org/sdk/</ulink>.
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Also available are VS project files.</para>
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</answer>
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</qandaentry>
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<qandaentry>
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<question>
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<para>What tools can I use to view PostGIS raster data?</para>
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</question>
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<answer>
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<para>You can use MapServer compiled with GDAL 1.7+ and PostGIS Raster driver support to view Raster data.
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In theory any tool that renders data using GDAL can support PostGIS raster data or
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support it with fairly minimal effort. Again for Windows Tamas binaries <ulink url="http://vbkto.dyndns.org/sdk/">http://vbkto.dyndns.org/sdk/</ulink> are a good choice if you don't want the hassle of having to setup to compile your own.</para>
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</answer>
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</qandaentry>
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<qandaentry>
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<question>
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<para>How can I add a PostGIS raster layer to my MapServer map?</para>
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</question>
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<answer>
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<para>You can much like you can with any other raster.
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Refer to <ulink url="http://mapserver.org/input/raster.html">MapServer Raster processing options</ulink>
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for list of various processing functions you can use with MapServer raster layers.</para>
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<para>What makes PostGIS raster data particularly interesting, is that since
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each tile can have various standard database columns, you can segment it in your data source</para>
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<para>Below is an example of how you would define a PostGIS raster layer in MapServer.</para>
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<note><para>The mode=2 is required for tiled rasters and was added in PostGIS 2.0 and GDAL 1.8 drivers. This does not exist in GDAL 1.7 drivers.</para></note>
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<programlisting>
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-- displaying raster with standard raster options
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LAYER
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NAME coolwktraster
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TYPE raster
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STATUS ON
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DATA "PG:host=localhost port=5432 dbname='somedb' user='someuser' password='whatever'
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schema='someschema' table='cooltable' mode='2'"
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PROCESSING "NODATA=0"
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PROCESSING "SCALE=AUTO"
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#... other standard raster processing functions here
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#... classes are optional but useful for 1 band data
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CLASS
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NAME "boring"
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EXPRESSION ([pixel] < 20)
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COLOR 250 250 250
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END
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CLASS
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NAME "mildly interesting"
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EXPRESSION ([pixel] > 20 AND [pixel] < 1000)
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COLOR 255 0 0
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END
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CLASS
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NAME "very interesting"
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EXPRESSION ([pixel] >= 1000)
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COLOR 0 255 0
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END
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END
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</programlisting>
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<programlisting>
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-- displaying raster with standard raster options and a where clause
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LAYER
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NAME soil_survey2009
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TYPE raster
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STATUS ON
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DATA "PG:host=localhost port=5432 dbname='somedb' user='someuser' password='whatever'
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schema='someschema' table='cooltable' where='survey_year=2009' mode='2'"
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PROCESSING "NODATA=0"
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#... other standard raster processing functions here
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#... classes are optional but useful for 1 band data
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END
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</programlisting>
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</answer>
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</qandaentry>
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<qandaentry>
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<question>
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<para>What functions can I currently use with my raster data?</para>
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</question>
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<answer>
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<para>Refer to the list of <xref linkend="RT_reference" />.
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There are more, but this is still a work in progress.</para>
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<para>Refer to the <ulink
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url="http://trac.osgeo.org/postgis/wiki/WKTRaster/PlanningAndFunding">PostGIS Raster roadmap page</ulink>
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for details of what you can expect in the future.</para>
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</answer>
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</qandaentry>
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<qandaentry>
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<question>
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<para>How is PostGIS Raster different from Oracle GeoRaster (SDO_GEORASTER) and SDO_RASTER types?</para>
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</question>
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<answer>
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<para>For a more extensive discussion on this topic, check out Jorge Arévalo <ulink url="http://gis4free.wordpress.com/2010/07/19/oracle-georaster-part-i/">Oracle GeoRaster and PostGIS Raster: First impressions </ulink></para>
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<para>The major advantage of one-georeference-by-raster over one-georeference-by-layer is to allow:</para>
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<para>* coverages to be not necessarily rectangular (which is often the case of raster coverage covering large extents. See the possible raster arrangements in the documentation)</para>
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<para>* rasters to overlaps (which is necessary to implement lossless vector to raster conversion) </para>
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<para>These arrangements are possible in Oracle as well, but they imply
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the storage of multiple SDO_GEORASTER objects linked to as many
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SDO_RASTER tables. A complex coverage can lead to hundreds of tables in
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the database. With PostGIS Raster you can store a similar raster arrangement into a unique table.</para>
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<para>It's a bit like if PostGIS would force you to store only full rectangular vector coverage without gaps or overlaps (a perfect rectangular topological layer).
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This is very practical in some applications but practice has shown that it is not realistic or desirable for most geographical coverages. Vector structures needs the flexibility to store discontinuous and non-rectangular coverages.
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We think it is a big advantage that raster structure should benefit as well. </para>
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</answer>
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</qandaentry>
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</qandaset>
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</chapter>
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