= '''GDAL WKT Raster driver documentation''' =

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= '''1 - Introduction''' =

WKT Raster is the project that provides '''raster support on PostGIS'''. 

This driver was developed during the [http://socghop.appspot.com/ Google Summer of Code] 2009. The driver only supports reading of regularly blocked in-db rasters. There are other functionalities under development:
  * Reading of non-regular blocked rasters.
  * Out-db raster support.
  * Create and modify rasters.
  * Full integration with the GDAL utility programs.

== '''1.1 - Credits''' ==

'''Development '''
 * '''Jorge Arévalo''' develops the driver


== '''1.2 - More information''' ==
  * WKT Raster documentation page [http://trac.osgeo.org/postgis/wiki/WKTRaster/Documentation01 here]
  * Introduction to WKT Raster format and description of the work done during the Google Summer of Code 2009 [http://trac.osgeo.org/gdal/wiki/WKTRasterDriver here]
  * Search for "WKT Raster" in the [http://postgis.refractions.net/pipermail/postgis-users/ PostGIS-users] and [http://postgis.refractions.net/pipermail/postgis-devel/ PostGIS-devel] forums archives or in [http://www.nabble.com/PostGIS-f1221.html Nabble] or write to these forums.


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= '''2 - Installation''' =

== '''2.1 - Requirements''' ==

For using GDAL WKT Raster driver, you will first need to install:

 * [http://www.postgresql.org/ PostgreSQL] version 8.3 or higher
 * [http://trac.osgeo.org/proj Proj4 library] version 4.4 or higher
 * [http://trac.osgeo.org/geos GEOS library] version 3.2.0 or higher
 * [http://postgis.refractions.net/ PostGIS] version 1.4.0 or higher
 * [http://trac.osgeo.org/postgis/wiki/WKTRaster WKTRaster PostGIS extension] version 0.1.6SVN or higher
 * [http://www.python.org/ Python] version 2.5 or higher and [http://pypi.python.org/pypi/GDAL/ GDAL for Python] version 1.6.0 or higher for the loader (gdal2wktraster.py).

 
== '''2.2 - Installed precompiled binaries''' ==

For now, there is '''no precompiled binaries with WKT Raster'''. The driver will be part of the version '''1.7.0''' of the library.

== '''2.3 - Compiling and installing from sources''' ==

=== '''2.3.1 - Downloading source''' ===

Follow the instructions to compile the requisites [http://www.gis4free.org/blog/2009/05/30/gsoc-09-weekly-report-1-2305-2905/ here] '''(only the 5 first steps)'''. After this, you can download and install GDAL library as usual. But please, take into account that the driver isn't included in stable version yet. You'll have to checkout the code from SVN:

{{{
>$ svn checkout https://svn.osgeo.org/gdal/trunk/gdal gdal
}}}

Or, if you prefer it, download one of the [http://download.osgeo.org/gdal/daily/ GDAL daily builds]


=== '''2.3.2 - Building''' ===

You can find instructions on how to build GDAL library [http://trac.osgeo.org/gdal/wiki/BuildHints here].


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= '''3 - Using GDAL WKT Raster driver''' =

== '''3.1 - Loading raster data''' ==

The GDAL WKT Raster driver isn't able to load raster data yet. For this proposal, you'll have to use '''gdal2wktraster''' script. This loader script is included with the WKT Raster extension installation, under the ''scripts'' subdirectory. To check the syntax of the script, execute this command from ''$WKT_RASTER/scripts'' subdirectory:

{{{
>$ python gdal2wktraster.py --help
}}} 

'''Important:''' The out-db raster support for WKT Raster is still under development. Please, don't use this option.

'''Example 1''': 

Load [http://www.gis4free.org/gdal_wktraster_autotest/autotest/gdrivers/data/utm.tif this one-band grayscale image] (utm.tif) on PostGIS using loader script:

{{{
>$ python gdal2wktraster.py -r utm.tif -t utm -l 1 -k 100x100 -o utm.sql -s 26711 -I -M
}}}

In this example, the script generates a SQL output (redirected to the file ''utm.sql''). This SQL code adds the image ''utm.tif'' to PostGIS, using a regular blocking arrangement with blocks of 100x100px. To execute the code, you must run this command as '''postgres''' user:

{{{
>$ psql -d <wktraster_database> -f utm.sql
}}}

The ''wktraster_database'' must be a PostgreSQL database with PostGIS and WKT Raster extensions enabled.

'''Example 2''':

Load [http://www.gis4free.org/gdal_wktraster_autotest/autotest/gdrivers/data/small_world.tif this RGB image] (small_world.tif) on PostGIS using loader script:

{{{
>$ python gdal2wktraster.py -r small_world.tif -t utm -l 1 -k 40x20 -o small_world.sql -s 4326 -I -M
}}}

As in ''Example 1'', this code generates a SQL file, called ''small_world.sql'' with the SQL code to add the image ''small_world.tif'' to PostGIS using a regular blocking arrangement with blocks of 40x20px. To execute the code, as '''postgres''' user, run:

{{{
>$ psql -d <wktraster_database> -f small_world.sql
}}}


'''Example 3''':

Using the first image (utm.tif), let's create an overview of the image of half size (meaning image dimensions, not file size) in PostGIS.

{{{
>$ python gdal2wktraster.py -r utm.tif -t utm -l 2 -V -k 100x100 -o utm_ov2.sql -s 26711 -I -M
}}}

The key concept here is the '''-V''' flag. This flag allows loader script to create a new table to store the overviews' metadata. If you want to load several images with overviews, you'll have to use this flag '''only the first time''' the loader script is called, to create the overviews' metadata table only once.

The '''-l 2''' flag represents the overview level. 2 means an overview of the 50% of the original image size.

As usual, to execute the generated SQL code, run as '''postgres''' this command:

{{{
>$ psql -d <wktraster_database> -f utm_ov2.sql
}}}

== '''3.2 - Reading data''' ==

If you want to use the GDAL WKT Raster driver, you must provide a '''connection string''' as Dataset's name. The syntax of this connection string is (respect the quotes):


{{{
 PG":host='<host>' dbname='<dbname>' user='<user>' password='<password>' table='<raster_table>' [where='<sql_where>' mode='<working_mode>']"
}}}

Note that the string, until the part that starts with "table='" is a libpq-style [http://www.gdal.org/ogr/drv_pg.html connection string]. That means that you can change the order of these fields (dbname, user, password, host), or leave out unnecessary ones (like password, in some cases). But the rest of the connection string must have the syntax and order shown above.

The "table" option requires the name of a WKT Raster table. This table only can be created by using the script gdal2tiles, from [http://trac.osgeo.org/postgis/wiki/WKTRaster WKTRaster code]

The "where" option is used to filter the results of the raster table. Any SQL-WHERE expression is valid. The "mode" option is used to know the expected arrangement of the raster table. As the driver is currently working with only one table arrangement (regularly blocked tables), you can omit this option, or use it with value "REGULARLY_TILED_MODE". Otherwise, the driver won't work.

You must use this dataset's format in all the gdal tools, like gdalinfo, gdal_translate, gdalwarp, etc.

'''Example 1:'''

To get info about ''utm.tif'' file stored in database (see section 3.1) run this command:

{{{
>$ gdalinfo -mm -stats -checksum "PG:host='localhost' dbname='<wktraster_database>' user='<wktraster_user>' password='<wktraster_password>' table='utm'"
}}}

As user / password, in a typical installation, you can use '''postgres / postgres'''


'''Example 2:'''

To get an overview of the original image with half size run this command:

{{{
>$ gdal_translate -outsize 50% 50% "PG:host='localhost' dbname='<wktraster_database>' user='<wktraster_user>' password='<wktraster_password>' table='utm'" utm_half_size.tif 
}}}

This will create a file called ''utm_half_size.tif'' like the original ''utm.tif'' but half size.


== '''3.3 - Creating and modifying data''' ==

The GDAL WKT Raster driver is not able to create and modify rasters yet. You'll have to use '''gdal2wktraster''' loader to create new ones.


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= '''4 - GDAL WKT Raster driver reference''' =

TODO

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= '''5 - Reporting problems''' =

Take into account this driver '''is not part of the official GDAL library yet'''. Anyway, if you use it and find any error, if you want to suggest something or if you simply want to say ''hello'' :-), write a mail to ''jorgearevalo at gis4free dot org''