# PostGISRaster --- PostGIS Raster driver

PostGIS Raster (previously known as WKT Raster) is the project that provides raster support on PostGIS. Since September 26st, 2010, is an official part of PostGIS 2.0+.

This driver was started during the ​Google Summer of Code 2009, and significantly improved since then.

Currently, the driver provides read-only support to PostGIS Raster data sources.

## Connecting to a database

To connect to a PostGIS Raster datasource, use a connection string specifying the database name, with additional parameters as necessary

    PG:"[host='<host>'] [port:'<port>'] dbname='<dbname>' [user='<user>'] [password='<password>'] [schema='<schema>'] [table='<raster_table>'] [column='<raster_column>'] [where='<sql_where>'] [mode='<working_mode>'] [outdb_resolution='<outdb_resolution>']"

Note that the string, up to the part starting with "table='" is a libpq-style ​connection string. That means that you can leave out unnecessary fields (like password, in some cases).

- schema - name of PostgreSQL schema where requested raster table is stored.
- table - name of PostGIS Raster table. The table was created by the raster loader (eg. raster2pgsql utility).
- column - name of raster column in raster table
- where - option is used to filter the results of the raster table. Any SQL-WHERE expression is valid.
- mode - option is used to know the expected arrangement of the raster table. There are 2 possible values
  - mode=1 - ONE_RASTER_PER_ROW mode. In this case, a raster table is considered as a bunch of different raster files. This mode is intended for raster tables storing different raster files. It's the default mode if you don't provide this field in connection string.
  - mode=2 - ONE_RASTER_PER_TABLE mode. In this case, a raster table is considered as a unique raster file, even if the table has more than one row. This mode is intended for reading tiled rasters from database.
- outdb_resolution - (GDAL >= 2.3.1) option to specify how out-database rasters should be resolved. Default is server_side.
  - server_side: The outDB raster will be fetched by the PostgreSQL server. This implies that outdb rasters are enabled on the server.
  - client_side: The outDB raster filenames will be returned to the GDAL PostGISRaster client, which will open it on the client side. This implies that the filename stored on te server can be accessed by the client.
  - client_side_if_possible: The outDB raster filenames will be returned to the GDAL PostGISRaster client, which will check if it can access them. If it can, that's equivalent to client_side. Otherwise that's equivalent to server_side. Note that this mode involves extra queries to the server.

### Additional notes

If a table stores a tiled raster and you execute the driver with mode=1, each image tile will be considered as a different image, and will be reported as a subdataset. There are use cases the driver can't still work with. For example: non-regular blocked rasters. That cases are detected and an error is raised. Anyway, as I've said, the driver is under development, and will work with more raster arrangements ASAP.

There's an additional working mode. If you don't provide a table name, the driver will look for existing raster tables in all allowed database' schemas, and will report each table as a subdataset.

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

### Performance hints

To get the maximum performance from the driver, it is best to load the raster in PostGIS raster with the following characteristics:

- tiled: -t switch of raster2pgsql
- with overview: -l 2,4,8,... switch of raster2pgsql
- with a GIST spatial index on the raster column: -I switch of raster2pgsql
- with constraints registered: -C switch of raster2pgsql

## Examples

To get a summary about your raster via GDAL use gdalinfo:

    gdalinfo  "PG:host=localhost port=5432 dbname='mydb' user='postgres' password='secret' schema='public' table=mytable"

For more examples, check the PostGIS Raster FAQ section: ​Can I export my PostGIS Raster data to other raster formats?

## Credits

The driver developers

- Jorge Arévalo (jorgearevalo at libregis.org)
- David Zwarg (dzwarg at azavea.com)
- Even Rouault (even.rouault at mines-paris.org)

## See Also

- GDAL PostGISRaster driver Wiki
- PostGIS Raster documentation