PgRaster

This plugin supports reading raster datasets from PostGIS.

Installation

Make sure that running python scons/scons.py shows the following line

Checking for pg_config... yes

To check if the gdal plugin built and was installed correctly you can do:

    >>> from mapnik import DatasourceCache as c
    >>> 'pgraster' in c.plugin_names()
    True

Parameters

name = default value	type	description
host	string	name of the postgres host
port	integer	name of the postgres port
dbname	string	name of the database
user	string	username to use for connecting
password	string	user password to use for connecting
application_name	string	connection application_name. If omitted, then fallback_application_name = "mapnik" will be set instead. Available in Mapnik >= 4.0
table	string	name of the table to fetch, this can be a sub-query; subquery has to use syntax of: '( ) as subquery'.
raster_field	string	name of the raster field, in case you have more than one in a single table. Deduced from metadata tables if possible
raster_table	string	name of the table containing the returned raster; for determining SRIDs with subselects
srid = 0	integer	srid of the table, if this is > 0 then fetching data will avoid an extra database query for knowing the srid of the table
extent	string	maxextent of the rasters; if omitted, the extent will be determined by querying the metadata for the table
extent_from_subquery = false	boolean	evaluate the extent of the subquery, this might be a performance issue
estimate_extent = false	boolean	estimate extent from statistics table if not specified
connect_timeout = 4	integer	timeout is seconds for the connection to take place
persist_connection = true	boolean	choose whether to share the same connection for subsequent queries
row_limit = 0	integer	max number of rows to return when querying data, 0 means no limit
cursor_size = 0	integer	if this is > 0 then server cursor will be used, and will prefetch this number of features
initial_size = 1	integer	initial size of the stateless connection pool
max_size = 10	integer	max size of the stateless connection pool
prescale_rasters = false	boolean	whether to automatically scale input rasters
use_overviews = false	boolean	whether to use raster overviews when available
clip_rasters = false	boolean	whether to automatically clip input rasters
max_async_connection = 1	integer	max number of PostGIS queries for rendering one map in asynchronous mode. Full doc here.
band = 0	integer	request for a specific raster band index (1-based). 0 means to read all bands. Note that a band read from a single band raster gets interpreted as Grayscale if band=0 is specified while they retain their original value when explicitly referenced with the "band" parameter. This affects effectiveness of RasterColorizer

Styling

To style a layer from PgRaster use the RasterSymbolizer

Using out-of-db rasters

If you are using out-of-db raster files, then the "outasin" parameter of PostGIS must be used otherwise PostGIS just returns the file path. Mapnik does not support this parameter yet but you can achieve the same with a subquery for the table parameter:

<Parameter name="table">(SELECT ST_AsBinary("rast", TRUE) FROM <table_name> WHERE "rast" &amp;&amp; !bbox!) as rast</Parameter>

Note: the above is only required if parameters prescale_rasters or clip_rasters are not used.

Additionally make sure you have set the POSTGIS_ENABLE_OUTDB_RASTERS and POSTGIS_GDAL_ENABLED_DRIVERSenvironment variables for PostGIS. See the PostGIS installation page.

On Ubuntu these variables are set in file /etc/postgresql/<postgresql_version/main/environment:

POSTGIS_ENABLE_OUTDB_RASTERS=1
POSTGIS_GDAL_ENABLED_DRIVERS=ENABLE_ALL