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This plugin supports reading raster datasets from [PostGIS](http://postgis.net).
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# Installation
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Make sure that running `python scons/scons.py` shows the following line
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Checking for pg_config... yes
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To check if the gdal plugin built and was installed correctly you can do:
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```python
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>>> from mapnik import DatasourceCache as c
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>>> 'pgraster' in c.plugin_names()
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True
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```
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## Parameters
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| *name = default value* | *type* | *description* |
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|:-----------------------------|:--------|:--------------|
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| host | string | name of the postgres host |
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| port | integer | name of the postgres port |
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| dbname | string | name of the database |
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| user | string | username to use for connecting |
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| password | string | user password to use for connecting |
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| application_name | string | connection [application_name](https://www.postgresql.org/docs/current/runtime-config-logging.html#GUC-APPLICATION-NAME). If omitted, then [fallback_application_name](https://www.postgresql.org/docs/current/libpq-connect.html#LIBPQ-CONNECT-FALLBACK-APPLICATION-NAME) = "mapnik" will be set instead. <br>Available in Mapnik >= 4.0 |
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| table | string | name of the table to fetch, this can be a sub-query; subquery has to use syntax of: '( ) as subquery'. |
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| 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 |
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| raster_table | string | name of the table containing the returned raster; for determining SRIDs with subselects |
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| 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 |
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| extent | string | maxextent of the rasters; if omitted, the extent will be determined by querying the metadata for the table |
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| extent_from_subquery = false | boolean | evaluate the extent of the subquery, this might be a performance issue |
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| estimate_extent = false | boolean | estimate extent from statistics table if not specified |
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| connect_timeout = 4 | integer | timeout is seconds for the connection to take place |
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| persist_connection = true | boolean | choose whether to share the same connection for subsequent queries |
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| row_limit = 0 | integer | max number of rows to return when querying data, 0 means no limit |
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| cursor_size = 0 | integer | if this is > 0 then server cursor will be used, and will prefetch this number of features |
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| initial_size = 1 | integer | initial size of the stateless connection pool |
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| max_size = 10 | integer | max size of the stateless connection pool |
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| prescale_rasters = false | boolean | whether to automatically scale input rasters |
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| use_overviews = false | boolean | whether to use raster overviews when available |
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| clip_rasters = false | boolean | whether to automatically clip input rasters |
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| max_async_connection = 1 | integer | max number of PostGIS queries for rendering one map in asynchronous mode. Full doc [here](Postgis-async). |
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| 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]] |
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# Styling
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To style a layer from PgRaster use the [[RasterSymbolizer]]
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# Using out-of-db rasters
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If you are using out-of-db raster files, then the ["outasin" parameter](http://postgis.net/docs/RT_ST_AsBinary.html) 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:
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```
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<Parameter name="table">(SELECT ST_AsBinary("rast", TRUE) FROM <table_name> WHERE "rast" && !bbox!) as rast</Parameter>
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```
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Note: the above is *only* required if parameters `prescale_rasters` or `clip_rasters` are *not* used.
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Additionally make sure you have set the `POSTGIS_ENABLE_OUTDB_RASTERS` and `POSTGIS_GDAL_ENABLED_DRIVERS`environment variables for PostGIS. See the [PostGIS installation page](http://postgis.net/docs/postgis_installation.html).
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On Ubuntu these variables are set in file `/etc/postgresql/<postgresql_version/main/environment`:
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```
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POSTGIS_ENABLE_OUTDB_RASTERS=1
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POSTGIS_GDAL_ENABLED_DRIVERS=ENABLE_ALL
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``` |
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\ No newline at end of file |
