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Created PgRaster (markdown)

Sandro Santilli 2016-03-23 11:02:17 +01:00
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This plugin supports reading raster datasets from [PostGIS](http://postgis.net).
# 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:
```python
>>> from mapnik import DatasourceCache as c
>>> 'pgraster' in c.plugin_names()
True
```
## Parameters
| *parameter* | *value* | *description* | *default* |
|:------------------|----------|---------------|----------:|
| 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 | |
| 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. This field and the SRID will be deduced from the query in most cases, but may need to be manually specified in some cases.| |
| raster_table | string | name of the table containing the returned raster; for determining SRIDs with subselects | |
| srid | 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 | 0 |
| extent | string | maxextent of the rasters | determined by querying the metadata for the table |
| extent_from_subquery | boolean | evaluate the extent of the subquery, this might be a performance issue | false |
| estimate_extent | boolean | estimate extent from statistics table if not specified | false |
| connect_timeout | integer | timeout is seconds for the connection to take place | 4 |
| persist_connection | boolean | choose whether to share the same connection for subsequent queries | true |
| row_limit | integer | max number of rows to return when querying data, 0 means no limit | 0 |
| cursor_size | integer | if this is > 0 then server cursor will be used, and will prefetch this number of features | 0 |
| initial_size | integer | initial size of the stateless connection pool | 1 |
| max_size | integer | max size of the stateless connection pool | 10 |
| prescale_rasters | boolean | whether to automatically scale input rasters | false |
| use_overviews | boolean | whether to use raster overviews when available | false |
| clip_rasters | boolean | whether to automatically clip input rasters | false |
| ~~asynchronous_request~~ | boolean | ~~Postgres queries are sent asynchronously : while rendering a layer, queries for further layers will run in parallel in the remote server. Available from version 2.3.x up.~~ | *DEPRECATED* (automatically set internally based on `max_async_connection > 1` condition) |
| max_async_connection | integer | max number of PostGIS queries for rendering one map in asynchronous mode. Full doc [here](Postgis-async). ~~Used only when asynchronous_request=true.~~ Default value (1) has no effect. | 1 |
| band | 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]] | 0 |