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SQLite

springmeyer edited this page Mar 14, 2013 · 9 revisions
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Mapnik's PluginArchitecture supports the use of different input formats.

One such plugin supports the sqlite (SQLite). The plugin works with two types of geometry storage methods - raw OGC WKB and (Spatialite) geometries.

You can create a pure SQLite + WKB geometry based sqlite db using ogr like:

ogr2ogr -f SQLite test.sqlite some.shp

You can create a spatialite enabled db also using ogr:

ogr2ogr -f SQLite test.sqlite some.shp -dsco SPATIALITE=YES

For more details see: http://www.gdal.org/ogr/drv_sqlite.html

The main difference is that a spatialite enabled db will include a spatial index inside the database. A pure SQLite db will not contain a spatial index, but Mapnik can create one on the fly.

Parameters

parameter value description default
file string sqlite database file path
base string optional base path where to search for the sqlite database file
table string name of the table to fetch, this can be a sub-query
metadata string name of the metadata table where the extent and srid of the table are specified
key_field string name of the id field of the table OGC_FID
geometry_field string name of the geometry field, in case you have more than one in a single table the_geom
extent string maxextent of the geometries determined by querying the metadata table
row_offset integer number of rows to skip when querying data 0
row_limit integer max number of rows to return when querying data, 0 means no limit 0
wkb_format string type of WKB in the geometry field blob, this can be "sqlite" or "spatialite" sqlite
use_spatial_index boolean choose wheter to use the spatial index when fetching data true
multiple_geometries boolean wheter to use multiple different objects or a single one when dealing with multi-objects (this is mainly related to how the label are used in the map, one label for a multi-polygon or one label for each polygon of a multi-polygon) false
encoding string internal file encoding utf-8

Usage

Note:

  • Spatial tables read from sqlite by Mapnik must have a cooresponding entry in geometry_columns.
  • Use the geometry_field parameter to specify which field to use if you have >1 geometry in the table/query.

C++

Plugin datasource initialization example code can be found on PluginArchitecture.

A Sqlite datasource may be created as follows:

    {
        parameters p;
        p["type"]="sqlite";
        p["file"]=sqlite_spatial_database_file;
        p["table"]="bridges";
        p["geometry_field"]="geom";
        p["extent"]="2309554.99818767,5024797.73763923,2318414.90507308,5040447.94690007";

        set_datasource(datasource_cache::instance()->create(p));

        // Bridges
        Layer lyr("Bridges");
        lyr.add_style("bridges"); // in style.xml
        m.addLayer(lyr);
    }

Further References

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