10 SQLite

rinigus edited this page 2017-04-24 12:28:54 +03:00

Table of Contents

• Parameters
• Usage
• C++
• Further References

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 "generic", "spatialite", or "twkb"	not set, determined automatically by testing for generic (WKB) or spatialite content
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