PostGIS Python tools
plpygis is a Python conveter to and from the PostGIS geometry type, WKB, EWKB, GeoJSON and Shapely geometries and additionally supports __geo_interface__. plpygis is intended for use in PL/Python functions.
The Geometry class and its subclasses can be used to convert to and from PostGIS geometries. The following example will take a PostGIS multipolygon geometry named geom and find its largest component polygon.
Geometry() can convert a Postigs geometry that has been passed as a parameter to a PL/Python function. A Geometry that is returned from the PL/Python function will automatically be converted back to a PostGIS geometry.
CREATE OR REPLACE FUNCTION largest_poly(geom geometry) RETURNS geometry AS $$ from plpygis import Geometry polygons = Geometry(geom) if polygons.type == "Polygon": return polygons elif polygons.type == "MultiPolygon": largest = max(polygons.shapely, key=lambda polygon: polygon.area) return Geometry.from_shapely(largest) else: return None $$ LANGUAGE plpythonu;
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