PostGIS Python tools
Project description
plpygis is a Python tool that can convert a PostGIS geometry into an equivalent WKB, EWKB, GeoJSON or Shapely geometry. plpygis is intended for use in PostgreSQL PL/Python functions.
Basic usage
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 PostGIS 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 plpython3u;
This can then be called as part of an SQL query:
SELECT largest_poly(geom) FROM countries;
Documentation
Full plpygis documentation is available at http://plpygis.readthedocs.io/.
Project details
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