plpygis is a pure Python module with no dependencies that can convert geometries between Well-known binary (WKB), Extended Well-known Binary (EWKB) and GeoJSON representations. plpygis is mainly intended for use in PostgreSQL PL/Python functions to augment PostGIS's native capabilities.
plpygis implements several subclasses of the Geometry class, such as Point, LineString, MultiPolygon and so on:
>>> from plpygis import Point
>>> p = Point((-124.005, 49.005), srid=4326)
>>> print(p.wkb)
0101000020e6100000b81e85eb51005fc0713d0ad7a3804840
>>> print(p.geojson)
{'type': 'Point', 'coordinates': [-124.005, 49.005]}plpygis is designed to provide an easy way to implement PL/Python functions that accept geometry arguments or return geometry results. The following example will take a PostGIS geometry(Point) and use an external service to create a geometry(PointZ).
CREATE OR REPLACE FUNCTION add_elevation(geom geometry(POINT))
RETURNS geometry(POINTZ)
AS $$
from plpygis import Geometry, Point
from requests import get
point = Geometry(geom)
response = get(f'https://api.open-meteo.com/v1/elevation?longitude={point.x}&latitude={point.y}')
if response.status_code == 200:
content = response.json()
point.z = content['elevation'][0]
return point
else:
return None
$$ LANGUAGE plpython3u;
The Geometry() constructor will convert a PostGIS geometry that has been passed as a parameter to the PL/Python function into one of its plpygis subclasses. A Geometry that is returned from the PL/Python function will automatically be converted back to a PostGIS geometry.
The function above can be called as part of an SQL query:
SELECT name, ST_AsText(add_elevation(geom)) FROM city;
Full plpygis documentation is available at http://plpygis.readthedocs.io/.
