plpygis

plpygis

plpygis is a pure Python module with no dependencies that can convert geometries between Well-known binary (WKB/EWKB), Well-known Text (WKT/EWKT) and GeoJSON representations. plpygis is mainly intended for use in PostgreSQL PL/Python functions to augment PostGIS's native capabilities.

Basic usage

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.ewkb)
0101000020e6100000b81e85eb51005fc0713d0ad7a3804840
>>> print(p.geojson)
{'type': 'Point', 'coordinates': [-124.005, 49.005]}
>>> p.z = 1
>>> print(p.wkt)
POINT Z (-124.005 49.005 1)

Usage with PostGIS

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
  from requests import get
  p = Geometry(geom)

  response = get(f'https://api.open-meteo.com/v1/elevation?longitude={p.x}&latitude={p.y}')
  if response.status_code == 200:
      content = response.json()
      p.z = content['elevation'][0]
      return p
  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,
    add_elevation(geom)
FROM
    city;

Documentation

Full plpygis documentation is available at http://plpygis.readthedocs.io/.