I am doing a small-scale workflow in ipython notebook with geopandas and shapely, pulling a bunch of geospatial data, sometimes from shapefiles, sometimes from postgis (where more expensive processing is performed).
Now, I then pull the postgis tables into python using sqlalchemy
, transforming the geometry to WKT along the way, getting something like:
sql = """
SELECT ST_AsText(ST_Transform(the_geom,4326)) as newgeom,*
FROM public.parcels2010_small limit 5;
"""
parcels = pd.read_sql(sql, engine)
parcels
+----+---------------------------------------------------+---------------------------------------------------+-----------+-------------+
| id | newgeom | the_geom | parcel_id | osm_node_id |
+----+---------------------------------------------------+---------------------------------------------------+-----------+-------------+
| 0 | MULTIPOLYGON(((-122.991093691444 38.4878691106... | 01060000209C0E00000100000001030000000100000097... | 1805792 | 66237 |
+----+---------------------------------------------------+---------------------------------------------------+-----------+-------------+
| 1 | MULTIPOLYGON(((-122.444576448624 37.7346386006... | 01060000209C0E0000010000000103000000010000008A... | 10435 | 123826 |
+----+---------------------------------------------------+---------------------------------------------------+-----------+-------------+
| 2 | MULTIPOLYGON(((-122.796785208193 38.5427593334... | 01060000209C0E0000010000000103000000010000007D... | 1817842 | 313047 |
+----+---------------------------------------------------+---------------------------------------------------+-----------+-------------+
| 3 | MULTIPOLYGON(((-122.695538506163 38.3618570798... | 01060000209C0E0000010000000103000000010000009B... | 1934612 | 63776 |
+----+---------------------------------------------------+---------------------------------------------------+-----------+-------------+
| 4 | MULTIPOLYGON(((-122.223424422869 37.8416019090... | 01060000209C0E00000100000001030000000100000072... | 861785 | 26369 |
+----+---------------------------------------------------+---------------------------------------------------+-----------+-------------+
This looks a lot like the geometry when loaded from a shapefile, but it is not cast as a shapely geometry. I couldn't find the canonical way to do it, either using shapely alone, or perhaps with Descartes
.
Best Answer
The default format for PostGIS geometry is hex-encoded WKB (Well-Known Binary). Shapely has the ability to convert this format into
shapely
geometry object with itswkb
module:if you were to then print the geometry it should look something like this:
See docs on the shapely.wkb module here.