[Django]-Intersecting multipolygon layer with polygon in GeoDjango

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Essentially we need to annotate the intersection (if any) of each Region‘s geom with the given query. Doing so with a DB query look like this:

from django.db.models import F
from django.contrib.gis.db.models.functions import Intersection
from django.contrib.gis.geos import GEOSGeometry

query = GEOSGeometry(
    '{"type":"Polygon","coordinates":[[[-80.983786,43.929011],[-80.511513,43.778458],[-80.291852,44.079184],[-80.775108,44.232127],[-80.983786,43.929011]]]}'
) 

results = Region.objects.filter(geom__intersects=query).annotate(
    intersection_geom=Intersection(F('geom'), query)
)

Query Explanation:

  1. Filter the Regions that intersect the query, using the intersects spatial lookup.
  2. Calculate the result of Intersection between a Region’s geom field and the query, using the F() expression to access the geom (an explanation on F() usage can be found in my Q&A example: How to execute arithmetic operations between Model fields in django)
  3. annotate the calculated Intersection into each corresponding Region as a field named intersection_geom.

After the query execution, the results will contain each Region that intersects the query geom, with the intersection_geom field containing the exact geometry of the corresponding intersection.

👤John Moutafis

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