django - GeoDjango: How to create a circle based on point and radius

Question

I have the following (simplified) Model:

class Zone(gismodels.Model):
    name = gismodels.CharField()
    poly = gismodels.PolygonField()

I want to create and save a polygon that represents a circle, based upon a given point and radius.

The only way I can figure out how to achieve this, is to call the postgis ST_Buffer function using raw SQL. I'm really hoping that there is another way.

Is it possible to access the GEOS buffer methods?

Answer 1

Yes, it is possible to use the geos buffer method:

>>> from django.contrib.gis import geos
>>> center = geos.Point(5, 5)
>>> radius = 2
>>> circle = center.buffer(radius)
>>> circle
<Polygon object at 0x1029d8370>

The radius here is in the same units as the coordinates of the points. This will work for some coordinate systems like UTM, but not as well for others.

Also, while this is appropriate for constructing a circular geometry, the PostGIS documentation notes that for doing radius searches ST_DWithin is more efficient.