Search code examples
djangogeometrypointgeodjango

Geodjango: PointField and GEOSGeometry

If I can do this:

>>> from django.contrib.gis.geos import GEOSGeometry
>>> from django.contrib.gis.geos import Point
>>> point = GEOSGeometry('POINT(1 5)')
>>> print point
POINT (1.0000000000000000 5.0000000000000000)

Why can I not do this:

>>> lat = 1
>>> lon = 5
>>> point = GEOSGeometry('POINT(lat lon)')

GEOS_ERROR: ParseException: Expected number but encountered word: 'lat'
GEOSException: Error encountered checking Geometry returned from GEOS C function "GEOSWKTReader_read_r".

How can I use a variable to create a GEOSGeometry object?

Solution

  • You can surely do that, but with a slight modification

    point = GEOSGeometry('POINT(%s %s)' % (lon, lat))

    OR

    point = GEOSGeometry('POINT(%d %d)' % (lon, lat))

    When you do 

    `'POINT(lat lon)'`

    you are not replacing the local variables lat and lon with their appropriate local variable values, and they are being evaluated literally. So, you would need to use substitution.

    EDIT: Changed order of (lat, lon) to (lon, lat) to match the order GEOSGeometry is expecting. Although not explicitly stated in the documentation, it is evident from their examples.