Filter zipcodes by proximity in Django with the Spherical Law of Cosines

Question

I\'m trying to handle proximity search for a basic store locater in Django. Rather than haul PostGIS around with my app just so I can use GeoDjango\'s distance filter, I\'d

Answer 1

Just to follow up on jboxer's answer, here's the whole thing as part of a custom manager with some of the hard-coded stuff turned into variables:

class LocationManager(models.Manager):
    def nearby_locations(self, latitude, longitude, radius, max_results=100, use_miles=True):
        if use_miles:
            distance_unit = 3959
        else:
            distance_unit = 6371

        from django.db import connection, transaction
        cursor = connection.cursor()

        sql = """SELECT id, (%f * acos( cos( radians(%f) ) * cos( radians( latitude ) ) *
        cos( radians( longitude ) - radians(%f) ) + sin( radians(%f) ) * sin( radians( latitude ) ) ) )
        AS distance FROM locations_location HAVING distance < %d
        ORDER BY distance LIMIT 0 , %d;""" % (distance_unit, latitude, longitude, latitude, int(radius), max_results)
        cursor.execute(sql)
        ids = [row[0] for row in cursor.fetchall()]

        return self.filter(id__in=ids)