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

To follow up on Tom, if you want to have a query that also works in postgresql, you can not use AS because you will get an error saying 'distance' does not exist.

You should put the whole spherical law expresion in the WHERE clause, like this (It also works in mysql):

import math
from django.db import connection, transaction
from django.conf import settings

from django .db import models

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

        cursor = connection.cursor()

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

        return self.filter(id__in=ids)

Please note that you have to select the latitude and longitude, otherwise you can not use it in the WHERE clause.