proper use of LatLonPoint class in queryset

queryset_with_LatLonPoint.py

class PopularityDistanceQuerySetMixin(object):
    """Mixin when you need to add popularity, distance,
    nearby calls to queryset, can be used as it for Coupon
    and Merchant models
    """

    def with_popularity(self):
        """Adds counted field popularity which is the value
        of redeemed coupon
        """
        return self.annotate(
            popularity=models.Count(
                models.Case(
                    models.When(
                        couponstat__action='R',
                        then=1,
                    )
                ),

            )
        )

    def distance(self, latitude, longitude):
        """Add distance information to merchant based on nearest
        place associated with the merchant
        """

        point = GEOSGeometry("SRID=4326;POINT ({lon} {lat})".format(
            lat=latitude, lon=longitude))

        return self.annotate(distance=models.Min(
            Distance('places__location', point)))

    def nearby(self, latitude, longitude, proximity=None):
        """Get nearby coupons.

        Custom queryset method for getting coupons for nearby places.

        Returns:
            A queryset of ``Coupon`` objects.

        """

        proximity = proximity or getattr(config, 'PROXIMITY')

        if proximity:
            point = LatLonPoint(latitude=latitude, longitude=longitude)

            # we query for location nearby for places first and then
            # annotate with distance to the same place
            return self.filter(
                places__location__distance_lte=(point, D(ft=proximity))).\
                annotate(distance=models.Min(Distance(
                    'places__location', point)))
        return self