code: def distance_in_km(geopoint,lng = nil)
        unless geopoint.is_a?(Parse::GeoPoint)
          geopoint = Parse::GeoPoint.new(geopoint, lng)
        end
  
        dtor = Math::PI/180
        r = 6378.14
        r_lat1 = self.latitude * dtor
        r_lng1 = self.longitude * dtor
        r_lat2 = geopoint.latitude * dtor
        r_lng2 = geopoint.longitude * dtor
  
        delta_lat = r_lat1 - r_lat2
        delta_lng = r_lng1 - r_lng2
  
        a = (Math::sin(delta_lat/2.0) ** 2).to_f + (Math::cos(r_lat1) * Math::cos(r_lat2) * ( Math::sin(delta_lng/2.0) ** 2 ) )
        c = 2.0 * Math::atan2(Math::sqrt(a), Math::sqrt(1.0-a))
        d = r * c
        d
      end
docs: Calculate the distance in kilometers to another GeoPoint using Haversine
   method. You may also call this method with a latitude and longitude.
   @example
     point.distance_in_km(geotpoint)
     point.distance_in_km(lat, lng)
  
   @param geopoint [GeoPoint]
   @param lng [Float] Longitude assuming that the first parameter is a latitude instead of a GeoPoint.
   @return [Float] number of miles between geopoints.
   @see #distance_in_miles