Ruby/Rails - Distance between latitude/longitude points

distance.rb

GeoName.find_by_sql("SELECT ordered.* FROM (SELECT gn.*, round(distance.d * 6371.0, 2) AS distance_km, round(distance.d * 6371.0 * 0.621371192, 2) as distance_miles FROM 
            (SELECT (2*atan2(sqrt(calcs.a), sqrt(1-calcs.a)))::numeric d, calcs.id FROM 
              (SELECT (sin(consts.dlat/2) * sin(consts.dlat/2) + sin(consts.dlon/2) * sin(consts.dlon/2) * cos(consts.lat1) * cos(consts.lat2)) as a, consts.id FROM 
                (SELECT f.id, abs((#{self.exif_data.latitude} - f.latitude)*(#{Math::PI}/180)) AS dlat, 
                  abs((#{self.exif_data.longitude} - f.longitude)*(#{Math::PI}/180)) AS dlon, 
                    #{self.exif_data.latitude} * (#{Math::PI}/180) as lat1, 
                      f.latitude * (#{Math::PI}/180) as lat2 FROM geo_names f) consts) calcs) distance, 
                        geo_names gn WHERE gn.id = distance.id ORDER BY distance.d ASC LIMIT 10) ordered ORDER BY random() LIMIT 1")