CREATE OR REPLACE FUNCTION CALC_DISTANCE_IN_METERS(alat double precision, alng double precision, blat double precision, blng double precision)
        RETURNS double precision AS
      $BODY$
      SELECT atan2(
        sqrt(
          sin(radians($3-$1)/2)^2 +
          sin(radians($4-$2)/2)^2 *
          cos(radians($1)) *
          cos(radians($3))
        ),
        1 - sqrt(
          sin(radians($3-$1)/2)^2 +
          sin(radians($4-$2)/2)^2 *
          cos(radians($1)) *
          cos(radians($3))
        )
      ) * 2 * 6369 * 1000 AS distance;
      $BODY$
        LANGUAGE sql IMMUTABLE
        COST 100;