Vincenty distance formula as a MySQL function

vincenty.sql

CREATE FUNCTION VINCENTY(
    lat1 FLOAT, lon1 FLOAT,
    lat2 FLOAT, lon2 FLOAT
) RETURNS FLOAT
NO SQL
DETERMINISTIC
COMMENT 'Returns the distance in degrees on the Earth between two known points
    of latitude and longitude using the Vincenty formula from:
    http://en.wikipedia.org/wiki/Great-circle_distance'
BEGIN
RETURN DEGREES(
    ATAN2(
        SQRT(
            POW(COS(RADIANS(lat2))*SIN(RADIANS(lon2-lon1)),2) +
            POW(COS(RADIANS(lat1))*SIN(RADIANS(lat2)) -
                (SIN(RADIANS(lat1))*COS(RADIANS(lat2)) *
                    COS(RADIANS(lon2-lon1))
                ),
                2
            )
        ),
        SIN(RADIANS(lat1))*SIN(RADIANS(lat2)) +
        COS(RADIANS(lat1))*COS(RADIANS(lat2))*COS(RADIANS(lon2-lon1))
    )
);
END