MySQL Haversine function

DELIMITER $$
CREATE FUNCTION `fnHaversine`(point1 point, point2 point) RETURNS double
    DETERMINISTIC
begin
    declare lon1, lon2 double;
    declare lat1, lat2 double;
    declare r_lat1, r_lat2 double;
    declare d_lat double;
    declare d_lon double;
    declare a, c, R double;
    
    -- Earth radius in KM
    set R = 6371000;

    set lat1  = ST_X( point1 );
    set lat2  = ST_X( point2 );
    set lon1  = ST_Y( point1 );
    set lon2  = ST_Y( point2 );
    
    set r_lat1 = radians( lat1 );
    set r_lat2 = radians( lat2 );
    set d_lat  = radians( lat2 - lat1 );
    set d_lon  = radians( lon2 - lon1 );

    set a = sin( d_lat / 2 ) * sin( d_lat / 2 ) + cos( r_lat1 ) * cos( r_lat2 ) * sin( d_lon / 2 ) * sin( d_lon / 2 );
    set c = 2 * atan2( sqrt( a ), sqrt( 1 - a ) );

    return R * c;
end$$
DELIMITER ;