Computing an initial bearing

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This MySQL Stored Function computes the initial bearing — the compass heading to follow — when moving from one point to another on the surface of the earth.  Here’s a web site describing this. http://www.movable-type.co.uk/scripts/latlong.html

DELIMITER $$
DROP FUNCTION IF EXISTS `initial_bearing`$$
CREATE FUNCTION `initial_bearing`(
        lat1 DOUBLE, lon1 DOUBLE,
        lat2 DOUBLE, lon2 DOUBLE
     ) RETURNS DOUBLE
    NO SQL
    DETERMINISTIC
    COMMENT 'Returns the initial bearing, in degrees, to follow the great circle route
             from point (lat1,lon1), to point (lat2,lon2)'
    BEGIN
    RETURN (360.0 +
      DEGREES(ATAN2(
       SIN(RADIANS(lon2-lon1))*COS(RADIANS(lat2)),
       COS(RADIANS(lat1))*SIN(RADIANS(lat2)) - SIN(RADIANS(lat1))*COS(RADIANS(lat2))*
            COS(RADIANS(lon2-lon1))
      ))
     ) % 360.0;
END$$
DELIMITER ;

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