Bearing Calculation

/*
 * calculate (initial) bearing between two points
 *   see http://williams.best.vwh.net/avform.htm#Crs
 */
LatLon.bearing = function(lat1, lon1, lat2, lon2) {
  lat1 = lat1.toRad(); lat2 = lat2.toRad();
  var dLon = (lon2-lon1).toRad();

  var y = Math.sin(dLon) * Math.cos(lat2);
  var x = Math.cos(lat1)*Math.sin(lat2) -
          Math.sin(lat1)*Math.cos(lat2)*Math.cos(dLon);
  return Math.atan2(y, x).toBrng();
}