gistfile1.txt

/**
 * Returns the destination point from this point having travelled the given distance (in km) on the
 * given initial bearing (bearing may vary before destination is reached)
 *
 *   see http://williams.best.vwh.net/avform.htm#LL
 *
 * @param   {Number} brng: Initial bearing in degrees
 * @param   {Number} dist: Distance in km
 * @returns {LatLon} Destination point
 */
LatLon.prototype.destinationPoint = function(brng, dist) {
    dist = typeof(dist)=='number' ? dist : typeof(dist)=='string' && dist.trim()!='' ? +dist : NaN;
    dist = dist/this._radius;  // convert dist to angular distance in radians
    brng = brng.toRad();  //
    var lat1 = this._lat.toRad(), lon1 = this._lon.toRad();
    
    var lat2 = Math.asin( Math.sin(lat1)*Math.cos(dist) +
                         Math.cos(lat1)*Math.sin(dist)*Math.cos(brng) );
    var lon2 = lon1 + Math.atan2(Math.sin(brng)*Math.sin(dist)*Math.cos(lat1),
                                 Math.cos(dist)-Math.sin(lat1)*Math.sin(lat2));
    lon2 = (lon2+3*Math.PI) % (2*Math.PI) - Math.PI;  // normalise to -180..+180º
    
    return new LatLon(lat2.toDeg(), lon2.toDeg());
}