GIS算法--已知一点经纬度，方位角，距离求另一点

已知一个点A的经纬度坐标，点B相对与A的方位角，B到A的距离，求B的经纬度坐标，用Javascript语言来完成该算法，借用了一下openL

CommonFunc.caculate={    VincentyConstants : {        a: 6378137,        b: 6356752.3142,        f: 1/298.257223563    },    /**    *Calculate destination point given start point lat/long (numeric degrees),    * bearing (numeric degrees) & distance (in m).    */    destinationVincenty : function(lonlat, brng, dist) {        var u = this;        var ct = u.VincentyConstants;        var a = ct.a, b = ct.b, f = ct.f;        var lon1 = lonlat.lon;        var lat1 = lonlat.lat;        var s = dist;        var alpha1 = u.rad(brng);        var sinAlpha1 = Math.sin(alpha1);        var cosAlpha1 = Math.cos(alpha1);        var tanU1 = (1-f) * Math.tan(u.rad(lat1));        var cosU1 = 1 / Math.sqrt((1 + tanU1*tanU1)), sinU1 = tanU1*cosU1;        var sigma1 = Math.atan2(tanU1, cosAlpha1);        var sinAlpha = cosU1 * sinAlpha1;        var cosSqAlpha = 1 - sinAlpha*sinAlpha;        var uSq = cosSqAlpha * (a*a - b*b) / (b*b);        var A = 1 + uSq/16384*(4096+uSq*(-768+uSq*(320-175*uSq)));        var B = uSq/1024 * (256+uSq*(-128+uSq*(74-47*uSq)));        var sigma = s / (b*A), sigmaP = 2*Math.PI;        while (Math.abs(sigma-sigmaP) > 1e-12) {            var cos2SigmaM = Math.cos(2*sigma1 + sigma);            var sinSigma = Math.sin(sigma);            var cosSigma = Math.cos(sigma);            var deltaSigma = B*sinSigma*(cos2SigmaM+B/4*(cosSigma*(-1+2*cos2SigmaM*cos2SigmaM)-                B/6*cos2SigmaM*(-3+4*sinSigma*sinSigma)*(-3+4*cos2SigmaM*cos2SigmaM)));            sigmaP = sigma;            sigma = s / (b*A) + deltaSigma;        }        var tmp = sinU1*sinSigma - cosU1*cosSigma*cosAlpha1;        var lat2 = Math.atan2(sinU1*cosSigma + cosU1*sinSigma*cosAlpha1,            (1-f)*Math.sqrt(sinAlpha*sinAlpha + tmp*tmp));        var lambda = Math.atan2(sinSigma*sinAlpha1, cosU1*cosSigma - sinU1*sinSigma*cosAlpha1);        var C = f/16*cosSqAlpha*(4+f*(4-3*cosSqAlpha));        var L = lambda - (1-C) * f * sinAlpha *            (sigma + C*sinSigma*(cos2SigmaM+C*cosSigma*(-1+2*cos2SigmaM*cos2SigmaM)));        var revAz = Math.atan2(sinAlpha, -tmp);  // final bearing        return new OpenLayers.LonLat(lon1+u.deg(L), u.deg(lat2));    },     /**     * 度换成弧度     * @param  {Float} d  度     * @return {[Float}   弧度     */    rad:function(d)    {       return d * Math.PI / 180.0;    },    /**     * 弧度换成度     * @param  {Float} x 弧度     * @return {Float}   度     */    deg:function(x) {        return x*180/Math.PI;    }   }

destinationVincenty方法返回的值即为B点的经纬度坐标。