leaflet 根据一个经纬度及距离角度，算出另外一个经纬度

/**
     * 根据一个经纬度及距离角度，算出另外一个经纬度
     * @param {*} lng 经度 113.3960698
     * @param {*} lat 纬度 22.941386
     * @param {*} brng 方位角 45 ---- 正北方：000°或360° 正东方：090° 正南方：180° 正西方：270°
     * @param {*} dist 90000距离(米)
     *
     * 1、角度转换为弧度公式：弧度=角度×(π ÷度180 )
     * 2、弧度转换为角度公式： 角度=弧度×（180÷π）
     */
    function getLonAndLat(lng, lat, brng, dist) {
        //大地坐标系资料WGS-84 长半径a=6378137 短半径b=6356752.3142 扁率f=1/298.2572236
        var a = 6378137;
        var b = 6356752.3142;
        var f = 1 / 298.257223563;

        var lon1 = lng * 1;
        var lat1 = lat * 1;
        var s = dist;
        var alpha1 = brng * (Math.PI / 180)//mapNumberUtil.rad(brng);
        var sinAlpha1 = Math.sin(alpha1);
        var cosAlpha1 = Math.cos(alpha1);

        //var tanU1 = (1 - f) * Math.tan(mapNumberUtil.rad(lat1));
        var tanU1 = (1 - f) * Math.tan(lat1 * (Math.PI / 180));
        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

        var lngLatObj = { lng: lon1 + L * (180 / Math.PI), lat: lat2 * (180 / Math.PI) }
        return lngLatObj;
    }