JS 根据经纬度计算距离

var EARTH_RADIUS = 6378137.0;    //单位M
    var PI = Math.PI;

    function getRad(d){
        return d*PI/180.0;
    }
// 经纬度计算
    /**

     * approx distance between two points on earth ellipsoid

     * @param {Object} lat1

     * @param {Object} lng1

     * @param {Object} lat2

     * @param {Object} lng2

     */

    function getFlatternDistance(lat1,lng1,lat2,lng2){

        var f = getRad((lat1 + lat2)/2);

        var g = getRad((lat1 - lat2)/2);

        var l = getRad((lng1 - lng2)/2);

        var sg = Math.sin(g);

        var sl = Math.sin(l);

        var sf = Math.sin(f);

        var s,c,w,r,d,h1,h2;

        var a = EARTH_RADIUS;

        var fl = 1/298.257;

        sg = sg*sg;

        sl = sl*sl;

        sf = sf*sf;

        s = sg*(1-sl) + (1-sf)*sl;

        c = (1-sg)*(1-sl) + sf*sl;

        w = Math.atan(Math.sqrt(s/c));

        r = Math.sqrt(s*c)/w;

        d = 2*w*a;

        h1 = (3*r -1)/2/c;

        h2 = (3*r +1)/2/s;

        return d*(1 + fl*(h1*sf*(1-sg) - h2*(1-sf)*sg));

    }