js两个点经纬度计算两点之间的距离。

百度地图经纬度坐标拾取：

http://api.map.baidu.com/lbsapi/getpoint/index.html

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

function getRad(d) {
  return d * PI / 180.0;
}

/**
 * caculate the great circle distance
 * @param {Object} lat1 纬度
 * @param {Object} lng1 经度
 * @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));
}
getFlatternDistance(22.576979, 114.065712, 22.574034, 114.065739);

结果如下：