js根据经纬度计算距离

var EARTH_RADIUS = 6378137.0;    //单位M
function getRad(d) {
    return d * Math.PI / 180.0;
}
/*参数：两地的经纬度数值*/
function getFlatternDistance(lat1, lng1, lat2, lng2) {
    var radLat1 = getRad(lat1);
    var radLat2 = getRad(lat2);
    var a = radLat1 - radLat2;
    var b = getRad(lng1) - getRad(lng2);
    var s = 2 * Math.asin(Math.sqrt(Math.pow(Math.sin(a / 2), 2) +
    Math.cos(radLat1) * Math.cos(radLat2) * Math.pow(Math.sin(b / 2), 2)));
    s = s * EARTH_RADIUS;// EARTH_RADIUS;
    s = Math.round(s * 10000) / 10000; //输出为米
    s = s.toFixed(0);
    return s;
}