Js算两经纬度间球面距离

function GetDistance( lat1,  lng1,  lat2,  lng2){
    var radLat1 = lat1 * Math.PI / 180.0
    var radLat2 = lat2 * Math.PI / 180.0
    var a = (lat1 - lat2) * Math.PI / 180.0;
    var b = (lng1 - lng2) * Math.PI / 180.0;
    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 * 6378137 ;// EARTH_RADIUS;
    s = Math.round(s * 10000) / 10000;
    return s;
}