Javascript 定位计算两点坐标距离

function gd_distance(user_x, user_y,dealer_x,dealer_y) {

    if (!user_x || !user_y || !dealer_x || !dealer_y)
    {
         return  '';
    }

    var startLatRads=degreesToRadians(user_y);
    var startLongRade=degreesToRadians(user_x);
    var destLatRads=degreesToRadians(dealer_y);
    var destLongRads=degreesToRadians(dealer_x);
    var Radius=6371;
    var distance=Math.acos(Math.sin(startLatRads)*Math.sin(destLatRads)+Math.cos(startLatRads)*Math.cos(destLatRads)*Math.cos(startLongRade-destLongRads))*Radius;

    return distance.toFixed(1);
}


function degreesToRadians(degrees){
      var radians=(degrees*Math.PI)/180;
      return radians;
}