public static double GetCoorDistance2(double x1, double y1, double x2, double y2)
{
    double num2 = 1.852;
    double num3 = 0.017453292519943295 * x1;
    double num4 = 0.017453292519943295 * x2;
    double a = 0.017453292519943295 * y1;
    double num6 = 0.017453292519943295 * y2;
    double d = (Math.Sin(a) * Math.Sin(num6)) + ((Math.Cos(a) * Math.Cos(num6)) * Math.Cos(num3 - num4));
    return ((((Math.Acos(d) * 57.295779513082323) * 60.0) * num2) * 1000.0);
}