public static int CalcDistance(double lat1, double lon1, double lat2, double lon2, out int heading)
{
    double lat = lat2 - lat1;
    double lon = (lon2 - lon1) * Math.Cos(Tools.deg2rad((int)((lat1 + lat2) / 2)));
    double dist = Math.Sqrt(lat * lat + lon * lon);

    heading = Tools.rad2deg(Math.Acos(lat / dist));
    if (lon < 0) // Western direction
	heading = 360 - heading;

    return (int)(dist * 60 * 1852);
}

private static double deg2rad(int degree)
{
    return degree * Math.PI / 180;
}

private static int rad2deg(double rad)
{
    return (int)(rad * 180 / Math.PI);
}