C# 經緯度計算

#region 計算經緯度距離
public const double EARTH_RADIUS = 6377.830;//地球半徑(千米)

/// <summary>
/// 角度換算成弧度
/// </summary>
/// <param name="d">角度</param>
/// <returns>弧度</returns>
public static double rad(double d)
{
return d * Math.PI / 180.0;
}
/// <summary>
/// 計算距離
/// </summary>
/// <param name="lat1">緯度1</param>
/// <param name="lng1">經度1</param>
/// <param name="lat2">緯度2</param>
/// <param name="lng2">經度2</param>
/// <returns>距離（千米）</returns>
public static double GetDistance(double lat1, double lng1, double lat2, double lng2)
{
double radLat1 = rad(lat1);
double radLat2 = rad(lat2);
double a = radLat1 - radLat2;
double b = rad(lng1) - rad(lng2);
double 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;
s = Math.Round(s * 10000) / 10000;
return s;
}
#endregion