【轉】C#計算兩坐標點距離

      //地球半徑，單位米
       private const double EARTH_RADIUS = 6378137;
       /// <summary>
       /// 計算兩點位置的距離，返回兩點的距離，單位 米
       /// 該公式為GOOGLE提供，誤差小於0.2米
       /// </summary>
       /// <param name="lat1">第一點緯度</param>
       /// <param name="lng1">第一點經度</param>
       /// <param name="lat2">第二點緯度</param>
       /// <param name="lng2">第二點經度</param>
       /// <returns></returns>
       public static double GetDistance(double lat1, double lng1, double lat2, double lng2)
       {
           double radLat1 = Rad(lat1);
           double radLng1 = Rad(lng1);
           double radLat2 = Rad(lat2);
           double radLng2 = Rad(lng2);
           double a = radLat1 - radLat2;
           double b = radLng1 - radLng2;
           double result = 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))) * EARTH_RADIUS;
           return result;
       }
 
       /// <summary>
       /// 經緯度轉化成弧度
       /// </summary>
       /// <param name="d"></param>
       /// <returns></returns>
       private static double Rad(double d)
       {
           return (double)d * Math.PI / 180d;
       }