根據高德地圖兩點坐標獲取兩點實際距離，用于高德地圖標記點范圍內距離計算

        /// <summary>
        /// 獲取高德地圖兩坐標點間的距離
        /// </summary>
        /// <param name="lat1">點1橫坐標</param>
        /// <param name="lng1">點1縱坐標</param>
        /// <param name="lat2">點2橫坐標</param>
        /// <param name="lng2">點2縱坐標</param>
        /// <returns></returns>
        public static double GetDistance(double lat1, double lng1, double lat2, double lng2)
        {
            try
            {
                var b = Math.PI / 180;
                var c = Math.Sin((lat2 - lat1) * b / 2);
                var d = Math.Sin((lng2 - lng1) * b / 2);
                var a = c * c + d * d * Math.Cos(lat1 * b) * Math.Cos(lat2 * b);
                return 12756274 * Math.Atan2(Math.Sqrt(a), Math.Sqrt(1 - a));
            }
            catch (Exception)
            {

                return 0;
            }
        }

參考文章：https://www.cnblogs.com/sylone/p/7473414.html