根据高德地图两点坐标获取两点实际距离，用于高德地图标记点范围内距离计算

        /// <summary>
        /// 获取高德地图两坐标点间的距离
        /// </summary>
        /// <param name="lat1">点1横坐标</param>
        /// <param name="lng1">点1纵坐标</param>
        /// <param name="lat2">点2横坐标</param>
        /// <param name="lng2">点2纵坐标</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;
            }
        }

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