地图上计算两点间的距离.(参考网络)

    public struct Location
    {
        /// <summary>
        /// 經度
        /// </summary>
        public double Longitude { get; set; }

        /// <summary>
        /// 緯度
        /// </summary>
        public double Latitude { get; set; }
    }

        /// <summary>
        /// 地球半径,单位米
        /// </summary>
        private const double EARTH_RADIUS = 6371393.0d;

　　　　　/// <summary>
        /// 计算两点位置的距离，返回两点的距离，单位 米
        /// 该公式为GOOGLE提供，误差小于0.2米
        /// </summary>
        /// <param name="first"></param>
        /// <param name="second"></param>
        /// <returns></returns>
        private static double Distance(Location first, Location second)
        {
            var radLat1 = Rad(first.Latitude);
            var radLng1 = Rad(first.Longitude);
            var radLat2 = Rad(second.Latitude);
            var radLng2 = Rad(second.Longitude);
            var a = radLat1 - radLat2;
            var b = radLng1 - radLng2;
            return 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;
        }

        /// <summary>
        /// 经纬度转化成弧度
        /// </summary>
        /// <param name="d"></param>
        /// <returns></returns>
        private static double Rad(double d) => (double)d * Math.PI / 180d;