通过地图上的两个坐标计算距离

/// <summary>
    /// 通过地图上的两个坐标计算距离(C#版本)
    /// Add by 成长的小猪（Jason.Song） on 2017/11/01
    /// http://blog.csdn.net/jasonsong2008
    /// </summary>
    public class MapHelper
    {
        /// <summary>
        /// 地球半径
        /// </summary>
        private const double EarthRadius = 6378.137;

        /// <summary>
        /// 经纬度转化成弧度
        /// Add by 成长的小猪（Jason.Song） on 2017/11/01
        /// http://blog.csdn.net/jasonsong2008
        /// </summary>
        /// <param name="d"></param>
        /// <returns></returns>
        private static double Rad(double d)
        {
            return d * Math.PI / 180d;
        }

        /// <summary>
        /// 计算两个坐标点之间的距离
        /// Add by 成长的小猪（Jason.Song） on 2017/11/01
        /// http://blog.csdn.net/jasonsong2008
        /// </summary>
        /// <param name="firstLatitude">第一个坐标的纬度</param>
        /// <param name="firstLongitude">第一个坐标的经度</param>
        /// <param name="secondLatitude">第二个坐标的纬度</param>
        /// <param name="secondLongitude">第二个坐标的经度</param>
        /// <returns>返回两点之间的距离，单位：公里/千米</returns>
        public static double GetDistance(double firstLatitude, double firstLongitude, double secondLatitude, double secondLongitude)
        {
            var firstRadLat = Rad(firstLatitude);
            var firstRadLng = Rad(firstLongitude);
            var secondRadLat = Rad(secondLatitude);
            var secondRadLng = Rad(secondLongitude);

            var a = firstRadLat - secondRadLat;
            var b = firstRadLng - secondRadLng;
            var cal = 2 * Math.Asin(Math.Sqrt(Math.Pow(Math.Sin(a / 2), 2) + Math.Cos(firstRadLat)
                * Math.Cos(secondRadLat) * Math.Pow(Math.Sin(b / 2), 2))) * EarthRadius;
            var result = Math.Round(cal * 10000) / 10000;
            return result;
        }


        //地球半径，单位米
        private const double EARTH_RADIUS = 6378137;
        /// <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="lat1">第一点纬度</param>
        /// <param name="lng1">第一点经度</param>
        /// <param name="lat2">第二点纬度</param>
        /// <param name="lng2">第二点经度</param>
        /// <returns>返回距离（米）</returns>
        public static double GetDistance2(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>
        /// 计算两个坐标点之间的距离
        /// Add by 成长的小猪（Jason.Song） on 2017/11/01
        /// http://blog.csdn.net/jasonsong2008
        /// </summary>
        /// <param name="firstPoint">第一个坐标点的（纬度,经度）</param>
        /// <param name="secondPoint">第二个坐标点的（纬度,经度）</param>
        /// <returns>返回两点之间的距离，单位：公里/千米</returns>
        public static double GetPointDistance(string firstPoint, string secondPoint)
        {
            var firstArray = firstPoint.Split(',');
            var secondArray = secondPoint.Split(',');
            var firstLatitude = Convert.ToDouble(firstArray[0].Trim());
            var firstLongitude = Convert.ToDouble(firstArray[1].Trim());
            var secondLatitude = Convert.ToDouble(secondArray[0].Trim());
            var secondLongitude = Convert.ToDouble(secondArray[1].Trim());
            return GetDistance(firstLatitude, firstLongitude, secondLatitude, secondLongitude);
        }

    }

https://www.cnblogs.com/chenkh/p/5661097.html

https://www.bbsmax.com/A/amd0QjZjzg/