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