C#根据经纬度计算两点距离（单位是千米）

SQL:

CREATE function [dbo].[fnGetDistance]  
(  
    @LatBegin REAL  
    , @LngBegin REAL  
    , @LatEnd REAL  
    , @LngEnd REAL  
)  
RETURNS FLOAT 
AS  
BEGIN  
    DECLARE @Distance REAL  
    DECLARE @EARTH_RADIUS REAL  
    SET @EARTH_RADIUS = 6378.137  
      
    DECLARE @RadLatBegin REAL, @RadLatEnd REAL, @RadLatDiff REAL, @RadLngDiff REAL  
    SET @RadLatBegin = @LatBegin * PI() / 180.0  
    SET @RadLatEnd = @LatEnd * PI() / 180.0  
    SET @RadLatDiff = @RadLatBegin - @RadLatEnd  
    SET @RadLngDiff = @LngBegin * PI() / 180.0 - @LngEnd * PI() / 180.0  
      
    SET @Distance = 2 * ASIN(SQRT(POWER(Sin(@RadLatDiff / 2), 2) + COS(@RadLatBegin) * COS(@RadLatEnd) * POWER(SIN(@RadLngDiff/2),2)))  
    SET @Distance = @Distance * @EARTH_RADIUS  
    --SET @Distance = Round(@Distance * 10000) / 10000  
      
    RETURN @Distance  
END

C#:

private const double EARTH_RADIUS = 6378.137;
private static double rad(double d)
{
   return d * Math.PI / 180.0;
}

public static double GetDistance(double lat1, double lng1, double lat2, double lng2)
{
   double radLat1 = rad(lat1);
   double radLat2 = rad(lat2);
   double a = radLat1 - radLat2;
   double b = rad(lng1) - rad(lng2);

   double s = 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)));
   s = s * EARTH_RADIUS;
   s = Math.Round(s * 10000) / 10000;
   return s;
}