两个经纬度算距离

两个经纬度算距离
class Earth
{
private const double EARTH_RADIUS = 6378.137;//地球半径
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;
}
}
用的这个算法,现在不知道精度到底如何?这个return的S是米还是千米.
我要算50米左右的距离.