Google Maps nearby location finder

you are right i found some thing similar, but the problem is it does not give accurate distance in some cases. the function is :


public class CDistanceBetweenLocations
{
public static double Calc(double Lat1,
double Long1, double Lat2, double Long2)
{
/*
The Haversine formula according to Dr. Math.
http://mathforum.org/library/drmath/view/51879.html

dlon = lon2 - lon1
dlat = lat2 - lat1
a = (sin(dlat/2))^2 + cos(lat1) * cos(lat2) * (sin(dlon/2))^2
c = 2 * atan2(sqrt(a), sqrt(1-a))
d = R * c

Where
* dlon is the change in longitude
* dlat is the change in latitude
* c is the great circle distance in Radians.
* R is the radius of a spherical Earth.
* The locations of the two points in
spherical coordinates (longitude and
latitude) are lon1,lat1 and lon2, lat2.
*/
double dDistance = Double.MinValue;
double dLat1InRad = Lat1 * (Math.PI / 180.0);
double dLong1InRad = Long1 * (Math.PI / 180.0);
double dLat2InRad = Lat2 * (Math.PI / 180.0);
double dLong2InRad = Long2 * (Math.PI / 180.0);

double dLongitude = dLong2InRad - dLong1InRad;
double dLatitude = dLat2InRad - dLat1InRad;

// Intermediate result a.
double a = Math.Pow(Math.Sin(dLatitude / 2.0), 2.0) +
Math.Cos(dLat1InRad) * Math.Cos(dLat2InRad) *
Math.Pow(Math.Sin(dLongitude / 2.0), 2.0);

// Intermediate result c (great circle distance in Radians).
double c = 2.0 * Math.Atan2(Math.Sqrt(a), Math.Sqrt(1.0 - a));

// Distance.
// const Double kEarthRadiusMiles = 3956.0;
const Double kEarthRadiusKms = 6376.5;
dDistance = kEarthRadiusKms * c;

return dDistance;
}

public static double Calc(string NS1, double Lat1, double Lat1Min,
string EW1, double Long1, double Long1Min, string NS2,
double Lat2, double Lat2Min, string EW2,
double Long2, double Long2Min)
{
double NS1Sign = NS1.ToUpper() == "N" ? 1.0 : -1.0;
double EW1Sign = NS1.ToUpper() == "E" ? 1.0 : -1.0;
double NS2Sign = NS2.ToUpper() == "N" ? 1.0 : -1.0;
double EW2Sign = EW2.ToUpper() == "E" ? 1.0 : -1.0;
return (Calc(
(Lat1 + (Lat1Min / 60)) * NS1Sign,
(Long1 + (Long1Min / 60)) * EW1Sign,
(Lat2 + (Lat2Min / 60)) * NS2Sign,
(Long2 + (Long2Min / 60)) * EW2Sign
));
}
}