Ok, because I led you up the garden path with my previous answer, I ported this to give you an algorithm that works:
void Main()
{
double lat1=12.916933d,
lon1=77.562658d,
lat2=12.930140d,
lon2=77.587732d;
double dist = GetDistanceFromLatLonInKm(lat1, lon1, lat2, lon2);
// dist == 3.08890370651166 yay!
}
double GetDistanceFromLatLonInKm(double lat1,
double lon1,
double lat2,
double lon2) {
var R = 6371d; // Radius of the earth in km
var dLat = Deg2Rad(lat2 - lat1); // deg2rad below
var dLon = Deg2Rad(lon2 - lon1);
var a =
Math.Sin(dLat / 2d) * Math.Sin(dLat / 2d) +
Math.Cos(Deg2Rad(lat1)) * Math.Cos(Deg2Rad(lat2)) *
Math.Sin(dLon / 2d) * Math.Sin(dLon / 2d);
var c = 2d * Math.Atan2(Math.Sqrt(a), Math.Sqrt(1d - a));
var d = R * c; // Distance in km
return d;
}
double Deg2Rad(double deg) {
return deg * (Math.PI / 180d);
}
Your calculation appears to work correctly when you supply fixed values:
var lat1 = 0d;
var lon1 = 52d;
var lat2 = 0d;
var lon2 = -52d;
which rather implies that these conversions are failing:
double lat1 = Convert.ToDouble(TextBox1.Text);
double lon1 = Convert.ToDouble(TextBox2.Text);
double lat2 = Convert.ToDouble(TextBox3.Text);
double lon2 = Convert.ToDouble(TextBox4.Text);
If you're still having trouble, place a breakpoint on these lines and take a look at the values of TextBox1.Text
etc.
For more predictable parsing of floating point numbers, it's best to supply culture information:
Convert.ToDouble("1.2", System.Globalization.CultureInfo.InvariantCulture)