public static int GetDistance(String location1, String location2)
{
// Haversine formula:
// a = sin²(delta_lat/2) + cos(lat1).cos(lat2).sin²(delta_long/2)
// c = 2.atan2(sqrt(a), sqrt(1-a))
// d = R.c
// where R is earth’s radius (mean radius = 6,371km);
// note that angles need to be in radians to pass to trig functions!
double lat1, lon1, lat2, lon2, d_lat, d_lon, a1, a2, a3, a, c, distance;
lat1 = GXGeolocation.GetLatitude(location1);
lon1 = GXGeolocation.GetLongitude(location1);
lat2 = GXGeolocation.GetLatitude(location2);
lon2 = GXGeolocation.GetLongitude(location2);
d_lat = GXGeolocation.DegreesToRadians(lat2 - lat1);
d_lon = GXGeolocation.DegreesToRadians(lon2 - lon1);
lat1 = GXGeolocation.DegreesToRadians(lat1);
lat2 = GXGeolocation.DegreesToRadians(lat2);
a1 = Math.Pow(Math.Sin(d_lat / 2), 2);
a2 = Math.Pow(Math.Sin(d_lon / 2), 2);
a3 = Math.Cos(lat1) * Math.Cos(lat2);
a = a1 + a2 * a3;
c = 2 * Math.Atan2(Math.Sqrt(a), Math.Sqrt(1 - a));
distance = 6371 * c * 1000;
return((int)distance);
}
