The following function is used to find the distance between two Latitude & Longitude co-ordinates using Haversine formula.

The haversine formula is an equation important in navigation, giving great-circle distances between two points on a sphere from their longitudes and latitudes. It is a special case of a more general formula in spherical trigonometry, the law of haversines, relating the sides and angles of spherical triangles.

1. public double HaversineDistance(LatLng pos1, LatLng pos2, DistanceUnit unit)
2. {
3.     double R = (unit == DistanceUnit.Miles) ? 3959 : 6371;
4.     var la1 = pos1.Latitude;
5.     var lo1 = pos1.Longitude;
6.     var la2 = pos2.Latitude;
7.     var lo2 = pos2.Longitude;
8.     var lat1 = la1 * Math.PI / 180;
9.     var lon1 = lo1 * Math.PI / 180;
10.     var lat2 = la2 * Math.PI / 180;
11.     var lon2 = lo2 * Math.PI / 180;
12.     var dLat = lat2 - lat1;
13.     var dLon = lon2 - lon1;
14.     var a = Math.Sin(dLat / 2) * Math.Sin(dLat / 2) + Math.Cos(lat1) * Math.Cos(lat2) * Math.Sin(dLon / 2) * Math.Sin(dLon / 2);
15.     var c = 2 * Math.Atan2(Math.Sqrt(a), Math.Sqrt(1 - a));
16.     var d = R * c;
17.     return d;
18. }

1. public class LatLng
2. {
3.     public double Latitude { get; set; }
4.     public double Longitude { get; set; }
5.     public LatLng()
6.     {
7.     }
8.     public LatLng(double lat, double lng)
9.     {
10.         this.Latitude = lat;
11.         this.Longitude = lng;
12.     }
13. }