how to calculate distance in km between two latitude and longitude in c#?
['public double GetDistanceBetweenPoints(double lat1, double long1, double lat2, double long2)', '{', 'double distance = 0;', 'double dLat = (lat2 - lat1) / 180* Math.PI;', 'double dLong = (long2 - long1) / 180 * Math.PI;', 'double a = Math.Sin(dLat / 2) * Math.Sin(dLat / 2)']