Calculate distance between two points on Earth

        public static Double CalculateDistance(Double latitude1, Double longitude1, Double latitude2, Double longitude2) {

            double theta = longitude1 - longitude2;

            double dist = Math.Sin(deg2rad(latitude1)) * Math.Sin(deg2rad(latitude2)) + Math.Cos(deg2rad(latitude1)) * Math.Cos(deg2rad(latitude2)) * Math.Cos(deg2rad(theta));

            dist = Math.Acos(dist);

            dist = rad2deg(dist);

            dist = dist * 60 * 1.1515;

            dist = dist * 1.609344;

            return (dist);

        }

        private static Double deg2rad(Double deg) {

            return (deg * Math.PI / 180.0);

        }

        private static Double rad2deg(Double rad) {

            return (rad / Math.PI * 180.0);

        }