distance calculator

  public enum DistanceType {
	Miles = 1,
	Kilometers,
	Feet,
	Meter
}

public static class DistanceCalculator {

	private const double radianCalculator = Math.PI / 180;

	public static DistanceResult CalculateDistance(double lat1, double lon1, double lat2, double lon2, DistanceType type) {
		return CalculateDistance(
			new LatLong { Latitude = lat1, Longitude = lon1 },
			new LatLong { Latitude = lat2, Longitude = lon2 }, type);
	}

	public static DistanceResult CalculateDistance(LocationConstraint loc1, LocationConstraint loc2, DistanceType type) {
		return CalculateDistance(new LatLong(loc1), new LatLong(loc2), type);
	}

	public static DistanceResult CalculateDistance(ILatLong pos1, ILatLong pos2, DistanceType type) {
		// This is the Haversine formula.

		double radiusOfEarth;
		switch (type) {
			case DistanceType.Miles:
				radiusOfEarth = 3960;
				break;
			case DistanceType.Kilometers:
				radiusOfEarth = 6371;
				break;
			case DistanceType.Feet:
				throw new NotImplementedException();
			case DistanceType.Meter:
				throw new NotImplementedException();
			default:
				throw new ArgumentOutOfRangeException(nameof(type), type, null);
		}

		double ToRadian(double value) {
			return radianCalculator * value;
		}

		double latitudeDistance = ToRadian(pos2.Latitude - pos1.Latitude);
		double longitudeDistance = ToRadian(pos2.Longitude - pos1.Longitude);

		double lat1Radians = ToRadian(pos1.Latitude);
		double lat2Radians = ToRadian(pos2.Latitude);

		var a = Math.Sin(latitudeDistance / 2) * Math.Sin(latitudeDistance / 2) +
				Math.Sin(longitudeDistance / 2) * Math.Sin(longitudeDistance / 2) *
				Math.Cos(lat1Radians) * Math.Cos(lat2Radians);

		double distance = radiusOfEarth * 2 * Math.Asin(Math.Sqrt(a));

		return new DistanceResult(distance, type);
	}
}