Bike In City with Windows Phone 7

using System;
using System.Net;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Documents;
using System.Windows.Ink;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Animation;
using System.Windows.Shapes;
using Microsoft.Phone.Controls.Maps.Platform;

namespace BikeInCity.Utils
{
  public class GeoMath
  {
    /// <summary>
    /// Converts degrees to radians. Used to convert the latitude and longitude coordinates.
    /// </summary>
    /// <param name="angle"></param>
    /// <returns></returns>
    public static double ToRad(double angle)
    {
      var r = angle * Math.PI / 180;
      return r;
    }

    /// <summary>
    /// Returns distsance in meters between two points of earth using the Spherical Law of Cosines
    /// </summary>
    /// <param name="start"></param>
    /// <param name="end"></param>
    /// <returns></returns>
    public static int ComputeDistance(Location start, Location end)
    {
      var R = 6371;
      double lat1 = ToRad(start.Latitude);
      double lat2 = ToRad(end.Latitude);

      double lng1 = ToRad(start.Longitude);
      double lng2 = ToRad(end.Longitude);

      double dlng = lng2 - lng1;
      double dlat = lat2 - lat1;

      var a = Math.Pow(Math.Sin(dlat / 2),2) + Math.Cos(lat1) * Math.Cos(lat2) * Math.Pow(Math.Sin(dlng/2),2);
      var c = 2*Math.Asin(Math.Min(1,Math.Sqrt(a)));

      var d = R * c;
      

      /*
      //spherical law of cosines
      
      var d = Math.Acos(Math.Sin(lat1) * Math.Sin(lat2) +
                        Math.Cos(lat1) * Math.Cos(lat2) *
                        Math.Cos(lng1 - lng2)) * R;
      */
      return (int)(d * 1000);
    }
  }
}