GPS Distance Function

Here's a C# method for calculating the distance (in nautical miles) between two GPS coordinates.

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Download GPSDistance.zip (~1KB)
Code
  1 /// <summary>
  2 /// Calculates the distance in nautical miles between two GPS coordinates.
  3 /// Equations from http://mathforum.org/library/drmath/view/51879.html
  4 /// </summary>
  5 /// <param name="lon1"></param>
  6 /// <param name="lat1"></param>
  7 /// <param name="lon2"></param>
  8 /// <param name="lat2"></param>
  9 /// <returns></returns>
 10 public static double CalculateDistanceBetweenGPSCoordinates(double lon1, double lat1, double lon2, double lat2) {
 11     const double R = 3956;
 12     const double degreesToRadians = Math.PI / 180;
 13
 14     //convert from fractional degrees (GPS) to radians
 15     lon1 *= degreesToRadians;
 16     lat1 *= degreesToRadians;
 17     lon2 *= degreesToRadians;
 18     lat2 *= degreesToRadians;
 19
 20     double dlon = lon2 - lon1;
 21     double dlat = lat2 - lat1;
 22     double a = Math.Pow(Math.Sin(dlat / 2), 2) + Math.Cos(lat1) * Math.Cos(lat2) * Math.Pow(Math.Sin(dlon / 2), 2);
 23     double c = 2 * Math.Atan2(Math.Sqrt(a), Math.Sqrt(1 - a));
 24     double d = R * c;
 25
 26     return d;
 27 }