1 /// <summary> 2     /// Calculates the distance between two geographics locations 3     /// </summary> 4     public static class GeoDistance 5     { 6         public static double Between(double latitude1, double longitude1, double latitude2, double longitude2, 7             DistanceUnits units = DistanceUnits.Kilometers) 8         { 9             double a1 = latitude1 * RadianConversionFactor;10             double b1 = longitude1 * RadianConversionFactor;11             double a2 = latitude2 * RadianConversionFactor;12             double b2 = longitude2 * RadianConversionFactor;13 14             double distance =15                 Math.Acos(Math.Cos(a1) * Math.Cos(b1) * Math.Cos(a2) * Math.Cos(b2) +16                     Math.Cos(a1) * Math.Sin(b1) * Math.Cos(a2) * Math.Sin(b2) + Math.Sin(a1) * Math.Sin(a2)) * DistanceConstants[units];17 18             return distance;19         }20 21         private const double RadianConversionFactor = Math.PI / 180;22 23         private static readonly Dictionary<DistanceUnits, double> DistanceConstants = new Dictionary<DistanceUnits, double>(3) {24             { DistanceUnits.Miles, 3963.1 },25             { DistanceUnits.NauticalMiles, 3443.9 },26             { DistanceUnits.Kilometers, 6378 }27         };28     }29 30     public enum DistanceUnits31     {32         Miles,33         NauticalMiles,34         Kilometers,35     }