计算2个坐标（经纬度）之间的距离，.Net

.Net 中计算2个点之间的距离的方法，或者叫计算2个坐标，2个经纬度之间的距离。

代码如下：

 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 DistanceUnits
31     {
32         Miles,
33         NauticalMiles,
34         Kilometers,
35     }

代码很简单，但是费了不少劲。就是还没测试效率怎么样。如果有高效的算法，请不要吝啬指教！！！