. NET data-calculation of straight distance based on two-point latitude and longitude

Recently do something encountered to be based on the two-point latitude and longitude of the distance between the calculation, on-line looked up the next information. Because this kind of contact is relatively few, directly to find the ready-made code, not how to study. The code is as follows, as a record.

Private Const Double Earth_radius = 6378.137;//Earth radius private static double rad (double D) {   return d * math.pi/180.0;} public static double Getdistance (double lat1, double lng1, double lat2, double lng2) {   double radLat1 = rad (LAT1);   Double radLat2 = rad (LAT2);   Double A = RADLAT1-RADLAT2;   Double b = rad (lng1)-Rad (lng2);   Double s = 2 * Math.asin (MATH.SQRT (Math.pow (Math.sin (A/2), 2) +    Math.Cos (RADLAT1) *math.cos (RADLAT2) *math.pow ( Math.sin (B/2), 2));   s = S * earth_radius;   s = Math.Round (S * 10000)/10000;   return s;}

Note: Here is the kilometer returned, if you need to be accurate to the meter of the words themselves or take a 1000 can, we all understand it.