iOS latitude and longitude calculation distance

#pragma  mark - calculate distance   calculate distance      #define based on 2 latitude and longitude  pi 3.1415926  + (Double)  lantitudelongitudedist: (Double) Lon1 other_lat: (Double) Lat1 self_lon: (Double) Lon2 self_lat: (double) lat2{      double er  = 6378137; // 6378700.0f;      //ave. radius =  6371.315  (someone said more accurate is 6366.707)        //equatorial radius = 6378.388      //nautical  mile = 1.15078      double radlat1 = pi*lat1/180.0f;       double radlat2 = PI*lat2/180.0f;       //now long.      double radlong1 = pi*lon1/ 180.0f;      double radlong2 = pi*lon2/180.0f;      if (  radlat1 < 0 )  radlat1 = pi/2 + fabs (RADLAT1);// south       if ( radlat1 > 0 )  radlat1 = pi/2 -  fabs (RADLAT1);// north      if ( radlong1 < 0 )  radlong1 = pi*2 - fabs (radlong1);//west      if (  radlat2 < 0 )  radlat2 = pi/2 + fabs (RADLAT2);// south       if ( radlat2 > 0 )  radlat2 = pi/2 -  fabs (RADLAT2);// north      if ( radlong2 < 0 )  radlong2 = pi*2 - fabs (radlong2);// west      // Spherical coordinates&nBsp;x=r*cos (AG) sin (at),  y=r*sin (AG) *sin (in),  z=r*cos (at)       //zero  ag is up so reverse lat      double x1  = er * cos (radlong1)  * sin (RADLAT1);      double  Y1 = er * sin (radlong1)  * sin (RADLAT1);       Double z1 = er * cos (RADLAT1);       double x2  = er * cos (radlong2)  * sin (RADLAT2);       double  y2 = er * sin (radlong2)  * sin (RADLAT2);       double z2 = er * cos (RADLAT2);       double d  = sqrt ((x1-x2) * (X1-X2) + (y1-y2) * (y1-y2) + (Z1-Z2) * (Z1-Z2));       //side,  side, side, law of cosines and arccos      double theta =  ACOs ((er*er+er*er-d*d)/(2*er*er));       double dist  = theta *er;      return dist;  }

Egg ache, the backstage bother let me mobile end calculate distance, really wonderful. No way to find the algorithm online.

iOS latitude and longitude calculation distance