Two latitude and longitude dimensions are input for the iPhone to calculate the distance between the latitude and longitude

Input two latitude and longitude dimensions to calculate the distance between latitude and longitude:

+(double)LantitudeLongitudeDist:(double)lon1 lat1:(double)lat1 lon2:(double)lon2 lat2:(double)lat2{double er = 6378137; // 6378700.0f;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);// southif( radlat1 > 0 ) radlat1 = PI/2 - fabs(radlat1);// northif( radlong1 < 0 ) radlong1 = PI*2 - fabs(radlong1);//westif( radlat2 < 0 ) radlat2 = PI/2 + fabs(radlat2);// southif( radlat2 > 0 ) radlat2 = PI/2 - fabs(radlat2);// northif( radlong2 < 0 ) radlong2 = PI*2 - fabs(radlong2);// west//spherical coordinates x=r*cos(ag)sin(at), y=r*sin(ag)*sin(at), z=r*cos(at)//zero ag is up so reverse latdouble 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 arccosdouble theta = acos((er*er+er*er-d*d)/(2*er*er));double dist  = theta*er;return dist;}