gistfile1.m

static double toRadians(double degrees) { return degrees / 180.0 * M_PI; };
static double toDegrees(double radians) { return radians * 180.0 / M_PI; };


@implementation NOTagDirectionManager

+ (double)directionInDegreesBetweenLocation:(CLLocationCoordinate2D)locationOne
                       andLocation:(CLLocationCoordinate2D)locationTwo
{
    double lat1 = toRadians(locationOne.latitude);
    double lng1 = toRadians(locationOne.longitude);
    double lat2 = toRadians(locationTwo.latitude);
    double lng2 = toRadians(locationTwo.longitude);
    
    double dLon = toRadians(lng2 - lng1);
    double dPhi = log(tan(toRadians(lat2) / 2 + M_PI / 4 ) / tan(toRadians(lat1) / 2 + M_PI / 4 ));
    if (fabs(dLon) > M_PI) {
        dLon = dLon > 0 ? -(2 * M_PI - dLon) : (2 * M_PI + dLon);
    }
    
    return toDegrees(atan2(dLon, dPhi));
}