Horizon Detection with Vision Framework

HorizonDetection.m

- (void)correctAngleWithImage:(UIImage *)image
{
    VNImageRequestHandler *handler = [[VNImageRequestHandler alloc] initWithCGImage:image.CGImage options:@{}];
    VNDetectHorizonRequest *request = [[VNDetectHorizonRequest alloc] initWithCompletionHandler:^(VNRequest * _Nonnull request, NSError * _Nullable error) {
        if (error) {
            NSLog(@"%@", error);
        }
        else {
            NSAssert(request.results.count > 0, @"No Results");
            
            VNHorizonObservation *horizonObservation = request.results.firstObject;
            NSLog(@"%@", horizonObservation);
            NSLog(@"%f %@", horizonObservation.angle, NSStringFromCGAffineTransform(horizonObservation.transform));
            self.imageView.transform = CGAffineTransformMakeRotation(-horizonObservation.angle);
//            self.imageView.transform = CGAffineTransformInvert(CGAffineTransformMakeRotation(horizonObservation.angle));
//            self.imageView.transform = CGAffineTransformInvert(horizonObservation.transform);
        }
    }];
    NSError *error;
    [handler performRequests:@[request] error:&error];
    if (error) {
        NSLog(@"%@", error);
    }
}