How to further transform/animate an already transformed/animated UIView in Swift?

Question

I am trying to rotate with animation a UIImageView by 5° each time it is tapped. However, each time I tap it, it seems to revert back to the original angle and start the animation from there, instead of starting from where it was already. I get that transformations need to be chained so I'm doing that, however it still doesn't work:

UIView.animate(withDuration: 1.0, animations: {
        self.imgView.transform = self.imgView.transform.concatenating(CGAffineTransform(rotationAngle: CGFloat.pi/180*5))
    }, completion: nil)

I found a promising option in a variant of the animate function, but that makes it look even worse (somehow even garbles up the image):

UIView.animate(withDuration: 1.0, delay: 0.0, options: .beginFromCurrentState, animations: {
        self.imgView.transform = self.imgView.transform.concatenating(CGAffineTransform(rotationAngle: CGFloat.pi/180*5))
    }, completion: nil)

What am I doing wrong?

BTW the view originally has a scale and translate transformation on it which is set once in viewDidLoad:

        imgView.frame = CGRect(x: 0, y: view.frame.maxY-view.frame.midX, width: view.frame.maxX, height: view.frame.maxX)
    imgView.transform = CGAffineTransform.identity.scaledBy(x: 14, y: 14).translatedBy(x: 0, y: 150)

I'm mentioning this just in case the problem has anything to do with this piece.

Answer 1

increase your angle each time you call the transform

angel = angel + 0.5
self.imgView.transform = self.imgView.transform.concatenating(CGAffineTransform(rotationAngle: CGFloat.pi/180* angel))

Answer 2

I found the problem. It is the initial translatedBy. If I take that out, it works perfectly. So now I know, positioning of the view should always be done via frame and/or constraints, not by translatedBy.