Rotate image layer maintaining center

Question

Consider this image (size is 10x140; arrow is 10x70):

The Red arrow is my problem, because I want it to rotate.

Now I'm using

CGFloat Angle = [Speed.text intValue] / 160.0;
_Arr.layer.transform = CATransform3DMakeRotation(Angle * M_PI * 2, 0, 0, 1);

When _Arr rotates, it loses the center. As you see in the picture, the center is the plus ("+") sign, and the arrows in opaque are the problems.

I tried also to set center and anchor point, but I get the same results. I made the arrow image double (double heigth, image half), same thing.

This is the interface builder:

What's could be the problem?

Is the CATransform3DMakeRotation the problem or the image? The anchor point? the degree formula? Both?

Answer 1

anchorPoint is the answer ("Shift the arrow center point to one of the end points of the image"). Check this tutorial http://www.mobisoftinfotech.com/blog/iphone/ios-tutorial-custom-speedometer-control/