Angle of Rotation of Circular Object in Z-angle

Hello,

I want to calculate the angle of rotation of this circular object on the z plane (i.e., parallel to the image sensor's plane).

I have already tried the following: 1. I used the same algorithm as in the [ MATLAB example ][2]. I tried changing the features detected (SURF, BRISK, MinEigen) to find feature points. I did not get proper output, there were incorrect angles as result. I guess the problem with this was that not many feature points were detected on my wheel rim.

 2. I tried to locate the notch (which I have circled in red for display) using normxcorr2(). If the notch's position is known, using geometry I can calculate the angle of rotation.

Here too, enough features are not detected therefore I am not able to determine the angle correctly. Sometimes there is false location detected for the notch.

Can you suggest any other method to calculate the angle of rotation?

Thanks