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A dent has been found on the outer edge of the circle. how to find the angle between the center point and the dent region?
Like I said in your related question, find the dents
dentsImage = bwconvhull(binaryImage) - binaryImage;
Then get the centroids
measurements = regionprops(binaryImage, 'Centroid');
which I'm sure you already know how to do because you've used regionprops many, many times in the past.