Generalized Hough is used for an arbitrary shape. The shape is parameterized by the center point and the set of vectors leading from the boundary points to the center. These displacement vectors are indexed by the orientation of the tangent of the shape boundary at that point. For an edge point in a test image we calculate its orientation angle (gradient?) and look up the corresponding displacement vectors (might be more than one depending on how discretized). Each vector votes for the shape's reference position. Votes will accumulate at the actual position as with the Hough line transform.