I am using estimateRigidTransform with about two vectors of 100 points and is working FINE. But somehow getAffineTransform doesn't work. I know that findHomography finds the best matrix using RANSAC and getPerspectiveTransform needs only 4 points. My question is what happens if I give more inputs in estimateRigidTransform or getAffineTransform? Does it take only 4 points from input matrix? Or do some kind of RANSAC?