How to estimate 2D similarity transformation (linear conformal, nonreflective similarity) in OpenCV?

Question

I\'m trying to search a specific object in input images by matching SIFT descriptors and finding the transformation matrix by RANSAC. The object can only be modified in scene by

Answer 1

You can use find an affine transformation between the point sets using opencv, this is slightly more general than the case you are describing (known as a similarity transform) as it describes shearing transformations of the shapes as well.

It can be performed using the function getAffineTransform(InputArray src, InputArray dst). This takes 2 sets of three points and calculates an affine transform between them.