undistortPoints, given R has no effect on result

[crackwitz]

Documentation says that R will be applied if given.

> For each observed point coordinate (u,v) the function computes: [...]

Actual behavior: giving a non-identity R appears to have no effect on the result.

The affected function appears to be cvUndistortPointsInternal and the involved variables are: matR (CvMat* parameter), _RR (local CvMat), RR (local C array used in the calculation).

related discussion including reproducer: https://forum.opencv.org/t/why-r-is-not-considered-in-cv2-undistortpoints/8483 and issue

[victor1234]

Please provide minimal reproducible example

[crackwitz]

Thank you for prompting me to re-examine this. I executed that user's code without checking exactly the function signature. The issue doesn't actually exist.

The function signature is

undistortPoints(src, cameraMatrix, distCoeffs[, dst[, R[, P]]]) -> dst

The user's code accidentally passed R, P in the parameters of dst, R. Using keyword arguments (Python feature), or passing None in place of dst will show the proper behavior.