cv::omnidir::stereoRectify returns wrong R2.

[dzywater]

Recently, I used cv::stereoRectify, cv::fisheye::stereoRectify and cv::omnidir::stereoRectify.

I found that cv::omnidir::stereoRectify returned R2 which could not get stereo images with epipolar constraint.

So I checked theirs sources.

I think that cv::omnidir::stereoRectify has a mistake.

That is omnidir.cpp, line 2225: _R2 = R21 * _R1;

Based on cv::stereoRectify and cv::fisheye::stereoRectify, this line should be: _R2 = _R1 * R21;

Besides, R2 is theoretically the rotation matrix from the coordinate system of the world to the second camera.

[alalek]

Thank you for the report!

Feel free to prepare PR with fix.

If you have some simple test case please add it into PR description (unfortunately there are no any tests for this module)