Access to rectification rotation matrices

[ozendelait]

Preliminary Checks

• This issue is not a duplicate. Before opening a new issue, please search existing issues.
• This issue is not a question, bug report, or anything other than a feature request directly related to this project.

Proposal

Please add means to access the rotation matrices used during rectification (equivalent to R1 and R2 of the stereoRectify openCV call https://docs.opencv.org/3.4/d9/d0c/group__calib3d.html) from ZED API. This could be added to CalibrationParameters in addition to stereo_transform (e.g. rectify_transform_left and rectify_transform_right)

Use-Case

Raw camera images cannot be converted/mapped to rectified camera images without R1/2. These are calculated within the closed-source part of the ZED SDK and currently no API call makes them available (also not visible in any ROS message).
The mapping is useful as it allows to store raw images together with depth and calculate rectified images dynamically (e.g. image messages from the zed-ros2-wrapper stored in bag files)

Anything else?

The rotation information of CalibrationParameters stereo_transform is only specifying the relation between left & right camera but not the rotation used during rectification to rotate left/right cameras in normed pixel space (before projection to rectified image pixels)