stereoRectity translation parameter

edit

Hello, I've a problem with the translation parameter of cv::sterorectify(). From the manual I read:

R – Rotation matrix between the coordinate systems of the first and the second cameras. T – Translation vector between coordinate systems of the cameras

In which coordinate system is T supposed to be expressed? From the manual it would seem in world coordinates
but that's not possible since R is the rotation from one camera coordinate system to the other, hence it does not contain info about how to stereo pair is oriented. My guess is in the coordinate system of one of the cameras??