I found a bunch of questions related to this and I haven't found a fully satisfactory answer. So, my question is:
"In which coordinate system is the point cloud resulting from reprojectImageTo3D?"
My guess is that as its origin is located at the principal point of the left rectified camera since I can map the rectified left image perfectly onto the point cloud. How can I then express the point cloud with respect to the original unrectified camera? My underlying goal being that I want to ask for a given pixel in the original image the corresponding 3d point and for a given 3d point how can I project it into the original image.