How to use 'orig_cam'

[Chuanlong-Zang]

Hi, thanks for your great work!

In your code, orig_cam is converted from pred_cam. However during 2D projection, a prespective camera is assumed by a given focal_length, which means pred_cam is actually used in prespective camera.

So I want to ask
(1) how can I use orig_cam? Should I use them in a weak-prespective or a prespective way?
(2) My goal in the end: if I assume a focal_length, can I also calculate the prespective camera translation in the original image space, using orig_cam?