Interpret the relation between R_ex, R_tilt, cam_R

Dear Author @yinyunie ,

I have a hard time to figure out the relation between these three rotation matrices as shown in

1. https://github.com/yinyunie/Total3DUnderstanding/blob/bf6c8a92d421e58727a8288a5f8849da408c556e/utils/sunrgbd_utils.py#L379
2. https://github.com/yinyunie/Total3DUnderstanding/blob/bf6c8a92d421e58727a8288a5f8849da408c556e/utils/sunrgbd_utils.py#L367
3. https://github.com/yinyunie/Total3DUnderstanding/blob/bf6c8a92d421e58727a8288a5f8849da408c556e/utils/sunrgbd_utils.py#L237 where is this left-handed coordinate system from? originally I thought all the coordinate system in SUN RGB-D is right-handed

BTW, the reference that I am currently using to interpret different kinds of coordinate systems is https://github.com/facebookresearch/votenet/blob/main/sunrgbd/sunrgbd_utils.py

Therefore I am kindly asking whether you could elaborate a little bit on how to interpret these three coordinate systems.
Best!