hand coordinates of the tag in static_cam_calibration.cpp

[sayali-purdue]

In file static_cam_calibration.cpp, the position of the tag in hand coordinates corresponds to the transform from 'base_link' to 'tcp_link'/'fake_tcp'; whereas position of the tag in eye coordinates corresponds to the transform from 'camera_link' to 'tag_0'.

For my understanding, I would like to know few details for the above statement:

1. why 'base_link' is used as the hand coordinate system, instead of 'ee_link'?
2. (just to confirm) do 'tag_0' and tcp_link/'fake_tcp' frame refer to the same tag in different coordinate systems (hand, i.e., 'ee_link' and eye, i.e., 'camera_link'?
3. why are two frames needed for the tag center: fake_tcp and tcp_link?

Would really appreciate if you could provide your insights.

Thank you!