Questions on Coordinate system, Transform direction and Scale

[leolin9248]

Hello, thanks for open‑sourcing MHR.

I'm using sam-3d-body(MHR) to get 6DoF poses of the wrists from pred_joint_coords
and pred_global_rots, and I have a few questions:

1. Coordinate system

   What coordinate system are pred_joint_coords and pred_global_rots in?
   Is it the standard OpenCV camera frame (+x right, +y down, +z forward),
   or something else?

2. Transform direction

   Do pred_global_rots (together with pred_joint_coords) represent a
   transform from camera → body or from body → camera?
   In other words, is it T_cam_wrist or T_wrist_cam?

3. Scale

   What is the unit / scale of pred_joint_coords? Are they in meters,
   or in some normalized space? If normalized, how can I convert them to
   metric coordinates consistent with a calibrated RGB camera?

A short clarification on these three points would be very helpful.
Thanks!

[JinlongYANG]

Hi @leolin9248, thank you for posting this issue! These parameters are not standard MHR parameters but customized output from SAM3D-body. I suggest you post this question there. Meanwhile, I'm waiting for the access to SAM3D-body model to examine the SAM3D-body outputs myself.

[leolin9248]

Hi @JinlongYANG,

Thanks for the quick response and clarification!

I have also opened an issue (facebookresearch/sam-3d-body#82) in the SAM3D-body repo as you suggested. If you get a chance to examine the SAM3D-body outputs later on, I would really appreciate it if you could share your findings here.

Thanks again for your help!