Question about calculation of smpl_trans in Human36M

[YxZhxn]

Hi! Firstly, thanks for your excellent work! I was learning your data processing procedure and had confusions about the following code:

3DCrowdNet_RELEASE/data/Human36M/Human36M.py

Line 216 in fde86df

smpl_trans = smpl_trans - root_joint_coord + np.dot(R, root_joint_coord.transpose(1,0)).transpose(1,0)

Could you kindly explain to me that what the physical meaning of 'smpl_trans - root_joint_coord + np.dot(R, root_joint_coord.transpose(1,0)).transpose(1,0)' is? As far as i understand that 'smpl_trans - root_joint_coord' represents the translation in the coordinate system that takes root joint as origin. My question is how to explain np.dot(R, root_joint_coord.transpose(1,0)).transpose(1,0)?

[hongsukchoi]

Hi!

The get_smpl_coord function is transforming the mesh in the world coordinate system (frame) to the camera coordinate system. Line 191 and line 216 are performing that.
Line 191 is rotating the mesh around the root_joint_coord (pelvis) without any translation change.
Line 216 is adding the appropriate translation.

See the equation I wrote below.

[YxZhxn]

I see. Thanks for your quick response!