horizontal flip (smpl_x)

[baeckgoo]

Hi.
Thank you very much for your smplx model.

I'm trying to flip the smpl_x model, given BEDLAM images, smpl_x parameters, and camera parameters.
(1) This is the original image and the rendered smpl_x model.

(2) When I flipped the mesh, the elbow was not flipped properly as follows.

I assume that the joint position of elbows (pivot for rotation) does not seem to be aligned as the following image, if the joints are correctly visualized:
https://user-images.githubusercontent.com/82434566/114505402-4bad1480-9c6b-11eb-81b6-f384df4eeb2f.png
You can find the elbow joints (18,19) do not seem to be aligned each other unlike SMPL.

The pairs of flipping index are as follows:

SMPL_X_FLIP_PAIRS = ( (1,2), (4,5), (7,8), (10,11), (13,14), (16,17), (18,19), (20,21), # body
                     (23,24), #eyes
                     (25,40), (26,41), (27,42), (28,43), (29,44), (30,45), (31,46), (32,47), (33,48), (34,49), (35,50), (36,51), (37,52), (38,53), (39,54) # hands
                    )

How can I correctly flip the mesh with smpl_x parameters?

[enesduran]

One thing to consider in SMPLX body model is that it is not perfectly symmetrical. Meaning that horizontal flip in poses do not correspond to the perfect horizontal flip of the body mesh. This is because joint locations (ex. left elbow-right elbow) are not perfectly symmetrical