Converting the rest pose to A pose & SMPL-X support

[jiaxilv]

Hi! Your script has been immensely helpful for my work. I have two questions:

1. How can I convert the rest pose from the default T pose to an A pose? (I need to perform this operation in bulk.)
2. Have you considered adding SMPL-X support to the existing script? Even just including hand gestures would be a great addition.

Thank you for your work!

[KosukeFukazawa]

Hi jiaxilv,
I'm sorry for the late reply.

1. How can I convert the rest pose from the default T pose to an A pose? (I need to perform this operation in bulk.)

If you want to change to A-pose, it is necessary to change joint positions of the rest pose and change joint rotations accordingly.

First, we need to create A-pose rotations before create the rest pose(87 line on smpl2bvh.py)

A_pose = torch.zeros((1, 72), dtype=torch.float32)
A_pose[:, 3 * 16 + 2] = -torch.pi / 3
A_pose[:, 3 * 17 + 2] =  torch.pi / 3
A_pose_quat = quat.from_scaled_angle_axis(
    A_pose.numpy().reshape(1, 24, 3)
)

Then, create the rest pose as A-pose (89~91 lines)

rest = model(
    # betas = torch.randn([1, num_betas], dtype=torch.float32)
    body_pose=A_pose[:, 3:]
)

After that, you need to add A-pose inverse rotations to rotations on your data, it will fix the change of the rest pose. (123 line)

rots = quat.inv_mul(A_pose_quat, rots)

I haven't tested it, but perhaps this will work!

2. Have you considered adding SMPL-X support to the existing script? Even just including hand gestures would be a great addition.

I added SMPL+H support on my another repo(https://github.com/KosukeFukazawa/CharacterAnimationTools), but I don't maintain for a long time.
SMPL-X uses face joints, which can be quite complex to define in a hierarchical structure like bvh.

If you face some problem, feel free to contact me again.

[iamthephd]

Hi, I have joint locations from SMPLX model of shape [N, 144, 3]. I understand that creating hierarchical structure for face is difficult, but is there a way to convert first 55 bones to BVH?