Rigging (skinning) : work flow if no neutral pose?
Question Rigging

Question

I have acquired an armature with a very nice mocap run cycle (about 20 frames). I would like to skin this armature and use it. The problem is that there is nothing close to a neutral pose for the armature. Skinning is a real nightmare, although it might eventually work.

After thrashing some, I'm attempting the following alternate (tedious) procedure:

Duplicate the armature
On the duplicate, delete all keyframes.
On the duplicate, pose all bones to neutral. Apply as rest pose.
On the duplicate (edit mode) fix all bone rolls, adjust symmetry, fix scaling...
Step through the animation of the original. Add new keyframes to all the duplicate bones, as needed, in order to reproduce the motion of the original.

I would have much preferred to have an operation like "apply new rest pose and adjust all keyframes accordingly." It might be theoretically impossible, or maybe there is a very clever addon which can do it. I don't think I've seen this specifically addressed in my training and investigation. Thanks in advance for any help.

Answer 1 · 2022-03-16T19:40:28Z

replied March 16, 2022 7:40pm

Consider looking into "retargeting" the armature. It is essentially what you are doing with a duplicate armature only its much more procedural. Instead of copy and pasting frames to each bone you would be using constraints and baking the animation to the new armature. There is an addon from Rokoko that does this pretty well for bi-pedal armatures. My research on the topic isn't vast so there may be better solutions for this out there.

Answer 2 · 2022-03-16T20:53:24Z

replied March 16, 2022 8:53pm

Thanks phoenix4690 . I have done rig-to-rig retargeting before (in a training exercise). I think it always works if source and target rigs have the same rest pose (i.e. neutral-A) and "nice" bone rolls. In my case the animation came from Unity, and doesn't meet those prerequisites.

I have used Mixamo before (maybe even with Unity, I can't remember) so that is another possible animation source. I just really liked this run cycle (very athletic).

I forgot to mention I changed all the Quaternion channels to XYZ Euler, to make it easier to fiddle with the curves.

[brute force always works as a last resort - I am very patient ;) ]

Answer 3 · 2022-03-21T14:47:59Z

replied March 21, 2022 2:47pm

End of story: In my case (probably unusual), the "quickest and easiest" path turned out to be the "most radical".

Attach markers to the important joints of a Unity rig
Play the animation in Unity. Screen capture a video (front and side view)
Animate a clean Blender rig from scratch, matching the video motions

The intuitive approach (import FBX and fiddle/tweak) actually took more time and gave an inferior result. I had a similar experience previously with a walk cycle.

For what little it's worth.