Fixing Sloping Shoulders

When we imported the UE4 animation in the post on FBX Files and BVH Retargeter, we noticed that the collar bones have a quite unnatural pose; the shoulders are sloping. This is unfortunately something that happens quite often, but not always. It depends on the rest pose of the rig in the BVH file.

This can sort of be fixed with the Shift Animation tool. Rotate the collar bones up, and then rotate the upper arms down to compensate. However this is quite annoying and the result is not always good, so I found a different solution. The new Clear Bones tool clears the animation of the collar bones, which usually shouldn't move so much anyway, and then rotates the upper arms so their rotation in world space remains unchanged.

Here we have a typical situation. The collar bones slope far too much.

With the collar bones selected, press Clear Bones.

Now the collar bones don't slope anymore, and the arms remain oriented in the same way as before. The pivot points of the upper arms have moved, since the collar bones are rotated differently, but the arm's world space rotation is unchanged.