is there really a general decomposition that can smoothly translate between motions? or is it something we should always optimize case by case? (for example, to tort a beam and to rotate a human joint, can they both perform well under a same decomposition & parameterization method)?

a follow up question: we can't always judge a transformation by bare eyes. How do we quantify the quality of transformation? in other words, how can we tell which transformation is better in an objective way, so that we know how to optimize?

Does skinning work by simulating different materials, and therefore are there lots of different skinning methods based on materials?