HAnim's "center of rotation" and glTF's TRS (translation/rotation/scale) are solving related but distinct problems, and conflating them causes confusion when converting rigs between the two.

HAnim, glTF, and VRM—three major frameworks for representing and animating humanoid characters. 

HAnim, the Humanoid Animation International Standard maintained by the Web3D Consortium, provides a rigorously defined, interoperable framework for representing, animating, and exchanging 3D human figures across tools, platforms, and applications.

Humanoid Animation (HAnim) Overview — Architecture, Strengths, and Strategic Value for Open, Interoperable 3D Human Representation