How to convert the quaternions of global joint rotations into SMPL style axis-angle representation of the relative rotation?

[DawnHH]

Thanks for the great work !
I‘m working on integrating the hand pose with the SMPL body pose. The outputs of the IKNet are global joint rotations in quaternions [J, 4], however the pose parameters in MANO or SMPL model are axis-angle representation of the relative rotation [J,3] with respect to its parent in the kinematic tree. In the paper, the authors mentioned this convertion.

Could the author share the code of this part? That would be very important and helpful to apply the model in practice.
I've got some ideas from issue:
#80
#66
But I can't make it right. And I notice that the author is also one of the contributors of SMPL project, so maybe the author is more familiar with this part of convertion.
Thank you again for the great work!