Hello everyone!!! I want to animate a human model with data provided by a set of sensors. The data are provided as quaternions. My problem is about how to combine quaternion for those bones that are connected to another one, when the first one is moved. I explain better: in my model the skeleton is formed by bones and for example the bones of the limbs are connected to the bone of the torso. When I apply a transformation to rotate the torso, the limbs follow its movement. If I would apply a transformation also to the limbs, I should compute the relative quaternion of the movements of the limbs with respect to movements to the torso. Can anyone tell me how is it possible?? Which is the mathematical formula to compute this relative quaternion??