The position data obtained from motion capture is relative to the origin point. However, the FBX model I want to animate has the waist as the parent, and all other parts have the waist as their origin. The data coming from motion capture includes the position information (tx, ty, tz) and the quaternion (rx, ry, rz, rw) for each point. Is there a way to convert this data so that the position information is relative to the waist as the origin?
Depending on your motion capture system the easiest way to do this is apply the global translation to the hip bone and then use the rotation values for each child only. Rotation should be local to the root bone by default. I would be surprised otherwise.