The present invention relates to a data processing method of determining a transformation for the relative positions of two body parts which are connected to each other by a joint, the method comprising the following steps:a) acquiring first body part position transformation data comprising first body part position transformation information describing a first body part position transformation for the position of a first body part of the two body parts relative to a first reference structure assigned to the first body part；b) acquiring second body part position transformation data comprising second body part position transformation information describing a second body part position transformation for the position of a second other body part of the two body parts relative to a second other reference structure assigned to the second body part；c) acquiring reference structure position transformation data comprising reference structure position transformation information describing a reference structure position transformation for the position of the first reference structure relative to the second reference structure for at least two movement states of the joint；d) determining, based on the first body part position transformation data and the second body part position transformation data and the reference structure position transformation data, joint position transformation data comprising joint position transformation information describing a joint position transformation for the position of the first body part relative to the second body part for the at least two movement states.
