A data processing method for determining a position of at least two body parts relative to one another, which at least two body parts are connected to one another by at least one joint, the method being executed by a computer and comprising acquiring initial body part position transformation data comprising initial body part position transformation information describing an initial transformation between positions of the at least two body parts in a predetermined pose of the at least two body parts acquiring alteration transformation data comprising alteration transformation information describing a transformation between a position of a first alteration part of at least one first body part of the at least two body parts, which first alteration part represents a first virtual anatomical alteration to the at least one first body part, and a position of an anatomically unaltered part of the at least one first body part determining, based on the initial body part position transformation data and the alteration transformation data, altered body part position transformation data comprising altered body part position transformation information describing a transformation between a position of the first alteration part and a position of a second other one of the at least two body parts in the predetermined pose.
