A method for mapping the trajectory of a part of the anatomy of a human or animal body. The method comprises receiving first sensor signals from a sensor attached to part of the anatomy of the human or animal body. The first sensor signals comprise three dimensional position information indicating the location of the sensor; determining from the first sensor signals at least two angles of rotation of the part of the anatomy to which the sensor is attached with respect to a centre of rotation of another part of the body, wherein the angles of rotation are selected from pitch, yaw and roll. Transforming the signals to provide two dimensional coordinate data defined in a two dimensional coordinate space wherein a first dimension in the two dimensional coordinate space represents a first angle of rotation of the part of the anatomy and a second dimension in the two dimensional coordinate space represents a second angle of rotation of the part of the anatomy; and stores the two dimensional coordinate data.