Sensors of relative position and orientation

This invention relates to the determination of position and orientation for a mechanical structure relative to a proximal point in space. Preferred embodiments of the invention determine the co-ordinates of the human head when an individual is seated. This information enables head and torso movements of the individual to form part of his/her interaction with software being executed by a computer (Browse R A, Rodger J C, Sewell I and Brooke J: " 3012, 448-53, 1997). An optical position and orientation determining system determines yaw, pitch, roll, lateral translation and longitudinal translation of a body with respect to a direction and intensity sensing receiver. The system comprises two energy beam emitters, mechanically mounted on a body, which illuminate the position sensing receiver. The energy beams are intermittently energized in a predefined fashion to enable the receiver and its associated signal porcessing means to determine the position and orientation of the body with respect to the receiver. The system can also be used to determine velocities and accelerations of the body relative to the receiver.