A display system includes a head-mountable 3D display device including at least one sensor to sense an absolute position and orientation of the 3D display device. The display system includes an accessory wearable by a user. The accessory includes at least one sensor to sense a relative position and orientation of the 3D display device relative to the accessory. An absolute position and orientation of a torso of the user may be determined based on the sensed absolute position and orientation of the 3D display device and the sensed relative position and orientation of the 3D display device relative to the accessory.