Tracking system for head-mounted display apparatus and method of tracking

A tracking system for use in a head-mounted display apparatus, the tracking system comprising:

• at least one emitter that, in operation, emits signals;
• a first receiver and a second receiver that, in operation, sense the emitted signals and generate sensor data, the first receiver and the second receiver being arranged on a first portion and a second portion of the head-mounted display apparatus, respectively, wherein the first portion faces a user when the head-mounted display apparatus is worn by the user, and the second portion is a part of a user-interaction controller of the head-mounted display apparatus;
• and
• a processor configured to process the generated sensor data to determine relative positions and orientations of the first receiver and the second receiver with respect to the at least one emitter, and to determine, based on the determined relative positions and orientations, a relative position and orientation of the second receiver with respect to the first receiver.