Head tracking system

Abstract

A head tracking system HTS, configured to determine a head position and a head orientation of a user to which display images are configured to align with the outside world scene and are configured to be presented, the HTS comprising: one or more optical sensors generating an optical measurement; and a number of inertial sensors generating an inertial measurement; a processor configured to determine the head position and the head orientation from one or both of the one or more optical sensors and the number of inertial sensors and configured to: determine an optical tracking state from the optical measurement and an inertial tracking state from the inertial measurement; when both the optical tracking state and the inertial tracking state are valid, flagging/asserting HTS operation as normal; when both the optical tracking state and the inertial tracking state are invalid, flagging/asserting HTS failure; when the optical tracking state and the inertial tracking state are valid comparing the optical measurement and the inertial measurement to determine if the HTS can operate safely based on a predetermined tracking performance required by the system.