Patent Document ID: 9811908
Application ID: 14896859
Patent Status: 1

Claim One:
1. A head mountable display (HMD) comprising: an upward facing camera associated with a wide angle lens configured to capture images of an environment of the HMD; an image comparator operatively coupled to the upward facing camera, the image comparator being arranged to derive an indication of yaw of the HMD from images captured by the upward facing camera at different points in time; and a processor configured to identify feature points in the images captured at different points in time, and to detect positions in the images of the identified feature points so as to provide an indication of rotational movement of the HMD between two respective images, in which the processor is configured to detect indications of the rotational movement from a plurality of pairs of image positions, each pair representing opposite viewpoints of the camera, and in which the processor is further configured to derive the indication of rotational movement from one or more pairs exhibiting a lowest difference between the viewpoints of that pair.