A camera comprising a lens forms images onto a two-dimensional array of photo-sensitive elements, e.g. a CCD or CID sensor. The lens has a well defined center of rotational symmetry, giving an unambiguous definition of spatial directions. Such cameras form angle sensors to measure spatial directions...http://www.google.ca/patents/US5196900?utm_source=gb-gplus-sharePatent US5196900 - Method and sensor for opto-electronic angle measurements
