The invention relates to a 3-dimensional computer graphics system in which an operator can effectively interact with a virtual model generated and displayed by a computer. In one embodiment the operator wears a helmet fitted with means which enable both the location of his head and its coordinates relative...http://www.google.com/patents/US4984179?utm_source=gb-gplus-sharePatent US4984179 - Method and apparatus for the perception of computer-generated imagery
