A game machine displays a target on a display plane with four known points. An image sensor with an image plane on which an image of the display plane is formed with the known points included. The game machine calculates an attitude of the image plane relative to the display plane in response to the...http://www.google.de/patents/US20020107069?utm_source=gb-gplus-sharePatent US20020107069 - Game machine, method of performing game and computer-readable medium
