An optical touch detection system may rely on triangulating points in a touch area based on the direction of shadows cast by an object interrupting light in the touch area. When two interruptions occur simultaneously, ghost points and true touch points triangulated from the shadows can be distinguished...http://www.google.de/patents/US20100045629?utm_source=gb-gplus-sharePatent US20100045629 - Systems For Resolving Touch Points for Optical Touchscreens
