..... > With IR you place a modulated IR beacon on the car and have > some CCD video cameras that have nice wide angle lenses > and IR filters to help them along and use a suitable frame > grabber system to receive the signals and then compare > the video frames at your beacon rate (say 15 Hz) and you should > be able to locate the vehicle..... Much easier to use lateral effect photodiodes, also called Position Sensing Diodes. These are used to determine range in AutoFocus cameras, but you can just as easily use them to determine position from an aerial view. Much, much simpler than video. Contact one of the PSD mfgrs, such as Hamamatsu, EG&G, UDT, Sharp for lots of applications info. -- Paul Mathews, consulting engineer AEngineering Co. optoeng@whidbey.com non-contact sensing and optoelectronics specialists