The picture below shows three of the four projectors, which project the signal via one mirror each to the rear side of the projection surface. You can also see the four cameras (simple webcam models) which scan the projection surface and send their video, via four firewire connections, to computer "datawall1" (Linux). The right screen's signal is transmitted at 30 fps to allow fast and precise processing, while the other three video signals are sent and processed but at 12 fps. "datawall1" analyzes the four video streams in real-time. Once the red and bright laser point (see left picture) is identified in one of the streams, its position will be recognized and, via UDP transfer, converted into a mouse position for the lecture hall computer ("datawall2", Windows XP).