Abstract: A multi-stage adder has a plurality of parallel inputs some fed to one stage of the adder and other inputs fed to a next stage of the adder. To effect selective inversion of a pair of inputs one of the pair is connected to one stage and the other of the pair is connected to the next stage. A cross-over switch is provided on both inputs so that their connection to the two successive stages can be interchanged.

Abstract: A visual display system of the computer generated image type, for a ground based flight-simulator having a rectangular raster-scanned display and having a surface detail information store for providing a visual display of textured surfaces in perspective during simulated flight. The system includes a surface detail generator comprising a perspective transformation computer and a surface detail store. The perspective transformation computer is organized as a pipeline processor to computete in real time the perspective transformation from the textured surface (ground) plane to the display plane. Scanning of the surface detail store is controlled in a manner comparable with a trapezium scan of a photographic image, for the purpose of the perspective transformation.

Abstract: Visual display apparatus for ground-based craft flight simulation apparatus using a raster scan display for viewing by the trainee pilot and providing an image comprising a target or other craft, together with cloud extending to the simulated horizon. The cloud image part has repetitively patterned features and is displayed in correct perspective, according to the simulated flight position relatively thereto, for providing speed and altitude cues. This part of the image is provided by digital means, a single cycle of the repetitive pattern being held in a digital store and perspective being computed continuously. The whole apparatus includes three generators providing respectively sky, horizon and patterned cloud surface all controlled by a general purpose computer receiving flight data from the simulator flight computer. Outputs from the three generators are selected appropriately during the raster scan of the display and also appropriately combined with a high-definition image of the target or other craft.