Patent GB-1135983-A (GB)
Title: Visual display apparatus
IPC: G09B9/02
Filed: 1966-03-01
Abstract: 1,135,983. Aircraft flight simulators. GENERAL PRECISION Inc. 1 March, 1966 [24 March, 1965], No. 8907/66. Heading B7W. [Also in Division H4] To provide visual displays in three-dimensional perspective to simulate flight over terrain having substantial altitude variation, a flying-spot scanner (FSS) simultaneously scans related portions of two transparencies (30) and (32), Fig. 4, not shown, one of which is a rectified aerial photograph of an area (i.e. it represents an image of the area viewed normally), and the other is an elevation map of the same area, and the video information derived from scanning the aerial photograph is applied to an intermediate display cathoderay tube the sweep operation of which is varied in accordance with elevation information derived from the scanning of the elevation map. If the rectified aerial photograph is in colour the video information is applied to three intermediate cathode-ray tubes (84), the screens of which are viewed by a closed circuit television system (86) including three vidicon cameras and a projection display tube which provides the final display image on a screen (14) in the flight simulator cockpit. The intermediate display cathode-ray tubes may comprise storage tubes, Fig. 8, not shown, plural separate banks of such storage tubes being used with one tube provided for each primary colour in each bank. In this arrangement the video signals from successive frames of the flying-spot scanner are applied alternately or in sequence to the separate banks, at a slow rate amenable to computation and read out at a faster rate for application to a final display cathode-ray tube. The elevation data is preferably coded on the elevation film in terms of density and/or colour, e.g. eight different discrete shades of red may be used, each representing a difference of elevation of 1600 ft. from the next shade, together with eight different shades of green, each representing an elevation difference of 200 ft. and ten shades of blue each representing an elevation difference of 20 ft. Alternatively, a monochrome transparency on which elevation information is stored in terms of grey-scale density graduations may be used. The elevation transparency, whether monochrome or colour, may be used alone to produce a computed image of terrain information which does not display any vegetation or water features but does present a well simulated representative terrain with variations in image brightness, Fig. 9, not shown. In another arrangement elevation and video information may be derived from the scanning of a single transparency on which the video information and elevation data are encoded as graduations of different colours, Fig. 10, not shown. In the embodiment using two transparencies, i.e. a colour aerial photograph and an elevation map, the F.S.S. (24), Fig. 4, not shown, is driven by m and r sweep waveforms so as to scan trapezoidal areas of the transparencies which are mounted on a film plate positioned with respect to the F.S.S. by E-W and N-S film drive servos (130) and (132). The r sweep computer (28) repetitively computes the exponential range quantity r 1 (t). Figs. 1-3, not shown, the sweep being exponential so that for a flat terrain the resultant colour video signals may be displayed on the screens of the intermediate cathode-ray tubes (84), to obtain a replica of the scene viewed by the observer, using vertical sweeps of constant speed. The colour video signals are processed (68), i.e. artificiallygenerated " sky " signals are substituted at appropriate times and the signals are blanked off at appropriate times (see later) and applied to the three intermediate cathode-ray tubes (84). The elevation video signals are processed (69) and used to accelerate or decelerate the sweep rates of the intermediate display cathoderay tubes (84), in order to provide threedimensional perspective in the simulated display, and to provide blanking and gain control signals (see later) for the colour video signal processing circuits (68). The apparatus for controlling the F.S.S. (24) is described with reference to Fig. 5a, not shown, and the colour video signals and elevation signals processing circuits (68) and (69) are described with reference to Fig. 5b, not shown. The processing circuits include a vertical sweep modifier (174) in which the vertical linear sweep for the intermediate cathode-ray tubes is multiplied by the function (1-h/a) where a is the altitude of the observer and h is the instantaneous height of the point of terrain simulated at any instant, above a reference level, e.g. sea level (see description in Specification relating to Figs. 1-3, not shown). The output signal from the sweep modifier (174) is routed through a shadow computer (234) and resolver (210) to the vertical deflection plates of the three intermediate display tubes. Shadow computer (234) operates to terminate the vertical sweep applied to the intermediate display tubes when the terrain being scanned at any given instant has a change in elevation such that the terrain could not be seen by an observer located at the instantaneous simulated aircraft altitude. Resolver (210) is positioned by the trainer bank angle servo and serves to rotate the images on the intermediate display tubes to simulate bank angle changes. To prevent undesired intensity variation in the final display due to variations in the vertical sweep in accordance with terrain elevation changes, the vertical sweep waveform from modifier (174) is applied through a video gain control circuit (228) to control the gain of each of the video amplifiers in order to decrease the amplifier gain as sweep rate decreases and to increase the gain as sweep rate increases. Heading changes may be introduced by rotation of the magnetic deflection yoke of the flying-spot scanner (24) to determine the angular sector through which the m sweep operates, and because the scanner tube deflection is intentionally offset from the centre of the tube, compensating inputs commensurate with heading components are applied to the film drive servos (130) and (132), Fig. 4, not shown. Instead of using resolver (210), Fig. 5b, not shown, to simulate bank angle changes the display on the intermediate cathode-ray tubes may be rotated. Pitch angles may be simulated effectively by moving the final display up and down using the trainer pitch angle servo to adjust the vertical position control on the closed circuit television projector, for example. This is not theoretically rigorous but results in only about 2% error in vertical scaling accuracy for pitch angles as great as 10 degrees.