Patent GB-1404093-A (GB)
Title: Simulator visual display system
IPC: G06T19/00
Filed: 1973-03-15
Abstract: 1404093 Flight simulator display SINGER CO 15 March 1973 [30 March 1972] 12462/73 Heading H4F Flight simulator display system in which a simulated horizon is correctly positioned with respect to a terrain video signal, produced by television camera 11, Fig. 1, viewing a model 13, and simulated cloud video signals together with limited visibility scenes. The colour signals from the camera control unit 15 are supplied to a special effects generator 19 (see later) together with position, attitude and visibility information from the simulators digital computer 21. The resulting outputs from generator 19 are displayed 27 for viewing by trainees in a simulated aircraft cockpit 29, simulated controls from the cockpit being supplied via line 31 to the computer and from the computer to the instruments in the cockpit via line 33. The whole system is synchronized by generator 17, a sweep reference generator 23 providing horizontal (H) and vertical (V) sweep waveforms to generator 19. Under good visibility conditions the terrain scene must appear in the foreground with a horizon and then sky or clouds. As visibility decreases portions of the terrain must be obscured to simulate this limited visibility; and as the aircraft climbs a white scene must be displayed as it enters clouds whereas when above the clouds a white foreground simulating clouds with blue sky of increasing intensity as altitude increases must be displayed. Generator 19 synthetically generates all these displays and includes, Fig. 2, a block 41 receiving inputs 10 sin #, cos #, sin #, cos #, cos #, RVR and h from computer 21 (where # and # are the simulated aircraft pitch and roll angles respectively, RVR is the runway visibility range and h the aircraft altitude), and H sweep and V sweep from generator 23. Block 41 develops on line 43 a horizon reference signal on a lineby-line basis which is used in function generator 45 to develop a gating signal for switching between terrain video and special effects. The gating signal from generator 45 is applied to gated video amplifiers 47, 49 and 51 which supply the red, green and blue information signals to the displays. When above the horizon the gating signal is zero and the upper inputs to amplifiers 47, 49 and 51 from potentiometers 53, 55 and 57 are passed to the displays. These signals are arranged to be in the ratio 0À3 : 0À59 : 0À11 so that white is displayed to thereby represent sky. When the gating signal is 2 (or more) volts the lower inputs from the television camera are passed, and in between the two inputs are mixed. Since the sky varies for various times of day, i.e. from bright white to grey for dusk and black for night, relays switches 63A and 65A are appropriately controlled by relays 63 and 65 under control of the computer. When the aircraft comes out of the clouds, i.e. is above the clouds, relay 81 is activated which causes amplifiers 75, 77 and 79 to switch to their lower inputs so that above cloud simulated signals from potentiometers 89, 91 or 93 (depending on time of day) are passed to the amplifiers 47, 49 and 51 instead of the terrain signals from a television camera. In addition relay 81 operates switch 81B which causes a computer signal representing altitude above clouds to be supplied to a unity gain summing amplifier 59 so that additional blue is added to the output, the amount of blue increasing as altitude increases since the sky above the clouds becomes a deeper blue as altitude increases. When in the clouds the gating signal from generator 45 remains at zero so that the whole display is white. The horizon generator 41 and function generator 45 are described with reference to Fig. 3 (not shown), generator 41 being such that the zero volts level of the vertical sweep waveform is automatically controlled to follow the horizon in response to the simulator computer output signals, and generator 45 being such that it transforms the resulting vertical sweep waveform from generator 41 to provide a voltage which goes from 2 to 0 volts each time zero volts is crossed. In generator 41 account is taken of the fact that as altitude increases less of the ground will be visible, e.g. at one mile altitude with a one mile visibility range none of the ground would be visible, a multiplying function RVR/h being used. Two circuits are included in generator 41 since the transition from sky-to-cloud is sharper than the transition from sky-toterrain, the appropriate one being selected by an above cloud output signal from the computer. When in the clouds switching from sky-to-cloud or sky-to-terrain is prevented.