Patent GB-829996-A (GB)
Title: Image perspective alteration means
IPC: G09B9/32
Filed: 1955-12-29
Abstract: 829,996. Optical-projection systems and apparatus. LINK AVIATION Inc. Dec. 29, 1955 [Jan. 5, 1955; April 11, 1955; April 22, 1955; May 27, 1955; Nov. 25, 1955(2)], No. 37283/55. Class 97(1) [Also in Groups XXXIII and XL(b)] An image is recorded to represent a view of a scene from a particular viewpoint and is distorted, during the formation on a viewing surface, of an image to produce a view of the scene from a different viewpoint. In the application of the invention to grounded aircraft training apparatus a kinematograph film is taken during an ideal, preferably linear, glide path to an actual or model runway and distorted during projection in the training apparatus so as to appear to the pupil as it would from the simulated path being "flown". A vertical change of effective viewpoint of a scene requires a change of vertical scale of the picture while a lateral change of viewpoint entails a "shearing" of the image i.e. distortion which changes a rectangle into a parallelogram so that near objects appear to move more than distant, objects on the horizon having no movement at all. Such distortions may be produced by the optical system of the kinematograph projector shown in Fig. 9. The vertical change of scale is effected by a variable power anamorphosing system comprising positive cylindrical lenses La, Lb and a negative cylindrical lens L2. A motor 132 can rotate a sleeve 126 in which are formed cam slots engaging pins 122, 123 to produce axial adjustment of the lens La, Lb to vary the anamorphosing power of the system. The "shearing" of the image is produced by relatively inverted prisms 108, 107, the latter being rotatable about a vertical axis by a motor 116. Such a rotation, from an initial position where both prisms are parallel and perpendicular to the axis, produces a lateral shift of the light beam decreasing to zero at the apex of the prism 107. The prism 107 may have a finite minimum thickness compensated by a parallel glass plate Lp rotated oppositely to the prism 107 about a parallel axis. A control system for operating the projector of Fig. 9 is shown in Fig. 10 and comprises servomotors M200, M201 forming part of the training apparatus which rotate to represent distances North and East of a datum position and rotate potentiometers R200, R201 to produce voltages representing these distances which are fed to summing amplifiers U200, U201. Voltages from potentiometers R203, R204 set by the instructor to represent the simulated airport position are also fed to the amplifiers whose outputs thus represent distances from the airport position. These output voltages energize the rotor coils of a resolver T1 the stator coil L 2  of which is connected to a servo M203 which positions the rotor to produce a minimum voltage on the coil L2. The rotor position thus 'represents the bearing of the airport from the simulated aircraft position: The voltage on the stator coil L 3 , perpendicular to L 2  represents the distance of the airport from the aircraft. According as this voltage is greater or less than that set by the instructor on potentiometer R206, so the relay PSR1 operates to close or open its contact a. The trainer height servo M204 operates a potentiometer R208 the voltage from which is fed to relays PSR2, PSR3, together with voltages set on potentiometers R209, R210 representing maximum and minimum altitudes. Only when the height is within the permitted limits are the contacts a of both these relays closed. The bearing drive from the servo M203 enters a differential 210 into which is set, by a knob 211, the heading of the airport runway, so that the shaft 212, with the cam 213, rotates in terms of the inclination of the flight path to runway. When this is within permissible limits and the switch S201 is closed by the cam and the relay contacts a are also closed the projection lamp 214 is illuminated from the source 200. So long as the distance is within the limit set on the potentiometer R206 the contact a of the relay PSR1 energizes the relay K200 to close its contact a and feed a distance signal from the coil L3 to a servo driving the film feed mechanism 103. The film feed continues whether or not the flight path is within the limits required to complete the lamp circuit. The latter may be opened by the manual switch S202 to simulate loss of visibility due to cloud &c. It is also opened when, at the end of a run, the switch S204 is moved to the "Re-set" position in which also the film drive servo is connected to the potentiometer R206 to be run back to a point corresponding to the distance set thereon. The distance signal from the coil L 3  is fed to a sine resolver R214 rotated by the shaft 212 to produce a signal representing the lateral displacement of the aircraft from the runway, fed to the servo M-L containing the motor 116 driving the prism 107 and also a potentiometer providing the rebalancing voltage and fed from the amplifier U203 providing, as an ideal altitude signal, a mean of the voltages from the potentiometers R209, R210 so that the rotation of the motor 116 is a measure of the ratio of lateral displacement and height, which is shown to be the function needed to operate the prism 107. The anamorphosing elements La, Lb are operated by the servo M-M containing the motor 132 and fed by a voltage representing simulated height from the potentiometer R208 and rebalanced by a voltage from the potentiometer R212 fed from the amplifier U203, so that the rotation of the motor 132 represents the ratio of simulated to ideal altitude. The above system uses a variable power anamorphoser and the prism system 107, 108. The necessary image distortions may also be produced by lenses of variable power only. As a general case the properties are investigated mathematically, in the Specification, of the combination of a system comprising a variable power spherical ("zoom") lens and two anamorphosers of variable power and orientation. Such a system thus comprises five variables. It is shown that variation of any three (the other two being kept constant) can produce in an image of the correct size and with the necessary distortion, but not necessarily the correct orientation, corresponding to any given change of viewpoint. Arrangements utilizing different combinations of variables, and control circuits for use with them, are described. If more than three quantities are variable some arbitrary restraint must be put on their variation. A typical example is shown in Fig. 5b and comprises two anamorphosers, both variable in power and orientation, but with their axes of maximum power maintained at right angles. All the lens elements are contained in a tubular housing 6105 carried on a flanged bearing ring 6104 secured to the front of the projector PR, the housing being rotatable by a motor M-6100 through gearing 6106, 6107. The rear anamorphoser comprises a negative cylindrical lens L-AN in front of axially adjustable positive lenses LA-1, LA-2 in mounts with pins 6113, 6114 projecting through an axial slot in the housing 6105 and through cam slots in a sleeve 6110 rotatable, to adjust the positive lenses, by the motor M-6300 through gearing 6108, 6109. The elements of the front anamorphoser, L-BN, LB-1, LB-2 are similarly mounted and adjusted by the motor M-6400. The entire projector is mounted in a gimbal system and is rotatable about the optical axis to orient the distorted image as required and about mutually perpendicular transverse axes to locate the image on the screen. Electrical circuits are described for calculating, from parameters representing the actual and ideal glide paths, the necessary settings of the optical elements and for applying the settings automatically. In an alternative embodiment the necessary image distortions are effected electrically in a television link included in the projection system.