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Visual Display for U.C.L.A. Driving Simulator:
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This article first appeared in |
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Written by:
S. F. Hulbert and C. K. Wojcik. Institute of Transportation and
Traffic Engineering University of California, Los Angeles. Document supplied to "..in 70mm - The 70mm Newsletter by Dr. Richard Vetter |
Issue 49 - June 1997 |
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The motion picture technique used in the U.C.L.A. Driving Simulator is a technique called Dimension-150. (Ref. 2). The Dimension-150 photographic system utilizes a conventional motion picture camera and a retrofocus lens. In addition, an afocal attachment, consisting of a conical anamorphosing mirror (see Figs. 4 and 5), and supplementary special cylindrical lens for negating astigmatism and reducing chromatic aberration. The function of the mirror is to receive a wide field of view compressed laterally at a ratio of 2:1. The camera, equipped with a wide angle prime lens, photographs this compressed image. The compression ratio of 2:1 has been selected, here, so that a standard anamorphic projection lens could be used for exhibition of the image. The shape of the mirror and the manner of which the optical axis of the camera is oriented to it are, of course, of great importance. Three types of precalculated distortions are present on the film image: lateral compression, negative keystoning of vertical imagery, and positive horizon curvature. All these distortions are canceled by the compensation distortions introduced in exhibition through the use of an anamorphopic lens, the oblique projection angle, and a deeply curved wide-angle screen. Fig. 6 illustrates a rectangular grid pattern in the real world, as it would appear on the film photographed using Dimension-150 technique. For the sake of clarity, the frame shown there is de-anamorphosed at the ratio 2:1. The vertical lines keystone and the horizontal lines curve toward the top of the frame. The radii of curvature increase slightly in the downward direction. In the Driving Simulator the outline of the curved screen, appears as seen in Fig. 7, when viewed from the location of the projector, or along the projection axis. The vertical edges keystone slightly, converging at the bottom; the bottom edge of the screen curves deeply inward, while there is little or no apparent curvature at the top. The screen outline appears quite different when it is viewed from the drivers´s point of view, i.e. along the mean viewing axis. The bottom edge of the screen appears to be straight while the top edge has definite apparent sag (Fig. 8). When the expanded (de-anamorphosed) film frame is projected onto the screen and viewed along the projection axis (Fig. 9), the vertical gridlines align with the vertical edges of the screen, although the keystone effect is evident. Note that the lowermost horizontal grid line follows the contour of the bottom edge of the screen. The top horizontal grid line, however, curves downward on both sides in such a way that is intersects the vertical edges of the screen at about one third of the screen height measured from the top. When viewed along the mean viewing axis (Fig. 10), the grid is seen to be restored to its original rectilinear format. The outer vertical grid lines align with the vertical edges of the screen, the bottom horizontal grid line follows the base of the screen, the uppermost grid line touches the top edge of the screen in the middle and intersects the vertical edges of the screen at a distance slightly less than one third of the screen height measured from the top. Thus, the distortions introduced in projection cancel one another. The aspect ratio of the projected image in the Driving Simulator is 3:1. This aspect ratio is attained with a standard anamorphic lens of "two times" anamorphosing power. Because in this process the image is laterally compressed, there is no loss of visual information as it is in the case when spherical optics are used for exhibiting the image of the same aspect ratio 3:1. The camera used for taking pictures of the road scenes is a conventional Mitchell VistaVision camera (shown in Fig. 5). The film used in the camera is standard 35mm film; however, it is transported horizontally and the image is double the regular size (i.e. two regular frames are used for one image). Later, in the printing process, the images are reduced to size of the single regular frame (wide aperture print) on 35mm film in a conventional arrangement for vertical transport of the film. The mirror, also shown in Fig. 5, is made out of polycarbonate clear plastic for greater flexibility and ease in forming a proper conical surface. For better optical performance it is the front surface that is silvered. (Hence, it is called a front surface mirror). The projection screen used in the U.C.L.A. Driving Simulator is high-gain screen developed by Dimension-150. It is a very directional screen that returns most of the light to the single viewer and in this way eliminates, for any practical purpose, the problem of cross-illumination so characteristic to all deeply curved screens. It is important to underline that the Dimension-150 process used in the U.C.L.A. Driving Simulator differs significantly from the Dimension-150 process used in the motion picture industry (Ref. 3). Conclusions The inherent shortcomings of motion picture displays for driving simulations have been partially offset by the development of the U.C.L.A. facility and the D-150 process. Further work is currently underway at UCLA to offset some of the remaining shortcomings. Three techniques are being developed for superimposing separately projected images on to the wide screen motion picture. A 16mm projector with a 3:1 zoom lens, driven synchrosly with the large scene projectors has been used to project an image only of the road surface and other vehicles ahead of the driver in the simulator. The brightness of this superimposed image and bleed through is coped with by using a mat to cast an appropriate shaped shadow on the screen onto which the superimposed image is projected. The zoom lens provides the capability of recapturing the dynamic interaction between the driver and other vehicles ahead of him. A similar approach is being used with a closed circuit projection TV system and model roadway to provide a realistic ability to change lanes as well as interact with other vehicles. A third system is proposed that would use a random access, rapid pull down film strip or slide projector with a zoom lens to again superimpose images of vehicles and to cause their signal lights to operate in dynamic interaction with driver of the simulator. |
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