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Fundamental to any visual simulation approach, regardless of the methods by which the image is generated, is the display system. Directly viewed display screens have been implemented which have the advantage of simplicity, but have the fundamental disadvantage of a parallax error. Various approaches have been implemented to correct this parallax by placing the scene at infinity through optical techniques. In the simplest of these, the projection screen has been viewed through a large collimating lens in the plane of the windscreen, which to date has been practical for only small fields of view. Various reflective schemes have also been implemented, generally involving a multiplicity of spherical mirrors and beamsplitters. In this paper, a comparison is made between these basic approaches and the limitations that exist. An analysis is made of the required future expansion to perfilit the heretofore unattained "wrap-around" system. Following the discussion on display subsystems, image generation will be explored, beginning with the applications of closed circuit television. Limitations in the state of the art of the medium of transmission itself will be explored, as well as limitations in various applications which are imposed by fundamental opticalproblems or limitations in the storage medium. Image generation systems that do not rely on closed circuit television are considered in the next section. Included here, is a fundamental discussion of motion picture film systems that employ distortion techniques to provide translational freedom. Holographic image generation systems are also discussed from a fundamental standpoint. In summation, required extensions in technology of display and image generation are presented in an effort to explore the most likely future configuration.
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