Have you ever really thought objectively about this business of visual simulation? Sure, I know everyone has said to himself: "I want to create a scene that will give the pilot - or operator - all of the visual cues that he needs to do his job". But isn't that really subjective? Wouldn't a truly objective approach go something like this: "I want to create a scene that will bring the part of the universe that I'm interested in into eyeball range of the pilot"? Stop a minute and think about the difference. In the first case, we tend to consider the view as a collection of parts that are combined to help the pilot. In the second case, we are considering the view from what the pilot sees - a sort of "inside out" rather than "outside in".
Simulation of the visual aspects to flight has been the curse of both the simulator user and the simulator producing industry for many years. The United States Air Force, during the past 15 years, has been involved in at least 12 visual simulation programs. The degree of success of these programs, with the exception of a few, has been limited.
In spelling out the requirements for real time display for airborne and space vehicles, it is normally necessary to employ recorded data obtained previously in flight. This may take the form of aerial photographs, radar photographs, IR photographs, moving pictures or video tapes taken by airborne systems. Generation of real time imagery for use in simulators is a complex and costly process. Further, the use of recorded data results in greater flexibility in variations of the data processing and display sub-system. The immediate drawback of such a method is the lack of flexibility in varying sensor characteristics.
The purpose of this paper is to bring a number of specific advances in light valve projectors and television cameras to the attention of visual training simulator system designers and users. As a result of these advances it will be shown that there still exists a gross disparity between our ability to generate video information versus the capability to present it in the form of a large screen real-time high-brightness image. Extrapolation of the present state of the light valve art will be made on the basis of recent laboratory feasibility studies in optical and electron optical systems specifically undertaken for ultra-high resolution projection display applications.
The advanced television systems used in modern visual simulation are widely recognized for their ability to produce highly accurate three-dimensional representations of the observer's visual surround with complete freedom of movement throughout the visual flight realm. Much work has been devoted---with a great measure of success---to the development and refinement of terrain models, optical probes, cameras, special effects generators and virtual image displays. This has resulted in the ready availability of a wide variety of sophisticated, high performance elements that are being used essentially as modular building blocks in the latest visual simulators. This degree of flexibility is particularly advantageous inasmuch as it permits easy adaptation to new requirements without the need for extensive new development.
The subject of this paper is a simulation technique which has been developed to evaluate the performance of standard scan (525 line) TV contrast trackers in the laboratory. The simulation, developed in conjunction with a comparative flight test of TV contrast trackers conducted at Holloman AFB, New Mexico, makes use of a basic technique similar to the "instant replay." Video tape recordings are made with appropriate video instru-ipentat.:_minstalled in a C-130 "flying laboratory" as the aircraft simulates attack passes against various ground targets. The recorded video is then played back into a contrast tracker in the laboratory to evaluate the contrast tracker performance. This simulation technique is discussed in detail in the paper along with a description of the technique employed to demonstrate the accuracy and validity of the simulation results. In addition, the paper includes a brief discussion of future simulation requirements.
The need for data on human performance when searching the ocean's bottom from submersibles has created a new application for optical simulation techniques. An existing facility designed originally for the simulation of lunar missions was converted to provide a realistic virtual image view of the seabed through the porthole in a mockup of the Navy's Deep Submergence Search Vehicle. A description of the equipment used for the simulation is presented along with a discussion of a 34 hour mission that was performed by a crew of 4 men in search of a number of targets randomly scattered on the ocean floor at a depth of 20,000 feet.
The visual display is the key to successful simulation and has been the subject of many intensive investigations. In the driving simulator it is desirable to present all of the normal visual environment to the driver--an unprogrammed display on a hemispherical screen in full color, fine detail, brightness, and stereoscopic vision. Unfortunately, the present state of the art in this field is still far from this goal. The following is a brief review of the most suitable techniques.
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.
The need for wide-angle displays apparently projected to infinity has led to the development of a series of systems which amount to wide-angle-erecting eyepieces with large exit pupils. Characteristics of systems with fields of view of 110° and exit pupils 12 inches in diameter are discussed. The application of these systems and the various techniques of image generation for the Mercury, Gemini, Apollo and LEM simulator programs are described. Realistic and accurate simulation of spacecraft out-of-the window displays of the Celestial Sphere, Rendezvous and Docking and Earth and Moon Orbital and Landing Views are included as image generation techniques.
Investigation of various display techniques for remote control of aircraft has resulted in the development of an experimental hemispherical rear projection TV system. The original concept, being developed by NWC, was to use a wide-angle TV camera in a target type aircraft to simulate a pilot's visual frame of reference for display to a ground controller (Fig. I).
In flight simulation, a need exists for a display that represents the outside world as seen from the cockpit of a flying aircraft. Such a display is difficult to produce because (1) it must cover a large field of view, (2) it must simultaneously reproduce those terrain details that are very close to the simulated aircraft as well as those that are very far away, (3) it must exhibit high resolution over the entire field of view, and (4) it must respond smoothly and rapidly to all motions of the simulated aircraft over wide ranges of positions and attitudes. Many devices (visual simulators) have been constructed that attempt to produce such a display; examples include film-based devices, computed displays, direct optical viewers, and various television systems. Each type of visual simulator has its own characteristic advantages and limitations.
There has been in recent years a renewed interest in flying spot scanners in relation with encoding and processing two dimensional pictorial information. Flying spot scanners have been used in pattern recognition to detect special information, in conjunction with digital computing equipment to digitize two dimensional information, in radiology to get improved X-ray displays, in flight simulation to generate and display a visual scene in pilot training programs, etc.
A general purpose hardware CRT display system is described which displays information from the memory of a general purpose digital computer. The system eliminates the tremendous burden of software calculations currently necessary to place the correct picture on the CRT. The resulting hundred-fold increase in capacity makes the system ideally suited for dynamic simulation of moving spacial objects.
Systems based on optical sensors form a major branch of missile defense technology. Examples include optical discrimination, scoring, fuzing, reconnaissance, homing, tracking, radiometric and spectrometric systems, both for flight and ground operation. When complete with signal processing chain, these systems are typically complex and costly, and their development poses major problems of product assurance. A common development sequence for such systems goes something like the following:
1. Paper design,
2. Idealized subsystem laboratory tests,
3. Subsystem fabrication,
4. Idealized subsystem laboratory,
5. System assembly
6. Idealized system laboratory test,
7. Operational system test,
8. Back to the drawing board.
Because of the accuracy needed in the operation of photo-optical systems of simulation, the present paper attempts to measure the differences in sensitivity of motion perception in the various portions of the retina. There is a noticeable difference between the central and peripheral retinal areas in the detection of angular movement and in threshold excitation. The peripheral area dominates the central area in motion detection because it has more rods, thus having a lower threshold excitation and a lower threshold of critical fusion frequency (c.f.f.). By measuring the c.f.f. gradient at varying visual angles on the nasal, temporal, inferior and superior coordinates, it was found that the peripheral area, specifically temporal area, has lower threshold to' motion perception than the central area.
Human factors are one of the most neglected aspects of reliability, even though they appear to be a major source of unreliability. Regardless of the accuracy of photo-optical instruments, if they are operated by a man, the reliability of the instruments will drop approximately 80 per cent. In this supplementary paper, some of the psychological aspects of the sources of unreliability in man-machine systems are briefly discussed. This discussion consequently helps in the consideration of the selection and training of users of photo-optical instruments.