Several trends in the use and development of visual displays for flight simulators may be of interest to this group. These trends reflect the evolution of the needs of the Department of Defense. Coming as I do from the Naval Training Equipment Center, the following comments are biased towards Navy needs.
Digitally generated images have a number of anomalies which are frequently referred to as rastering or aliasing. These effects are due to sampling in both the spatial and time domains. This paper examines how aliasing affects the observer of dynamic scenes. Present techniques for suppressing or eliminating these undesirable effects are described.
In the course of our Periscope View Simulator improvement program, ATS investigated new CGI techniques. It coincided with efforts at HumRRO. A development agreement was formulated to cooperate on a day/dusk/ night Computer Generated Image System now called COMPUTROL*. A key ingredient is the "atom" philosophy of geometric forms used as building blocks. Basic forms are stretched, squashed, lengthened and/or added to develop a particular scene. With exception of a flight data or other vehicle interface resident within the simulator "host computer", our visual system is a self-contained digital image generator with bulk storage of specific geographic areas. Current design has a 30,000 edge display capability. Surfaces can be planer, or spherical due to the ability to smooth-shade curved surfaces. There is virtually no limit to the number of edges contained within the gaming area data base. The CPU used has been especially developed to provide the computational speed necessary within our system. Use of standard MOS chips and straight-foward computer architecture have eliminated the risk normally associated with a specially designed computer system. The resulting CGI system promises to set the standard for visual simulators for many years to come.
This paper discusses the development of a three-channel high-resolution image-generation system consisting of a matrix of three TV cameras capable of operating with the output of a single wide-(140° FOV) angle optical probe. The TV cameras are capable of correcting the geometric errors of the optical probe, the television display, and the display optics as well as the internal scanning errors of the cameras themselves from an external control panel. The cameras achieved an overall geometric error of less than 0.25% and exhibited a stability of 0.1% for a 24-hr. period. The three video images, in conjunction with a suitable matrix of displays, are capable of presenting a continuous visual scene 140 wide and 45 high, with a resolution of 2400 TV lines per picture width. This program also included a three-channel special-effects generator capable of electronic generation of fog, haze, clouds, and electronic sky for the upper portion of the scene above the model board and operation under day, dusk, and night conditions. The unit also has the capability to enhance cultural lighting which can be accomplished without any change in the model lighting or camera operation. The unit allows for dynamic flight characteristics such as roll, pitch, yaw, and flight above and below clouds across the entire matrix of video scenes displayed.
This paper is intended to provide a continuance of information and data on the Navy's Wide Angle Visual Flight Simulator, designed to investigate improvements in visual systems technology and define simulator hardware performance requirements for Naval Aviation training. A general overview of the visual system hardware and its developed performance levels is presented. The initial configuration for carrier takeoff and landings includes a high resolution monochrome television camera which generates a narrow field of view target displayed in a low resolution seascape background. The target image is inset into the background and both images are electronically corrected for lens and perspective distortions by raster computers. The simulation has negligible error in perspective distortion to a target range of 2300 feet, and within 2 arc minutes beyond. Current visual performance measurements will be presented and discussed.
The Air Force has recently completed construction of a Boom Operator Part Task Trainer (BOPTT) ,(See Figure 1). Its purpose is to teach the aerial refueling task to KC-135 boom operators. It is hoped that the trainer will enable substitution of simulator training for that of expensive in-flight training. A unique visual system on this trainer provides a field of view nearly that of the aircraft's. The boom operator sees the refueling boom, the receiver aircraft image, and background terrain through the rear window on the KC-135. All of these images appear at their correct distances with true parallax between the image planes. This paper discusses the visual display and image generation systems for the Boom Operator Part Task Trainer. . .
The Naval Training Equipment Center (NAVTRAEQUIPCEN) is in the process of developing a large screen laser display system for training. This system incorporates several novel concepts and components, some of which were developed at NAVTRAEQUIPCEN and others that were developed in industry. The display area is a 3 meter radius spherical screen with a laser display coverage of 360° horizontally and 60° vertically. The display pickup is a probe over a model board. The image transfer system from the probe to the projection lens makes use of 12 linear charge coupled device arrays, each one constituting one channel of video data. A novel concept involving channel interlace of the twelve channels produces a continuous, seamless laser display with no problems such as color matching, edge matching or brightness matching that arise in multiple discrete channel display systems. The purpose of this paper is to briefly describe the system and then report on the design, fabrication and testing of the major subsystems. The subsystems that will be reviewed are the laser scanner, the prism rotators, the projection lens and the electronic synchronization of the systems.
This paper describes the development of a high-resolution 25-in. color display for simulator visual systems. One of the unique features of the display is the incorporation of a microprocessor-based digital convergence system capable of achieving absolute convergence at 256 points. This system permits the operator to adjust convergence, geometry, size, position, brightness, and contrast of the display through the simulator optics system by means of a remote-control unit. This feature can be used to correct for color aberrations of the optics as well as the normal misregistration (misconvergence) associated with color cathode ray tubes (CRTs). Linear feedback amplifiers are used in the display to achieve superior long-term convergence stability. The control functions available include not only the normal red, green, and blue adjustments but also dynamic blue-lateral control. These unique design features greatly simplify the convergence- and geometry-correction process; and, as a result, a relatively unskilled operator can accomplish precision registration of a simulator visual system, even with a matrix of color displays.
Two experimental investigations were performed with C-141 pilots making aircraft landings with a 727-200 flight crew training simulator mounted on a three-degree-of-freedom motion base. The terrain image was computer-generated and the 1000 TV line, full color scene was displayed at optical infinity with a resolution of 2.9 arc minutes. All pilots were extensively tested for visual skills. Optical distortion panels between the pilot and the visual scene simulated a range of windscreen image qualities from excellent to poor. One study used 8 pilots, 4 windscreen qualities, 2 times-of-day and 2 visibility conditions. A second study used 6 pilots, 3 windscreen qualities, 2 times-of-day, and 4 replications. In both studies, ten dependent measures were taken of pilots' perfor-mance. Decreased windscreen optical quality increased centerline deviations at touchdown point Windscreen quality and time-of-day significantly interacted. Night approaches with poor windscreens were significantly above glide slope, but on glide slope with better wind-screens. Approaches were low for all windscreens in daytime landings. Poor optical quality windscreens caused apparently more cautious night landings: higher faster approaches, more rapid descents and touchdowns that were harder and further down the run-way. Recommendations are made for measuring windscreen optical quality effects on flight performance.
Simulation is of continually increasing importance in training. Cost, energy, and safety are among the driving factors. The goal of simulator development is to provide increased training effectiveness. This is frequently considered to be almost synonymous with increased simulation realism. Actually, the relationship between simulation realism and training effectiveness is far from simple. Realism itself is not a simple scalar there are types of realism, and functions of realism must be considered in multidimension space. This applies to cost as well as to training effectiveness. Questions in this area may not be difficult to answer, once they are asked. There is a continual danger that important decisions will be made, and made incorrectly, due to failure to ask the pertinent questions. This paper considers results from simulation experiments and training activities over the years. In particular, surprising and nonintuitive results are examined. The major goal is to illuminate areas of pertinent questions, although in some cases tentative answers are presented.
An aircraft simulator with a closed-loop computer-generated visual display, was used to teach flight-naive subjects to land. A control training condition in which subjects learned to land with reference to a skeletal airport scene consisting of a horizon, runway, center-line, and aiming bar, was tested against training with constantly augmented feedback, adaptively augmented feedback, and a flightpath tracking display. A simulator-to-simulator transfer-of-training design showed that adaptively trained subjects performed best in a transfer task that was identical to the control group's training condition. Several subjects attempted six landings in a light airplane after they had completed their experimental work in the simulator. They performed better than another group of subjects that had not had any landing practice in the simulator.
The design of present-day color-sensing devices (such as color TV cameras) is generally based on Young's 1801 trichromatic theory as quantified in the CIE system of color mixture. But the actual makeup of the human color-vision mechanism remains unknown to this day. Indeed - contrary to what the trichromatic theory hypothesizes - it now seems likely that the human color-vision system operates on a brightness-hue-saturation basis instead of a red-green-blue basis. For example, there exists significant evidence that neural hue signals originate in the retina from direct rod-cone interaction. ISAAC-I is a simple opto-electronic device which models a possible neural mechanism for generating such retinal hue signals. The model produces a pulse train simulating the neural signal. The frequency of this pulse train varies with changes in stimulus wavelength in a manner similar to the way retinal hue signals are believed to vary. Thus these signals represent primitive hue information extracted from the stimulus. A demonstration is given (during the course of this presentation) of ISAAC-I in action. Different colored stimuli are presented to ISAAC and the audience. ISAAC's resulting "neural" signal is presented aurally to the audience via the PA system.
When performing psychovisual experiments, the averaged results from a multiplicity of trials are a more reliable measure of image quality than the results from a single trial, e.g., such as those obtained from conventional three-bar measurements. This paper describes the use of multiple targets as a technique for image evaluation of an optical instrument such as a microscope. On the basis of experiments conducted at Perkin-Elmer, related to specialized photographic test targets, the Landolt Ring target array was chosen as a basic image evaluation probe signal. The targets, organized in groups having different sizes, modulations, and magnifications, are in circular arrays with the opening in the Landolt Rings randomly placed in four orientations. An observer is asked to identify the orientation of the opening. After the identification, his responses are scored against the known orientations, and the curves of probability of correct orientation are plotted as a function of target size. This function forms a quantitative measure for evaluating the performance of optical instruments. The theoretical analysis portion of this paper is concerned with the development of a mathematical model by which optical instrument performance may be ranked. By means of a series of psychovisual experiments, Human Factors Research, Incorporated, has independently determined curves for probability of correct orientation for a number of observers. There is generally good agreement between empirical data and model predictions, approximately 90% for both unaided eye viewing and microscope viewing of test target arrays.
This paper presents, in three parts, morphological and functional assessment of retinal changes due to laser radiation at various wavelengths at energy levels significantly below those previously considered "safe" for direct beam viewing. The third part offers suggestions for safe levels in pulsed scanned laser displays.
A laser scanned visual display system was evaluated with respect to recent research data and permissible exposure limits. Wide angle laser scanned visual displays can be considered in the following three ways. (1) Instantaneously, the illuminated area can be considered as a finite point, which, if continuously observed, will appear to pulsate at the frame rate. (2) The display can be considered as an extended source, which is pulsating asyncronously at the framing rate. (3) The display can be considered as a continuously illuminated extended source with an average irradiance. Repetitive pulse exposure conditions are implied by the first two considerations, while the third implies a continuous exposure condition. The most stringent restriction on the illuminance of the display screen results when the display is considered as a continuously illuminated extended source. The permissible irradiance on the screen for a 2-hour exposure is 9.2 mw/cm2. The average irradiance (26 Âµw/cm2) of proposed laser scanned displays is well within acceptable limits based upon current permissible exposures.
Although present laser safety standards are based on an adequate data base for acute viewing situations, they are limited in predicting the type of change in visual function that might be induced from prolonged or repetitive viewing of laser sources. Viewing requirements in holography, laser display systems and, in general, repeated exposure to low levels of laser radiation require a more complete data base for optimizing the environmental protection of individuals who will be required to work in such environments. In these studies, we have simulated very low level laser radiation environments and determined the effects of repetitive prolonged exposure on the visual function of the Rhesus. Our data suggest that prolonged viewing of such sources, even though they are well below present laser safety standards, can produce permanent changes in visual processes that underlie normal human day (photopic) and night (scotopic) vision. The coherency of laser light is implicated as a significant factor in inducing these effects. It is recommended that individuals required to work in these situations be frequently evaluated for changes in visual function by presently available clinical instruments for assessment of visual function. Further confirmation of these studies will determine the impact of these research findings on present laser safety standards.
The Farrand Optical Co., Inc. PANCAKE WINDOWTM optical simulator is a very fast, large aperture magnifier which can present to the observer a displayed image at optical infinity. The superb optical quality of this magnifier is due to the fact that reflective, and not refractive elements are used in this system. The unique configuration of this on-axis reflective system, and the optical properties of its elements will be presented. Also, its latest improvement incorporating a spherical holographic beam-splitter mirror will be discussed.
Virtual image systems, in which a presentation of a scene appears to lie at infinity, play an important role in a variety of training devices. Significant advantages are gained through the use of dioptic systems, but the sizes of optical elements required has hitherto prevented their use. This situation has been radically changed with the development of methods of making precision Fresnel lenses. The application of such Fresnel lenses to a specific application is discussed in detail. Two versions have been developed, one with chromatic correction and one without chromatic correction. The result of this work shows that it is feasible to use combinations of Fresnel lenses in systems to be used for virtual image display.
Brightness, resolution and color required of simulation visuals challenge the display state of the art. The recently emerged liquid crystal light valve technology has the potential for high brightness and resolution and, by virtue of its modularity, can be implemented in a variety of configurations to meet specific requirements. The basic building blocks of the projector are the display channel (including the light valve), illumination system, polarizing prism and the projection optics. Each is described and their range of performance characteristics is indicated. Two examples of possible projector configurations are given to illustrate the modularity and flexibility of the technology: a medium resolution full-color back-ground projector, and a higher resolution color background projector with the capability of displaying high resolution monochrome targets inset into the main raster. Finally, the paper discusses features of liquid crystal light valve projectors which are particularly attractive for simulation applications: flexibility in display formats, high resolution, polarized light output, telecentric projection optics and modularity.
A facility was developed for assessing operator performance in target detection, recognition, and identification against simulated real-time and near real-time electro-optical sensor imagery. The basic element in the facility is a programmable image scanner utilized to generate simulated sensor imagery from a variety of sensors and under a wide range of flight profiles. The facility was applied to the evaluation of candidate sensors for a new reconnaissance system. A two-factors, repeated measures design was used in comparing three types of sensor at each of two combinations of airspeed and altitude. Significant findings were developed for the dependent measures of: percent of targets detected, time on display until detection, ground range at detection, slant range at detection, and displayed image scale at detection. Accuracy of interpretation and interpreter confidence did not yield significant results. Additionally, the facility is being used in studying FLIR operator display requirements and several weapon delivery concepts.
The use of only one stereo-pair of images in an autostereoscopic projection results in severe viewing limitations. Such displays are rediscovered from time to time and then proposed as a magical solution to the problems of viewing a three dimensional display without glasses. The method of viewing a stereoscopic projection by using viewing means, such as special glasses to channel a stereo-pair of images to the left and right eyes of the viewer, is well known. Auto-stereoscopic screens, such as a grid screen, a fresnel lens screen, or a lenticular screen can be used to channel and present a stereopair of projected images in appropiate eye zones located in space in front of the display. However, group viewing is limited and head movement is restricted to a short narrow space, no more than about 2.5 inches wide. This type of display can not be successfully utilized for entertainment, such as home television, or theatrical or amateur motion pictures, because the public will not accept a system which requires they hold their heads in a vice-like position. Industrial displays, such as closed-circuit television, computer graphics, and industrial motion pictures can occassionaly use a stereo-pair autostereoscopic system. Most of these applications are better served by the use of polarized glasses or a viewing hood. The conclusion drawn is that only an autostereoscopic display which projects a stereo continuum of multiple stereo images will allow sufficient head movement to be useful for entertainment and other applications.
This paper presents a method to visually display, in true three dimensions, light spots representing objects or targets. They can move in three spatial directions within a specified volume as directed by incoming electronic information. Spots of light positionable in the X and Z directions are flashed onto an oscillating screen moving in the Y direction. If the flashing of spots is synchronized with the position of the screen, the spots, generated by a cathode ray tube (CRT), can be made to appear stationary in space. The spots are flashed onto the screen through an optical system consisting of mirrors, a collimating lens, and a focusing lens. The translucent screen and focusing lens oscillate together in a direction perpendicular to the planes of the screen and focusing lens. Since the screen and focusing lens move together, the focal distance is held constant. A key to the method is the mechanical drive system for the reciprocating motion of the screen and lens. The drive provides: (1) theoretically perfect rigid body dynamic balancing to minimize vibration, shock, and noise; (2) simple and low power mechanical drive system, offering continuous unidirectional rotation; (3) constant inertial load; (4) harmonic motion, providing for simple data inputs; and (5) low friction losses.