Gregory F. Gustin


The relatively new and widespread use of computer image generators to produce visual cues in training simulator devices may be ascribed to new developments in real time image technology. The recent introduction of high speed circuitry such as LSI, VLSI, Custom Gate Arrays and PLD, has provided computer image generator (CIG) engineers with vast new capabilities at producing very powerful systems capable of operating at 30hz or faster.

The availability of high speed, inexpensive, large memory devices such as one megabyte DRAMS now allows for real time interactive data bases that were unheard of just two decades ago. To compare, the first visual simulation devices were produced for training military pilots in the late 1960's; they incorporated a total of 48K RAM -- and they cost several million dollars each!

The exotic flight simulators in use today, primarily by the commercial air carriers and by the military, incorporate multi-million dollar computer image generation (CIG) visual systems. The visual display greatly enhances acceptance of the simulator as a real "aircraft". The pilot becomes much more accepting of the illusion of flight as the visual scenes make him aware of the position, orientation, rotation and translation of his aircraft in three dimensional space.

Visual simulation, however, has been without a doubt the most elusive phase in the development of simulators for training applications. When one ponders the requirement, it is not hard to understand that simulating the world as seen by the human eye is much more difficult than merely duplicating a set of flight equations, controls, dials, and switches. Out-of-the-window visual simulation is a formidable challenge because of the fantastic performance capabilities of the human eye. The human visual system provides the user with most of his sensory input: the peripheral retina answers the "where" question and the central fovea area the "what" of pattern vision.

The eyes are our most important sense organs for gaining information about the world around us. It is estimated that over 90% of the information that we receive during our normal daily activities come through the eyes. The real world is infinitely variable. Scenes produced by a simulator's computer image generator, however, need be only realistic enough only to facilitate development of the trainee's skills. Nevertheless, if even one aspect of the imagery falls below the threshold of acceptability, the training value of the device is seriously diminished, if not totally lost.

The importance and usefulness of out-of-the-window visual simulation displays can be gauged by the recent large increase in the use of this equipment for commercial air carrier flight simulators. The world's military community has followed suit in that the visual system for combat vehicle simulators have become the major portion of an already large flight simulator budget.


The first CIG device suitable for training began its evolution at General Electric in the United States in the early 1960's. GE undertook this effort on behalf of NASA to support vehicle docking training for the Gemini space vehicle program. The earliest versions of the device displayed little more than a checkered earth surface and simple vehicle replication. Development of the basic technology continued during the next ten years, and by 1972 GE was able to deliver to the United States Navy the first full color raster CIG device for use as a visual flight simulator in military training applications.

Although this prototype system was found to provide inadequate velocity and attitude cues for landings, the potential of CIG technology was not itself held in question. Rather, as GE continued to evolve its system's capabilities, other major companies undertook development of similar devices. McDonnell Douglas introduced the first CIG system to the commercial airline industry in 1971. By 1982, four companies had become recognized as primary suppliers of CIG simulation systems: General Electric, McDonnell Douglas, Rediffusion/Evans and Sutherland, and Singer-Link.

During the early 1980's, real time imaging capabilities increased significantly, but the prices remained very high. Real time image generator systems that produced only dusk/night scenes were being sold for upwards of two million dollars per channel. Color day displays, introduced in the late 1970's, continued to cost nearly an additional million dollars per channel more than dusk/night systems.


At the end of the 1970's, over 300 visual simulation systems were in use by the world's air carriers. The relatively recent but now common utilization of computer imaging systems with aviation simulator training devices may be ascribed to several factors. A paramount influence has been the recent rapid development of micro-computer and television technology. This greatly increased the quality and reliability of components essential to producing visual simulation equipment at a reasonable cost. Another factor is the ongoing successes of early users of visual simulation equipment. Their proof of the concept has led to decreased training costs by legitimatizing the substitution of simulator devices for training time in the actual aircraft or other vehicle.

 Visual simulation for air carrier use was initially restricted to primarily a forward-looking view of the airstrip and its surroundings during takeoff, approach, and landing. The conventionally-used 48 degree horizontal by 36 degree vertical field-of-view proved satisfactory for training pilots for straight-in approaches. Regulatory agencies, such as the Federal Aviation Administration in the United States, have certified systems of this type as capable of substituting for a large portion of aircraft training time.

 Decreases in cost per channel of information have now stimulated the desire for increases in the field-of-view by employing multiple displays. That is, the same section of the geography that is viewed through the front "window" of the simulator will moments later appear moving past the side windows. Today's commercial aircraft simulator typically requires three to four channels to present the viewpoints for the front and adjacent side windows. A common visual display configuration is a three channel, four window system, where the pilot and copilot are presented with identical forward views.


Military training use has lagged behind commercial systems because of the more varied visual simulation requirements associated with military missions. The tasks performed by aviators in the modern battlefield environment are many and diverse. They range from takeoffs and landings at airports with all the normal aids, to operations out of hastily prepared landing strips in unfamiliar terrain; from air-to-air combat to nap-of-the-earth missions; from in-flight refueling to air-to-ground weapons delivery. These military tasks impose severe requirements on the out-of-the-window visual simulation system and make the hardware solutions much more difficult. It was the realization by the military community of the value gained from such simulation, however, which has pushed real time computer visual technology to today's standards.

Modern combat aircraft simulators, with their sophisticated visual systems, provide a means by which flight crew members can experience manuevers and situations that in reality would be either too dangerous to risk in training or are such that they would only be encountered in actual combat. The full capability of the flight simulator and its visual data bases may be further exploited with the aid of additional parameters. Instructors may schedule weather effects such as fog, snow, rain, lightning and clouds; they can trigger threat aggressor effects including planes, helicopters, or tanks with the firing of bullets, missiles, and rockets also being simulated.


Rapidly advancing simulator technology now permits full scale, dynamic, high fidelity reproductions of virtually all sensory elements of vehicle operation, including: the various sensations of movement, the scenes observed through the vehicle's windows, as well as virtually all control and instrument responses. With a high degree of realism, pilots can achieve proficiency practicing take-offs, flying at altitudes, and making approaches and landings under normal, peak workload and emergency conditions. And, all these training scenarios can be accomplished with absolutely no danger to the pilot, instructor, or "aircraft".

The technology mainly responsible for this state of evolution is the real time imaging system. Although aviators have a variety of electronic aids to assist them, many tasks still require the human visual system and the intimate knowledge that system gives the aviator of his external environment. To replicate visual world for the trainee, today's real time computer imaging systems recompute and display a new perspective view at least 30 times every second (i.e., 30hz). Scene content, a critical factor in providing adequate visual cues to the trainee, is determined by the number of polygons which can be transformed, color-filled and displayed in three-dimensional perspective per frame.

Taking full advantage of recent advances in computational power, hi-tech MARKETING CORPORATION (HTM) of Orlando, Florida USA recently developed its Black BoxTM Realtime Visual Simulation system specifically to maximize performance for training device use while simultaneously reducing user costs to an unprecedented minimum. This HTM imaging system can process more than 300 polygons at 30hz, yet a single unit is priced at just $35,000.

Continuing to advance the state-of-the-art, the ParagonTM was introduced in November, 1986. This CIG system generates over 1000 fully shaded polygons in realtime, and it is equivalent in performance to all but the most sophisticated and expensive CIG systems available. Of revolutionary significance is that the price for the ParagonTM system is less than one-tenth than the price of previously available products. Special capabilities rarely provided by other CIG visual systems are integral to the Paragon system, including anti-aliasing, independently moving models within the dynamic display, transparent surfaces and multiple viewpoints.

 With performance equaling and exceeding that of realtime imaging systems previously in use, the new realtime imaging systems make it quite exciting to imagine the future of visual simulation. This dramatic change in the price-performance ratio for image generators--as evidenced by the Black BoxTM and ParagonTM CIG systems--clearly indicates that it is now possible to employ visual simulation to provide operator training for virtually any vehicle, including ships, tanks, buses and autos.