The Use of Computer Image Generators

 For Visual Simulation

 By: Gregory F. Gustin,
President, PARAGON

The term simulation has been mentioned with increasing frequency during the past few years, especially when associated with today's modern graphics processors.  The capabilities of these new devices which present to the user a pictorial display of any process in fast or realtime, has generated a tremendous boon in the productivity of all engineering disciplines, including phases from initial concept to final fabrication and testing. 

The prevalent connotation of the term simulation is that of vehicle operator training.  Historically, this has been limited to the training of aircraft pilots, for, who else but the owners/operators of multi-million dollar vehicles could afford the capital outlay needed to acquire a high fidelity training device.

The exotic flight simulators we see today in use by the commercial air carriers and by the military were not always built using computer visual systems.  Early ground based systems were used principally as instrument trainers.  In spite of their widespread use over many years, instrument flying trainers were never enthusiastically received by the pilots.  The illusion of flight in the simulator is only successful if the pilot can relate to the flight situation and divorce himself from the idea of sitting in a box.  Acceptance of the simulator as an "aircraft" is greatly assisted by the visual display, whereby the pilot is made aware of the position, orientation, rotation and translation of his aircraft in space.


The visual flight simulation (display) is that part of the simulation which presents scenes for the pilot to view out-of-the-window of the mock cockpit.  The visual display presents the flight trainee with scenes representative of those that would have been seen if the actual mission being trained for was flown.  On takeoff for example, the pilot is made aware of the increasing speed and height of the aircraft over the ground from the visual display  an impression that is then reinforced by the readings of his simulated flight instruments.

Visual simulation has been without a doubt the most elusive phase in the development of flight simulators for aircraft training.  When one ponders the requirement, however, it is not hard to understand that simulating the world as seen by the human eye is much more difficult than 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, and certainly that much or more when an aviator is involved in flight tasks.  Even with the tremendous advancements of the most sophisticated visual systems, computer generated image systems lack the processing and storage capacity to provide anything approaching real world detail.

The importance and usefulness of out-of-the-window visual simulation displays can be best judged by the recent large increase in the use of this equipment in air-carrier trainer simulators.  The military has followed suit in that the visual system for flight simulators have become the major portion of an already large simulator budget, especially since the feasibility and flexibility of computer generated image systems have been demonstrated.

Equipment for out-of-the-window visual simulation was largely developed in the 1960's by aircraft manufacturers who used the simulators for engineering and test purposes.  By the end of that decade, the equipment had proved sufficiently useful and dependable that it was being adopted for training.  At the end of the 1970's, over 300 visual simulation systems were in use by the world's air carriers. 



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.  But it was the realization of the value gained from such simulation which has pushed 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 maneuvers or 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 can be exploited with the aid of additional parameters.  Instructors may schedule weather effects such as fog, snow, rain, lightning and clouds; they can trigger threat effects including planes, helicopters, or tanks with their associated bullets, missiles, and rockets. 


Rapidly advancing simulator technology now permits full scale, dynamic, high fidelity reproductions of virtually all sensory elements of flying, including: the motion and sounds of the aircraft, the scenes observed through the cockpit windows and the manner in which controls and instruments respond.  With a high degree of realism, pilots can achieve proficiency by practicing take-offs, climbing to and flying at altitudes, approaches and landings under normal, peak workload and emergency conditions  all with no danger to the pilot, instructor, or "aircraft".

The simulator component which is mainly responsible for the present level of believable realism is the CIG visual system.  Visual simulation will certainly continue to advance beyond the present capabilities of the PARAGON and equivalent systems.  The promise of the future is for system prices low enough to allow use for all types of vehicle training -- not just pilots of sophisticated aircraft.  Future performance enhancements, such as vast increases in total scene content through the use of photographic mapping of real world imagery, will cause users to query, "Is it real or is it ...?"



(This article appeared in the October, 1986 edition of Computer Graphics Today magazine in edited form.)