ADA039999 NTIS
One Source. One Search. One Solution.
A
VISUALLY-COUPLED AIRBORNE SYSTEMS SIMULATOR (VCASS) - AN APPROACH TO VISUAL
SIMULATION
AEROSPACE
MEDICAL RESEARCH LAB WRIGHT-PATTERSON AFB OHIO
1977
U.S.
Department of Commerce National Technical Information Service
A VISUALLY-COUPLED AIRBORNE SYSTEMS
SIMULATOR (VCASS) - AN APPROACH TO VISUAL SIMULATION
DEAN F. KOCIAN
6570 Aerospace Medical Research Laboratory
[1] In recent years Air Force operational
units have experienced a continuing trend downward in the number of flight
hours in aircraft that can be provided to each individual pilot for training
and maintaining proficiency. This comes at a time when aircraft systems are
becoming ever more complex and sophisticated requiring comparatively more hours
for training to maintain the same relative flying proficiency. With increasing
costs for fuel and aircraft and the failure of DoD funding to keep pace with
these costs, the trend is almost sure to continue. In adjusting to the realities
of keeping overall experience at a satisfactory level and reducing costs,
procurement of aircraft simulators has become a necessity.
[2] The rapid proliferation of simulators
with no standard technical criteria as a guide has resulted in the evolution of
several different design approaches. Most existing visual scene simulators
utilize electro-optical devices which project video imagery (generated from a
sensor scan of a terrain board or a computer generated imagery capability) onto
a hemispherical dome or set of large adjacent CRT displays arranged in optical
mosaics with the weapon, vehicle, and threat dynamics being provided by
additional computer capabilities.
[3] These large fixed-base simulators suffer
from the following drawbacks. The majority of the visual projection techniques
used in these simulators do not incorporate infinity optics which provide
collimated visual scenes to the operator. Those which do are large and
expensive and incorporate large CRT displays. The luminance levels and resolution
of these displays are usually low and do not represent true ambient conditions
in the real environment. Additionally, hemispherical infinity optics are
difficult to implement and this technique requires excessive computer capacity
to generate imagery due to the need for refreshing an entire hemisphere
instantaneously, regardless of where the crew member is looking. In this
regard, existing computer capability is not used effectively to match the
channel capacity of the human visual system. There are also generally no
stereoscopic depth cues provided for outside of-cockpit scenes. Another
important drawback to these simulators is that the visual simulation is not
transferrable to the actual flight environment, i.e., the ground-based system
cannot be transferred to an actual aircraft to determine simulation validity.
Finally, most existing techniques are very expensive and do not allow the
flexibility of incorporating other display design factors such as different
head-up display image formats, fields-of-view (FOV), representative cockpit
visibilities, and optional control and display interfaces.
[4] A quite different approach to solving
the visual presentation problems of aircraft simulators is to employ the use of
visually coupled systems (VCS). For many years it has been the mission of the
Aerospace Medical Research Laboratory to optimize the visual interface of crew
members to advanced weapon systems. This mission has been primarily pursued in
two areas: (1) the establishment of control/display engineering criteria; and
(2) the prototyping of advanced concepts for control and display interface. An
important part of fulfilling this mission has been the development of VCS
components which includes head position sensing systems or helmet mounted
sights (HMS), eye position sensing systems (EPS) and helmet mounted displays
(HMD).
[5] In the process of accomplishing this
work, it has been ascertained that many of the current Air Force air-to-air and
air-to-ground weapon systems problems can be related to deficiencies in the
configurations of control and display components which interface the crew
member to aircraft fire control, navigation, flight control and weapon delivery
subsystems. These interfaces tend to either overly task load the crew member or
prevent optimum utilization of innate visual, perceptual and motor
capabilities. These limitations are especially apparent in fire control and
weapon delivery applications where visual target acquisition and weapon aiming
are required along with primary piloting tasks. Under high threat conditions,
the flight profiles necessary for survivability, as well as mission success,
dictate that all essential tasks be performed effectively, accurately and most
important expediently. With the recent advent of advanced digital avionics
systems, the control and display design issue is further complicated. The
proliferation of dedicated control and display subsystems in current aircraft
cockpits has necessitated the development of multi-mode displays and control
input devices. In addition, more exotic virtual image display devices (head-up
display/ helmet-mounted display) and unique control devices such as the
multi-function keyboard, helmet-mounted sight and fly-by-wire subsystems have
appeared. In this regard, the design options open to the avionics as well as
control and display designer are great, thereby generating a real need for
human engineering design criteria to elucidate the image quality
characteristics, information formatting and interface dynamics which optimize
the operator interface with these advanced systems.
[6] The process of establishing practical
design criteria with the number of options that are available is a laborious
and time consuming task, especially if validation in flight environments
becomes necessary. Typically, flight testing is very expensive and does not
allow flexibility as well as consistent replication of experimental conditions.
Due to these factors, high fidelity ground-based simulation is the only
realistic alternative. However, it now becomes necessary to develop simulation
methodology, techniques and apparatus which are subject to flight test
validation. It is felt that the unique capabilities of a visually-coupled
system (VCS - combination of a helmet-mounted sight and helmet-mounted display)
can meet the simulation requirement stated above as well as improve upon
existing ground based simulation techniques described earlier. It is out of
this thinking that the VCASS concept evolved.
[7] A more detailed analysis of the problem
has produced a set of characteristics which a more ideal aircraft simulator
might possess. Of primary importance is that it should be a flexible visual
scene simulation providing synthesized out-of-the-cockpit visual scenes and
targets, a representative vehicle whose type can be altered, threat and weapon
dynamics, flexibility of control and display configurations, and inputs from
sensor or real world imagery. It should be portable if possible and provide
alternatives for crew station display options including number and
configuration. This simulator should also be useable in both simulated
air-to-ground weapon delivery and air-to-air engagement scenarios. Finally, it
should be possible to use the same system in ground fixed base and motion base
simulators as well as in aircraft.
[8] As an approach to meeting these
requirements the VCASS concept and program was initiated. Its objective is to
develop and demonstrate a self-contained airborne and ground-based
man-in-the-loop visual simulator for the engineering of advanced weapon
systems. The approach that will be followed to obtain this objective will be to
integrate VCS hardware with state-of-the-art computer image generators to
provide a synthesized hemispherical visual space that will display target and
environmental images. Included in this approach is the use of real and/or
simulated plant dynamics.
[9] The key components of VCASS will be VCS
hardware which includes the HMS and HMD. These components are used to
"visually-couple" the operator to the other system components he is
using. AMRL has pioneered efforts in the research, development and testing of
these hardware techniques.
[10] Specifically, the concept of the VCASS is
to utilize the HMS as a means of selecting information within a synthesized
visual space and to use the helmet display as the visual input device for
presenting that information to the operator as a collimated virtual image. This
allows head-up display type symbology and/or imagery to be generated to
represent a full hemisphere, out-of-the-cockpit view, a portion of which the
operator perceives on the helmet display. The scale or size of this
instantaneous portion of the total field is a function of the field-of-view of
the HMD. The orientation of the instantaneous field-of-view is determined and
selected in accordance with head orientation as measured by the HMS. In other
words, if the field-of-view of the HMD is 30 degrees the observer sees a 30
degree instantaneous view of a hemispherical digital symbol set. This
instantaneous view moves in a one-to-one correspondence with head movement. In
essence, the total hemispherical scene is available to the operator a
field-of-view at a time.
[11] A system diagram and pictoral of the
functional elements required to accomplish the VCASS are depicted in Figure 1.
The operator utilizes conventional control devices (control stick, throttle,
rudder pedals, etc.) to input a digital computer which provides the
manipulation of the vehicle, weapon and threat states as a function of
preprogrammed dynamic characteristics. This information is then used to
manipulate synthesized symbology and imagery in terms of orientation, scale,
target location, etc. as a function of the plant state. A representative visual
scene generated by the graphics or sensor imagery generators is selected by the
operator line-of-sight orientation as measured by the helmet-mounted sight.
Again, the amount of information selected is governed by the instantaneous
field-of-view of the helmet-mounted display (typically 30 degrees to 40
degrees). The helmet display electronics receives the selected portion of the
symbology and sensor information and displays the video imagery to the operator
through the helmet display optics in the proper orientation within
three-dimensional space. For an airborne VCASS capability, it is only necessary
to install the VCS components along with a small airborne general purpose
computer in a suitable aircraft and interface a representative programmable
symbol generator to an on-board attitude reference system in order to
synthesize either airborne or ground targets. This approach has the ultimate
flexibility of utilizing the same symbol set, threat dynamics, etc., in the air
that were originally used in the ground simulation. In either case, the crew
member will engage electronic targets (either air-to-air or air-to-ground) and
launch electronic weapons. His performance in these tasks in turn will be
recorded and assessed for performance or utilized as training aids for the crew
member or operator.
[12] Figure 2 depicts a more advanced
configuration of the helmet-mounted sight and display that will be used in the
VCASS installation. The helmet-mounted sight and display are integrated into
one compact unit that allows a prealigned visually-coupled system package to be
easily connected and disconnected from a standard flight helmet. The
helmet-mounted sight transducers represented by the STA and SRAH are small and
compact and allow a more or less benign mounting in the aircraft cockpit. The
side mounted helmet-mounted display is capable of at least a sixty degree
field-of-view in this configuration as compared to 30 to 40 degrees for a visor
display with a reasonable form factor. Compared to other simulation systems
this configuration permits a relatively easy transition from the ground to
airborne environment for feasibility studies and demonstrations.
[13] The VCASS concept of simulation provides a
method of artificially duplicating all the standard scenarios that are provided
by more conventional simulators plus more. For air-to-air formats the
simulation can take the form of programmed maneuvers as a function of time,
evasive maneuvers based on a set of computer algorithms that permit an adaptive
strategy for the target, or a totally competitive simulation where the
instructor maneuvers the target. For air-to-ground formats the target or threat
can be stabilized at prestored ground coordinates, survivability against an
active threat can be tested, and target size and vulnerability can be varied.
Additionally, visual display design criteria can be developed for fixed base,
moving base, and airborne type simulators to investigate and enhance techniques
for simulation optimization. Finally, prototype visual display configurations
in virtual space can be developed and altered by simply changing the related
software.
[14] The cost/performance advantages of the
VCASS concept as depicted above appear to be numerous and worthwhile. Of
primary importance is the fact that a full hemisphere of collimated visual
information can be provided which depends solely on the head orientation limits
of the user. This hemisphere of synthesized visual target and environmental
images can be accomplished without the need for costly domes or fixed mosaic
infinity optics. Conservation of computer capacity is provided as a result of
necessitating only the small instantaneous field-of-view of the HMD to be
provided to the operator. This suggests that it should be possible to use
conventional general purpose computers for computing and creating the environment,
vehicle threat and weapon plant dynamics as well as to control a small special
purpose symbology generator. The image quality should be very high at the
greater luminance levels and color and stereo capabilities are also possible.
Also, all threat aircraft and weapon dynamics are programmable providing an
ultimate flexibility in design parameters and the cockpit display ( HUD .
symbolorgy sets) can be manipulated easily to determine the interaction between
the symbol sets and the synthesized real world imagery. Finally, almost all
components including the most critical ones can be utilized in either a
ground-based or airborne simulator.
[15] If all the critical components were in an
ideal form for the VACS application it would merely require that one perform
the hardware interface, software development, and test the performance obtained
out of the final system configuration. However, VCS hardware development and
performance has lagged somewhat relative to the performance capabilities of
other components that are to be used in the VCASS simulation.
[16] Added to this is the fact that the VCASS
simulation imposes certain psychophysical considerations on the entire system
configuration. Among the most important of these is the required instantaneous
field-of-view of the helmet-mounted display beyond which there will be
relatively little improvement in operator performance when flying the VCASS
system. The important decisions to be made here are the amount of area on the
display that must have a high resolution format and how large the display
field-of-view must be to provide necessary information cues in the peripheral
vision. Another important requirement is to determine the required update rates
and throughput delays to be allowed in the head position sensing information in
order to minimize perceptable lags in the change of information on the
helmet-mounted display. The symbology and environmental information presented
on the display must also change realistically in relation to changes in observer
look angle and aircraft parameters in a manner that appears natural with no
confusing contradictions. The crew member must be able to relate to aircraft
attitude and heading at any look angle. Experience already gained on an interim
VCASS configuration has shown that these requirements will necessitate a major
symbology and format design effort.
[17] Some of the above mentioned areas of
consideration must wait for further testing before a design approach can be
formulated while others will not. To some extent the maximum obtainable
performance of certain parameters of the most suitable VCS components is
already known and must be accepted or its effects reduced by changes to other
portions of the VCASS system. For the helmet-mounted sight the individual added
requirements are both more easily defined and met than is the case for the
helmet-mounted display.
[18] Even though individual requirements for
the helmet-mounted sight are straightforward in an engineering sense the total
design change package represents a significant increase in performance over
systems currently available. To minimize perceptual lags and prevent loss of
head movement coverage, the update rate must be increased from the presently
available 33Hz to 100Hz or more and the motion box must be enlarged from one to
four cubic feet. In order to provide sufficient information to simulate the
parallax of aircraft structures on the helmet-mounted display as the operator
moves his head, a six-degree-of-freedom HMS is required that provides not only
attitude information (azimuth, elevation and roll) but x, y, z position
information as well. Another significant problem is the smallest change in head
movement which can be measured by the HMS and therefore provide updated
information for changing the video imagery on the helmet-mounted display.
Preliminary studies have suggested that resolution must be increased from 0.097
to 0.03 degrees to eliminate noticeable step changes in the display
presentation as perceived by the observer. Finally, some form of output
stabilization must be provided to reduce head jitter noise from whatever source
to an acceptable level that would not visibly degrade display resolution.
[19] The design considerations involved in
building a helmet-mounted display for the VCASS simulation present a more formidable and subjective set of
problems whose solution is not entirely clear. It is certain that a larger
display field-of-view is required but how large remains an unanswered question.
The optical physics that are part of the display design imposed constraints
which are difficult to resolve. Currently, an interim display possessing a 60
degree instantaneous field-of-view is planned for the VCASS; however, recent
studies have shown that this may not be large enough especially when viewed
with one eye. This leads naturally to biocular or binocular configurations. A
whole host of human factors problems then becomes important including
brightness disparity, display registration, and eye dominance. The decision
whether or not to include color also becomes a major design decision not only
because of the engineering development required but because user acceptance may
weigh heavily on this factor.
[20] If the design problems can be overcome it
appears that the benefits of the VCASS for training are great. Experience for
the crew member can be provided in many aircraft types against a wide variety
of threats, armament, encounter dynamics, etc. Feedback in the training
situation can be significant and rapid with optional instructor involvement,
repetition and instant replay on all encounters, and the fact that an airborne
vehicle can use VCASS components to correlate ground-based results. The cost
effectiveness of this approach seems to be overwhelming. The cost of this
system is assured of being significantly less than the costly ground visual
simulators now in existance. One system can be used for the air and ground
environment. In the airborne case no darts, drones, chase planes or bombing
ranges are required and no aircraft armament installation or expenditure of
munitions is needed.