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Dr. James L. ~ a v i s *
Downloaded by UNIVERSITY OF NEW SOUTH WALES (UNSW) on October 27, 2017 | | DOI: 10.2514/6.1989-3321
Rediffusion Simulation, Ltd.
Crawley, West Sussex, England
Aircrew training with flight simulators is accepted as
being a valuable supplement to training in the actual
aircraft. Enhancing a simulator with an out-of-cockpit
visual simulation system further expands this training
role, yielding improved training or comparable training at
reduced cost. However, a problem exists in providing
visual simulation to aircraft users who can't justify
typical visual system expense.
The chosen approach examined total system cost
rather than component costs, and sought to strike a new
balance between cost and performance. Selective
capability with flexibility was found to be the key to
good performance, while increased standardization was
critical for reducing cost. One possible implementation
of these findings is Novoviewm LCV, a complete visual
system package comprised of computer image generator,
generic data base, one of several standardized displays, a
visual control console, installation & integration
support, and overall product support.
Training aircrew in flight simulators, even those
without visual systems, is becoming more commonplace
owing to well-established cost savings and trainee safe0
considerations. Despite simulator costs of about $10
million, choosing to use simulator training is relatively
easy for major commercial airlines since regulatory
agencies such as America's FAA and the UK's CAA
allow simulator training to replace time otherwise spent
in the actual aircraft. Similarly, it is an easy choice for
the military in many cases, either because of the high
costs incurred in operating an actual aircraft, or because
peacetime flight rules do not permit the range of training
needed for combat preparation.
Justifying this level of expenditure is not difficult
when dealing with aircraft having a purchase cost of
Manager, Low Cost Visual Products
Member AIAA
several tens of millions of dollars and an operating cost
of several thousand dollars per hour. However, where
does this leave the operators of smaller aircraft costing
less than one-tenth as much? Certainly they stand to
reap the same benefits from training on a visuallyequipped flight simulator. One scheme for satisfying the
simulation needs of the smaller operators is to provide
less expensive simulators possessing less expensive
visual systems. However, where does one cut comers in
providing the visual aspect of the simulation? The view
from the flight deck of a Shorts 360 is not much different
from that of a Boeing 747. And the pilot of the smaller
aircraft is probably less experienced than the 747 pilot
and thus needs proper training that much more.
To appreciate what "low cost" means in terms of
this paper, it's beneficial to first examine the spectrum of
simulation devices currently available. Figure 1
graphically illustrates the range of entries in today's
simulation marketplace. Plotted are approximate ranges
of cost for both the simulator (without visual capability)
and a typical visual system appropriate to the device
type. These devices range from simple fixed-base
procedure and instrument trainers, to motion-base
procedure and instrument trainers, to FAA Phase I1 and
Phase I11 certified flight simulators, to military air
combat and weapons tactics simulators/trainers.
As shown, the fixed-based trainers cost about
$100,000 and can justify a visual system cost of about
$50,000; anything much more or less would not offer the
user a balanced capability. This caliber of visual is often
satisfied by graphics workstation technology (or its
equivalent) running customized flight simulation
software. The motion-based trainers typically cost $1-2
million and require a visual system costing about $0.5-1
million. Some companies have sold into this market;
however, it is not a thriving market niche. Historically,
this can be attributed to an inability to get "good" visual
value at this price level. Such is certainly not the case
with the well-regulated commercial flight simulation.
Simulators costing between $5- 10 million usually have
visual systems costing several million dollars. This
Copyright Q 1989 by James L. Davis. Published by the American Institute
of Aemautiu and Astronautics with pamission.
Fixed-Base CPT's and
'Instrument Trainers
Downloaded by UNIVERSITY OF NEW SOUTH WALES (UNSW) on October 27, 2017 | | DOI: 10.2514/6.1989-3321
Motion-Base CPT's and
Instrument Trainers
Phase I1 and Phase I11
Full Flight Simulators
Air Combat And
Weapons Tactics
::.. .
trend holds as well in the military arena, where both
simulator and visual system can each cost close to $10
The concern here is not the bottom end of the
marketplace, as represented by the left side of Figure 1.
Rather, the particular low-cost visual market segment to
be addressed is those fixed-base and motion-base cockpit
procedure and instrument trainers (costing $1-2 million)
that would benefit from a visual package costing $0.5-1
In defining and developing Novoview LCV,
Rediffusion Simulation had as its goal satisfying a new
visual cost/performance equation aimed at certain users
willing to purchase sophisticated flight trainers, but
unable to justify a comparable or larger capital
expenditure for a visual system. In the past, this
problem was attacked by producing an IG of limited
capability (e.g., flat-world, little or no surface texture,
digital artifacts) and combining it with a simple data base
and collimated or non-collimated display. Often the
supplier of the IG or data base was not the same as that
for the display. Indeed, often neither was the integrator
of the visual system with the simulator; hence, yet
another party became involved.
For better or for worse, Rediffusion approached
this problem from the standpoint of already being the
major supplier of visual systems for the Phase 11 and
Phase I11 commercial flight simulation market. The
standard visual product was and still is customized high
performance "complete" visual systems using proven,
state-of-the art technology having all the "bells and
whistles". Restating the problem from this angle, it is
necessary to selectively alter the visual system to reduce
cost, but not degrade performance to a point where users
feel they are not getting value for money. The previous
section pointed out how the visual system is only one of
several systems in a flight simulator; the solution to the
cost/performance problem begins with a similar
decomposition of the visual system.
A visual system is itself comprised of several
subsystems, including Image Generator (IG), data base,
and display. Because the visual must properly interface
with the rest of the flight simulator, mechanical effort is
needed to integrate it with the simulator fuselage and
motion system (if present) and software effort is needed
to integrate it with the host computer and Instructor
Operator Station (10s). Additionally, out-of-cockpit
imagery must correlate and be compatible with serisor
imagery, cockpit avionics (e.g., HUD), and other
perceptual cues (motion, sound, etc.).
Downloaded by UNIVERSITY OF NEW SOUTH WALES (UNSW) on October 27, 2017 | | DOI: 10.2514/6.1989-3321
A cursory analysis reveals two important keys to
the low-cost puzzle. First, care must be exercised to
avoid reducing individual component costs at the expense
of overall system cost. For example, there is no point in
reducing manufacturing cost by relaxing tolerances on the
display system if it produces an even larger increase in
labor cost owing to complications in assembly and
installation. Secondly, standardization must be
maximized in order to reduce nonrecumng costs, yet the
resulting system must not be so inflexible as to unduly
limit its general applicability.
Getting beyond top-level results requires a detailed
examination of those visual system attributes that are
both performance- and cost-drivers. Such an analysis has
been previously described1. A summary of this analysis
It's not unusual for the IG to represent more than
50% of the cost of a visual system. Hence, attributes of
the IG play a significant role in any trade-off analysis,
and some impact the choice of display system as well.
Important atmbutes include:
Resolution - More pixels imply more video
memory, higher video bandwidth, and more high-speed
processing for pixel-rendering; all at increased cost.
However, decreasing resolution reduces the maximum
range at which objects can be discriminated.
Of View (FOV) - Larger FOV generally
demands more IG channels and displays, brighter display
devices, or servo-controlled Area Of Interest (AOI)
technology. Reducing FOV saves on cost but limits
out-of-cockpit viewing and hence the tasks to be trained.
Scene- More surfaces and lights in a
scene require more IG processing to yield perspectivelycorrect imagery. Less scene content makes for simplistic
imagery that can limit training effectiveness. Often 2-D
texture is incorporated to enhance apparent scene content,
the principle being that an expenditure for texture has
more benefit than a comparable expenditure for additional
Co- The IG's ability to handle
greater scene complexity relates to supporting more scene
occultation. Though most flight tasks don't make heavy
demands in this area, periods when the eyepoint is close
to a 3-D ground and 3-D objects can increase the need for
high scene complexities, as can the use of transparency.
Picture 0- Good value requires that full
use is constantly made of expensive IG processing
capability. Additionally, any generated imagery should
be free of computational artifacts arising from spatial and
temporal aliasing, and jitter. For example, not having
anti-aliasing can save on IG cost, but only at the risk of
distracting the trainee with unrealistic scene content.
Moving Oblech - Moving objects unrelated to
the eyepoint (e.g., other aircraft, ground objects, and
munitions) permit greater complexity of the training
environment. However, aside from impact on IG
complexity, moving objects serve as a cost driver since
either software or Instructor control must be provided to
direct their movements.
Meteorological And E n v i r o n m e n t a l
Effects - Because pilots usually fly at all times of day
in all types of weather, it is desirable to have a visual
system capable of day/dusk/night ambient lighting,
limited visibility, reduced ceiling, etc. As with moving
objects, flexibility demands control. So aside from
increasing the complexity of the IG, variable
environmental conditions demand that they be provided
for during data base construction and that their control is
imparted to the Instructor. These effects also have an
impact on display capability and hence cost. For
example, daylight simulation (as opposed to duswnight)
generally demands (i) a full color gamut, (ii) more
display intensity to yield simulated daylight brightness,
and (iii) higher refresh rate to guard against image flicker
at the higher brightness.
Uadate - Increasing update rate means that
the displayed scene is recomputed more often for changes
in pilot eyepoint location or line-of-sight. It is a costdriver since rate increases are obtained only from
increases in amount or sophistication of computational
hardware. Lowering update rate saves money, but the
penalty is increased temporal aliasing (manifested as
image-stepping or double-imaging). Alternatively,
training can be limited to slower eyepoint movement or
to reduced FOV's, either tending to reduce the angular
rates of objects in the visual scene and thereby making
the scene more forgiving of low update rates.
Data - Often a simulator user will want
training to occur in a world closely resembling that in
which the actual aircraft flies. For example, a pilot
spending most of his time in the Boston area would
probably obtain additional benefit from having a
simulator data base depicting Eastern Massachusetts and
Logan Airport. The cost of this "custom" data base will
be related to (i) quantity of data involved (size of data
base) and the difficulty of acquiring source data, (ii) the
required fidelity of the data base, (iii) tools available for
constructing the data base, and hence (iv) the time (labor)
required to build the data base. Efforts exceeding one
man-year are not unusual. An alternative to a custom
data base is a "generic" data base. If care is taken
initially to give it training flexibility, then often it can
be provided more cheaply since many users can take
advantage of it. The downside, however, is a lack of geospecific or airport-specific training.
The display is comprised of (i) a display input
device (monitors or projectors), (ii)optical elements (e.g.,
Downloaded by UNIVERSITY OF NEW SOUTH WALES (UNSW) on October 27, 2017 | | DOI: 10.2514/6.1989-3321
beamsplitters, mirrors, or screens), and (iii)a support
structure. After the IG, the display sub-system shares
with installationlintegration the distinction of being the
next costliest portion of the visual system. The role of
the display cannot be overstated; the quality of even the
most pristine IG imagery will rise and fall with the
presentation made by the display system to the trainee.
Display attributes affecting both performance and cost are
listed below.
better contrast relative to the surfaces against which they
appear, (iii) finer positioning, and (iv) improved dynamic
behavior. However, calligraphy makes severe demands
on a display device in terms of power required for linear
deflection. In addition, care must be exercised to avoid
hysterisis artifacts and improper alignment of rasterdrawn surfaces with calligraphically-drawn lights.
Collimation - There is good reason why
collimation has historically found a niche in aircraft
flight simulation. First of all, it enhances eye relief
(distance from eyepoint to first optical surface) for a FOV
and thus often simplifies positioning of the display on
the simulator fuselage. Secondly, image size doesn't
change with fore and aft head movement, just as in the
real world for distant objects). Thirdly, an object's
angular position does not change with sideways head
movement or, more importantly, with laterally-displaced
eyepoints as found in multi-crew cockpits. Finally, the
eyes accommodate (focus) and converge (tilt inwards or
outwards) as if viewing distant objects, which is
comparable to what occurs most of the time from an
actual cockpit. Because additional optical components
are needed to perform collimation, display costs are
higher. Additionally, the additional weight of the optics
can have a cost-impact on other parts of the simulator,
such as the motion system.
Though many users of computer image generation
equipment simply need a graphics engine and a display
for viewing, the user of a flight simulator is not so
fortunate. The IG and display must be successfully
integrated with the flight simulator in both a hardware
and software sense. And, since the simulator is either a
training or engineering device, integration must also be
accomplished with an InstructorfOperator Station (10s)
to permit control of visual system parameters such as
ambient lighting, visibility, and location of moving
objects. Some aspects of integration are discussed in
more detail below.
Increased FOV Via -ioning
common technique for extending FOV is to mosaic
several display channels (which in turn requires several
IG channels). To obtain a continuous FOV, each display
channel is often blended both in geometry and intensity
to ensure continuity between adjacent channels. This
blending increases cost owing to the added sophistication
needed by the displays. An alternative is simply to abut
adjacent channels, leaving a small gap over which no
imagery is presented. The argument against abutment is
that it's unrealistic and small objects can disappear into
the gaps. However, abutment is less expensive both in
initial display cost and routine alignment. Also, one can
argue that small objects never disappear into gaps for
very long owing to the dynamic nature of aircraft
Field/Frame- The best way to handle
a sudden excess in IG scene capacity is to simply extend
the period during which that scene can be processed. The
impact, as far as the display is concerned, is a longer field
or frame time. Most commercial displays offer only a
fmed field and frame rate; having an "extend" capability is
more costly. However, the alternative to providing for
sudden overloads is to ensure that they never occur. This
is only accomplished by building sparser data bases and
not utilizing the IG to its fullest capacity.
r vs.
- The calligraphic
portrayal of lights yields enhanced realism compared with
raster-drawn lights owing to (i) higher brightness, (ii)
er Of mart
- Increasing the
number of available airports implies that a means of
selection must be provided at the IOS. Additionally,
runways need to be aligned with Radio Aids residing in
the host computer to ensure correlation of visual with
navigation instruments.
i t i o u - Every
environmental condition must be controllable from the
10s; this control ranges from a simple onfoff to
selection from a range of parameters.
M o v i n ~0- As previously stated, each
moving object needs a provision for activation and
subsequent control.
ht Above
C o l l l. s .l p n
- Both of these attributes often require that
the IG pass information back to the controlling host
computer, thereby complicating an interface that would
be unidirectional otherwise.
WeaDonry - It's straightforward graphically to
depict weapons firing and those effects associated with a
hit or miss. However, accurate simulation in a training
environment requires computation of trajectory and target
correlation with other onboard avionics (e.g.. radar,
gunsight, or HUD). The implication on integration is
added cost.
DisDlav - Ease of fitting affects
installation cost. For example, the rake of a canopy or
the method by which it opens will influence the choice
of display. The amount and type of light-tighting can
also be a cost-driver. The presence of a motion system
implies that greater rigidity with lower weight and inertia
are desirable.
Downloaded by UNIVERSITY OF NEW SOUTH WALES (UNSW) on October 27, 2017 | | DOI: 10.2514/6.1989-3321
Host -C
- The IG demands
of the host computer certain information at the
commencement of a training exercise, and additional
information at regular intervals thereafter. Initially, the
host sends information regarding (i) choice of data base,
(ii) environmental conditions, and (iii) status of moving
objects. Afterwards, the host must communicate to the
IG data concerning (i) positional and attitudinal updates
of moving objects and (ii) any changes in environmental
conditions. The integration required to fulfill this
mission must include software to collect and transmit the
data residing in the host, and it must include a hardware
link capable of communicating the required information
at the needed rate.
Povoview LCVTM: A Solution
The remainder of this paper addresses one possible
approach to the problem of providing a relatively lowcost visual system having good value. Termed
Novoview LCV, it is comprised of an IG, data base,
display, a visual control console, installation &
integration support, and product support (both before and
after delivery).Each area will be described in more detail.
The IG selected for Novoview LCV is the ESIG100 from Evans & Sutherland. Derived from the SP-X
family of image generation equipment, it represents
proven (over 100 sold to date) state-of-the-art technology
with good reliability and low technical risk. In terms of
performance, it offers dayldusklnight simulation for up to
four channels, both intensity and color-blended texture on
surfaces of any orientation, anti-aliasing, up to three
simultaneous moving objects, and control of
meteorological effects including visibility, RVR, cloud
height and thickness, scud, and rain/snow/ice effects.
Because of its importance, special mention will be made
of scene management. By way of reminder, scene
management refers to efforts taken to ensure that the IG
(i) operates close to capacity most of the time, (ii)
utilizes this capacity in a manner most beneficial to the
pilot (i.e., concentrating detail in the foreground where
the pilot can see it), and (iii) in the event of system
overload, degrades the image in a graceful rather than
abrupt and distracting manner. The ESIG-100 uses the
following techniques to guarantee the optimum level of
Perspective culling - Small objects
subtending an angle of less than a given
threshold are eliminated from further
processing by the IG, thus freeing processing
capacity for more significant objects.
Level-of-detail management - Objects
are modelled in several different ways. Crude
models having a small number of polygons
are used for representation at medium to large
distances; a detailed model having a higher
polygon count is normally used for
representation when the object is close to the
eyepoint. Transitioning between models
occurs at a range sufficiently large to
minimize observance of a discontinuity. The
net effect of this capability is that scene detail
is concentrated close to the pilot where hisher
acuity can resolve it, and not wasted in the
distance where it's not readily discernible
In the event that the IG detects an overload
situation arising gradually, the transition
distances used for switching among crude and
detailed models are decreased. This results in
the cruder models being used more often and
for longer times than designed for originally,
but it does reduce IG processing requirements
until the overload condition is past.
FieldIFrame extend - In the event of a
sudden overload (as might occur if a complex
moving object enters the FOV of an already
complex scene) in which the IG does not have
time to execute level-of-detail changes,
field/frame extend provides a mechanism for
avoiding scene collapse. The time available
for processing the image is increased, and the
net effect is that the drawing of the new image
is delayed and the updatelfield rate
momentarily decreases.
The ESIG-100 differs from the more sophisticated
SP-X and ESIG products in several respects. One of
these is resolution. Whereas some products have over
700,000 pixels, the ESIG-100 has a bit over 300,000
(yielding roughly 4 arcmin resolution with most display
systems). In those applications demanding detection or
recognition of small objects at long ranges, this level of
resolution will prove inadequate. However, many tasks
such as low-level navigation can be satisfactorily trained
with this resolution. Furthermore, the anti-aliasing
found in the ESIG-100 tends to enhance discernibility of
individual small objects!
Update rate is another important differentiator
between the ESIG-100 and other systems. Phase I1 and
Phase I11 visual systems generally update imagery at field
rate; i.e., 50 or 60 Hz. A rate of 25 Hz was chosen for
Novoview LCV because (i) it allows scene capacities of
500 surfaceslchannel and 1000 lightslsystem and (ii) it
compares favorably with motion picture film rates of 24
Hz. In addition, because lower cost visual systems tend
to have narrower fields of view than more expensive
ones, streaming effects in the peripheral field are less
pronounced, thus making temporal aliasing less of an
Downloaded by UNIVERSITY OF NEW SOUTH WALES (UNSW) on October 27, 2017 | | DOI: 10.2514/6.1989-3321
The ESIG-100 is a pure raster device unlike other
products in the SP-X range. Though not a significant
cost driver in the IG (it was already designed into it), it
would have had a significant impact on display cost. The
net effect is to compromise light fidelity; this is
especially noticeable at dusklnight. However, light
attributes such as (i) straight and curved strings, (ii)
random intensity, (iii) horizontal and vertical
directionality, and (iv) flashing, blinking, strobing, etc.
are still present.
Novoview LCV offers either a generic civil or
military data base comprising (i) an airportlairfield, (ii)
surrounding 3-D terrain with cultural features out to a
radius of 40-50 miles, and (iii) single textured polygon
representations of earth and sky that are automatically
placed in the visual scene if the trainee travels beyond the
boundary of the normal generic data base. To help cater
for individual training needs, the airportlairfield model is
adjustable by the instructor in terms of runway length,
airport lighting, approach lighting, and terminal location.
Modem display systems run the gamut from
single-channel direct-viewing to wide-angle collimation
to area-of-interest projection slaved to headleye
movement. A low cost visual needs to be more modest
in outlook, yet cater to a wide variety of aircraft types.
Potential users encompass operators of fixed and rotary
wing aircraft having both single- and multi-crew flight
decks. Hence, Novoview LCV offers a family of display
options in configurations of one to four channels.
Monitor-based displays with beamsplitterlmirror
collimation are advocated for multi-crew cockpits,
whereas front-projectiononto an 8' radius spherical screen
for direct viewing is recommended for single-seat
cockpits or those multi-seat situations where only one
crew member is trained at a time. Use of commercial
equipment in conjunction with standardized display
structures helps to ensure low cost.
A standardized Workshare and Interface Control
Document (ICD) is part of Novoview LCV and defines
the responsibilities of both Rediffusion and the user in
terms of installation and integration of the visual system
with the simulator. Essentially, Rediffusion installs the
equipment and ensures that the host computer can
communicate with it (currently via Ethernet); the user is
expected to ensure (with Rediffusion's technical advice)
that the simulator is mechanically compatible and that
the other simulator sub-systems are compatible with the
addition of the visual. This permits the use of more
standardized display structures than would otherwise be
the case. Often this approach represents a turnkey
approach for the user. To simplify integration and
thereby reduce system cost, Novoview LCV comes with
an Instructor's Visual Control Unit that provides control
of visual functions in those cases where no capability
exists at the 10s.
Novoview LCV is provided with both componentlevel and system-level documentation. After acceptance,
the customer is provided with an on-site operations and
maintenance course for up to three weeks. And, as long
as the equipment is in service, a Customer Service
Engineer will pay a one-day visit annually. Optional
services are also available at added cost; these include (i)
spares, (ii) tools and test equipment, (iii) on-site
technical support, (iv) customized data bases, and (v)
additional integration tasks, to name just a few.
Striking a balance between visual system
performance and cost is very much a function of the type
of simulator for which it is intended. Market trends
indicate that sophisticated trainers costing about $1-2
million need a visual system costing on the order of
$0.5-1 million. Because the bulk of the training market
avails itself of more expensive Phase 11- and Phase IIIcompatible visual systems, it was necessary to find a
means of trading-off performance and cost to yield a
system capable of satisfying this A $1-2 million trainer
Looking at the system rather than individual
components, it was realized that the key to reducing cost
lay in (i) judiciously reducing performance to reduce cost,
(ii) implementing standardization to reduce non-recurring
costs, and (iii) maintaining system flexibility to ensure
economies of scale through broad applicability to a a
large user population. Putting these three concepts into
practice then required a careful examination of visual
system attributes affecting both performance and cost.
One result of this analysis is a product from
Rediffusion termed Novoview* LCV. It is a complete
visual system package comprised of (i) an ESIG-100
dayldusldnight high-performance computer image
generator, (ii) generic commercial or military data base
with adjustable airport, (iii) either collimated or noncollimated display of up to four distinct channels, (iv)
Instructor's visual control console, (v) installation and
integration support, and (vi) overall product support. A
system has already been sold and is due for delivery later
this year.
1. James L. Davis, "Managing Performance
Trade-offs in Low Cost Visuals", Low Cost Visual
Systems Conference sponsored by the Royal
Aeronautical Society (23 November 1988) London.
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