1. Abstract
The transfer of Computer Generated Forces (CGF) technology
between government simulation and commercial entertainment communities,
facilitates the development of more evolved and cost effective
Autonomous Intelligent Adversaries (AIA). As commercial AIA requirements
begin to also meet government CGF requirements, breakthroughs
in intelligent adversary technology are incorporated into Commercial
Off The Shelf (COTS) and Value Added software. The commercial
reusable software tools are in turn made available to government
CGF managers who realize immediate reductions in development costs
and program maintainability.
This paper will describe early applications of CGF
technology to both government simulation and commercial gaming
environments. More recent applications of the technology will
also be discussed to show that the fidelity requirements of AIA
in simulation and gaming are, by todayís standards, nearly
identical. Motivation to reduce the development, acquisition
and operations cost of CGF and AIA software tools that increase
the fidelity, performance and portability of behavior models is
also offered.
2. Common Vision
The Distributed Interactive Simulation (DIS) glossary
defines CGF and Semi-automated Forces (SAFOR) as the ìSimulation
of friendly, enemy and neutral entities on the virtual battlefield
in which the individual platforms are operated by computer simulation
of the crew and command hierarchy.î The Virtual or Electronic
Battlefield is likewise defined as the ìIllusion resulting
from simulating the actual battlefield (IST, 1994).î
The application of CGF technology in government military
Test, Training and Analysis exercises satisfies the governmentís
need to reduce cost and logistics support while maintaining the
density, depth and diversity of forces required to accomplish
the exercise objectives. Though the human or live forces
in the exercise remain the focal point, the use of CGF provides
an economic solution that stimulates interactions between ìplayersî
on the virtual battlefield.
The commercial entertainment industry, like the military,
has similar needs for an economic solution that stimulates live
(i.e., cash paying) customers. The profit for commercial entertainment
is derived from enticing the customer to participate in and repeatedly
return to the gaming environments and location based experiences.
Commercial Virtual Reality opportunities are growing through the
application of technology that offers a solution.
The DIS glossary defines VR as the ìeffect
created by generating an environment that does not exist in the
real world. Usually, a stereoscopic display and computer-generated
three-dimensional environment giving the immersion effect. The
environment is interactive, allowing the participant to look and
navigate about the environment, enhancing the immersion effect.
Virtual environment and virtual world are synonyms for virtual
reality (IST, 1994).î
Notice that a ìvirtual battlefieldî
is one representation or application of ìvirtual reality.î
GreyStone Technologyís commercial virtual reality entertainment
systems combine multi-sensory human-computer interfaces
with real-time simulations and dynamic models that display intelligent
and interactive behaviors
As outlined above, government simulation and commercial
entertainment managers now share a common goal to reduce the cost
of development, acquisition and operation of CGF technology. In
the sections that follow, early applications of CGF technology
to both government simulation and commercial gaming environments
will be presented to show that CGF requirements across the two
environments were at one time distinct. More recent applications
of CGF technology, however, will also be discussed to show that
the fidelity requirements of Intelligent Adversaries in simulation
and gaming are by todayís standards nearly identical. Closing
sections of this paper will offer motivation to reduce
the development, acquisition and operations cost of CGF and AIA
software tools that increase the fidelity, performance
and portability of behavior models.
3. Early Applications of CGF Technology
Until recently, user requirements across government
simulation and commercial gaming environments have placed differing
emphasis on the fidelity of the CGF and AIA. While the government
simulation environments required high fidelity CGF , the commercial
gaming environments required high fidelity presentation systems.
In the sections that follow, several exemplar applications of
early work from both government simulation and commercial gaming
will be presented to show that computational resources were not
sufficient to simultaneously host both CGF and display technology.
3.1 Early Government Simulation
The government has shown an interest in modeling
adversarial forces since WWII. Much of modern CGF technology can
in fact be traced back to the work of
John Von Neumann and his
theories of game play (Von Neumann, 1944). This section will trace
early work in game theory and Operations Research to motivate
the discussion of applications that show governmentís early
emphasis on CGF.
Adversarial Agent Modeling
and Computer Generated Vehicle Commanders are applications
that are also described to show an early government emphasis on
CGF technology rather than on presentation technology. Following,
GreyStone Technologyís Advanced Maneuvering Logic -
90 (AML-90) (GreyStone, 1994) will be presented to illustrate
a government interest in CGF technology hosted in a computational
environment sufficient enough to also provide two dimensional
bitmapped graphics.
3.1.1 Operations Research
Operations Research is an activity with a long history
that dates back to World War II. Methods of Operations Research,
including statistical analysis, theory of probability and gaming
theory, have been applied to tactical analysis and operational
experiments with equipment and procedure for over half a century.
(Morse and Kimball, 1951).
Tactical analysis became necessary as the onset of
WWII introduced many new tactics and equipment types for which
effective measure-counter measures were needed. A counter measure
to minimize the threat of the Japanese Kamikaze, for example,
was found through statistical solutions that considered damage
due to suicide planes, the effects of maneuvering and the effect
of angle of approach. The results of the Kamikaze study
produced a number of suggested tactics which resemble, in content,
the consequent of modern day expert system rules. Below
is a summary table of some of the tactics learned through the
statistical analysis of suicide planes.
| Rule No | Tactic Learned |
| 1 | All ships should attempt to present their beams to high-diving planes. |
| 2 | All ships should attempt to turn their beams away from low-diving planes. |
| 3 | Battleships, cruisers, and carriers should employ radical changes of course |
| 4 | Destroyers and smaller fleet units should turn slowly to present the proper aspect to the diving plane. |
| 5 | Destroyers and smaller fleet units should not turn rapidly enough to affect the accuracy of their AA. |
Table 1: Tactics Learned
In addition to statistical analysis, search
and game theories were developed to provide more analytical
solutions to tactical analysis. Search theories, for example,
can state the probability of making contact with a target placed
at random within some given area. The probability of hit
(Pk) is likewise computed using statistical theory.
Game theories were also developed as problem solving
methodologies to tactical analysis. Specifically, the analysis
of countermeasure action is accomplished using principals established
by Von Neumann. These principals are particularly effective under
situations where battlefield intelligence is complete and the
opposing forces are reasonably familiar with measures and countermeasures
that apply to the tactical situation. The driving principal under
such situations, know as the minmax principal, works to
maximize gain while minimizing loss.
3.1.2 Enemy Platforms
Much of the Operations Research described above was
conducted at the very dawn of the computer revolution. Since then,
a number of research efforts have contributed towards the development
of computerized tactical decision aids which incorporate
many of the principals and strategies developed through Operations
Research.
The Naval Air Development Center, for example, has
sponsored research efforts to model plan recognition agents that
operate within adversarial domains. For program development, verification
and validation purposes, Computer Adversarial Agents that model
enemy platforms (e.g. aircraft and ships) are generated. These
computer adversaries pose a threat to Naval aircraft carrier Task
Forces and are capable of interaction in a dynamically changing
world.
The intelligently guided operators of Azarewiczís
plan recognition systems, project plan hypothesis forward in time
much like implementations of the minmax game principal. Due to
the dynamics of the battlefield, however, Azarewiczís models
use differential gaming principals that better model domains
where joint moves by both opposing forces might simultaneously
occur (Azarewicz, 1987).
3.1.3 Combat Commanders
The preceding section introduced the application
of game theory to computer generated autonomous adversaries.
This section will introduce the use of expert system technology
as it is applied to model a combat vehicle commander.
Gibson describes an expert system used to model a
combat vehicle commanderís thought or combat decision-making
process (Gibson, 1989). Additionally, Gibsons system applies MYCIN
certainty factor methodology to model uncertainty common to many
battlefield situations.
3.1.4 Adaptive Maneuvering Logic - 90
While the previous section introduced an expert system
based vehicle commander, this section will describe a fully autonomous
rule based air combat adversary that GreyStone Technology has
commercialized.
Adaptive Maneuvering Logic - 90 (AML-90) is an advanced,
synthetic adversary control model that allows for real-time, interactive
air combat with a six degree-of-freedom air combat simulation
for one-versus-one and two-versus-one engagements (GreyStone,
1994). The decision-making process is implemented using a rule-based
system that contains a set of air combat rules and associated
target behavior modes that consider multiple phases of a fighter
combat mission including: Beyond Visual Range (BVR), Intercept,
Close-in-Combat (CIC), and Bugout. The adversaries execute in
real-time to provide realistic air target simulation for air engagements.
The GreyStone Adaptive Maneuvering Logic - 90 (AML-90)
software provides several user selectable aerodynamic models of
fighter aircraft platform and allows for 4 computer generated
pairs (ownship and wingman), 8 aircraft total, to be simulated
simultaneously during a session. The AML-90 pairs can be controlled
as adversarial forces within a simulation exercise and may be
directed by the user to engage other aircraft entities in either
a 1-v-1 or a 2-v-1 engagement.
The Relative Reference Display (RRD) allows the user
to control and monitor the AML-90 simulation environment. The
RRD provides a two dimensional gods-eye-view of both the simulated
arena and the CGF. A Graphical User Interface (GUI) is provided
by the RRD which allows the user to set-up the initial positions
of AML-90 entities and to establish routes of flight. The GUI
also allows the user to specifically control the targets that
the AML aircraft will intercept or engage.
3.2 Early Entertainment Environments
The previous section (3.1) offers examples of early
applications of CGF technology to government simulation and decision
aiding environments. The early government applications clearly
demonstrate that limited computer processing power forced a development
emphasis on high fidelity Intelligent Adversaries. At the same
time, however, commercial gaming applications were developed with
an emphasis on high fidelity presentation because the limited
computer processing power allowed for only rudimentary or brute
force computer adversaries in the gaming environments.
The following sections offer examples of early applications
of CGF technology to commercial gaming environments. GreyStoneís
Purple Heart Corner is exemplar of the presentation fidelity
common to high end adversarial gaming environments. GreyStoneís
Pteranodon Experience is also an early example of the high
fidelity presentation system common to many commercial gaming
environments.
3.2.1 Purple Heart Corner
Purple Heart Corner is a commercially available entertainment
game that combines state-of-the-art in virtual reality computer
graphics with a detailed mock-up of a WWII bomber gun station.
The shell of the gaming simulator closely represents the interior
of the B-17 bomber at the waist gunner position, complete with
stringers and bulkhead rings. An accurately-sized window
opening in the fuselage side holds a copy of the 50 caliber Browning
machine gun, and is flanked by a standard issue ammunition box
(GreyStone, 1992).
The replica 50-cal Browning machine gun faithfully
reproduces the heft and feel of the original gun, while a built-in
pneumatic actuator recreates the hammering recoil of the big weapon.
The sights are also accurately replicated, allowing the user to
glimpse the skill required to aim the Browning accurately in the
heat of the battle.
A description of the action of air combat experience
shows that a heavier emphasis is placed on presentation rather
than on the intelligence of the computer adversaries.
Me109ís and FW190ís, silhouetted
against the sky, drop in from the south west, ahead of the formation.
The relentless drone of the engines is interrupted, first by the
top turret gunner, as he sends orange-red tracers out to greet
the incoming fighters. Wave after wave of fighters dive through
the formation. Tracers arc across the smoky sky. The 50-caliber
Browning clatters on its mount as the fighters loom in the sights,
with muzzles flashing. A hit! White flames claw the fighter to
pieces as it spins downward, raining embers and trailing smoke.
No time to exult; you turn to face the next attacker.
The above excerpt illustrates that a heavier emphasis
is placed on graphics and sound technology. Though the experience
provides computer generated targets as well as adversaries, they
are controlled using scripted programming techniques.
3.2.2 Pteranodon
The Pteranodon experience, first developed as a showcase
for Silicon Graphicsí powerful Onyx image generator, represents
the state of the art in premium virtual reality. The Pteranodon
experience offers 180 degree visibility afforded by three large
screens, and thousands of fully-textured, anti-aliased polygons
refreshing the screens at thirty times a second. The detailed,
colorful textures and realistic movement of objects in the simulation
are complemented by the rich, booming, natural sounds of the environment
(Crowe, B., 1994).
Although the Pteranodon is programmed to follow the
commands of a rider, an intelligent obstacle avoidance system
will execute a course deviation when necessary to avoid a collision
with obstacles. The Pteranodon is also programmed to search for
and follow other creatures with its gaze.
A description of the action of the Pteranodon experience
shows that a heavier emphasis is placed on display and presentation.
Echoes of a primal screech rumble through the
canyon, announcing the arrival of the raptor. Wings sweep the
sky, mocking the winds. A rider guides the beast around cascades
of water which plummet from dizzy heights to the river below ...
vampire bats flutter above the next bend and monstrous wasps dive
and swoop over a whirlpool that devours the river.
As the master of the Pteranodon, you guide it
with the reins and by leaning in the saddle. It obeys your every
command, but as you cruise through the canyons of this fantasy
world, it skillfully avoids obstacles on its own.
The above excerpt should illustrate that a heavier
emphasis is placed on graphics and sound and other presentation
technology.
4. Recent Simulation and Gaming
The previous section (3.0) describes early applications
of CGF Technology and shows that limited computational resources
forced government and commercial CGF applications to place
differing emphasis on the fidelity of the Intelligent Adversary.
This section will demonstrate that increased processing power
has made it possible to incorporate both high fidelity CGF and
high fidelity virtual reality in todayís simulation and
gaming environments.
4.1 Recent Government Simulation
A review of more recent application of CGF technology
to government simulation environments will show a continued emphasis
on high fidelity Intelligent Adversary technology but will also
show a move towards the coupling of the technology with a high
fidelity real-time virtual reality graphics environment.
The government simulation community has realized
the full potential of todayís computer technology and has
coupled Computer Generated Forces technology with high fidelity
real-time Virtual Reality. The Naval Postgraduate Schoolís
continued development of NPSNET, internationally known
for its networked virtual environments technology, has incorporated
Autonomous Players into their virtual battlefield. GreyStone Technologyís
AML-D RAGE , like NPSNET, is a networked application that
combines the latest in real-time VR technology with high fidelity
Computer Generated Forces technology. Both the NPSNET and AML-D
RAGE environments will be discussed in detail.
4.1.1 NPSNET Autonomous Players
The Navel Postgraduate School has included Autonomous
Players in the NPSNET simulation environment to ìprovide
interactive players when live players are not available or affordable
(Zyda 1994)î. The NPS Intelligent behaviors are modeled
using expert system rule based technology capable of commanding
unmanned vehicles in the simulation environment.
Among the autonomous NPS players are the autonomous
tank forces players that provide intelligent behavior models which
have the capability to work cooperatively. If numerous entities,
for example, approach the autonomous tank force from several directions,
then the NPS autonomous computer generated force can distribute
their fire such that some tanks fire one direction and others
in another direction. Should the autonomous player become outnumbered,
it has the additional capability to call for reinforcements.
The NPSNET autonomous players are also using elevation
data to reason about terrain. If, for example, a forward observation
vehicle has Line of Site (LOS) with an enemy vehicle, the Autonomous
Player can relay the coordinates to one of several howitzers.
The threat is fired upon if it is in range of the howitzer.
Additionally, the autonomous players are equipped
with intelligence reports that provide them with knowledge of
the battlefield. Given whether a vehicle is friendly or not, the
autonomous players can prioritize targets so that those targets
with a higher priority are fired upon before lower priority vehicles.
4.1.2 RAGE AML-D
GreyStoneís Real-time Advanced Graphics Environment
(RAGE) coupled with AML-D is a showcase of both high fidelity
graphics and intelligent adversaries running seemlessly together.
RAGE™ is a 3D visualization product designed
for US and foreign government agencies and military services,
and any members of the US or international defense industries
who simulate operational scenarios, avionics and weapons systems,
airframes, and mission planning/preview/rehearsal/training systems
or conduct range operations for test or training, or manage C4I
systems. It is particularly designed for organizations that have
a need for advanced visualization but do not have the time, resources,
or expertise to buy and build their own visualization products.
RAGE™ provides a 3D visualization component
for avionics, weapons and aircraft system simulations, constructive
and virtual mission simulations, mission preview, rehearsal and
training systems/simulators, live training missions and actual
combat missions. It can receive object (entity) state and event
data from multiple intelligence and instrumentation sources and
present a near real-time representation of live or simulated events
at a 30Hz refresh rate. In addition to three standard viewpoint
options: Stealth, Out-the-Window, and Tethered, RAGE™ features
two simultaneous viewpoints (i.e., Stealth on one monitor, out-the-window
on another), sensor-related control functions including scan,
slave, and zoom, and 3D visualization of non-visible phenomena
such as weapons envelopes, platform signatures, EW signals, sensor
beams and scan volumes, and operational area boundaries. RAGE™
can interface with large multi-screen displays, single screen
systems, standard system monitors, helmet mounted displays and
mini-domes (Shillicutt, 1994).
Depending on user requirements, RAGE™ can be
integrated with multiple simulations, various user input/output
interfaces, and display alternatives. Specific models and environment
renderings can be produced. Non-visible phenomena functionality
can be made dynamic such that they respond to the physical criteria
which influence their behavior. Examples include dynamic SAM envelopes
based on target altitude, and velocity vector and radar detection
volumes based on pulse repetition interval or radar cross section.
Distributed Interactive Simulation provides a specialized
method for integrating simulations into your visualization environment.
RAGE™ is certified to receive DIS entity state and event
PDUs. If a user needs to add a 3D visualization product to any
entity state source (constructive or virtual simulation, live
range data or live combat data), entity state source can be translated
into DIS protocols.
AML-D is a (DIS) compliant version of the Adaptive
Maneuvering Logic - 90 software (detailed in section 3.1.4 and
GreyStone ë93) that translates entity state data to DIS PDU
which are forwarded to the RAGE application. This combination
of high fidelity VR and CGF technology allows for interaction
between dynamic AML-90 aircraft and large multi-player exercises
(GreyStone, 1994).
4.2 Commercial Entertainment
The following sections will show that commercial
entertainment has realized the full potential of todayís
computer technology and has incorporated intelligent adversary
technology and high fidelity real-time virtual reality technology
in a single synthetic environment.
The ThunderBolt commercial gaming environment,
developed at GreyStone for a state-of-the art amusement park ride,
is a synthetic environment that satisfies many requirements also
common to government simulation. Thunderbolt has successfully
combined high fidelity adversary technology with state of art
presentation technology.
4.2.1 The Thunderbolt Experience
The computer generated forces developed for the ThunderBolt
application are designed to provide a constant level of action
for the human players who participate in the gaming environment.
The underlying goal is to keep a continuous flow of adversary
aircraft (both target and threat) in the field of view of each
of the human players.
The technologies used to develop the ThunderBolt
intelligent adversary fundamental behaviors are based on the modeling
techniques utilized within the AML-90 adversary software. Although
the number of actual CGF players required for the experience is
significant, the constraints of the ThunderBolt compute environment
allowed a CGF design based on a derivative of AML-90 behavioral
model.
Like AML-90 adversaries, the ThunderBolt CGF derive
relative threat geometry and apply a set of logic in order to
assess an appropriate action. The logic is both phase and goal-based
in that geometrical parameters such as range and target aspect
are determined. The four CGF phases are Intercept, Engage,
CIC, and Bugout. The phase is used to determine
the set of tactical logic to apply to the situation and ultimately
determines the CGF's flight behavior and actions. While the AML-90
CGF includes a robust set of tactical logic, including cooperative
logic with a wingman, the ThunderBolt CGF operate independently
of one another.
5. Conclusion
GreyStone Technology believes that many of the needs
of both government simulation and commercial entertainment communities
can be satisfied through Virtual Environments technology. Furthermore,
these virtual environments are combinations of Multi-Sensory
Human-Computer interfaces with real-time simulations that are
populated by dynamic, intelligent and interactive behavioral models
(CGF). In the final solution, the distinction between government
CGF and commercial Intelligent Adversaries, is defined by the
userís needs and the personality or behavior of
the application. The underlying software structures and technologies
should be common and reusable. As the user determines the fidelity
of both the adversaries and the interfaces needed, a compromise
must be made on the requirements of costs and operational logistics.
Figure 1: VR Application Axioms
As a single solution for all applications will unlikely
satisfy all users, we propose that a common foundation class of
object oriented CGF libraries can be cost effectively shared across
both commercial entertainment and government simulation applications.
With the axioms shown in figure 1 above, the end user can determine
the optimal operations point and the developer can determine which
of the libraries are needed to ensure the requirements of a specific
exercise or experience are met with optimal efficiency.
6. References
Azarewicz, J., et. al. (1987) Multi-Agent Plan Recognition in an Adversarial Domain, Third Annual Expert Systems in Government Proceedings, pages 188-193, Washington, DC, October, 1987.
Crowe, B., Pteranodon Sighting at SIGGRAPH '93, Virtual Reality World, November 1994
Crowe, M., Virtual Environments at GreyStone, technical presentation, GreyStone Technology
Gibson, T. J., Modelling a Combat Vehicle Commander with an Expert System, DTIC, AD-A208 533, 1989.
GreyStone (1994), AML-D Userís Manual , GSD-AMLD-UM110, GreyStone Technology.
GreyStone (1992), Purple Heart Corner, Tech Memo, GreyStone Technology.
GreyStone (1993), ThunderBolt, Tech Memo, GreyStone Technology
IST, A Glossary of Modeling and Simulation Terms for Distributed Interactive Simulation, 11th DIS Workshop on Standards for the Interoperability of Distributed Simulation, Vol. 1, 1994
Morse, P.M., Kimball, G. E. (1951) Methods of Operations Research, First Edition, Peninsula Publishing.
Shillicutt, D., On the Cover ..., Simulation, Vol. 63, No. 5, 1994
Von Neumann, J. and Morgenstern, O. (1944) Theory of Games and Economic Behavior, Princeton University Press.
Zyda et. al., The Software Required for the
Computer Generation of Virtual Environments,
Presence, Vol. 2, No. 2.
Rich Warren is a Staff
Engineer and Intelligent Systems Technology Group Leader at GreyStone.
Mr. Warren holds a Bachelors degree in Computer/Cognitive Science.
His research interest is in Artificial Intelligence and Autonomous
Intelligent Adversaries.
