Subject Terms: COMPUTER interfaces; INFORMATION technology; VIRTUAL
reality; SUTHERLAND, Ivan; COMPUTER users
Source: Scientific American, Apr2002, Vol. 286 Issue 4, p48, 8p, 3c
Authors: Feiner, Steven K.
Abstract: Discusses the outlook for computer interfaces,
specifically the outlook for augmented reality, which adds virtual
information to a user's sensory perceptions. Mention of various devices
to be developed, including optical see-through and video see-through
devices; Benefits of the technology; Developments in information
technology; Role of Ivan Sutherland in the field. INSETS: OPTICAL
Accession Number: 6293713
ISSN: 0036-8733
Full Text Word Count: 4281

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Augmented Reality: A New Way Of Seeing


Computer scientists are developing systems that can enhance and enrich a
user's view of the world

What will COMPUTER USER INTERFACES look like 10 years from now? If we
extrapolate from current systems, it's easy to imagine a proliferation
of high-resolution displays, ranging from tiny handheld or wrist-worn
devices to large screens built into desks, walls and floors. Such
displays will doubtless become commonplace. But I and many other
computer scientists believe that a fundamentally different kind of user
interface known as augmented reality will have a more profound effect on
the way in which we develop and interact with future computers.

Augmented reality (AR) refers to computer displays that add virtual
information to a user's sensory perceptions. Most AR research focuses on
"see-through" devices, usually worn on the head, that overlay graphics
and text on the user's view of his or her surroundings. (Virtual
information can also be in other sensory forms, such as sound or touch,
but this article will concentrate on visual enhancements.) AR systems
track the position and orientation of the user's head so that the
overlaid material can be aligned with the user's view of the world.
Through this process, known as registration, graphics software can place
a three-dimensional image of a teacup, for example, on top of a real
saucer and keep the virtual cup fixed in that position as the user moves
about the room. AR systems employ some of the same hardware technologies
used in virtual-reality research, but there's a crucial difference:
whereas virtual reality brashly aims to replace the real world,
augmented reality respectfully supplements it.

Consider what AR could make routinely possible. A repairperson viewing a
broken piece of equipment could see instructions highlighting the parts
that need to be inspected. A surgeon could get the equivalent of x-ray
vision by observing live ultrasound scans of internal organs that are
overlaid on the patient's body. Firefighters could see the layout of a
burning building, allowing them to avoid hazards that would otherwise be
invisible. Soldiers could see the positions of enemy snipers who had
been spotted by unmanned reconnaissance planes. A tourist could glance
down a street and see a review of each restaurant on the block. A
computer garner could battle 10foot-tall aliens while walking to work.

Getting the right information at the right time and the right place is
key in all these applications. Personal digital assistants such as the
Palm and the Pocket PC can provide timely information using wireless
networking and Global Positioning System (GPS) receivers that constantly
track the handheld devices. But what makes augmented reality different
is how the information is presented: not on a separate display but
integrated with the user's perceptions. This kind of interface minimizes
the extra mental effort that a user has to expend when switching his or
her attention back and forth between real-world tasks and a computer
screen. In augmented reality, the user's view of the world and the
computer interface literally become one.

Although augmented reality may seem like the stuff of science fiction,
researchers have been building prototype systems for more than three
decades. The first was developed in the 1960s by computer graphics
pioneer Ivan Sutherland and his students at Harvard University and the
University of Utah. In the 1970s and 1980s a small number of researchers
studied augmented reality at institutions such as the U.S. Air Force's
Armstrong Laboratory, the NASA Ames Research Center and the University
of North Carolina at Chapel Hill. It wasn't until the early 1990s that
the term "augmented reality" was coined by scientists at Boeing who were
developing an experimental AR system to help workers assemble wiring
harnesses. The past decade has seen a flowering of AR research as
hardware costs have fallen enough to make the necessary lab equipment
affordable. Scientists have gathered at yearly AR conferences since

Despite the tremendous changes in information technology since
Sutherland's groundbreaking work, the key components needed to build an
AR system have remained the same: displays, trackers, and graphics
computers and software. The performance of all these components has
improved significantly in recent years, making it possible to design
experimental systems that may soon be developed into commercial

Seeing Is Believing


BY DEFINITION, the see-through displays in AR systems must be able to
present a combination of virtual and real information. Although the
displays can be handheld or stationary, they are most often worn on the
head. Positioned just in front of the eye, a physically small screen can
create a virtually large image. Head-worn displays are typically
referred to as head-mounted displays, or HMDs for short. (I've always
found it odd, however, that anyone would want to "mount" something on
his or her head, so I prefer to call them head-worn displays.)

The devices fall into two categories: optical see-through and video
see-through. A simple approach to optical see-through display employs a
mirror beam splitter--a half-silvered mirror that both reflects and
transmits light. If properly oriented in front of the user's eye, the
beam splitter can reflect the image of a computer display into the
user's line of sight yet still allow light from the surrounding world to
pass through. Such beam splitters, which are called combiners, have long
been used in "head-up" displays for fighter-jet pilots (and, more
recently, for drivers of luxury cars). Lenses can be placed between the
beam splitter and the computer display to focus the image so that it
appears at a comfortable viewing distance. If a display and optics are
provided for each eye, the view can be in stereo [see illustration

In contrast, a video see-through display uses video mixing technology,
originally developed for television special effects, to combine the
image from a head-worn camera with synthesized graphics [see
illustration on next page]. The merged image is typically presented on
an opaque head-worn display. With careful design, the camera can be
positioned so that its optical path is close to that of the user's eye;
the video image thus approximates what the user would normally see. As
with optical see-through displays, a separate system can be provided for
each eye to support stereo vision.

In one method for combining images for video see-through displays, the
synthesized graphics are set against a reserved background color. One by
one, pixels from the video camera image are matched with the
corresponding pixels from the synthesized graphics image. A pixel from
the camera image appears in the display when the pixel from the graphics
image contains the background color; otherwise the pixel from the
graphics image is displayed. Consequently, the synthesized graphics
obscure the real objects behind them. Alternatively, a separate channel
of information stored with each pixel can indicate the fraction of that
pixel that should be determined by the virtual information. This
technique allows the display of semitransparent graphics. And if the
system can determine the distances of real objects from the viewer,
computer graphics algorithms can also create the illusion that the real
objects are obscuring virtual objects that are farther away. (Optical
see-through displays have this capability as well.)

Each of the approaches to see-through display design has its pluses and
minuses. Optical see-through systems allow the user to see the real
world with full resolution and field of view. But the overlaid graphics
in current optical see-through systems are not opaque and therefore
cannot completely obscure the physical objects behind them. As a result,
the superimposed text may be hard to read against some backgrounds, and
the three-dimensional graphics may not produce a convincing illusion.
Furthermore, although a user focuses physical objects depending on their
distance, virtual objects are all focused in the plane of the display.
This means that a virtual object that is intended to be at the same
position as a physical object may have a geometrically correct
projection, yet the user may not be able to view both objects in focus
at the same time.

In video see-through systems, virtual objects can fully obscure physical
ones and can be combined with them using a rich variety of graphical
effects. There is also no discrepancy between how the eye focuses
virtual and physical objects, because both are viewed on the same plane.
The limitations of current video technology, however, mean that the
quality of the visual experience of the real world is significantly
decreased, essentially to the level of the synthesized graphics, with
everything focusing at the same apparent distance. At present, a video
camera and display are no match for the human eye.

The earliest see-through displays devised by Sutherland and his students
were cumbersome devices containing cathode-ray tubes and bulky optics.
Nowadays researchers use small liquid crystal displays and advanced
optical designs to create systems that weigh mere ounces. More
improvements are forthcoming: a company called Microvision, for
instance, has recently developed a device that uses low-power lasers to
scan images directly on the retina [see "Eye Spy," by Phil Scott; News
Scan, SCIENTIFIC AMERICAN, September 2001]. Some prototype head-worn
displays look much like eyeglasses, making them relatively
inconspicuous. Another approach involves projecting graphics directly on
surfaces in the user's environment.

Keeping Track

A CRUCIAL REQUIREMENT of augmented-reality systems is to correctly match
the overlaid graphics with the user's view of the surrounding world. To
make that spatial relation possible, the AR system must accurately track
the position and orientation of the user's head and employ that
information when rendering the graphics. Some AR systems may also
require certain moving objects to be tracked; for example, a system that
provides visual guidance for a mechanic repairing a jet engine may need
to track the positions and orientations of the engine's parts during
disassembly. Because the tracking devices typically monitor six
parameters for each object--three spatial coordinates (x, y and z) and
three orientation angles (pitch, yaw and roll)they are often called
six-degree-of-freedom trackers.

In their prototype AR systems, Sutherland and his colleagues
experimented with a mechanical head tracker suspended from the ceiling.
They also tried ultrasonic trackers that transmitted acoustic signals to
determine the user's position. Since then, researchers have developed
improved versions of these technologies, as well as electromagnetic,
optical and video trackers. Trackers typically have two parts: one worn
by the tracked person or object and the other built into the surrounding
environment, usually within the same room. In optical trackers, the
targets--LEDs or reflectors, for instance-can be attached to the tracked
person or object, and an array of optical sensors can be embedded in the
room's ceiling. Alternatively, the tracked users can wear the sensors,
and the targets can be fixed to the ceiling. By calculating the distance
to each visible target, the sensors can determine the user's position
and orientation.

In everyday life, people rely on several senses--including what they
see, cues from their inner ears and gravity's pull on their bodies--to
maintain their bearings. In a similar fashion, "hybrid trackers" draw on
several sources of sensory information. For example, the wearer of an AR
display can be equipped with inertial sensors (gyroscopes and
accelerometers) to record changes in head orientation. Combining this
information with data from the optical, video or ultrasonic devices
greatly improves the accuracy of the tracking.

But what about AR systems designed for outdoor use? How can you track a
person when he or she steps outside the room packed with sensors? The
outdoor AR system designed by our lab at Columbia University handles
orientation and position tracking separately. Head orientation is
determined with a commercially available hybrid tracker that combines
gyroscopes and accelerometers with a magnetometer that measures the
earth's magnetic field. For position tracking, we take advantage of a
high-precision version of the increasingly popular Global Positioning
System receiver.

A GPS receiver determines its position by monitoring radio signals from
navigation satellites. The accuracy of the inexpensive, handheld
receivers that are currently available is quite coarse--the positions
can be off by many meters. Users can get better results with a technique
known as differential GPS. In this method, the mobile GPS receiver also
monitors signals from another GPS receiver and a radio transmitter at a
fixed location on the earth. This transmitter broadcasts corrections
based on the difference between the stationary GPS antenna's known and
computed positions. By using these signals to correct the satellite
signals, differential GPS can reduce the margin of error to less than
one meter. Our system is able to achieve centimeterlevel accuracy by
employing real-time kinematic GPS, a more sophisticated form of
differential GPS that also compares the phases of the signals at the
fixed and mobile receivers.

Unfortunately, GPS is not the ultimate answer to position tracking. The
satellite signals are relatively weak and easily blocked by buildings or
even foliage. This rules out useful tracking indoors or in places like
midtown Manhattan, where rows of tall buildings block most of the sky.
We found that GPS tracking works well in the central part of Columbia's
campus, which has wide open spaces and relatively low buildings. GPS,
however, provides far too few updates per second and is too inaccurate
to support the precise overlaying of graphics on nearby objects.

Augmented-reality systems place extraordinarily high demands on the
accuracy, resolution, repeatability and speed of tracking technologies.
Hardware and software delays introduce a lag between the user's movement
and the update of the display. As a result, virtual objects will not
remain in their proper positions as the user moves about or turns his or
her head. One technique for combating such errors is to equip AR systems
with software that makes short-term predictions about the user's future
motions by extrapolating from previous movements. And in the long run,
hybrid trackers that include computer vision technologies may be able to
trigger appropriate graphics overlays when the devices recognize certain
objects in the user's view.

Managing Reality

THE PERFORMANCE OF GRAPHICS hardware and software has improved
spectacularly in the past few years. In the 1990s our lab had to build
its own computers for our outdoor AR systems because no commercially
available laptop could produce the fast 3-D graphics that we wanted. In
2001, however, we were finally able to switch to a commercial laptop
that had sufficiently powerful graphics chips. In our experimental
mobile systems, the laptop is mounted on a backpack. The machine has the
advantage of a large built-in display, which we leave open to allow
bystanders to see what the overlaid graphics look like alone.

Part of what makes reality real is its constant state of flux. AR
software must constantly update the overlaid graphics as the user and
visible objects move about. I use the term "environment management" to
describe the process of coordinating the presentation of a large number
of virtual objects on many displays for many users. Working with Simon
J. Julier, Larry J. Rosenblum and others at the Naval Research
Laboratory, we are developing a software architecture that addresses
this problem. Suppose that we wanted to introduce our lab to a visitor
by annotating what he or she sees. This would entail selecting the parts
of the lab to annotate, determining the form of the annotations (for
instance, labels) and calculating each label's position and size. Our
lab has developed prototype software that interactively redesigns the
geometry of virtual objects to maintain the desired relations among them
and the real objects in the user's view. For example, the software can
continually recompute a label's size and position to ensure that it is
always visible and that it overlaps only the appropriate object.

It is important to note that a number of useful applications of AR
require relatively little graphics power: we already see the real world
without having to render it. (In contrast, virtual-reality systems must
always create a 3-D setting for the user.) In a system designed for
equipment repair, just one simple arrow or highlight box may be enough
to show the next step in a complicated maintenance procedure. In any
case, for mobile AR to become practical, computers and their power
supplies must become small enough to be worn comfortably. I used to
suggest that they needed to be the size of a Walkman, but a better
target might be the even smaller MP3 player.

The Touring Machine and MARS

WHEREAS MANY AR DESIGNS have focused on developing better trackers and
displays, our laboratory has concentrated on the design of the user
interface and the software infrastructure. After experimenting with
indoor AR systems in the early 1990s, we decided to build our first
outdoor system in 1996 to find out how it might help a tourist exploring
an unfamiliar environment. We called our initial prototype the Touring
Machine (with apologies to Alan M. Turing, whose abstract Turing machine
defines what computers are capable of computing). Because we wanted to
minimize the constraints imposed by current technology, we combined the
best components we could find to create a test bed whose capabilities
are as close as we can make them to the more powerful machines we expect
in the future. We avoided (as much as possible) practical concerns such
as cost, size, weight and power consumption, confident that those
problems will be overcome by hardware designers in the coming years.
Trading off physical comfort for performance and ease of software
development, we have built several generations of prototypes using
external-frame backpacks. In general, we refer to these as mobile AR
systems (or MARS, for short) [see left illustration below].

Our current system uses a Velcro-covered board and straps to hold many
of the components: the laptop computer (with its 3-D graphics chip set
and IEEE 802.11b wireless network card), trackers (a real-time kinematic
GPS receiver, a GPS corrections receiver and the interface box for the
hybrid orientation tracker), power (batteries and a regulated power
supply), and interface boxes for the head-worn display and interaction
devices. The total weight is about 11 kilograms (25 pounds). Antennas
for the GPS receiver and the GPS corrections receiver are mounted at the
top of the backpack frame, and the user wears the head-worn see-through
display and its attached orientation tracker sensor. Our MARS prototypes
allow users to interact with the display--to scroll, say, through a menu
of choices superimposed on the user's view--by manipulating a wireless
trackball or touch pad.

From the very beginning, our system has also included a handheld display
(with stylus input) to complement the headworn see-through display. This
hybrid user interface offers the benefits of both kinds of interaction:
the user can see 3-D graphics on the see-through display and, at the
same time, access additional information on the handheld display.

In collaboration with my colleague John Pavlik and his students in
Columbia's Graduate School of Journalism, we have explored how our MARS
prototypes can embed "situated documentaries'' in the surrounding
environment. These documentaries narrate historical events that took
place in the user's immediate area by overlaying 3-D graphics and sound
on what the user sees and hears. Standing at Columbia's sundial and
looking through the head-worn display, the user sees virtual flags
planted around the campus, each of which represents several sections of
the story linked to that flag's location. When the user selects a flag
and then chooses one of the sections, it is presented on both the
head-worn and the handheld displays.

One of our situated documentaries tells the story of the student
demonstrations at Columbia in 1968. If the user chooses one of the
virtual flags, the head-worn display presents a narrated set of still
images, while the handheld display shows video snippets and provides
in-depth information about specific participants and incidents. In our
documentary on the prior occupant of Columbia's current campus, the
Bloomingdale Asylum, 3-D models of the asylum's buildings (long since
demolished) are overlaid at their original locations on the see-through
display. Meanwhile the handheld display presents an interactive
annotated timeline of the asylum's history. As the user chooses
different dates on the timeline, the images of the buildings that
existed at those dates fade in and out on the see-through display.

The Killer App?

AS RESEARCHERS CONTINUE to improve the tracking, display and mobile
processing components of AR systems, the seamless integration of virtual
and sensory information may become not merely possible but commonplace.
Some observers have suggested that one of the many potential
applications of augmented reality (computer gaming, equipment
maintenance, medical imagery and so on) will emerge as the "killer
app"--a use so compelling that it would result in mass adoption of the
technology. Although specific applications may well be a driving force
when commercial AR systems initially become available, I believe that
the systems will ultimately become much like telephones and PCs. These
familiar devices have no single driving application but rather a host of
everyday uses.

The notion of computers being inextricably and transparently
incorporated into our daily lives is what computer scientist Mark Weiser
termed "ubiquitous computing" more than a decade ago [see "The Computer
for the 21st Century," by Mark Weiser; SCIENTIFIC AMERICAN, September
1991]. In a similar way, I believe the overlaid information of AR
systems will become part of what we expect to see at work and at play:
labels and directions when we don't want to get lost, reminders when we
don't want to forget and, perhaps, a favorite cartoon character popping
out from the bushes to tell a joke when we want to be amused. When
computer user interfaces are potentially everywhere we look, this
pervasive mixture of reality and virtuality may become the primary
medium for a new generation of artists, designers and storytellers who
will craft the future.

Overview/Augmented Reality

Augmented-reality(AR)systems add computer-generated information to a
user's sensory perceptions. Whereas virtual reality aims to replace the
real world, augmented reality supplements it.

Most research focuses on "see-through" devices, usually worn on the
head, that overlay graphics and text on the user's view of the world.

Recent technological improvements may soon lead to the introduction of
AR systems for surgeons, repairpeople, soldiers, tourists and computer
gamers. Eventually the systems may become commonplace.

More To Explore

A Survey of Augmented Reality. Ronald T. Azuma in Presence:
Teleoperators and Virtual Environments, Vol. 6, No. 4, pages 355-385;
August 1997. Available at www.cs.unc.edu/~azuma/ARpresence.pdf

Recent Advances in Augmented Reality. Ronald T. Azuma, Yohan Baillot,
Reinhold Behringer, Steven K. Feiner, Simon Julier and Blair Maclntyre
in IEEE Computer Graphics and Applications, Vol. 21, No. 6, pages 34-47;
November/December 2001. Available at www.cs.unc.edu/~azuma/cga2001.pdf

Columbia University's Computer Graphics and User Interfaces Lab is at
www.cs.columbia.edu/graphics/ <http://www.cs.columbia.edu/graphics/>

A list of relevant publications can be found at

AR research sites and conferences are listed at
www.augmented-reality.org <http://www.augmented-reality.org>
Information on medical applications of augmented reality is at
www.cs.unc.edu/~us/ <http://www.cs.unc.edu/~us/>





By Steven K Feiner

STEVEN K. FEINER is professor of computer science at Columbia
University, where he directs the Computer Graphics and User Interfaces
Lab. He received a Ph.D. in computer science from Brown University in
1987. In addition to performing research on software and user interfaces
for augmented reality, Feiner and his colleagues are developing systems
that automate the design and layout of interactive graphics and
multimedia presentations in domains ranging from medicine to government
databases. The research described in this article was supported in part
by the Office of Naval Research and the National Science Foundation.

Glimpses of Augmented Reality

COLUMBIA UNIVERSITY'S Computer Graphics and User Interfaces Lab built an
experimental outdoor system designed to help a tourist explore the
university's campus. The laptop on the user's backpack supplies the
computer graphics that are superimposed on the optical see-through
display. GPS receivers track the user's position.

The lab created a historical documentary that shows three-dimensional
images of the Bloomingdale Asylum, the prior occupant of Columbia's
campus, at its original location.

A user viewing the documentary can get additional information from a
handheld display, which provides an interactive timeline of the
Bloomingdale Asylum's history.

MEDICAL APPLICATION was built by researchers at the University of
Central Florida. The system overlaid a model of a knee joint on the view
of a woman's leg. The researchers tracked the leg's position using
infrared LEDs. As the woman bent her knee, the graphics showed how the
bones would move.





Video See-Through Display

VIDEO SYSTEMS mix computer graphics with camera images that approximate
what the user would normally see. In this design, light from the
surrounding world is captured by a wedge prism and focused on a
charge-coupled device that converts the light to digital video signals.
The system combines the video with computer graphics and presents the
merged images on the liquid-crystal display. Video systems can produce
opaque graphics but cannot get match the resolution and range of the
human eye.

1. View of the real world captured and converted to a video image
2. computer graphics set against a reserved background color
3. Merged image shown on the liquid-crystal display






Optical See-Through Display

OPTICAL SYSTEMS superimpose computer graphics on the user's view of the
world. In this current design, the prisms reflect the graphics on a
liquidcrystal display into the user's line of sight yet still allow
light from the surrounding world to pass through. A system of sensors
and targets keeps track of the position and orientation of the user's
head, ensuring that the graphics appear in the correct places. But in
present-day optical systems, the graphics cannot completely obscure the
objects behind them.

1. View of the real world from a computer gamer's perspective
2. Graphics synthesized by the augmented reality system
3. Image on optical display with superimposed graphics







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Source: Scientific American, Apr2002, Vol. 286 Issue 4, p48, 8p
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