Argumented Reality Report
Augmented Reality
Introduction
Augmented
Reality (AR) is a growing area in virtual reality research. The
world environment around us provides a wealth of information that is
difficult to duplicate in a computer. This is evidenced by the
worlds used in virtual environments. Either these worlds are very
simplistic such as the environments created for immersive
entertainment and games, or the system that can create a more
realistic environment has a million dollar price tag such as flight
simulators. An augmented reality system generates a composite view
for the user. It is a combination of the real scene viewed by
the user and a virtual scene generated by the computer that augments
the scene with additional information. Augmented reality
presented to the user enhances that person's performance in and
perception of the world. The ultimate goal is to create a system
such that the user cannot tell the difference between the real world
and the virtual augmentation of it. To the user of this ultimate
system it would appear that he is looking at a single real scene.
Augmented Reality vs. Virtual
Reality
Virtual reality
is a technology that encompasses a broad spectrum of ideas. The term
is defined as "a computer generated, interactive, three-dimensional
environment in which a person is immersed. There are three key
points in this definition. First, this virtual environment is a
computer generated three-dimensional scene, which requires high
performance computer graphics to provide an adequate level of
realism. The second point is that the virtual world is interactive.
A user requires real-time response from the system to be able to
interact with it in an effective manner. The last point is that the
user is immersed in this virtual environment. One of the identifying
marks of a virtual reality system is the head mounted display worn
by users. These displays block out all the external world and
present to the wearer a view that is under the complete control of
the computer. The user is completely immersed in an artificial world
and becomes divorced from the real environment. For this immersion
to appear realistic the virtual reality system must accurately sense
how the user is moving and determine what effect that will have on
the scene being rendered in the head mounted display.
The discussion
above highlights the similarities and differences between virtual
reality and augmented reality systems. A very visible difference
between these two types of systems is the immersiveness of the
system. Virtual reality strives for a totally immersive environment.
In contrast, an augmented reality system is augmenting the real
world scene necessitating that the user maintains a sense of
presence in that world. The virtual images are merged with the real
view to create the augmented display. There must be a mechanism to
combine the real and virtual that is not present in other virtual
reality work. The computer generated virtual objects must be
accurately registered with the real world in all dimensions. Errors
in this registration will prevent the user from seeing the real and
virtual images as fused. The correct registration must also be
maintained while the user moves about within the real environment.
Discrepancies or changes in the apparent registration will range
from distracting which makes working with the augmented view more
difficult, to physically disturbing for the user making the system
completely unusable. An immersive virtual reality system must
maintain registration so that changes in the rendered scene match
with the perceptions of the user. Milgram defines the Reality-Virtuality
continuum shown as Figure 1.
Figure 1 -
Milgram's Reality-Virtuality Continuum
The real world
and a totally virtual environment are at the two ends of this
continuum with the middle region called Mixed Reality. Augmented
reality lies near the real world end of the line with the
predominate perception being the real world augmented by computer
generated data. Augmented Virtuality is a term created by Milgram to
identify systems, which are mostly synthetic with some real world
imagery added such as texture mapping video onto virtual objects.
This is a distinction that will fade as the technology improves and
the virtual elements in the scene become less distinguishable from
the real ones.
Video Merging
The task in the
augmented reality system is to register the virtual frame of
reference with what the user is seeing. Registration is more
critical in an augmented reality system because we are more
sensitive to visual misalignments than to the type of
vision-kinesthetic errors that might result in a standard virtual
reality system. Figure shows the multiple reference frames that must
be related in an augmented reality system.
 The
scene is viewed by an imaging device, which in this case is depicted
as a video camera. The camera performs a perspective projection of
the 3D world onto a 2D image plane. The generation of the virtual
image is done with a standard computer graphics system. The virtual
objects are modeled in an object reference frame. The graphics
system requires information about the imaging of the real scene so
that it can correctly render these objects. This data will control
the synthetic camera that is used to generate the image of the
virtual objects. This image is then merged with the image of the
real scene to form the augmented reality image.
Components of Augmented Reality
System
1.
Head Mounted Display
2.
Tracking System (GPS)
3.
Mobile Computing Power
Head Mounted
Displays
They enable us
to view graphics and text created by the augmented reality system.
There are two basic types of head mounted displays being used.
1. Video
See-Through Display
The
"see-through" designation comes from the need for the user to be
able to see the real worldview that is immediately in front of him
even when wearing the HMD. This system blocks the wearers
surrounding environment using small cameras attached to the outside
of the goggle to capture images. On the inside of the display, the
video image is played in real-time and the graphics are superimposed
on the video. One problem with the use of video cameras is that
there is more lag, meaning that there is a delay in image-adjustment
when the viewer moves his or her head.
Video
See-through Display
The head
position obtained through the video camera by the process as
explained above is the input to the graphics system. Graphics System
produces the virtual objects, which are aligned to that of real
objects, virtual objects are then merged with the real objects
generated by the video camera and sent to the monitor from where it
is displayed to the user.
2.Optical
See-Through Displays
The optical
see-through HMD eliminates the video channel that is looking at the
real scene. Instead merging of real world and virtual augmentation
is done optically in front of the user.
Optical
See-Through Display
There are
advantages and disadvantages to each of these types of displays.
With both of the displays that use a video camera to view the real
world there is a forced delay of up to one frame time to perform the
video merging operation. At standard frame rates that will be
potentially a 33.33 millisecond delay in the view seen by the user.
Since everything the user sees is under system control compensation
for this delay could be made by correctly timing the other paths in
the system. Or, alternatively, if other paths are slower then the
video of the real scene could be delayed. With an optical
see-through display the view of the real world is instantaneous so
it is not possible to compensate for system delays in other areas.
On the other hand, with monitor based and video see-through displays
a video camera is viewing the real scene. An advantage of this is
that the image generated by the camera is available to the system to
provide tracking information. The optical see-through display does
not have this additional information. The only position information
available with that display is what position sensors on the head can
provide mounted display itself. The major advantage of optical see
through display is that they could be made very small however the
biggest constraint in using this technology is the prohibitive cost.
The main
components of our system are a backpack computer (with 3D
graphics acceleration), a differential GPS system, a
head-worn display interface (with orientation tracker), and a
spread spectrum radio communication link, all attached to the
backpack
The above shown
figure is the block diagram of AR system. It consists of a backup PC
to which two inputs one from the GPS receiver and other from the
head mounted display comes. The signal from the GPS receiver tells
the co-ordinates of the person and the orientation tracker gives the
orientation of the head. These two inputs will be transferred
through the satellite to the database server. This server based
according to the information received sends the related database to
the satellite, which is then transmitted to the backpack PC. The
graphics card will generate the virtual objects, which are then
merged with the real environment by the head worn display interface
and displayed to the user.
Our
Research
The discipline
of
affective computing studies how computers can recognize,
understand, and mimic human emotions. Now, in most cyberpunk stories
where humans merge their minds with computers, the computer is able
to interpret the symbolic thinking of its human companion, and
insert symbolic ideas back into the human brain. But wouldn't it be
better if the computer could interpret our values instead?
In fact, it would probably be far easier for computers to learn to
recognize what we like, dislike, approve of or are uncomfortable
with--these base responses tend to be similar between people, and
even across cultural and linguistic barriers. While each of us
probably has a unique encoding for the concept "carrot" in our
brains, we almost certainly share a basic neural and physiological
response when asked whether we like carrots. I.e. you can
teach a computer to recognize that someone is enjoying the carrot
they're munching--but probably you can't teach the computer to
recognize when someone is thinking about carrots.
Basically it's
just that the internet is so full of information, we end up spending
most of our time filtering out the irrelevant data. If you think
about it, like/dislike is the basic crap filter--a computer that
could tell you hated pop-up browser ads without being asked would be
a good thing.
Looking not too
far in the future, we see a world where everybody is immersed in one
form or another of
augmented reality. Everywhere we look, we see annotations on
reality, provided by our AR glasses. The issue then becomes the same
as the one we face with the Internet today: how to filter out all
the crap?
This is where
the values-driven interface becomes crucial. Our AR system needs to
be able to recognize our reactions to the various cues, annotations,
pop-ups, overlays, sims, and pointers. If our system can do this, it
can edit out the things we don't want to see.
e.g. Orthodox
religious types no longer see ads for girlie shows or salacious
lingerie models on billboards; serious rationalists no longer see
the corner church as they walk by. Something else replaces it, a
soothing image of the Gandhiji or something... The point is, the
augmented world reflects the values of whoever is using it, and it
does so seamlessly and automatically.
We introduce a hand
held PC in the basic AR diagram. This handheld PC has been
specifically trained by the users to understand his likes and
dislikes. Now the Back Pack pc will receive input not only from GPS
and orientation tracker but also from the hand held PC. Now
according to this information it would be decided which data has to
be accessed. e.g. if the person is in front of a real object which
he hated to see, this information will be conveyed by the handheld
pc to the back pack pc which in turn will generate virtual objects
so to superimpose the real object the user hates. Thus filtering all
the irrelevant information for the user and helping him.
GLOBAL POSITIONING SYSTEM
Where am I? The
question seems simple; the answer, historically, has proved not to
be. For centuries, navigators and explorers have searched the
heavens for a system that would enable them to locate their position
on the globe with the accuracy necessary to avoid tragedy and to
reach their intended destinations. On June 26, 1993, however, the
answer became as simple as the question. On that date, the
U.S. Air Force
launched the
24th Navstar satellite
into orbit, completing a network of 24 satellites known as the
Global Positioning System,
or GPS. With a GPS receiver that costs less than a few hundred
dollars you can instantly learn your location on the planet--your
latitude, longitude,
and even altitude--to within a few hundred feet.
This incredible new technology was made possible
by a combination of scientific and engineering advances,
particularly development of the world's most accurate timepieces:
atomic clocks
that are precise to within a billionth of a second. The clocks were
created by physicists seeking answers to questions about the nature
of the universe, with no conception that their technology would some
day lead to a global system of navigation. Today, GPS is saving
lives, helping society in countless other ways, and generating
100,000 jobs in a multi-billion-dollar industry. It provides a
dramatic
example
of how science works and how basic
GPS SYSTEM
SEGMENTS
The GPS consists of three major
segments: SPACE, CONTROL and USER.
1.SPACE SEGMENT
The SPACE
segment consists of 24 operational satellites in six orbital planes
(four satellites in each plane). The satellites operate in circular
20,200 km orbits at an inclination angle of 55 degrees and with a
12-hour period. The position is therefore the same at the same
sidereal time each day, i.e. the satellites appear 4 minutes earlier
each day.
2.CONTROL SEGMENT
The CONTROL
segment consists of five Monitor Stations (Hawaii, Kwajalein,
Ascension Island, Diego Garcia, Colorado Springs), three Ground
Antennas, (Ascension Island, Diego Garcia, Kwajalein), and a
Master Control Station (MCS) located at Schriever AFB in
Colorado. The monitor stations passively track all satellites in
view, accumulating ranging data. This information is processed at
the MCS to determine satellite orbits and to update each satellite's
navigation message. Updated information is transmitted to each
satellite via the Ground Antennas.
3.USER SEGMENT
The USER
segment consists of antennas and receiver-processors that provide
positionin
research leads to technologies that were virtually unimaginable at
the time the research was done.
HOW GPS WORKS
-
The basis of
GPS is "triangulation"
from satellites.
-
To
"triangulate," a GPS receiver measures distance using the travel
time of radio signals.
-
To measure
travel time, GPS needs very accurate timing, which it achieves
with some tricks.
-
Along with
distance, we need to know exactly where the satellites are in
space. High orbits and careful monitoring are the secret.
-
Finally you
must correct for any delays the signal experiences as it travels
through the atmosphere.
Triangulation from Satellites:
Suppose we
measure our distance from a satellite and find it to be 11,000
miles. Knowing that we're 11,000 miles from a particular satellite
narrows down all the possible locations we could be in the whole
universe to the surface of a sphere that is centered on this
satellite and has a radius of 11,000 miles. Next, say we measure our
distance to a second satellite and find out that it's 12,000 miles
away. That tells us that we're not only on the first sphere but
we're also on a sphere that's 12,000 miles from the second
satellite. Or in other words, we're somewhere on the circle where
these two spheres intersect. If we then make a measurement from a
third satellite and find that we're 13,000 miles from that one, that
narrows our position down even further, to the two points where the
13,000 mile sphere cuts through the circle that's the intersection
of the first two spheres. So by ranging from three satellites we can
narrow our position to just two points in space.
To decide which
one is our true location we could make a fourth measurement. But
usually one of the two points is a ridiculous answer (either too far
from Earth or moving at an impossible velocity) and can be rejected
without a measurement.
Measuring distance from satellite:
The basic
problem is in finding the distance of the user from the four
satellites. This can be done if we know the time taken by the signal
from the satellite to reach to the receiver. Then the total distance
is given by
DISTANCE (between the satellite and the user) = TIME (taken by the signal
to reach earth)* SPEED (of the signal which is the speed of light).
The time taken
by the signal to reach from satellite to the receiver can be found
by calculating the phase shift of the
Pseudo Random Code
Pseudo Random Code:
The Pseudo
Random Code is a fundamental part of GPS. Physically it's just a
very complicated digital code, or in other words, a complicated
sequence of "on" and "off" pulses. The
signal is so
complicated that it almost looks like random electrical noise. Hence
the name "Pseudo-Random." There are several good reasons for that
complexity: First, the complex pattern helps make sure that the
receiver doesn't accidentally sync up to some other signal. The
patterns are so complex that it's highly unlikely that a stray
signal will have exactly the same shape. Since each satellite has
its own unique Pseudo-Random Code this complexity also guarantees
that the receiver won't accidentally pick up another satellite's
signal. So all the satellites can use the same frequency without
jamming each other. And it makes it more difficult for a hostile
force to jam the system. We assume that both the satellite and the
receiver start generating their codes at exactly the same time.
Distance to a satellite is determined by measuring how long a radio
signal takes to reach us from that satellite.
-
To make the
measurement we assume that both the satellite and our receiver are
generating the same pseudo-random codes at exactly the same time.
-
By comparing
how late the satellite's pseudo-random code appears compared to
our receiver's code, we determine how long it took to reach us.
-
Multiply that
travel time by the speed of light and you've got distance.
But how
do we make sure everybody is perfectly synchronized?
If measuring the
travel time of a radio signal is the key to GPS, then our stop
watches had better be darn good, because if their timing is off by
just a thousandth of a second, at the speed of light, that
translates into almost 200 miles of error!
On the satellite
side, timing is almost perfect because they have incredibly precise
atomic clocks
on board.
Atomic clocks
don't run on atomic energy. They get the name because they use the
oscillations of a particular atom as their "metronome." This form of
timing is the most stable and accurate reference man has ever
developed.
Remember that
both the satellite and the receiver need to be able to precisely
synchronize their pseudo-random codes to make the system work. Our
receivers needed atomic clocks (which costs a lot) nobody could
afford it. The secret to perfect timing is to make an extra
satellite measurement. If our receiver's clocks were perfect, then
all our satellite ranges would intersect at a single point (which is
our position). But with imperfect clocks, a fourth measurement, done
as a crosscheck, will NOT intersect with the first three. Since any
offset from universal time will affect all of our measurements, the
receiver looks for a single correction factor that it can subtract
from all its timing measurements that would cause them all to
intersect at a single point. That correction brings the receiver's
clock back into sync with universal time . Once it has that
correction it applies to all the rest of its measurements and now
we've got precise position of accuracy upto 3-6 mts.
Precise Positioning Service (PPS)
-
Authorized
users with cryptographic equipment and keys and specially equipped
receivers use the Precise Positioning System. U. S. and Allied
military, certain U.S Government agencies, and selected civil
users specifically approved by the U.S. Government, can use the
PPS.
-
PPS
Predictable Accuracy
-
22 meter
Horizontal accuracy
-
27.7 meter
vertical accuracy
Standard Positioning Service (SPS)
-
Civil users
worldwide use the SPS without charge or restrictions. Most
receivers are capable of receiving and using the SPS signal. The
SPS accuracy is intentionally degraded by the DOD by the use of
Selective
Availability.
-
SPS
Predictable Accuracy
-
100 meter
horizontal accuracy
-
156 meter
vertical accuracy
GPS Satellite
Signals
-
The SVs
transmit two microwave carrier signals. The L1 frequency (1575.42
MHz) carries the navigation message and the SPS code signals. The
L2 frequency (1227.60 MHz) is used to measure the ionospheric
delay by PPS equipped receivers.
-
Three binary
codes shift the L1 and/or L2 carrier phase.
-
The C/A Code
(Coarse Acquisition) modulates the L1 carrier phase. The C/A
code is a repeating 1 MHz Pseudo Random Noise (PRN) Code. This
noise-like code modulates the L1 carrier signal, "spreading" the
spectrum over a 1 MHz bandwidth. The C/A code repeats every 1023
bits (one millisecond). There is a different C/A code PRN for
each SV. GPS satellites are often identified by their PRN
number, the unique identifier for each pseudo-random-noise code.
The C/A code that modulates the L1 carrier is the basis for the
civil SPS.
-
The P-Code
(Precise) modulates both the L1 and L2 carrier phases. The
P-Code is a very long (seven days) 10 MHz PRN. The P-Code is
encrypted into the Y-Code. The encrypted Y-Code requires a
classified AS Module for each receiver channel and is for use
only by authorized users with cryptographic keys. The P (Y)-Code
is the basis for the PPS.
-
The
Navigation Message also modulates the L1-C/A code signal. The
Navigation Message is a 50 Hz signal consisting of data bits
that describe the GPS satellite orbits, clock corrections, and
other system parameters.
GPS Data
-
The GPS
Navigation Message consists of time-tagged data bits marking the
time of transmission of each sub frame at the time they are
transmitted by the SV. A data bit frame consists of 1500 bits
divided into five 300-bit sub frames. A data frame is transmitted
every thirty seconds. Three six-second sub frames contain orbital
and clock data. SV Clock corrections are sent in sub frame one and
precise SV orbital data sets (ephemeris data parameters) for the
transmitting SV are sent in sub frames two and three. Sub frames
four and five are used to transmit different pages of system data.
An entire set of twenty-five frames (125 sub frames) makes up the
complete Navigation Message that is sent over a 12.5 minute
period.
-
Data frames
(1500 bits) are sent every thirty seconds. Each frame consists of
five sub frames.
-
Data bit sub
frames (300 bits transmitted over six seconds) contain parity bits
that allow for data checking and limited error correction
Factors
affecting GPS signals:
1.Ionosphere and
Troposphere delays: The signal from the satellite slows down while
passing through the ionosphere and troposphere before reaching the
receiver. GPS system uses an inbuilt model that calculates the
average amount of delay.
2. Signal and
Multipath: While coming from the satellite signal may get reflected
of by high buildings or some other objects before it reaches the
receiver. Thus causing an extra timing error.
3. Orbital
Errors: These errors are also known as ephemeris error. These are
the inaccuracy of satellites while orbiting the earth.
4. Receiver
Clock errors: As we use an ordinary quartz clock in the GPS receiver
it introduces certain timing errors.
Geometric
Dilution of Precision (GDOP):
There are
usually more satellites available than a receiver need to fix a
position so the receiver picks a few and ignores the rest. These
picks should be as far from each other in the space as possible as
for maximum accuracy the spheres should intersect at almost right
angles.
The accuracy
achieved by this GPS system is 3-6 mts. but for Augmented Reality
accuracy in centimeters is required. For that purpose we use
Differential GPS Systems.
Differential
GPS Systems:
It is a way to
correct various inaccuracies. It involves the co-operation of two
receivers out of which one is stationary and the other one is with
the user. The stationary receiver ties all the satellite
measurements into a solid local reference. The reference receiver is
put onto a point that has been very accurately surveyed. It receives
the GPS signal and works in reverse order that is instead of using
timing signal to calculate the position, It uses the known position
to calculate the time and then compare it with the actual time that
the signal must have taken from the satellite to reach the receiver.
This error information is then transferred to the roving receiver.
At a particular moment the stationary receiver doesn’t know which
satellites are being used by the roving receiver. So it calculates
the timing error from all the 24 satellites and sends this
information to the roving one. The roving receiver then uses the
required information to calculate the correction factor and neglect
the rest of information.
Mobile Computing Power
This is the
component of the AR system, which generates all the virtual objects
and merges the real based environment with the virtual objects. It
is a communicator between the AR system and the database server.
APPLICATIONS DOMAINS OF AR SYSTEM
1.
Entertainment
A simple form of
augmented reality has been in use in the entertainment and news
business for quite some time. Whenever you are watching the evening
weather report the weather reporter is shown standing in front of
changing weather maps. In the studio the reporter is actually
standing in front of a blue or green screen. This real image is
augmented with computer-generated maps using a technique called
chroma keying.
2. Military
Training
The military has
been using displays in cockpits that present information to the
pilot on the windshield of the cockpit or the visor of their flight
helmet. This is a form of augmented reality display. SIMNET, a
distributed war games simulation system, is also embracing augmented
reality technology. By equipping military personnel with helmet
mounted visor displays or a special purpose rangefinder the
activities of other units participating in the exercise can be
imaged. While looking at the horizon, for example, the
display-equipped soldier could see a helicopter rising above the
tree line. This helicopter could be being flown in simulation by
another participant. In wartime, the display of the real battlefield
scene could be augmented with annotation information or highlighting
to emphasize hidden enemy units.
3.
Engineering Design
Imagine that a
group of designers are working on the model of a complex device for
their clients. The designers and clients want to do a joint design
review even though they are physically separated. If each of them
had a conference room that was equipped with an augmented reality
display this could be accomplished. The physical prototype that the
designers have mocked up is imaged and displayed in the client's
conference room in 3D. The clients can walk around the display
looking at different aspects of it. To hold discussions the client
can point at the prototype to highlight sections and this will be
reflected on the real model in the augmented display that the
designers are using. Or perhaps in an earlier stage of the design,
before a prototype is built, the view in each conference room is
augmented with a computer-generated image of the current design
built from the CAD files describing it. This would allow real time
interaction with elements of the design so that either side can make
adjustments and changes that are reflected in the view seen by both
groups.
4.Manufacturing, Maintenance and Repair
When the
maintenance technician approaches a new or unfamiliar piece of
equipment instead of opening several repair manuals they could put
on an augmented reality display. In this display the image of the
equipment would be augmented with annotations and information
pertinent to the repair. For example, the location of fasteners and
attachment hardware that must be removed would be highlighted. Then
the inside view of the machine would highlight the boards that need
to be replaced worn by personnel that is attached to an optical
see-through display The wireless connection allows the soldier to
access repair manuals and images of the equipment. Future versions
might register those images on the live scene and provide animation
to show the procedures that must be performed.
5. Consumer
Design
Virtual reality
systems are already used for consumer design. Using perhaps more of
a graphics system than virtual reality, when you go to the typical
home store wanting to add a new deck to your house, they will show
you a graphical picture of what the deck will look like. It is
conceivable that a future system would allow you to bring a video
tape of your house shot from various viewpoints in your backyard and
in real time it would augment that view to show the new deck in its
finished form attached to our house. Or bring in a tape of your
current kitchen and the augmented reality processor would replace
your current kitchen cabinetry with virtual images of the new
kitchen that you are designing.
Applications in
the fashion and beauty industry that would benefit from an augmented
reality system can also be imagined. If the dress store does not
have a particular style dress in your size an appropriate sized
dress could be used to augment the image of you. As you looked in
the three-sided mirror you would see the image of the new dress on
your body. Changes in hem length, shoulder styles or other
particulars of the design could be viewed on you before you place
the order. When you head into some high-tech beauty shops today you
can see what a new hairstyle would look like on a digitized image of
yourself. But with an advanced augmented reality system you would be
able to see the view as you moved. If the dynamics of hair were
included in the description of the virtual object you would also see
the motion of your hair as your head moved
6.Instant information
Tourists and
students could use these systems to learn more about a certain
historical event. Imagine walking onto a Civil War battlefield and
seeing a re-creation of historical events on a head-mounted,
augmented-reality display. It would immerse you in the event, and
the view would be panoramic.
7.Gaming
How cool would
it be to take video games outside? The game could be projected onto
the real world around you, and you could, literally, be in it as one
of the characters. When one uses this system, the game surrounds him
as he walks across campus.
There are
hundreds of potential applications for such a technology, gaming and
entertainment being the most obvious ones. Any system that gives
people instant information, requiring no research on their part, is
bound to be a valuable to anyone in pretty much any field.
Augmented-reality systems will instantly recognize what someone is
looking at, and retrieve and display the data related to that view.
Performance issues of augmented
reality system
Augmented
reality systems are expected to run in real-time so that a user will
be able to move about freely within the scene and see a properly
rendered augmented image. This places two performance criteria on
the system. They are:
-
Update rate
for generating the augmenting image,
-
Accuracy of
the registration of the real and virtual image.
Visually the
real-time constraint is manifested in the user viewing an augmented
image in which the virtual parts are rendered without any visible
jumps. To appear without any jumps, a standard rule of thumb is that
the graphics system must be able to render the virtual scene at
least 10 times per second. This is well within the capabilities of
current graphics systems for simple to moderate graphics scenes. For
the virtual objects to realistically appear part of the scene more
photorealistic graphics rendering is required. The current graphics
technology does not support fully lit, shaded and ray-traced images
of complex scenes. Fortunately, there are many applications for
augmented reality in which the virtual part is either not very
complex or will not require a high level of photorealism.
Failures in the
second performance criterion have two possible causes. One is a
misregistration of the real and virtual scene because of noise in
the system. The position and pose of the camera with respect to the
real scene must be sensed. Any noise in this measurement has the
potential to be exhibited as errors in the registration of the
virtual image with the image of the real scene. Fluctuations of
values while the system is running will cause jittering in the
viewed image. As mentioned previously, our visual system is very
sensitive to visual errors, which in this case would be the
perception that the virtual object is not stationary in the real
scene or is incorrectly positioned. Misregistrations of even a pixel
can be detected under the right conditions. The second cause of
misregistration is time delays in the system. As mentioned in the
previous paragraph, a minimum cycle time of 0.1 seconds is needed
for acceptable real-time performance. If there are delays in
calculating the camera position or the correct alignment of the
graphics camera then the augmented objects will tend to lag behind
motions in the real scene. The system design should minimize the
delays to keep overall system delay within the requirements for
real-time performance.
Summary
Though Augmented
Reality is in a nascent stage and is still not being used in mass.
We feel that with the growing research in AR and shrinking size and
complexity of AR system it is not far away in time where everybody
will own his own AR system |
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