02-01-2013, 11:09 AM
A Survey of Augmented Reality
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Abstract
This paper surveys the field of Augmented Reality, in which 3-D virtual
objects are integrated into a 3-D real environment in real time. It describes the
medical, manufacturing, visualization, path planning, entertainment and military
applications that have been explored. This paper describes the characteristics of
Augmented Reality systems, including a detailed discussion of the tradeoffs between
optical and video blending approaches. Registration and sensing errors are two of the
biggest problems in building effective Augmented Reality systems, so this paper
summarizes current efforts to overcome these problems. Future directions and areas
requiring further research are discussed. This survey provides a starting point for
anyone interested in researching or using Augmented Reality.
Introduction
Goals
This paper surveys the current state-of-the-art in Augmented Reality. It
describes work performed at many different sites and explains the issues and
problems encountered when building Augmented Reality systems. It summarizes the
tradeoffs and approaches taken so far to overcome these problems and speculates on
future directions that deserve exploration.
A survey paper does not present new research results. The contribution comes
from consolidating existing information from many sources and publishing an
extensive bibliography of papers in this field. While several other introductory
papers have been written on this subject [Barfield95] [Bowskill95] [Caudell94]
[Drascic93b] [Feiner94a] [Feiner94b] [Milgram94b] [Rolland94], this survey is more
comprehensive and up-to-date. This survey provides a good beginning point for
anyone interested in starting research in this area.
Definition
Augmented Reality (AR) is a variation of Virtual Environments (VE), or
Virtual Reality as it is more commonly called. VE technologies completely immerse
a user inside a synthetic environment. While immersed, the user cannot see the real
world around him. In contrast, AR allows the user to see the real world, with virtual
objects superimposed upon or composited with the real world. Therefore, AR
supplements reality, rather than completely replacing it. Ideally, it would appear to
the user that the virtual and real objects coexisted in the same space, similar to the
effects achieved in the film "Who Framed Roger Rabbit?" Figure 1 shows an
example of what this might look like. It shows a real desk with a real phone. Inside
this room are also a virtual lamp and two virtual chairs. Note that the objects are
combined in 3-D, so that the virtual lamp covers the real table, and the real table
covers parts of the two virtual chairs. AR can be thought of as the "middle ground"
between VE (completely synthetic) and telepresence (completely real) [Milgram94a]
[Milgram94b].
Motivation
Why is Augmented Reality an interesting topic? Why is combining real and
virtual objects in 3-D useful? Augmented Reality enhances a user's perception of and
interaction with the real world. The virtual objects display information that the user
cannot directly detect with his own senses. The information conveyed by the virtual
objects helps a user perform real-world tasks. AR is a specific example of what Fred
Brooks calls Intelligence Amplification (IA): using the computer as a tool to make a
task easier for a human to perform [Brooks96].
At least six classes of potential AR applications have been explored: medical
visualization, maintenance and repair, annotation, robot path planning, entertainment,
and military aircraft navigation and targeting. The next section describes work that
has been done in each area. While these do not cover every potential application area
of this technology, they do cover the areas explored so far.
Medical
Doctors could use Augmented Reality as a visualization and training aid for
surgery. It may be possible to collect 3-D datasets of a patient in real time, using
non-invasive sensors like Magnetic Resonance Imaging (MRI), Computed
Tomography scans (CT), or ultrasound imaging. These datasets could then be
rendered and combined in real time with a view of the real patient. In effect, this
would give a doctor "X-ray vision" inside a patient. This would be very useful during
minimally-invasive surgery, which reduces the trauma of an operation by using small
incisions or no incisions at all. A problem with minimally-invasive techniques is that
they reduce the doctor's ability to see inside the patient, making surgery more
difficult. AR technology could provide an internal view without the need for larger
incisions.
AR might also be helpful for general medical visualization tasks in the
surgical room. Surgeons can detect some features with the naked eye that they cannot
see in MRI or CT scans, and vice-versa. AR would give surgeons access to both
types of data simultaneously. This might also guide precision tasks, such as
displaying where to drill a hole into the skull for brain surgery or where to perform a
needle biopsy of a tiny tumor. The information from the non-invasive sensors would
be directly displayed on the patient, showing exactly where to perform the operation.
Annotation and visualization
AR could be used to annotate objects and environments with public or private
information. Applications using public information assume the availability of public
databases to draw upon. For example, a hand-held display could provide information
about the contents of library shelves as the user walks around the library
[Fitzmaurice93] [Rekimoto95a] [Rekimoto95b]. At the European Computer-Industry
Research Centre (ECRC), a user can point at parts of an engine model and the AR
system displays the name of the part that is being pointed at [Rose95]. Figure 7
shows this, where the user points at the exhaust manifold on an engine model and the
label "exhaust manifold" appears.
Robot path planning
Teleoperation of a robot is often a difficult problem, especially when the robot
is far away, with long delays in the communication link. Under this circumstance,
instead of controlling the robot directly, it may be preferable to instead control a
virtual version of the robot. The user plans and specifies the robot's actions by
manipulating the local virtual version, in real time. The results are directly displayed
on the real world. Once the plan is tested and determined, then user tells the real
robot to execute the specified plan. This avoids pilot-induced oscillations caused by
the lengthy delays. The virtual versions can also predict the effects of manipulating
the environment, thus serving as a planning and previewing tool to aid the user in
performing the desired task. The ARGOS system has demonstrated that stereoscopic
AR is an easier and more accurate way of doing robot path planning than traditional
monoscopic interfaces [Drascic93b] [Milgram93]. Others have also used registered
overlays with telepresence systems [Kim93] [Kim96] [Oyama93] [Tharp94] [Yoo93].
Figure 10 shows how a virtual outline can represent a future location of a robot arm.