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AUGMENTED REALITY K.S.I.T
INTRODUCTION
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. In general it superimposes graphics over a real world environment in real time.
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.
MIXED REALITY
Real Augmented Virtual Virtual environment Reality Reality environment
Milligrams Reality-Virtuality Continuum
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- Tracking and sensing: While in the previous two cases AR had lower requirements than
VE, that is not the case for tracking and sensing. In this area, the requirements for AR are much stricter than those for VE systems. A major reason for this is the registration problem.
2. DEVELOPMENTS
- 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.
- In 1996 developers at Columbia University developed ‘The Touring Machine’
- In 2001 MIT came up with a very compact AR system known as ‘MIThrill’
- Presently research is being done in developing BARS( Battlefield Augmented Reality Systems) by engineers at Naval Research Laboratory ,Washington D.C.
3. WORKING
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
AUGMENTED REALITY K.S.I.T
virtual-reality research, but there's a crucial difference: whereas virtual reality brashly aims to replace the real world, augmented reality respectfully supplements it. Augmented reality is still in an early stage of research and development a
various universities and high-tech companies. Eventually, possibly by the end of this decade, we will see the first mass-marketed augmented-reality system, which one researcher calls
"the Walkman of the 21st century." What augmented reality attempts to do is not only superimpose graphics over a real environment in real-time, but also change those graphics to accommodate a user's head- and eye- movements, so that the graphics always fit the perspective. Here are the three components needed to make an augmented-reality system work:
- Head Mounted Display
- Tracking System
3.1 Head Mounted Displays
Just as monitors allow us to see text and graphics generated by computers, Head- Mounted Displays (HMDs) will enable us to view graphics and text created by augmented- reality systems
There are two basic types of HMDS:
- Optical See-through device
- Video See-through device
3.1.1 Optical see-through displays:
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
Video composition can be done in more than one way. A simple way is to use chroma-keying: a technique used in many video special effects. The background of the
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computer graphic images is set to a specific color, say green, which none of the virtual objects use. Then the combining step replaces all green areas with the corresponding parts from the video of the real world. This has the effect of superimposing the virtual objects over the real world. A more sophisticated composition would use depth information. If the system had depth information at each pixel for the real world images, it could combine the real and virtual images by a pixel-by-pixel depth comparison. This would allow real objects to cover virtual objects and vice-versa.
A different approach is the virtual retinal display, which forms images directly on the retina. These displays, which Micro Vision is developing commercially, literally draw on the retina with low-power lasers whose modulated beams are scanned by micro electro- mechanical mirror assemblies that sweep the beam horizontally and vertically. Potential advantages include high brightness and contrast, low power consumption, and large depth of field.
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
AUGMENTED REALITY K.S.I.T
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 synthesized graphics, with everything focusing at the same apparent distance. At present, a video camera and display are no match for the human eye.
3.2 An optical approach has the following advantages over a
video
approach:
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3.3 Video blending offers the following advantages over optical
blending:
• Flexibility in composition strategies : A basic problem with
optical see-through I that the virtual objects do not completely obscure the real world objects, because the optical combiners allow light from both virtual and real sources. Building an optical see-through HMD that can selectively shut out the light from the real world is difficult. Any filter that would selectively block out light must be placed in the optical path at a point where the image is in focus, which obviously cannot be the user's eye. Therefore, the optical system must have two places where the image is in focus: at the user's eye and the point of the hypothetical filter. This makes the optical design much more difficult and complex. No existing optical see-through HMD blocks incoming light in this fashion. Thus, the virtual objects appear ghost- like and semi-transparent. This damages the illusion of reality because occlusion is one of the strongest depth cues. In contrast, video see-through is far more flexible about how it merges the real and virtual images. Since both the real and virtual are available in digital form, video see-through compositors can, on a pixel-by-pixel basis, take the real, or the virtual, or some blend between the two to simulate transparency. Because of this flexibility, video see-through may ultimately produce more compelling environments than optical see-through approaches.
• Wide field-of-view: Distortions in optical systems are a function of the radial
distance away from the optical axis. The further one looks away from the center of the view, the larger the distortions get. A digitized image taken through a distorted optical system can be undistorted by applying image processing techniques to unwarp the image, provided that the optical distortion is well characterized. This requires significant amounts of computation, but this constraint will be less important in the future as computers become faster. It is harder to build wide field-of-view displays with optical see-through techniques. Any distortions of the user's view of the real world must be corrected opticall y, rather than digitally, because the system has no digitized image of the real world to manipulate. Complex optics are expensive and
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add weight to the HMD. Wide field-of-view systems are an exception to the general trend of optical approaches being simpler and cheaper than video approaches.
• Real and virtual view delays can be matched : Video offers an approach
for reducing or avoiding problems caused by temporal mismatches between the real and virtual images. Optical see-through HMDs offer an almost instantaneous view of the real world but a delayed view of the virtual. This temporal mismatch can cause problems. With video approaches, it is possible to delay the video of the real world to match the delay from the virtual image stream.
• Additional registration strategies: In optical see-through, the only
information the system has about the user's head location comes from the head tracker. Video blending provides another source of information: the digitized image of the real scene. This digitized image means that video approaches can employ additional registration strategies unavailable to optical approaches.
• Easier to match the brightness of real and virtual objects: Both optical
and video technologies have their roles, and the choice of technology depends on the application requirements. Many of the mechanical assembly and repair prototypes use optical approaches, possibly because of the cost and safety issues. If successful, the equipment would have to be replicated in large numbers to equip workers on a factory floor. In contrast, most of the prototypes for medical applications use video approaches, probably for the flexibility in blending real and virtual and for the additional registration strategies offered.
4. TRACKING AND ORIENTATION:
The biggest challenge facing developers of augmented reality is the need to know where the user is located in reference to his or her surroundings. There's also the additional problem of tracking the movement of users' eyes and heads. A tracking system has to recognize these movements and project the graphics related to the real world environment the user is seeing at any given moment. Currently, both video see through and optical see-
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