Museum exhibit designers often have the dilemma of balancing too much text for the easily bored public with too little text for an interested visitor. With wearable computers, large variations in interests can be accommodated. Each room could have an inexpensive computer embedded in its walls, say in a light switch or power outlet. When a visitor enters the room, the wall computer can wirelessly download museum information to the visitor's computer. Then, as the visitor explores the room, graphics and text overlay the exhibits according to his interests. Taking this example farther, such a system can be use to create a physically-based extension of the ``Web.'' With augmented reality, hypertext links can be associated with physical objects detailing instructions on use, repair information, history, or information left by a previous user. Such an interface can make more efficient use of workplace resources, guide tourists through historical landmarks, or overlay a role-playing game environment on the physical world.
Figure:
Multiple graphical overlays aligned through visual tag tracking. Such
techniques as shown in the following 3 figures can provide a dynamic,
physically-realized extension to the World Wide Web.
In order to experiment with such an interface, the head-mounted camera and display system as shown in Figure 5 is used. Visual ``tags'' uniquely identify each active object. These tags consist of two red squares bounding a pattern of green squares representing a binary number unique to that room. A similar identification system has been demonstrated by [Nagao and Rekimoto, 1995] for a tethered, hand-held system. These visual patterns are robust in the presence of similar background colors and can be distinguished from each other in the same visual field. Once an object is identified, text, graphics, or a texture mapped movie can be rendered on top of the user's visual field as shown in Figure 5. Since the visual tags have a known height and width, the visual tracking code can recover orientation and distance, providing 2.5D information to the graphics process. Thus, graphics objects can be rotated and zoomed to match their counterparts in the physical world. This system is used to give mini-tours of the laboratory space as shown in Figures 6 - 8. Active LED tags are shown in this sequence, though the passive tags work as well. Whenever the camera detects a tag, it renders a small red arrow on top of that object indicating a hyperlink (Figure 6). If the user is interested in that link and turns to see it, the object is labeled with text (Figure 7). Finally, if the user approaches the object, 3D graphics or a texture mapped movie are rendered on the object to demonstrate its function (Figure 8). Using this strategy, the user is not overwhelmed upon walking into a room but can explore interesting objects at leisure.
Figure:
When a tag is first located, a red arrow is used to indicate
a hyperlink.
Figure:
If the user shows interest, the appropriate text labels are displayed.
Figure: If the user approaches the object, 3D graphics or movie
sequences are displayed.
By recognizing and tracking physical objects, the wearable computer can assign computation to passive objects. The virtual version of the object maintained in the wearable computer (or on a wireless network) can then perform tasks on behalf of the user, communicate with other objects or users, or keep track of its own position and status. For example, the plant in Figure 5 may ``ask'' passers-by for water based on a time schedule maintained by its virtual representation. This method is an effective way to gain the benefits of ubiquitous computing [Weiser, 1991] with a sparse infrastructure.
Unfortunately, the visual tag system described above has a limited number of unique codes. To avoid running out of identifiers for objects, an additional sense of location is needed. Outdoors, the Global Positioning System can be used to subdivide the space. However, for indoor use, a system of low-cost, infrared, light-powered beacons was developed to serve this purpose (Figure 9) [Poor, 1996]. Each of these beacons consists of a low-power microprocessor, an infrared transmitter, and an infrared receiver. A solar cell is used to avoid constant battery replacement. These systems are typically mounted under fluorescent light fixtures where they can draw power and effectively cover a region.
Figure:
Environmentally-powered, microcontroller-based IR transponders.
By listening to these IR transmitters, the user's wearable computer can determine its location and load the appropriate set of tag identifiers for the region. In addition, the IR receiver and microprocessor enable location based information uploading. Users can leave location-based, encrypted ``Post-it'' notes or graphics for each other, thus extending the physical hypertext system.
Such a beacon architecture protects user privacy. While the user's computer listens to the beacons to determine its position, it does not reveal its position without explicit instruction by the user. If the user desires to reveal his position, a location daemon can be run over the wearable's wireless data network to process inquiries. Significantly, since the beacons themselves are not networked even in upload mode, there is no remotely monitorable network traffic to reveal the presence of a user at a particular node.