1. a t m o s p h e r e s e n s o r t e c h n o l o g i e s
atmosphere is a collaboration of the aesthetics + computation group,
the Responsive Environments group and Steelcase Inc.
Overview
The Sensors
Infrastructure
Related Works
Atmosphere presents a large cloud of information on a wide presentation screen that can be manipulated by three handheld devices mounted on plinths within the gallery space. The visitor takes one of the devices and physically moves it within a designated area, thereby manipulating the information presented both on the screen and the larger projection.
All three devices are able to navigate the same information, but each at a different level--macro, medium, and micro. The interface presents not only the discrete information but also an organic ensemble view of the intensity of each project and the workload impact distributed across time. The interface presents an alternative visual format to the folders and windows to which we have become accustomed through computer usage.
A simple magnetic coupling system was used to track the position and orientation of the handheld device. Inside each of the cases, three inductive tags are arranged about the PDA to provide the three axes of sensitivity. Signals are magnetically coupled into these tags from coils embedded within the forms shown at left. These coils are driven in round-robin format with a 170 kHz sine wave. The tags are tuned to this same frequency.
The magnitude of the coupling is inversely proportional to the distance from the coils and proportional to the sine of the angle between the tag and the normal of the coil. Using the magnitude of the recovered signal from each tag for each coil, it is possible to calculate both the position and (unsigned) orientation of the device relative to the reference frame formed by the coils.
To be able to properly interpret the data for the tags in each individual PDA case, it is necessary to have the whole system running synchronously. A master driver board was constructed to fill this role. This board is responsible for generating the 170 kHz sine wave, and distributing it to each of the pedestals. One coil on each of the pedestals is on at any given time. At the pedestal itself, the drive signals are amplified and fed into the individual coils.
The data from each PDA case is then sent back to a master computer using a serial link. Since this master computer also instructs the master driver to pulse, the collected data can now be lined up with the appropriate coil before analysis. Note that it is possible to decouple the drive and collection portions of the system to make a stand-alone PDA which knows its location, though sync must then be established in another fashion.
Magnetic tracking systems are well known, and have been used in a wide variety of situations, mostly for motion capture. This sensor system, especially with its ability to be used wirelessly, is directly related to two other systems, one from the Media Lab, and one commercial.
This system is effectively a scaled-down version of the Polhemus magnetic tracker (top image), which uses pulsed magnetic fields to track the position of the tags (small white cube on coiled wire) relative to the main coils (big black cube). This system provides high accuracy at the cost of a fixed connection.
Another wireless tracking system built at the Lab is the swept RF tracker (bottom image). This system detects the presence of passive tags with its space, and then performs a similar calculation to the atmosphere system to determine position and (unsigned) orientation.