The Upoint Tracker

The Tracker

The Upoint Tracker

The core of a Upoint system is the tracker. The technology used needs to be able to provide information on both the orientation and the position of the handheld remote (in some coordinate system), measured relative to some fixed coordinate system, in a fast and reliable way.

Many technologies may meet the requirements above. For example, orientation measurement may be based on the fact that gravity and the Earth's magnetic field are locally uniform. Position measurements may conceivably be based on technologies involving ultrasonics, electromagnetics, magnetics, inertia, LED/CCD units, etc - or combinations of the above.

For the Upoint prototype a magnetic tracker was chosen to form it's core. One of the reasons is that magnetic trackers only need one transmitter (the 'base-station') and one relatively small receiver (incorporated in the remote) to give simultaneous and instantaneous information on both position and orientation of the tracked object relative to the base-station (i.e., the magnetic transmitter). Specifically, the Fastrak system (manufactured by Polhemus) was used to construct the prototype around. Fastrak features an operating range of 7-8’ radius around its base-station, within which the user can move whilst pointing to and interacting with the display – more powerful systems are available.

The Fastrak Unit, as manufactured by Polhemus.

It should be realized that the accuracy of Fastrak (arguably the work-horse in the magnetic tracking arena) is far better than what is needed for the Upoint invention. Indeed, Upoint will still work quite adequately with a tracking system that has a positional accuracy of several inches up to 1-2 ft, and an accuracy in orientation up to several degrees. The reason for this is that not too large discrepancies between true point-of-aim and calculated point-of-aim will in general not be noticed by the presenter, since the cursor itself provides the only visual feedback.

As may be anticipated from the section describing the operation of the device, the accuracy in orientation is far more important than the accuracy in position. To see this, note that an error in position measurement will translate 1-to-1 to an error in point-of-aim calculation, while an error in orientation measurement will show up in a magnified way in the calculated point-of-aim. For this reason, it makes sense to use a combination of an active-source and an Earth-field tracker. That is, position sensing is probably best done using an active EM transmitter (like the Fastrak system), but orientation sensing should be done based on the Earth's magnetic and gravity fields (for more info on Earth-field trackers: see the IDLpoint invention)

The first order of business of the Upoint company would be to farm-out a research project with the goal to arrive at a blueprint for a cheap tracking device that serves Upoint's purposes, possibly by combining AC or DC magnetic tracking with MEMS devices (or Honeywell's electronic compass solutions) that measure orientation with respect to the Earth's magnetic and gravity fields.