Figure 3.20: Tracker view of the Tracker form
A Tracker is an external device capable of measuring the spatial (3D) position of one or more Sensors. The Available Trackers browser allows you to start a tracker with a given number of sensors. Most of the selections are for various UNC trackers, but only the Fastrak has been tested in the last two years. (The CAVE tracker is started automatically when the CAVE display is used.) The text emulation modes do not start a physical tracker but instead start a `software' tracker with position and orientation values which are never updated. The tracker command can then be used to override the current tracker coordinates and move the tool by hand. Indeed, that is how an external gesture user interface component has been tested with the program.
Press the Start Running button to start the tracker selected in the available browser. Be warned that there is a limitation in our interface to the UNC tracker library which does not allow you to try to start the same tracker more than once. Usually this isn't a problem, but sometimes the tracker doesn't work the first time (this usually happens when VMD previously exited accidentally while connected to the tracker. If the tracker doesn't start but you need to use it, the only thing to do in this case is quit VMD and try again.
The running trackers are listed in the lower browser. Only two things can be done to a tracker if selected: pause or unpause. When paused, none of the sensor coordinates will be updated. There is currently no way to delete a running tracker.