Chapter 6 Position Sensors 21
Reducing Tracker Jitter
Electromagnetic trackers are prone to jitter. This effect can be subtle, or hor-
rendous, depending on the conditions in which the tracker is used. A good
place to start is with a diagnostic setup. Place the receiver and transmitter near
each other and well away from other possible sources of interference. We find
it is easiest to diagnose if we view a virtual scene on a large monitor and watch
for image jitter in that scene. Don’t use the HMD display for this; it’s hard to
move equipment while looking into an HMD and impossible to test for HMD
interactions. While watching the monitor, move the transmitter and receiver
apart and watch the jitter increase.
ambient jitter.
You should now-have a fair sense of your
Now bring suspect pieces of electronics or metal into the area of the receiver.
Turn the electronics on and off. Move the transmitter/receiver farther apart and
the electronics closer to the receiver, then try again. Notice how objects cause
warpage of the electromagnetic field--causing the sensor output position to
change, as well as jitter.
Bring the FS5 near the receiver. Notice that the jitter becomes severe when the
receiver is near the CRTs or the circuitry at the rear end of the HMD. At the
tracker mount, the sensor should be nearly unaffected by the HMD.
Try the following jitter reduction steps if you are having problems:,
1.
2.
3.
4.
Keep the source and receiver as close together as possible. More than
anything else you do, the distance from source to receiver will effect you
performance.
Turn off or move away equipment that causes interference. Monitors and
computers (especially computers that are partially open) produce fields that
will add jitter to your tracker.
Mount the transmitter above the receiver. This will maintain a clearer line
of sight from transmitter to receiver and reduce field warpage due to metal
parts of the FS5.
If the I-IMD seems to be a significant source of jitter or field warpage,
mount the receiver on a plastic arm that moves it farther from the electronics
of the HMD. Use the diagnostic setup described above to figure out the po-
sition that works best for your situation.
