From: jpc@tauon.ph.unimelb.edu.au (John Costella)
Subject: Re: TECH: Angular Velocity Sensors in VR
Date: Wed, 5 May 93 10:24:21 EET


> I have recently come across an angular velocity sensor (AVS), which is
> used to measure the deflection of a video camera and then adjust the
> lens to compensate for the shake.  These AVSs seem as though they
> would be graet in HMD tracking, no electric fields needed etc.  I was
> wondering if anybody has ever used them in such a way, and if so what
> were the results and errors associated with them.  I'd like to know a
> bit more before I purchase a sensor.

Whoa!---watch out here about extrapolating the idea.

The problem is that angular velocity sensors measure just that---angular
velocity. They don't measure angular position. Thus you have to integrate
the measurements to get angular position. Integration = boost low
frequency noise; the net result is that the calibration of the `zero
angle' direction (dc) drifts with time.

Video cameras couldn't care less about drift: all that they care about
is smoothing out the HIGH-frequency shakes. In fact, in order for them
to work, the circuitry will have a *high-pass filter* (on the order of
small fractions of a second) so that it smooths only the high-frequency 
jitters, not the panning action itself!

Economy dictates that they will only install angular velocity sensors
sufficient to do the job, i.e. they won't (usually) over-engineer.
This probably means that the low-frequency response of the device will
be lousy, especially since angular velocity is harder to measure as
it gets smaller. So you could definitely use it to correct your HMD
for wobbly-cam, but it may make a very disappointing tracker.

> Mathew Verdouw
> R.M.I.T Melbourne Australia.
> email s914502@godzilla.cgl.rmit.oz.au
 
Hey you're just down the road. Give me a yell, 543-7795 :-)

John

----------------------------------------------------------------------------
John P. Costella              School of Physics, The University of Melbourne
jpc@tauon.ph.unimelb.edu.au          Tel: +61 3543-7795;  Fax: +61 3347-4783
----------------------------------------------------------------------------