From: dstamp@watserv1.waterloo.edu (Dave Stampe-Psy+Eng)
Subject: Re: head tracking
Date: Wed, 4 Dec 1991 14:05:07 GMT
Message-ID: <1991Dec4.140507.2645@watserv1.waterloo.edu>
Organization: University of Waterloo



brucec@phoebus.labs.tek.com (Bruce Cohen) writes:

>OK, but couldn't you get even more change by mounting lots of LEDs in
>the room, along with a few cameras, and then putting mirrors on the
>user?  (ignore my previous posting about retro-reflective mirrors; they
>won't help with the field of view problem).  If a mirror rotates by N
>degrees, the beam of a given LED reflected in that mirror sweeps 2N
>degrees, twice was much as a camera or LED would.

For any decent sized flat mirror, you'd have to have the LEDs spaced
about the width of the mirror apart.  Since you need to be able to control 
ALL the LEDs, this ends up being a VERY expensive method.  You could 
use a semispherical mirror to get around that, but still, think about
it.  You'd be measuring angle by which LED appeared in the mirror, 
as there's only be a TINY range of movement of the LED in the mirror
before the light dot moved from one side to the other.  Also, how
are you going to seperate movements of the mirrors from rotation of
the mirrors, if you try to enhance the angular resolution that way?
Don't think it can be done...

The other option is the multi-LEDs-per-body-part system.  This is on the
borderline of workability for the head (about 1 degree resolution in
a 1.5 x 1.5 m workspace with 30 cm between LEDS) and you dont care too
much about the orientation of anything else till you get to the wrists
(other joint angles can be deduced from position of other segments
of the body).  The wrists seem to be a bigger problem, since hands
don't lend themselves well to the LED methods except in special cases.

--------------------------------------------------------------------------
| My life is Hardware,                    |                              | 
| my destiny is Software,                 |         Dave Stampe          |
| my CPU is Wetware...                    |                              | 
| Anybody got a SDB I can borrow?         | dstamp@watserv1.uwaterloo.ca |
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