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From: brucec%phoebus.labs.tek.com@RELAY.CS.NET (Bruce Cohen;;50-662;LP=A;)
Newsgroups: sci.virtual-worlds
Subject: Re: rambling on motion
Message-ID: <11016@milton.u.washington.edu>
Date: 12 Nov 90 17:59:21 GMT
References: <10924@milton.u.washington.edu> <10958@milton.u.washington.edu>
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On a cheaper note, the following idea came out of a conversation I had with
Jim Kajiya of CalTech a couple of years ago.  I'd been showing him the
liquid-crystal shutter stereo display system on the Tektronix 3D graphics
workstation, which prompted him to mention some work he wanted to do on the
use of vertical parallax in depth cueing.  He explained that he wanted to
have the system detect the vertical position of the viewer's head with
respect to the display screen center, then vary the eye-point of the
picture to match, so that you see changes in parallax when you bob your
head.  This would not require stereo, but it would make stereo even more
effective.

We knocked around some ideas of how to detect the viewer's head position,
and at some point we realized that the glasses we use for the stereo
display were the answer.  These are passive glasses, just polarizing
filters, with the shutter over the screen, so the glasses are light and
unobtrusive.  But they do uniquely determine the viewer's head position and
orientation.  Rather than put a heavy Polhemus sensor on the glasses (and
have to put the screen on the floor because no one could raise their
head :-)) we thought about putting a reflective strip on the glasses, with
some easily recognizable pattern, perhaps akin to the UPC bar code clock
pattern.

Sensing the pattern could be done by a camera but it might be even simpler
to have a scanner like a check-out stand bar-code reader and a set of
light detectors with half-silvered mirrors in front of them.  The light
from the scanner is split and sent to all the detectors, where it bounces
off the half-silvered mirrors to go towards the viewer.  The detector picks
up the returned light, and its output signal can be convolved with the
pattern on the reflective strip over one scanning frame to determine the
angle of the line from the detector to the glasses relative to the zero
point angle of the scan.  Alternately scanning horizontally and vertically
gives you a solid angle; Two detectors gives you triangulation for head
position and tilt.
--
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Speaker-to-managers, aka
Bruce Cohen, Computer Research Lab        email: brucec@tekchips.labs.tek.com
Tektronix Laboratories, Tektronix, Inc.                phone: (503)627-5241
M/S 50-662, P.O. Box 500, Beaverton, OR  97077