From: mike@x.co.uk (Mike Moore)
Subject: Re: head tracking
Date: Fri, 06 Dec 1991 12:07:27 GMT
Organization: IXI Limited, Cambridge, UK



In article <1991Dec3.204005.11220@milton.u.washington.edu> brucec@phoebus.
labs.tek.com (Bruce Cohen) writes:

>In article <1991Dec2.152517.17607@milton.u.washington.edu> jim@baroque.
>stanford.edu (James Helman) writes:
>
>>    2) Head mounted cameras tracking a set of LEDs in the ceiling.
>> 
>> There's no comparison.  #2 give very big motions on the image plane.
>> But in order to get any kind of angular resolution out of #1, you'd
>> need to have cameras which could zoom and pan to track the head, or
>> lots of fixed cameras with narrow fields of view.  Otherwise, the
>> change in positions of the LEDs on the image would be too small for
>> any kind of decent resolution.  Also, if you want wide area tracking,
>> you'd need lots of cameras in the ceiling.  LEDs are cheaper.
>
>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.

Why all this big deal about cameras?  If all you want is motion tracking
then a simple set of LED's in the ceiling, minute mirrors on the user and
sensitive Photo Voltaic cells mounted all over the room surface should
suffice surely?  Another method altogether would be to criss-cross the room
with (very) low power lasers with as small a gridding (cubing?) as you
required to measure movement, get the user to wear a mirror suit that had
specific reflectance qualities for each area of the body you were interested
in (e.g. colour, intensity) and have some system to recognise which laser
hit which part of the body and landed where.


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