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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: <10958@milton.u.washington.edu>
Date: 11 Nov 90 20:28:44 GMT
References: <10924@milton.u.washington.edu>
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In article <10924@milton.u.washington.edu> frerichs@ux1.cso.uiuc.edu writes:
> motion sensing...
> A very sticky problem.

Too true, but there are interesting special cases which are useful too.
One very important one, which you alluded to, is detecting the position and
orientation of the user's head, so you can adjust the view in a pair of
eyephones.  A relatively cheap way (cheaper than a Polhemus, anyway) to do
that is to have the user wear a special hat with pieces of retro-reflective
tape on it.  Then mount two cheap TV cameras (B&W is fine) from the
ceiling, with a light coaxial with the lens of each or right next to it.

The cameras will see an image which consists almost completely of the
reflections from the tape.  The lights could be infra-red, so as not to
distract the user.  The output of the cameras is run to the controlling
computer where image processing software extracts the position and
orientation of the head from the spots of reflected light; two cameras
provide stereopsis to determine the plane the eyes lie in, so moving the
head up and down, or tilting it, will produce the appropriate parallax.

There are all kinds of variations: a special-purpose DSP unit to do the
image processing, multiple camera setups using color filters or pulsed
lights and shutters on the cameras for multiple simultaneous users, etc.

The technique can be extended to detecting hand position by having the user
wear gloves with reflective stripes on the front and back of the fingers, but
there are problems with detecting finger position and orientation:
    1) The user's hands can be held in positions which hide some or all of
       the fingers from the view of the caneras; you need more cameras,
       including a pair looking up from the floor.
    2) The image-processing task is far more compute-intensive, since
       you're keeping track of more things that move faster.

> we could use sensor arrays, but who want's to limit themselves to VR that
> takes up a whole room...???

1) Nicholas Negroponte :-) After all, his group built the Media Room at MIT.

2) The same people who shell out $5-20K for "home entertainment systems"

3) the military

Ok, Ok, so it was a rhetorical question ...

--
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