From: kpc@panix.com (Kevin Centanni)
Subject: Re: Question about SEGA's Time Traveller mirror effects
Date: Wed, 15 Jan 1992 00:14:01 GMT
Organization: PANIX - Public Access Unix Systems of NY



In article <1992Jan13.031723.23513@milton.u.washington.edu> dither@vms.
macc.wisc.edu (Dennis Adams) writes:

>I am not sure if the "reflection" on the virtual ground
>is an artifact of the system.  It was present in the demo, and it is
>present in the SEGA game.
>
>The mirrors cause a "virtual image" of the CRT face in the space above
>the protective plexiglass.  You can reach out and put your hand where
>the image appears to be.
>
>Another interesting aspect of the system is the fact that the image
>always seems to be facing you, regardless of where you stand (left or
>right).
>
>Anyone know the optics involved?  It would be fun to build a small version.

An update:

Using some cheap, plastic, convex mirrors i bought down on Canal Street
here in New York City, I've created a crude, but effective '3D Display'.
It's made out of cardboard boxes, black posterboard, and gaffers tape.
Using some FLI files created in AutoDesk's 3d-Studio and Animator, I've
been able to get a pretty realistic effect.  A small (8" diagonal) monitor
is hidden under a horizontal surface.. the monitor is facing AWAY from the
user.  Approximately 12" in front of the monitor is a 12" convex mirror
(firmly attached to a camcorder tripod with double-sided-foam-tape) -
this mirror 'assembly' is sheilded from the light by another cardboard
box sitting on it's side (the open end is facing the user and opens right
into the area where the monitor is sitting).  Using a couple of sheets of
ND (neutral density plastic film) framed by black poster-board, I have
been able to get the light levels inside of the boxes to a point where
you really can't tell where the mirror or monitor ends.  If your image
is on a black background, it just sort of appears to 'float' in space...
the effect is heightened by the use of the convex mirror - as you move
your head from side to side, the curvature of the mirror allows the image
to still be reflected off of the monitor properly.  I've found that it
works better if the mirror is just far back enough to be a SLIGHT bit out
of focus.

My next step is to get a larger convex mirror (down on Canal Street, FOUR
stores stock them up to 48" diameter!) and cut it so that it completely
fills the interior of my cardboard box... the way it's set up now, if you
move your head more than 6 inches or so, the mirror is not wide enough
to still reflect the monitor's image.

Yes, in the SEGA game, the images on screen look like they're standing
on a piece of black plexiglass (although the effect was probably created
digitally in the edit room).  That reflection effect greatly enhances the
3D realism.  We've begun to play around with similiar visual clues using
3D-Studio.

Now, all I have to do is make the IR positioning system!! :)

(Has anyone else played with silly, plastic, convex mirros?)



-- 
Kevin P. Centanni
Corporate Communication Group
212.268.2100
kpc@panix.com       {cmcl2,apple}!panix!kpc