From: jim@baroque.stanford.edu (James Helman)
Subject: Re: TECH: goggle/tracker/tactile product reviews
Date: 29 Feb 92 00:53:54
Organization: Stanford University



In article <1992Feb28.163902.10887@u.washington.edu> bcsaic!chrise@cs.
washington.edu (Chris Esposito) writes:

   1. New Goggles - the Cyberface 2 from LEEP Optics appears to have it
   all over the VPL HRX - wider field of view, comparable pixels/degree,
   greater apparent resolution 1481 H by 84 V (although I don't think I
   completely understand how they derive these "equivalent linear
   resolution" numbers), both RGB and NTSC input, and a SUBSTANTIALLY
   lower price ($8K vs $50K).

In principle, it's a great idea, but you have to be careful how you
use them.

The Cyberface 2 provides what LEEP claims is "equivalent linear
resolution" by more dramatically increasing magnification as a
function of angle.  Thus pixels in the center appear more closely
packed that at the periphery.

This is almost what you want, except that ideally the region of high
pixel density would track the eye's fovea.  Most of the familiar
headmounts have this distortion to some extent, it's just a little
more extreme on the Cyberface 2.  So if you want the best resolution,
you need to turn your head to match your gaze direction.  That's not
so bad really.  Well worth it given the limited resolution LCDs we
currently have to work with.  Great idea so far.

Problem: if you want straight lines away from the center to appear
straight, you need to render them as curves.

One way of doing this without sacrificing performance is to use LEEP's
camera optics, which match those of the headmount (this also buys you
correction for chromatic aberration), and put video cameras in front
of your hi-res graphics monitors.

Alternately, you can predistort your geometry and then render it with
standard 3D graphics hardware.  This requires subdivision and
elimination of T-vertices for polygons.  The performance penalty for
this might be unacceptable.  Of course, you could always build your
own 3D graphics system capable of doing the proper rendering.

OK, you might say.  I'll live with curvy things in the periphery.

Whoops.... another problem.  The Cyberface 2 also diverges the optics
of the two eyes more than previous headmounts (hence that nice wide
field of view).  This puts the left edge of your right eye's field of
view near the middle of your left eye's and vice versa.  Thus looking
straight ahead, you have one eye seeing highly distorted geometry and
the other seeing less distorted geometry.  Oh-oh.  Image registration
and stereo problems.....

Going the LEEP CF2/camera/optics route probably costs less than an
HRX.  It also eliminates the need for scan converting to NTSC.  But
there's also the issue of whether a 1024x1280 display has enough
pixels to both fill the camera's field of view and give adequate
resolution at the center.... but this posting is way too long already.

The bottom line is that there's no free lunch.....

Jim Helman
Silicon Graphics				SGI:  (415) 335-1151
(jimh@surreal.asd.sgi.com)			FAX:  (415) 591-8165

"The power of the computer is locked behind a door with no knob."
							-B. Laurel