From: drascic@ie.utoronto.ca (SpIke)
Subject: Re: How do I generate the two views for a 3d image (LCD glasses)
Organization: University of Toronto, Department of Industrial Engineering
Date: Wed, 26 Aug 1992 18:04:15 GMT

busey@milton.u.washington.edu (Thomas Busey) writes:
>  I'm designing a stereo VR system to do some psychology research on the
>contribution of depth information for the perception of direction and
>speed of motion. 

>  I'm using a (low-tech, I know) Mac II with a graphics system that gives
>me control over the "camera" of a 3-d presentation system.  I can
>control position, yaw, pitch, roll, focal length, etc. of the eye.

>  My question is how to generate the left and right images for a
>stereo display.  Three transforms come to mind:  1) pan the "camera" left
>and right about 10 degrees (or less) 2) dolly the camera left or right
>perpendicular to "forward" 3) dolly the camera one way and pan back the
>other simultaneously, which I think is what they eyes do relative to the
>nose.  I may be missing the actual transform entirely- I haven't given this
>too much thought yet. 

The person who has done the most work on the distortion issues of
stereoscopic displays is Dan Diner.  He's written a lot of stuff on this.

You are partly right, in that the transformation you choose is dependent on
your purposes.  The work we are doing here at the University of Toronto
involves combining computer generated stereoscopic graphics (SG) with
stereoscopic video (SV), resulting in an "augmented reality", "virtual
reality", and/or "multi-media" display. :-)  Anyway, for our purposes, the
graphics must match the view from the cameras, and so we use a "converged
camera" model, where the two cameras are separated by a certain distance
(which is situation dependent), and where the cameras converge at a certain
distance.  (The convergence point determines where the SG appear relative to
the glass surface of the monitor.  Everything between the cameras and the
convergence point appears in front of the monitor, while everything on the
far side of the convergence point appears inside or behind the monitor.)

This model works great for SV and for SV+SG (our combined system).  We've
done a lot of work with both, and have had great success.

However, as Diner and others point out in miriad papers, there are distortions
inherent in this approach, as well as vertical disparities.  Distortions
aren't a problem, per se; they can be used to make a more useful (if less
stricly "realistic") image.

Another approach uses a parallel camera configuration.  The problem with
this is that everything appears in front of the monitor, making it pretty
awful to use.  On the other hand, some distortions and vertical disparities
are reduced.

In order to move the display space back with respect to the monitor, you can
manually slide the left and right views, thereby creating a
psuedo-convergence point.  You can slide the views at the display
(electronicially, or through software), or at the camera, by shifting the
CCD sensor relative to the lens.

Doing this gives you a good relatively-distortionless image.  See "A New
Definition of Orthostereopsis for 3-D Television", by Daniel B. Diner, 1991
IEEE International Conference on Systems, Man (no women, though) and
Cybernetics, 13-16 Oct 91, 1053-1058.

Hope this helps.

	David Drascic
	Dept of Industrial Engineering
	University of Toronto

	drascic@ie.utoronto.ca
Newsgroups: alt.3d