From: Jayson Raymond <jraymond@BBN.COM>
Subject: Re: sci.virtual-worlds
Date: Wed, 13 Nov 91 12:08:49 PDT



Dave Stampe and Craig Hubley write:

>> (Craig Hubley) you
>>render furiously, starting with gross shapes and going to more detail as
>>you get background objects roughed in... when he moves his head you 
>>rapidly do it again... anyone else get angry when you want to flip a view of
>>some complex object around 60 degrees and the stupid draw/CAD-CAD/anything
>>software insists on rendering the entire thing in full detail at each 5 
>>degree increment ?

 Arghhh yes! Definitely yes. 

>(Dave Stampe)
>Problem with variable-resolution is that it's unnatural if done
>indisciminantly.  Does the world "decay" when you move your head, 
>then slowly recover?  Of course not.  You'll see it too, since
>your eyes can see very well during head movements, due to nystagmus
>stablization.  

While the world may not actually decay as you turn your head,
your ability to detect details in moving objects does. This is in fact
being exploited by HDTV/video compression researchers trying to get the
most bang (aesthetic appeal) for the byte. Even the Mac and other
windowing systems recognize that while something in is in motion, you
don't have to draw the whole thing to clue the user, such as in the acts
of moving or closing windows. 

What Craig describes is an approach I have seen before, where a very
course image is rendered, and continually refined as time goes on (if I
recall correctly, a UW professor was working on just such a system for
medical imaging). It has very powerful potential, and I would caution
against it's quick dismissal. 

>Don't get me wrong: I'm not against variable-resolution objects-- in
>fact, I consider them essential to the implementation of low-end
>VR.  But only small, distant objects can be considered for simplifying,
>if we're not to have a hallucinatory, changing world.

Again, not only are Level-of-Detail changes useful (simplifying distant
objects), but so are near ground moving objects, if you can't spare the
CPU's to render them. Another instance of variable resolution worlds is
the variable acuity systems by the large simulator companies (GE/E&S),
which track the eye and give high resolution insets where one is looking
(though perhaps this has already been covered, before I caught on to
this thread).

--Jayson

Jayson Raymond
jraymond@bbn.com

BBN Advanced Simulation