From: gay@mr4dec.enet.dec.com
Subject: SCI: How many dimensions does V.R. have?
Date: Mon, 27 Apr 92 11:11:11 PDT



Which way is up?

I've just spent a day watching a few hundred people using a virtual reality
that I built for The Computer Museum in Boston.

My next month will be spent taking the bare universes presented there
and upgrading them to the final form for the permanent exhibit (opens 
early June).  One of the universes is a "whimsical" one, and designing it
has given me a chance to really explore what the coordinates mean in virtual
space.

I've been very interested by people in the usenet newsgroup alt.cyberspace 
wrestling with the question of how many dimensions there are in V.R.  

The concrete answer is that there are "Three dimensions plus time", just 
like in the real world.  The kicker is that the designer (and maybe the user) 
get to map those three onto anything they want.  Obviously, the farther you 
go from "normal" space, the less the user can rely on their intuition for
navigation.

For instance, maneuvering in a house built in V.R. is instantly 
understandable.  X, Y, Z work just like they have since you were born.  
The only difference is that you can reach the high shelf just by rising up, 
you don't need a ladder (unless the author of the space was being obsessive 
about realism).

Stepping a little bit away from reality, a fractal pattern that can be 
infinitely approached (continually being recalculated for more detail the 
closer you get) can be more confusing.  There are no recognizable objects 
to supply scale and motion maps to infinite "zooming in" on the data instead
of motion across it.

The ultimatly bizarre world would be a universe where the data displayed 
was a function of XYZ position so it changed as you moved (oh, heck, change 
it over time too).  The entire worldview could meld and flow - or jump and 
thrash - as the viewer moved.  It would be seriously disorienting but might 
be very useful for some applications (it could easily approach "virtual 
LSD").  

If the designer adds another control to change the worldview then there 
are four motion dimensions - XYZ position plus worldview at that position.  
Appropriately designed this would be really useful.  For instance,  for 
programming your virtual objects within your virtual world you could have 
the end user's view of the objects, the program view of the objects (as 
3d icons in a 3d programming language), the debugging view, .. etc.).  
It would make sense to the user too, because it fit into the application.  

So, in summary, the number of dimensions is limited to three (plus time) 
for display but can be much higher for maneuvering.  The cost will be in
design time to prevent user confusion.

Eben Gay

gay@mr4dec.enet.dec.com
Software engineering is my vocation, Virtual Reality design is my avocation
"That's the trouble with Reality. It's taken far too seriously" Emotional Fish