From: Robert_Grant.LAX1B@xerox.com
Newsgroups: sci.virtual-worlds
Subject: TECH: Virtual Reality Systems Discussion
Date: 15 Sep 92 22:26:22 GMT
Organization: University of Washington
Originator: hlab@milton.u.washington.edu



Hi all,

[Apologies to BITNET VIRTU-L Listservers who get this twice, I sent it
there first, and now it appears that I should have sent it here! :-)]

I just wondered what had happened to the discussion about creating a
*good* virtual reality system (networked, client-server stuff)? There
was talk about a month back about handling coordinates and portals
etc., but it appears to have dried up :-(. I was finding it all quite
fascinating! :-)

Some people also mentioned theories about various layered approaches
to the VR system: would it not be interesting to try to come up with
an acceptable hierarchy of layers and then enable discussions of the
features those layers should have? I know many people probably feel
that it is too early to try to constrain thinking and I agree in large
part, but I also feel that without some guidelines people (especially
me :-) have great difficulty thinking about parts without being
swamped by the whole!

If people think this might be a good idea, then here's my suggestion
for the VR system layers:

Layer 4 Interaction Layer
                        
                        This would be where we would interact with the objects
                        around us. Must be independent of implementation
Layer 3 Object Layer
                        This would be where the objects reside; they must be
                        independent of the implementation.
Layer 2 System Layer
                        This layer would provide the general management of
                        reality we are now in, it provides all the
communication
                        services, and "reality checking" services etc. Should
                        also
                        be independent of the implementation Layer1     
Interface Layer
                        Provides the system layer with all the functions that
                        are
                        needed to make the system run!

Layer 0 Device Dependant Layer

                        Self explanatory!

What do people think - I'm sure this needs lots of discussion :-) ;-)


I got a response from Steve Hayden on BITNET <shayden@bnr.ca> who, in
drastic summary, said:

>>It would be nice if the VR layering could fit nicely into some
     existing model such as the OSI 7 layer model<<

My response:

I agree absolutely - no need to reinvent the wheel!! This is how I
would see it all fitting together:

Basically the ISO model would fit within the Interface / Device
Dependent Layer parts of the proposed "Virtual Layer Cake" :-)

Virtual Layers          Iso Layers
------------
INTERACTION          I
------------
OBJECT       I
---------------------------
SYSTEM       I  APPLICATION
---------------------------
INTERFACE            I  PRESENTATION
---------------------------
DEVICE DEP.          I  SESSION
                     ---------------
                     I  TRANSPORT
                     ---------------
                     I  NETWORK
                     ---------------
                     I  DATA LINK
                     ---------------
                     I  PHYSICAL
                     ---------------

I see the VR system as going dramatically beyond the traditional
Application Level of the ISO model - that has been produced for
non-distributed operating systems, whereas the VR system is
essentially distributed; that's why the comms protocol fits below the
VR layers, it's the foundation!

My name for layer 0 is not particularly good perhaps "Real World
Layer" would be more appropriate ? :-)

Robert.  RGrant.LAX1B@Xerox.com

Of course these are all my own foolish ramblings!!
Newsgroups: sci.virtual-worlds