From: S.A.Bensalem@sheffield.ac.uk
Subject: TECH: VR vs 3D Graphic Animation
Date: Wed, 20 Jan 1993 19:47:51 CST


There's a difference between VR, 3D Graphics, Real-time animation and
Realistic Rendering.

3D Graphics is a field of CS about rendering and representing objects
in 3d in the screen (which is obviously in 2D) this is done through a
viewing pipline which transform the coordinates of any point in the
(World) to coordinates in the screen (which are in 2D). Then the
surface or the line which is described by those points is rendered
actually I know 4 methods:

The wire frame rendering (the first one used by Sutherland in 1965
for his HMD )
The hidden removal rendering (the 1st step leading to
realistic rendering)
The Warnock Algorithms, also called the Constant Shading model,
The Gouraud Algorithms interpolating the intensities of the shading
through the intensities of the Points (called vertex) describing the
surface,
The Phong Modeling using the interpolation of the Normal vector of
each vertex to determine the intensity of the shading,
The Ray tracing here the screen is considered as a ray gun and we
calculate each intersection of each ray with each surface (including
reflexion of the beam in surface and we stop after having  subdivised
enough the beam (on of the parameters of the methods)
And last but not least (a really nice expression 'first one I lurnt
in English' ) The radiosity method WHICH IS VIEWPOINT INDEPENDANT,
and which calculate the radiation (here's the light) emmitted by each
surface in the scenery.

Realistic rendering is a purpose of 3D Graphic, trying to render so
realistic images that we've hard time to distinguish them from a
photography.

3d Animation is a purpose of 3D Graphics, were we render a scenery,
moving , generaly through a script the view point, and projecting
each frame rendered at a rate as similar as the TV rate (24
frames/second), The reader should notice that the viewer, do not have
any influence in what he see, exeptc through the alteration of the
script, and so NOT IN REAL TIME

The real time animation is more interesting, here the viewer can
alterate the coordinates of the viewpoint, and so, here start a kind
of immersivity feeling in the scenery rendered, actually we have this
kind of realtime rendered applied (at the beginning) to the Fly
simulator (which are at the origin of the VR with the Air-Synthetiser
of Zimmerman).

The  VR is more complex its a real time rendering with a powerful
interfacing WHICH ALLOW THE USER TO TOUCH OBJECTS IN THE VIRTUAL WORLD
CALLED ALSO THE CYBERSPACE, and also with the HMD he feel in the VW
where he is working with objects surrounding him.
THERE IS NO DIFFERENCE BETWEEN VIRTUAL REALITY AND ARTIFICIAL REALITY,
check the article from Van Dam in Scientific America 1985 or 1987
about New Computer (I forgot the references but If you're interested
I can found them again.

So if anybody have any comment , let's know as: the knowledge is like
the light, if it's hidden it lost its value (from me)

Virtually,
Bens.