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environment in which the user becomes a participant with the computer in a virtually real
Emphasizing the interaction and interface aspects, Stone in 1995 regarded virtual reality
as an “interface between human and computerized applications based on real-time, three-
dimensioned graphical worlds”. Most VR systems therefore try as much as possible to provide
users with the capability to interact with the system in the same way as their interaction
with objects and events in the real world. Essentially, the basic objective is to provide a
shared 3-D experience between people and computer with certain unique capabilities that
allows the user to experience an artificially generated environment as if it is real.
To extend the impact of realistic visualization and experience, Isdale in 1995 defined
virtual reality as “a way for humans to visualize, manipulate and interact with computers
and extremely complex data”. Such visualization is not limited to just graphics, but may
also takes on a more general form of visual, auditory or other sensual outputs to the user.
According to these definitions, a virtual reality application has the following inherent
important features.
Interactive: Realistic interactions with virtual objects via data gloves and similar
devices to support the manipulation, operation, and control of objects in a virtual
Realtime: Viewing, interactions, and other related tasks have to be executed with
real-time response so that the resulting illusion of being fully immersed in an artificial
world is as convincing as possible.
Immersive: Head-referenced viewing can be taken as an example to provide a natural
interface for navigation in a 3D space, and can give the user the ability to look-around,
walk-around, and fly-through in the virtual environment. Sound, haptic devices, and
other non-visual technologies can also be used to enhance the virtual experience
The creation of a realistic virtual 3D world is a long term goal in interactive computer
graphics, requiring hardware and software systems that have yet to be constructed. Spe-
cifically, real-time rendering at the rate of at least 20fps very often requires significant
computational power.
Since the rendering speed is a function of the number of polygons for the entire model in
the application, this is a critical performance or complexity factor as a PC may only be able
to render tens of thousands of polygons in real-time. In large scale applications involving
complex models with up to a million polygons, powerful computer systems with special
graphics hardware are often needed. This may be a major consideration in the deployment
of virtual reality systems.
Unlike passive holographic or stereoscopic 3D video, virtual reality is inherently an
interactive application. With the rapid advancement of computer hardware, the field of
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