This article intends to give the readers a broad view of what the term Virtual Reality represents. It is not meant to be the definition of VR, but it comprises a collection of ideas from people in the leading areas of this field. Later we will discuss the various human-computer interface involved in VR.
The term Virtual Reality (VR) is used by many different people with many meanings. There are some people to whom VR is a specific collection of technologies, that is a Head Mounted Display, Glove Input Device and Audio. Some other people stretch the term to include conventional books, movies or pure fantasy and imagination. In this section we shall discuss theatre performance as an analogy for Virtual Reality.
Acting, is not just a form of expression, but a fundamental way of knowing. To act is to become someone else, in another set of circumstances, and thereby know and experience different reality. By giving his/her body over to a character, an actor enters a character's reality and he can be said to embody (or provide a body for) the character. The character lives through the actor, but so does the actor lives through the character. An actor in cyberspace is no different, except that the body he/she gives to her character is not his/her, but rather his/her virtual one. He/she embodies the character but he/she, personally, is embodied by cyberspace. This is a very powerful metaphor, and greatly simplifies the problem of creating complex environments. The actor can represent a car which responds to other objects (of known type, e.g. roads, trees, pedestrians) in a predefined way. This is possible by encapsulating all attributes of an object, visual, acoustic, behaviour, etc. in the virtual environment, like the script of a play predefines the personality of the characters.
Cyberspace is a medium, it gives people the feeling that they have been transported from ordinary physical world to worlds of pure imagination. It has a lot in common with stage and film, but it is unique in the power it yields to its audience.
Film yields little power to its audience since everything is preset and can only be watched. Stage is a little better since the actors can respond to the audience reactions, which affects their performance. Cyberspace will allow everyone to play a role and to interact with each other. In cyberspace, under the theatrical paradigm, patrons always have virtual bodies and always play the roles of virtual beings called characters. It is the new experience of being another self totally different to that of the patron in the real world which simulates a Virtual Reality.
Not all Virtual Reality systems requires gloves and goggles as seen in most technological amusement centres and scientific magazines. A major distinction of VR systems is the mode with which they are interfaced to the users. The following describes some of the common modes used in VR systems: they include Video Mapping, Immersive Systems and Telepresence.
This type of VR is best demonstrated in the famous computer game DOOM. The game
involves a player to control a battlehardened warrior to fight through a
virtual world of Hell. In this hell, there are monsters you have to kill or
they will kill you. The interface of the user to the virtual world of monsters
is in the form of a two dimension display (i.e. a monitor) to put the patron
in the eyes of the seemingly indestructable warrior. The game provides stereo
sound which gives the patron an idea of the distance and direction of a nearby
roaring monster. By using the keybroad, the player can control the warrior to
run, turn, shoot or pick up things.
Everything shown on the screen seems real; i.e. moving about in the corridors,
monsters dies in respond to your actions but it is all based on a set of very
complex data stored in the computer. It is these visual, audio senses etc. as
described above together with the independent monsters doing different
actions intelligently, which puts the game in the VR category.
The ultimate VR systems completely immerse the user's personal viewpoint
inside the virtual world. These "immersive" VR systems are often equipped with
a Head Mounted Display (HMD). This is a helmet or a face mask that holds the
visual and auditory displays. The helmet may be free ranging, tethered, or it
might be attached to some sort of a boom armature.
A nice variation of the immersive systems use multiple large projection
displays to create a 'Cave' or room in which the viewer(s) stand. An early
implementation was called "The Closet Cathedral" for the ability to create the
impression of an immense environment. within a small physical space.
Unlike the two as described above, this technology links remote sensors in the real world with the senses of a human operator. The remote sensors might be located on a robot. Fire fighters use remotely operated vehicles to handle some dangerous conditions. Robots equipped with telepresence systems have already changed the way deep sea and volcanic exploration is done. NASA plans to use telerobotics for Mars exploration. Therefore the telepresence does not give a virtual world to the operator but it gives him/her enough visual and audio senses to make him/her feel virtually there.
The idea behind distributed VR is very simple; a simulated world runs not on one computer system, but on several. The computers are connected over a network (possibly the global Internet) and people using those computers are able to interact in real time, sharing the same virtual world. Examples are Military simulations involving multiple aircrafts to fly in the same simulator. Each of the computers participating in the simulation is called a "host". On each host there are a number of "entities" (things in the virtual environment) that communicate their changing state by sending "update messages". Communication between hosts will be considered in details in other sections of this survey report.