VIRTUAL REALITY

SEMINAR REPORT

A Seminar report submitted

For the partial fulfillment of the degree of

Bachelor of Engineering in

Computer Engineering

(Session 2014-2015)

Seminar Coordinator: HOD - CSE: Submitted by:

Mrs. Narina Thakur Dr. Bindu Garg Gaurav

Saxena(03811502711)

Department of Computer Engineering

BHARATI VIDYAPEETH COLLEGE OF ENGINEERING PASCHIM VIHAR,

NEW DELHI

September-2014

ABSTRACT

The purpose of this report is to familiarize the readers with the concept of Virtual Reality(VR).

The report presents the readers with an introduction to virtual reality, early attempts at creating a

virtual reality system, various types of virtual reality system, components of a VR system,

devices used in a VR system and applications in various fields.

TABLE OF CONTENTS

INTRODUCTION

Virtual reality (VR), sometimes referred to as immersive multimedia, is a computer-simulated

environment that can simulate physical presence in places in the real world or imagined worlds.

Some basic definitions of Virtual Reality are:

1. “Real-time interactive graphics with three-dimensional models, combined with a sdisplay

technology that gives the user the immersion in the model world and direct

manipulation.”

2. “The illusion of participation in a synthetic environment rather than external

observationof such an environment. VR relies on a three-dimensional, stereoscopic head-

tracker displays, hand/body tracking and binaural sound. VR is an immersive, multi-

sensory experience.”

3. “Computer simulations that use 3D graphics and devices such as the DataGlove to allow

the user to interact with the simulation.”

4. “Virtual reality refers to immersive, interactive, multi-sensory, viewer-centered, three-

dimensional computer generated environments and the combination of

technologiesrequired to build these environments.”

5. “Virtual reality lets you navigate and view a world of three dimensions in real time, with

six degrees of freedom. In essence, virtual reality is clone of physical reality.”

There are two important terms that must be mentioned when talking about virtual reality,

telepresence and cyberspace. They are both tightly coupled with virtual reality, but have a

slightly different context:

1. Telepresence : Telepresence is a specific kind of virtual reality that simulates a real but

remote (in terms of distance or scale) environment. Another more precise definition says

that telepresence occurs when “ at the work site, the manipulators have the dexterity to

allow the operator to perform normal human functions; at the control station, the operator

receives sufficient quantity and quality of sensory feedback to provide a feeling of actual

presence at the worksite”.

2. Cyberspace : Cybersoace was invented and defined by William Gibson as “ a consensual

hallucination experienced daily by billions of legitimate operators a

graphicsrepresentation of data abstracted from the banks of every computer in human

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system”. Today the term Cyberspace is rather associated with entertainment systems and

World Wide Web (Internet).

HISTORYConcept of virtual reality has been around for decades, even though the public really only

became aware of it in the early 1990s. In the mid 1950s, a cinematographer named Morton

Heilig envisioned a theatre experience that would stimulate all his audiences’ senses, drawing

them in to the stories more effectively. He built a single user console in 1960 called the

Sensorama that included a stereoscopic display, fans, odor emitters, stereo speakers and a

moving chair. He also invented a head mounted television display designed to let a user watch

television in 3-D. Users were passive audiences for the films, but many of Heilig’s concepts

would find their way into the VR field.

Philco Corporation engineers developed the first HMD in 1961, called the Headsight. The helmet

included a video screen and tracking system, which the engineers linked to a closed circuit

camera system. They intended the HMD for use in dangerous situations -- a user could observe a

real environment remotely, adjusting the camera angle by turning his head. Bell Laboratories

used a similar HMD for helicopter pilots. They linked HMDs to infrared cameras attached to the

bottom of helicopters, which allowed pilots to have a clear field of view while flying in the dark.

In 1965, a computer scientist named Ivan Sutherland envisioned what he called the “Ultimate

Display.” Using this display, a person could look into a virtual world that would appear as real as

the physical world the user lived in. This vision guided almost all the developments within the

field of virtual reality. Sutherland’s concept included:

1. A virtual world that appears real to any observer, seen through an HMD and

augmented through three-dimensional sound and tactile stimuli

2. A computer that maintains the world model in real time

3. The ability for users to manipulate virtual objects in a realistic, intuitive way

In 1966, Sutherland built an HMD that was tethered to a computer system. The computer

provided all the graphics for the display (up to this point, HMDs had only been linked to

cameras). He used a suspension system to hold the HMD, as it was far too heavy for a user to

support comfortably. The HMD could display images in stereo, giving the illusion of depth, and

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it could also track the user’s head movements so that the field of view would change

appropriately as the user looked around.

COMPONENTS OF VIRTUAL REALITY SYSTEM

Components of a virtual reality system include:

1. Effectors: Effectors are any type of interface device that provides access to a virtual

environment examples include head-mounted display devices, data gloves, 2d or 3d mice,

2d screens, and head phones.

2. Reality Simulator: It is the hardware that supplies the effectors with the necessary

sensory (visual or acoustic) information depending on the degree of immersion needed,

examples include “Silicon Graphics Reality Engine” workstations.

3. Application: Application is the software that describes the context of the simulation.

There is a wide variety of software depending on the system platforms including “Intel”

PC, “Silicon Graphics” (SGI), and “Sun” platforms. An examples of “Intel” based PC

software is “Division” (from “AutoDesk”).

4. Geometry: Geometry is the information that describes the physical attributes of objects

in the virtual environment. Basically geometry is built by CAD software. The most

common 3D modelling CAD is AutoCAD from “AutoDesk” that runs on “Intel” based

PC. CAD files can be exported to rendering and Virtual Reality authorising software on

the form of DXF as a drawing interchange format.

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TYPES OF VIRTUAL REALITY SYSTEM

In a virtual environment system a computer generates sensory impressions that are delivered to

the human senses. The type and the quality of these impressions determine the level of

immersion and the feeling of presence in virtual reality.

Ideally the high-resolution, high-quality and consistent over all the displays, information should

be presented to all of the user’s senses. Moreover, the environment itself should react

realistically to the user’s actions. The practice, however, is very different from this ideal case.

Many applications stimulate only one or a few of the senses, very often with low-quality and

unsynchronized information.

1. Window on World Systems (WoW) : Some systems use a conventional computer

monitor to display the visual world. This sometimes called Desktop virtual reality or a

Window on a World (WoW). This concept traces its lineage back through the entire

history of computer graphics. In 1965, Ivan Sutherland laid out a research program for

computer graphics in a paper called "The Ultimate Display" that has driven the field for

the past nearly thirty years.

2. Video Mapping : A variation of the WoW approach merges a video input of the user's

silhouette with a 2D computer graphic. The user watches a monitor that shows his body's

interaction with the world. Myron Kruger has been a champion of this form of VR since

the late 60's. He has published two books on the subject: "Artificial Reality" and

"Artificial Reality II".

3. Immersive Systems: 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

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viewer(s) stand.

4. Mixed Reality: Merging the Telepresence and Virtual Reality systems gives the

Mixed Reality or Seamless Simulation systems. Here the computer generated inputs are

merged with telepresence inputs and/or the users view of the real world. A surgeon's view

of a brain surgery is overlaid with images from earlier CAT scans and real-time

ultrasound. A fighter pilot sees computer generated maps and data displays inside his

fancy helmet visor or on cockpit displays.

VIRTUAL REALITY HARDWARE

1. Head Mounted Display (HMD): A head-mounted display or helmet mounted

display, both abbreviated HMD, is a display device, worn on the head or as part of a

helmet, that has a small display optic in front of one (monocular HMD) or each eye

(binocular HMD).

There is also an optical head-mounted display (OHMD), which is a wearable display that

has the capability of reflecting projected images as well as allowing the user to see

through it. A typical HMD has either one or two small displays with lenses and semi-

transparent mirrors embedded in a helmet, eyeglasses (also known as data glasses) or

visor. The display units are miniaturised and may include CRT, LCDs, Liquid crystal on

silicon (LCos), or OLED. Some vendors employ multiple micro-displays to increase total

resolution and field of view.

HMDs differ in whether they can display just a computer generated image (CGI), show

live images from the real world or a combination of both.

Most HMDs display only a computer-generated image, sometimes referred to as a virtual

image. Some HMDs allow a CGI to be superimposed on a real-world view. This is

sometimes referred to as augmented reality or mixed reality. Combining real-world view

with CGI can be done by projecting the CGI through a partially reflective mirror and

viewing the real world directly.

2. Binocular Omni-Orientation Monitor (BOOM): A head-coupled stereoscopic

display device. Screens and optical system are housed in a box that is attached to a multi-

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link arm. The user looks into the box through two holes, sees the virtual world, and can

guide the box to any position within the operational volume of the device. Head tracking

is accomplished via sensors in the links of the arm that holds the box. BOOM was created

by Fakespace Systems Inc.

3. Cave Automatic Virtual Environment (CAVE): A computer assisted virtual

environment (better known by the acronym CAVE) is an immersive virtual reality

environment where projectors are directed to three, four, five or six of the walls of a

room-sized cube. The name is also a reference to the allegory of the Cave in Plato's

Republic in which a philosopher contemplates perception, reality and illusion. A lifelike

visual display is created by projectors positioned outside the CAVE and controlled by

physical movements from a user inside the CAVE. A motion capture system records the

real time position of the user. Stereoscopic LCD shutter glasses convey a 3D image. The

computers rapidly generate a pair of images, one for each of the user's eyes, based on the

motion capture data. The glasses are synchronized with the projectors so that each eye

only sees the correct image. Since the projectors are positioned outside the cube, mirrors

are often used to reduce the distance required from the projectors to the screens. One or

more computers drive the projectors. Clusters of desktop PCs are popular to run CAVEs,

because they cost less and run faster.

4. Data Glove: A wired glove (sometimes called a "dataglove" or "cyberglove") is an

input device for human–computer interaction worn like a glove. Various sensor

technologies are used to capture physical data such as bending of fingers. Often a motion

tracker, such as a magnetic tracking device or inertial tracking device, is attached to

capture the global position/rotation data of the glove. These movements are then

interpreted by the software that accompanies the glove, so any one movement can mean

any number of things. Gestures can then be categorized into useful information, such as

to recognize Sign Language or other symbolic functions. Expensive high-end wired

gloves can also provide haptic feedback, which is a simulation of the sense of touch. This

allows a wired glove to also be used as an output device. Traditionally, wired gloves have

only been available at a huge cost, with the finger bend sensors and the tracking device

having to be bought separately.

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APPLICATIONS OF VIRTUAL REALITY

1. Military

Virtual reality is used in military for training purposes, particularly for combat situations

or other dangerous settings where they have to learn how to react in an appropriate

manner.

A virtual reality simulation enables them to do so but without the risk of death or a

serious injury. They can re-enact a particular scenario, for example engagement with an

enemy in an environment in which they experience this but without the real world risks.

This has proven to be safer and less costly than traditional training methods.

Military uses of virtual reality include:

4. Flight simulation

5. Battlefield simulation

6. Medic training (battlefield)

7. Vehicle simulation

8. Virtual boot camp

Virtual reality is also used to treat post-traumatic stress disorder. Soldiers suffering from

battlefield trauma and other psychological conditions can learn how to deal with their

symptoms in a ‘safe’ environment. The idea is for them to be exposed to the triggers for

their condition which they gradually adjust to. This has the effect of decreasing their

symptoms and enabling them to cope to new or unexpected situations.

2. Health Care

Healthcare is one of the biggest adopters of virtual reality which encompasses surgery

simulation, phobia treatment, robotic surgery and skills training. One of the advantages of

this technology is that it allows healthcare professionals to learn new skills as well as

refreshing existing ones in a safe environment. Plus it allows this without causing any

danger to the patients.

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Human simulation software enables doctors, nurses and other medical personnel to

interact with others in an interactive environment. They engage in training scenarios in

which they have to interact with a patient but within a 3D environment only. This is an

immersive experience which measures the participant’s emotions via a series of sensors.

Virtual reality diagnostics.

Virtual reality is often used as a diagnostic tool in that it enables doctors to arrive at a

diagnosis in conjunction with other methods such as MRI scans. This removes the need

for invasive procedures or surgery. Virtual robotic surgery A popular use of this

technology is in robotic surgery. This is where surgery is performed by means of a

robotic device – controlled by a human surgeon, which reduces time and risk of

complications.

Virtual reality has been also been used for training purposes and, in the field of remote

telesurgery in which surgery is performed by the surgeon at a separate location to the

patient. The main feature of this system is force feedback as the surgeon needs to be able

to gauge the amount of pressure to use when performing a delicate procedure. But there is

an issue of time delay or latency which is a serious concern as any delay – even a fraction

of a second – can feel abnormal to the surgeon and interrupt the procedure. So there

needs to be precise force feedback in place to prevent this. Robotic surgery and other

issues relating to virtual reality and medicine can be found in the virtual reality and

healthcare section.

Medical fields in which virtual reality is/can be used

1. Dentistry

2. Medicine

3. Nursing

4. Surgery simulation

5. Therapies

6. Phobia treatment

7. Post traumatic stress disorder (PTSD)

8. Autism

9. Disabled

10.

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3. Entertainment

The entertainment industry is one of the most enthusiastic advocates of virtual reality,

most noticeably in games and virtual worlds. But other equally popular areas include:

1. Virtual Museums, e.g. interactive exhibitions

2. Galleries

3. Theatre, e.g. interactive performances

4. Virtual theme parks

5. Discovery centres

Audience engagement environments enable members of the public to engage with the

exhibits in ways which were previously forbidden or unknown. They wear virtual reality

glasses with stereoscopic lenses which allow them to see 3D objects and at different

angles. And in some cases they can interact with the exhibits by means of an input device

such as a data glove.

An example of this is a historical building which the member of the public can view at

different angles. Plus they are able to walk through this building, visiting different rooms

to find out more about how people lived at that particular time in history.

They are able to do this by means of a tracking system (built into the glasses) which

tracks their movements and feeds this information back to a computer. The computer

responds by changing the images in front of the person to match their change in

perception and maintain a sense of realism.

There are a range of virtual reality systems available for audience entertainment which

includes CAVE systems, augmented reality systems, simulators and 3D display

platforms.

Virtual reality gaming is a very popular form of entertainment which is discussed in more

detail in a separate section. Visit the virtual reality games section which contains a set of

individual articles discussing VR games for Xbox, PC and PS3 as well as virtual worlds.

4. Reality and Heritage

This refers to the use of virtual reality in museum and historical settings, e.g. visitor

centres. These settings employ interaction as a means of communicating information to

the general public in new and exciting ways.

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There has been a move away from the traditional type of experience associated with

museums, galleries and visitor centres. The old model was that of passive engagement in

which people viewed the exhibit/s but did not get involved to an experience in which

interaction is the main feature.

Interactive displays form a large part of many exhibitions and particularly appeal to

children. Children are often difficult to attract to a museum or gallery as they tend to see

this as a boring experience. But the use of interactive technologies such as virtual reality

has changed that perception and opened up these spaces to a new audience.

1. Virtual reality heritage sites

2. Examples of virtual heritage sites include:

3. Monuments

4. Stonehenge

5. Sculptures

6. Caves

7. Historical buildings

8. Archaeological digs

9. Old towns and villages

Virtual reality has been used to construct virtual walkthroughs of these sites which

enhances the visitor’s experience.

5. Business

Virtual reality is being used in a number of ways by the business community which

include:

1. Virtual tours of a business environment

2. Training of new employees

3. A 360 view of a product

Many businesses have embraced virtual reality as a cost effective way of developing a

product or service. For example it enables them to test a prototype without having to

develop several versions of this which can be time consuming and expensive.

Plus it is a good way of detecting design problems at an early stage which can then be

dealt with sooner rather than later.

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For some businesses, fully immersive virtual reality a la CAVE system is the way

forward. They like the fact that they can use this to test drive a product in the early stages

of development but without any additional costs (or risks) to themselves.

This is particularly useful for companies who produce dangerous or potentially harmful

products which need to be evaluated before use. They can test their product within a

virtual environment but at no risk to themselves or their employees. And virtual reality

technology has advanced to the stage where it has a high degree of realism and

efficiency.

Some companies use virtual reality to help with data analysis and forecasting trends in

order to gain an edge over their competitors. One example of this is a system developed

by researchers at the University of Warwick which is designed to help businesses gain a

greater understanding of their data.

6. Engineering

Virtual reality engineering includes the use of 3D modelling tools and visualisation

techniques as part of the design process. This technology enables engineers to view their

project in 3D and gain a greater understanding of how it works. Plus they can spot any

flaws or potential risks before implementation. This also allows the design team to

observe their project within a safe environment and make changes as and where

necessary. Saving both time and money. What is important is the ability of virtual reality

to depict fine grained details of an engineering product to maintain the illusion. This

means high end graphics, video with a fast refresh rate and realistic sound and movement.

In some cases, virtual reality can be used from the start of the design lifecycle, e.g. the

initial concept through to the build and implementation stages. This is reviewed at stages

to check for faults, structural weaknesses and other design issues.

Virtual reality and rail construction

7. Sports

Virtual reality is used as a training aid in many sports such as golf, athletics, skiing,

cycling etc. It is used as an aid to measuring athletic performance as well as analysing

technique and is designed to help with both of these. It also used in clothing/equipment

design and as part of the drive to improve the audience’s experience.

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The athlete uses this technology to fine tune certain aspects of their performance, for

example, a golfer looking to improve their swing or a track cyclist wanting to go faster in

the individual pursuit. Three dimensional systems can pinpoint aspects of an athlete’s

performance which require changing, for example, their biomechanics or technique.

Another popular use is sports manufacture: virtual reality is used in the design of sporting

clothes and equipment, e.g. running shoe design. Innovation is a key factor in this

industry as the bar is raised higher and higher in terms of sporting achievement.

Sportspeople are constantly looking at ways of gaining them that edge which can mean

being faster, stronger, better endurance etc. They are constantly pushing boundaries as

regards what their bodies can do which drives the sports clothing and equipment industry.

This industry has to keep pace with this constant drive for sporting perfection and uses

the very latest technology to do so.

Virtual reality has also been used to improve the audience’s experience of a sporting

event. Some systems allow the audience to walkthrough a stadium or other sporting

location, which helps them when purchasing a ticket to an event.

And then there are virtual reality games with a sports theme which allow the player to

become part of the competition. One example is an interactive football game which

projects this match onto a real world surface.

8. Media

Virtual reality has featured in several film and television programmes. It is often used to

illustrate the concept of being trapped within the machine (or in this case, cyberspace), or

as a form of advanced technology.

Examples of VR inspired films include:

1. The Lawnmower Man2.

2. The Matrix

3. Tron (1982 version)

4. The Thirteenth Floor

5. eXistenZ

6. Vanilla Sky

There are television programmes such as selected episodes of Doctor Who, Red Dwarf

and Star Trek: The Next Generation which utilise virtual reality technology. One example

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is the holodeck as seen in Star Trek which enables the person to experience any situation

they so wish.

This technology has formed part of experimental sound displays and sound installations.

Another use is virtual reality musical instruments which the person can interact with

these instruments as a new type of performance or to create new compositions.

Virtual reality has been a staple theme of many fictional stories such as William Gibson’s

Neuromancer and Mona Lisa Overdrive as well as Orson Scott Card’s Enders Game.

There are artists who use virtual reality to explore certain ideas or concepts. They create a

three dimensional environment as a form of communication with the audience. One

example is the work of Kenneth Rinaldo who uses robotics and augmented reality to

explore ideas related to the human-technology boundary.

9. Telecommunications

Telecommunications is another field which has utilised virtual reality technology, in

particular mobile communications which enables easy access to a variety of VR based

projects. The main challenge is that of dealing with a medium which mainly relies upon

tone of voice, intonation, gesture and body language as compared to spoken words. In

fact, spoken words only account for a very small percentage of the overall

communication.

But traditional forms of communication such as the telephone are being superseded by

video conferencing, Skype and live chat. These communication mediums can be used on

the internet and other similar systems and are seen as cheaper and more flexible.

Telecommunications can be used to help virtual reality systems such as surgery

simulation or telemedicine. An example of this is remote surgery in which images from

that surgery can be transmitted to various locations around the world. It also enables

surgery to be performed in remote locations using robotic technology and virtual reality.

10.Scientific Visualisation

Virtual reality is being increasingly used in the field of scientific visualisation. This field

is based upon using computer graphics to express complex ideas and scientific concepts,

for example molecular models or statistical results.

Scientific visualisation is used as a means of communicating abstract concepts to an

audience which also aids with understanding. The audience can interact with these

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images, for example, viewing a molecular structure at different angles or as a means of

problem solving.

Virtual reality enables scientists to demonstrate a method or convey complex ideas in a

visual format. This includes semi-immersive and full immersive environments in which

they visualise research theories or discuss large data sets.

This technology raises possibilities for collaboration between different disciplines or new

forms of research and development. Virtual reality is considered alongside other forms of

visualisation technology such as computer simulation, animation and information

visualisation. All of these are designed to show a visual model of a live system, e.g.

human body, complex data set or a large collection of numerical information.

LITERATURE SURVEY

Frank Steinicke et al [1] in December 2005 presented Virtual Reality VRS (VR2S), a generic VR

software system, an extension of the high-level rendering system VRS. Use of VR2S allowed

rendering to be performed with several low-level rendering APIs such as OpenGL, Render- Man

or ray-tracing systems, and the interface can be implemented by arbitrary user interface toolkits

to support both desktop- and VR-based interaction. He put forward the main objective of VR2S,

which is to provide VR software developers with a suite of APIs that abstract, and hence

simplify all interface aspects of applications including the user interface and typical VR system

tasks. VR2S applications are essentially independent of the VR system, and hence applications

run on different system architectures in both VR systems and desktop environments. The

modular and flexible design of VR2S permits individual as well as combined usage of VR

components.

Oluleke Bamodu et al [2] in 2013 put forward a definition of virtual reality, it’s various features,

components and its application. He refers to virtual reality as an oxymoron, as it is referred as

“reality that does not exist”. Virtual reality environment is classified into 3 levels depending on

the level of immersion and type of components utilized in the system, viz. immersive, semi-

immersive and non-immersive. He has identified 3 main components of virtual system, input

devices, VR engine and output devices. The input devices are used for recording actions of user,

to provide appropriate reactions. VR engine required to make the virtual environment react to

user’s actions. Output devices to get feedback from the VR engine and pass it on to the users

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through the corresponding output devices to stimulate the senses. He also discussed about VR

development tools and various considerations to select the appropriate tool. Lastly he lists

various fields viz. Architecture, Arts, Business, Design and Planning, Education and Training,

Entertainment, Manufacturing, Medical and Scientific Visualization, which have application of

VR systems.

Tom Fellmann et al [3] discusses various virtual reality (VR) tools, main components for a

generic VR Engine. In this paper, they discuss the system architecture of a VR Engine (VaiR),

and demonstrate the basic elements of this generic VR programming interface. The VaiR Engine

integrates VR hardware and software within a graphics Application Programming Interface

(API) (e.g. OpenSceneGraph). VaiR Engine providing the ability to use stereoscopic goggles,

trackers, head mounted displays, etc with a number of 3D Modeling and Animation Packages

(e.g. 3ds Max and Softimage) and scripting languages (e.g., XML). VaiR combines the important

characteristics of many other VR tools and brings them together to generate a more powerful

tool.

Tomasz Mazuryk et al [4] talks about Virtual Reality (VR), sometimes called Virtual

Environments (VE) Extensive media coverage causes this interest to grow rapidly. In this paper a

historical overview of virtual reality is presented, basic terminology and classes of VR systems

are listed, followed by applications of this technology in science, work, and entertainment areas.

An insightful study of typical VR systems is done. All components of VR application and

interrelations between them are thoroughly examined. Additionally human factors and their

implication on the design issues of VE are discussed. Finally, the future of VR is considered in

two aspects: technological and social. New research directions, technological frontiers and

potential applications are pointed out. The possible positive and negative influence of VR on life

of average people is speculated.

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REFERENCES

[1] Frank Steinicke, Timo Ropinski and Klaus Hinrichs,“A Generic Virtual Reality

Software System’s Architecture and Application”, ICAT, December 2005

[2] Oluleke Bamodu and Xuming Y, “Virtual Reality and Virtual Reality System

Components”, 2nd International Conference On Systems Engineering and Modeling,

2013

[3] Tom Fellmann and Manolya Kavakli,“VaiR: System Architecture of a Generic

Virtual Reality Engine”

[4] Tomasz Mazuryk and Michael Gervautz, “Virtual Reality History, Applications,

Technology and Future”

[5] http://vr.isdale.com/WhatIsVR/frames/WhatIsVR4.1.html.

[6] http://www.mic.atr.co.jp/~poup/research/ar/.

[7] http://vresources.jump-gate.com/applications/applications.shtml.

[8] http://www.vrs.org.uk/

[9] http://www-vrl.umich.edu/intro/

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