**4.2.3 Visual Display Unit (VDU) or monitors**

There are two types of computer visual display unit. The CRT monitors and the LCD monitors. The distinguishing characteristics of the two types are beyond the scope of this piece.

#### **4.3 Process acceleration cards**

Process acceleration card is an expansion card whose function is to generate output images to a display. Most video cards offer added functions, such as accelerated rendering of 3D scenes and 2D graphics, video capture, TV-tuner adapter, MPEG-2/MPEG-4 decoding, FireWire, light pen, TV output, or the ability to connect multiple monitors (multi-monitor). These cards help to update the display with new sensory information. Examples are 3D graphic cards and 3D sound cards. Other modern high performance video cards are used for more graphically demanding purposes, such as PC games (http://en.wikipedia.org/wiki/Video\_card). Examples are 3D Nvidia Video Card and 3D ATI Video Card

#### **4.4 Tracking system**

This system tracks the position and orientation of a user in the virtual environment. The purpose of a tracking device is to determine the x, y, and z position, and the orientation (yaw, pitch, and roll) of some part of the user's body in reference to a fixed point. Most types of virtual reality interaction devices have a tracker on them. HMDs need a tracker so that the view can be updated for the current orientation of the user's head. Datagloves and flying joysticks usually have trackers so that the virtual "hand" icon will follow the position and orientation changes of the user's real hand. Full body datasuits will have several trackers on them so that virtual feet, waist, hands, and head are all slaved to the human user. This system is divided into: mechanical, electromagnetic, ultrasonic, infrared and inertial trackers.

There are two types of computer visual display unit. The CRT monitors and the LCD monitors. The distinguishing characteristics of the two types are beyond the scope of this

Process acceleration card is an expansion card whose function is to generate output images to a display. Most video cards offer added functions, such as accelerated rendering of 3D scenes and 2D graphics, video capture, TV-tuner adapter, MPEG-2/MPEG-4 decoding, FireWire, light pen, TV output, or the ability to connect multiple monitors (multi-monitor). These cards help to update the display with new sensory information. Examples are 3D graphic cards and 3D sound cards. Other modern high performance video cards are used for more graphically demanding purposes, such as PC games (http://en.wikipedia.org/wiki/Video\_card).

This system tracks the position and orientation of a user in the virtual environment. The purpose of a tracking device is to determine the x, y, and z position, and the orientation (yaw, pitch, and roll) of some part of the user's body in reference to a fixed point. Most types of virtual reality interaction devices have a tracker on them. HMDs need a tracker so that the view can be updated for the current orientation of the user's head. Datagloves and flying joysticks usually have trackers so that the virtual "hand" icon will follow the position and orientation changes of the user's real hand. Full body datasuits will have several trackers on them so that virtual feet, waist, hands, and head are all slaved to the human user. This system

is divided into: mechanical, electromagnetic, ultrasonic, infrared and inertial trackers.

Fig. 2. A binocular omni-orientation monitor (BOOM)

Examples are 3D Nvidia Video Card and 3D ATI Video Card

**4.2.3 Visual Display Unit (VDU) or monitors** 

**4.3 Process acceleration cards** 

**4.4 Tracking system** 

piece.

Fig. 3. Patriot wireless electromagnetic tracker

Fig. 4. A.R.T. optical tracking system

A mechanical tracker is similar to a robot arm and consists of a jointed structure with rigid links, a supporting base, and an "active end" which is attached to the body part being tracked (Sowizral, 1995) often the hand. This type of tracker is fast, accurate, and is not susceptible to jitter. However, it also tends to encumber the movement of the user, has a restricted area of operation, and the technical problem of tracking the head and two hands at the same time is still difficult.

An electromagnetic tracker (EMT) allows several body parts to be tracked simultaneously and will function correctly if objects come between the source and the detector. In this type of tracker, the source produces three electromagnetic fields each of which is perpendicular to the others. The detector on the user's body then measures field attenuation (the strength and direction of the electromagnetic field) and sends this information back to a computer. The computer triangulates the distance and orientation of the three perpendicular axes in the detector relative to the three electromagnetic fields produced by the source (Baratoff & Blanksteen, 1993). Electromagnetic trackers are popular, but they are inaccurate. They suffer from latency problems, distortion of data, and they can be thrown off by large amounts of metal in the surrounding work area or by other electromagnetic fields, such as those from

A Survey of Some Virtual Reality Tools and Resources 31

Dataglove is a neoprene fabric glove with two fiber optic loops on each finger. Each loop is dedicated to one knuckle and this can be a problem. If a user has extra large or small hands, the loops will not correspond very well to the actual knuckle position and the user will not be able to produce very accurate gestures. At one end of each loop is an LED and at the other end is a photosensor. The fiber optic cable has small cuts along its length. When the user bends a finger, light escapes from the fiber optic cable through these cuts. The amount of light reaching the photosensor is measured and converted into a measure of how much the finger is bent (Aukstakalnis & Blatner, 1992). Dataglove requires recalibration for each user (Hsu, 1993). Fatigue effects and recalibration during a session are problems associated

Powerglove uses strain gauges to measure the flexion of each finger. A small strip of mylar plastic is coated with an electrically conductive ink and placed along the length of each finger. When the fingers are kept straight, a small electrical current passing through the ink remains stable. When a finger is bent, the computer can measure the change in the ink's electrical resistance (Aukstakalnis & Blatner, 1992). Powerglove is less accurate than the Dataglove, and also needs recalibration for each user, but is more rugged than the

The dexterous hand master (DHM) is not exactly a glove but an exoskeleton that attaches to the fingers with velcro straps. A mechanical sensor measures the flexion of the finger. Unlike the Dataglove and Powerglove, the DHM is able to detect and measure the side-toside movement of a finger. The other gloves only measure finger flexion. The DHM is more accurate than either of the gloves and less sensitive to the user's hand size, but can be

The main strength of the various types of gloves is that they provide a more intuitive interaction device than a mouse or a joystick. This is because the gloves allow the computer to read and represent hand gestures. Objects in the environment can therefore be "grasped" and manipulated, the user can point in the direction of desired movement, windows can be dismissed, etc (Wilson & Conway, 1991). Wilson and Conway (1991) opined that more work is needed to expand glove's set of command gestures beyond the current simple mapping. Another area of improvement is feedback for the user to aid hand-eye coordination and proprioceptive feedback to let a user know when an object has been successfully grasped

with long term use of Dataglove (Wilson & Conway, 1991).

Fig. 5. An instrumented glove (Nintendo power glove)

Dataglove.

awkward to work with (Hsu, 1993).

(Wilson & Conway, 1991).

other pieces of large computer equipment. In addition, the detector must be within a restricted range from the source or it will not be able to send back accurate information (Sowizral, 1995), so the user has a limited working volume.

Ultrasonic tracking devices consist of three high frequency sound wave emitters in a rigid formation that form the source for three receivers that are also in a rigid arrangement on the user. There are two ways to calculate position and orientation using acoustic trackers. The first is called "phase coherence". Position and orientation is detected by computing the difference in the phases of the sound waves that reach the receivers from the emitters as compared to sound waves produced by the receiver. The second method is "time-of-flight", which measures the time for sound, emitted by the transmitters at known moments, to reach the sensors. Only one transmitter is needed to calculate position, but the calculation of orientation requires finding the differences between three sensors (Baratoff & Blanksteen, 1993). Unlike electromagnetic trackers that are affected by large amounts of metal, ultrasonic trackers do not suffer from this problem. However, ultrasonic trackers also have a restricted workspace volume and, worse, must have a direct line-of-sight from the emitter to the detector. Time-of-flight trackers usually have a low update rate, and phase-coherence trackers are subject to error accumulation over time (Baratoff & Blanksteen, 1993). Additionally, both types are affected by temperature and pressure changes (Sowizral, 1995), and the humidity level of the work environment (Baratoff & Blanksteen, 1993).

Infrared (optical) trackers utilize several emitters fixed in a rigid arrangement while cameras or "quad cells" receive the IR light. To fix the position of the tracker, a computer must triangulate a position based on the data from the cameras. This type of tracker is not affected by large amounts of metal, has a high update rate, and low latency (Baratoff & Blanksteen, 1993). However, the emitters must be directly in the line-of-sight of the cameras or quad cells. In addition, any other sources of infrared light, high-intensity light, or other glare will affect the correctness of the measurement (Sowizral, 1995).

Inertial trackers apply the principle of conservation of angular momentum (Baratoff & Blanksteen, 1993). Inertial trackers allow the user to move about in a comparatively large working space where there is no hardware or cabling between a computer and the tracker. Miniature gyroscopes can be attached to HMDs, but they tend to drift (up to 10 degrees per minute) and to be sensitive to vibration. Yaw, pitch, and roll are calculated by measuring the resistance of the gyroscope to a change in orientation. If tracking of position is desired, an additional type of tracker must be used (Baratoff & Blanksteen, 1993). Accelerometers are another option, but they also drift and their output is distorted by the gravity field (Sowizral, 1995).

#### **4.5 Input (interaction) devices**

They are used to interact with the virtual environment and objects within the virtual environment. Examples are joystick (wand), instrumented glove, keyboard, voice recognition etc.

For interaction with small objects in a virtual world, the user can use one of several gloves designed to give feedback on the characteristics of the object. This can be done with pneumatic pistons, which are mounted on the palm of the glove, as in the Rutgers Master II (Gomez, Burdea, & Langrana, 1995). Gloves are used for sensing the flexion of the fingers.

other pieces of large computer equipment. In addition, the detector must be within a restricted range from the source or it will not be able to send back accurate information

Ultrasonic tracking devices consist of three high frequency sound wave emitters in a rigid formation that form the source for three receivers that are also in a rigid arrangement on the user. There are two ways to calculate position and orientation using acoustic trackers. The first is called "phase coherence". Position and orientation is detected by computing the difference in the phases of the sound waves that reach the receivers from the emitters as compared to sound waves produced by the receiver. The second method is "time-of-flight", which measures the time for sound, emitted by the transmitters at known moments, to reach the sensors. Only one transmitter is needed to calculate position, but the calculation of orientation requires finding the differences between three sensors (Baratoff & Blanksteen, 1993). Unlike electromagnetic trackers that are affected by large amounts of metal, ultrasonic trackers do not suffer from this problem. However, ultrasonic trackers also have a restricted workspace volume and, worse, must have a direct line-of-sight from the emitter to the detector. Time-of-flight trackers usually have a low update rate, and phase-coherence trackers are subject to error accumulation over time (Baratoff & Blanksteen, 1993). Additionally, both types are affected by temperature and pressure changes (Sowizral, 1995),

and the humidity level of the work environment (Baratoff & Blanksteen, 1993).

Infrared (optical) trackers utilize several emitters fixed in a rigid arrangement while cameras or "quad cells" receive the IR light. To fix the position of the tracker, a computer must triangulate a position based on the data from the cameras. This type of tracker is not affected by large amounts of metal, has a high update rate, and low latency (Baratoff & Blanksteen, 1993). However, the emitters must be directly in the line-of-sight of the cameras or quad cells. In addition, any other sources of infrared light, high-intensity light, or other glare will

Inertial trackers apply the principle of conservation of angular momentum (Baratoff & Blanksteen, 1993). Inertial trackers allow the user to move about in a comparatively large working space where there is no hardware or cabling between a computer and the tracker. Miniature gyroscopes can be attached to HMDs, but they tend to drift (up to 10 degrees per minute) and to be sensitive to vibration. Yaw, pitch, and roll are calculated by measuring the resistance of the gyroscope to a change in orientation. If tracking of position is desired, an additional type of tracker must be used (Baratoff & Blanksteen, 1993). Accelerometers are another option, but they also drift and their output is distorted by the gravity field

They are used to interact with the virtual environment and objects within the virtual environment. Examples are joystick (wand), instrumented glove, keyboard, voice

For interaction with small objects in a virtual world, the user can use one of several gloves designed to give feedback on the characteristics of the object. This can be done with pneumatic pistons, which are mounted on the palm of the glove, as in the Rutgers Master II (Gomez, Burdea, & Langrana, 1995). Gloves are used for sensing the flexion of the fingers.

(Sowizral, 1995), so the user has a limited working volume.

affect the correctness of the measurement (Sowizral, 1995).

(Sowizral, 1995).

recognition etc.

**4.5 Input (interaction) devices** 

Dataglove is a neoprene fabric glove with two fiber optic loops on each finger. Each loop is dedicated to one knuckle and this can be a problem. If a user has extra large or small hands, the loops will not correspond very well to the actual knuckle position and the user will not be able to produce very accurate gestures. At one end of each loop is an LED and at the other end is a photosensor. The fiber optic cable has small cuts along its length. When the user bends a finger, light escapes from the fiber optic cable through these cuts. The amount of light reaching the photosensor is measured and converted into a measure of how much the finger is bent (Aukstakalnis & Blatner, 1992). Dataglove requires recalibration for each user (Hsu, 1993). Fatigue effects and recalibration during a session are problems associated with long term use of Dataglove (Wilson & Conway, 1991).

Fig. 5. An instrumented glove (Nintendo power glove)

Powerglove uses strain gauges to measure the flexion of each finger. A small strip of mylar plastic is coated with an electrically conductive ink and placed along the length of each finger. When the fingers are kept straight, a small electrical current passing through the ink remains stable. When a finger is bent, the computer can measure the change in the ink's electrical resistance (Aukstakalnis & Blatner, 1992). Powerglove is less accurate than the Dataglove, and also needs recalibration for each user, but is more rugged than the Dataglove.

The dexterous hand master (DHM) is not exactly a glove but an exoskeleton that attaches to the fingers with velcro straps. A mechanical sensor measures the flexion of the finger. Unlike the Dataglove and Powerglove, the DHM is able to detect and measure the side-toside movement of a finger. The other gloves only measure finger flexion. The DHM is more accurate than either of the gloves and less sensitive to the user's hand size, but can be awkward to work with (Hsu, 1993).

The main strength of the various types of gloves is that they provide a more intuitive interaction device than a mouse or a joystick. This is because the gloves allow the computer to read and represent hand gestures. Objects in the environment can therefore be "grasped" and manipulated, the user can point in the direction of desired movement, windows can be dismissed, etc (Wilson & Conway, 1991). Wilson and Conway (1991) opined that more work is needed to expand glove's set of command gestures beyond the current simple mapping. Another area of improvement is feedback for the user to aid hand-eye coordination and proprioceptive feedback to let a user know when an object has been successfully grasped (Wilson & Conway, 1991).

A Survey of Some Virtual Reality Tools and Resources 33

user's eyes. The glasses are synchronized with the projectors so that each eye only sees the correct image. Since the projectors are positioned outside of the cube, mirrors often reduce the distance required from the projectors to the screens. One or more computers, often SGI workstations, drive the projectors. Clusters of desktop PCs are popular to run CAVEs, because they cost less and run faster (http://en.wikipedia.org/wiki/

The biggest issue that researchers are faced with when it comes to the CAVE is size and cost. Researchers have realized this and have come up with a derivative of the CAVE system, called ImmersaDesk. With the ImmersaDesk, the user looks at one projection screen instead of being completely blocked out from the outside world, as is the case with the original CAVE. The idea behind the ImmersaDesk is that it is a single screen placed on a 45-degree angle so that the person using the machine has the opportunity to look forward and downward. The screen is 4' X 5', so it is wide enough to give the user the width that they need to obtain the proper 3D experience. The 3D images come out by using the same glasses as were used in the CAVE. This system uses sonic hand tracking and head tracking, so the system still uses a computer to process the users' movements (http://en.wikipedia.org/

This system is much more affordable and practical than the original CAVE system for some obvious reasons. First, one does not need to create a "room inside of a room". That is to say that one does not need to place the ImmersaDesk inside of a pitch-black room that is large enough to accommodate it. One projector is needed instead of four and only one projection screen. One does not need a computer as expensive or with the same capabilities that are necessary with the original CAVE. Another thing that makes the ImmersaDesk attractive is the fact that since it was derived from the original CAVE, it is compatible with all of the CAVE's software packages and also with all of the CAVE's libraries and interfaces

The concept of the original CAVE has been reapplied and is currently being used in a variety of fields. Many universities own CAVE systems. CAVEs are used for many things. Many engineering companies use CAVEs to enhance product development. Prototypes of parts can be created and tested, interfaces can be developed, and factory layouts can be simulated, all before spending any money on physical parts. This gives engineers a better idea of how a part will behave in the entire product (http://en.wikipedia.org/wiki/

As interest in Virtual Reality technology has increased, so has the number of tools available to the developers of virtual worlds. Some of these are libraries and toolkits, while others are application frameworks, and still others are full development environments, integrating every aspect of the creation of a VR application – modeling, coding, and execution – into a single package (Bierbaum & Just, 1998). The software

(http://en.wikipedia.org/wiki/Cave\_Automatic\_Virtual\_Environment).

Cave\_Automatic\_Virtual\_Environment).

**4.6.4 Developments in CAVE research** 

wiki/Cave\_Automatic\_Virtual\_Environment).

**4.6.5 Applications of CAVE** 

Cave\_Automatic\_Virtual\_Environment).

**5. Software tools for VR application development** 

The final category of interaction device is the wand or floating joystick. Basically, this device works exactly the same as a conventional joystick, but it is not attached to a base that sits on a tabletop. Instead, the joystick is equipped with an orientation tracker so the user simply holds it in their hand and tilts it. Most flying joysticks also have some buttons on the stick for "clicking" or selecting, similar to a mouse (Hsu, 1993).

#### **4.6 Cave Automatic Virtual Environment**

Cave Automatic Virtual Environment (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 (Fisher, 2003; http://en.wikipedia.org/wiki/Cave\_Automatic\_Virtual\_Environment).
