Field of View (FOV). The whole of what we are able to see with our two eyes. FOV is measured as an angle in degrees. The normal computer display at an average viewing distance of 30 inches subtends an angle of about 5 degrees. Large screen displays cover an angle of 20 to 30 degrees. Most HMDís offer from 40 to 100 degrees FOV.

Fish Tank VR. A computer monitor fitted with a stereographic display device that lets the viewer peer into a 3-D virtual space, as if looking into a fish tank. Fish tank systems can be fitted with head tracking which improves the feeling of immersion.

Flat Shading. The simplest form of shading, where a single value of color is applied to each face of a polygon, as opposed to Phong Shading.

Frame Rate. The major consideration of a graphic renderer for VR applications is the frame generation rate. It is necessary to create a new frame every 1/20 of a second or faster. 20 frames per second (fps) is roughly the minimum rate at which the human brain will merge a stream of still images and perceive a smooth animation. 24 fps is the standard rate fore limb, 25 fps is PAL TV, 30 fps is NTSC TV. 60 fps is Showscan film rate. This requirement eliminates a number of rendering techniques such as ray tracing and radiosity. These techniques can generate very realistic images but often take hours to generate single frames.

Freeware VR Programs. There are a number of free programs available to create and render virtual environments. This software is generally copyrighted freeware, which means that the original authors retain the copyright to commercial use, but distribute the software free to interested users. Most of these programs are not as highly polished as commercial software, and support can often be totally lacking for the would-be developer. But all things considered, freeware can be an excellent first entrance into the world of virtual reality.

Geometry. The description of an object in terms of its dimensions

Graphics Accelerators. Specialized hardware to increase speed of graphics manipulation.

Haptic Displays/Interfaces. Devices that use all the physical sensors that provide us with a sense of touch at the skin level and force feedback information from our muscles and joints.

Hierarchical Structure. Within a virtual environment, objects that have relationship to other objects are described within a hierarchy. The ‘world’ is the highest level in the hierarchy, often followed by different ‘rooms’ or ‘sections’ of the ‘world’, followed by the objects associated with that section, and so on. This structure defines what are called ‘parent-child’ relationships, with the ‘parent’ object higher within the hierarchy than the child object.

HMD (Head Mounted Display). 1. A set of goggles or a helmet with tiny monitors in front of each eye that generate images, seen by the wearer as being 3-D. VPL Research refers to the HMD’s they sell as Eyephones. 2. A device, which is fastened to the head, and used to display a computer-generated scene. A Head Mounted Display typically provides a stereo-optic (3D) view through the use of two LCD or small CRT displays. Brand names include EyePhone (VPL Research), Visette (W-Industries), Private Eye (Reflection Technologies) and others.

Hypermedia. A form of media in which information is linked to other related information, in which the user has control over the dynamic movement from link to link. This kind of media presents design challenges in attempting to provide relevant links that make sense to the user. World Wide Web browsers are an excellent example of hypermedia in practice.

Immersion; Immersive. The user feels as if he or she is ‘placed’ within the environment. This feeling is often referred to as presence. This feeling of presence is generated and enhanced in two ways: 1) using a stereoscopic viewing device; 2) having a wide field of view. The feeling of presence, of "being there", surrounded by space and capable of interacting with all available objects is one of the hallmarks of good VR.

Input Device. A device used to communicate with and control the user’s actions within a virtual (or non-virtual) environment. Most virtual input devices, such as a dataglove or flying mouse are externally ‘tracked’ for their location in Cartesian space, relative to the Cartesian coordinates of the virtual environment. It is through this device that the computer can interpret relative spatial relationships of the user and objects in the environment, providing the user with an added sense of presence as he or she navigates within the environment.

Interaction; Interactive. Interaction implies that the participant or user is engaged with the system, usually in more than just a perceptual or cognitive sense. Interaction is often defined at the system level, in that the system will not function without input from the participant. In the virtual environment, the user should be able to interact with objects and other participants, hopefully by natural movements, gestures or words. For example: users can physically extend their hand and grasp a virtual object using a dataglove, open and close doors as one would in the real world, or move freely through a virtual rendition of an architectural space.

Interactions. Interactions are those behaviors that occur between participant and environment, participant and object, or object to object. They are often cause-and-effect driven, though they can certainly be programmed to be much more arbitrary. Interactions are what make virtual environments interesting.

Lag. Delay between an action and its visual, acoustic, or other sensory feedback, often because of inherent delays in the tracking devices, or in the computation of the scene.

LBE (location based entertainment). A VR game that involves a scenario based on another time and place; filling a studio or space with VR games.

LCD (Liquid Crystal Display). Display devices that use bipolar films sandwiched between thin panes of glass. They are lightweight and transmissive or reflective, and ideal for HMD.

Lighting. Lighting is used in a virtual environment to enhance and focus one’s attention in much the same way that lighting is used in theater. There are different kinds of lighting (and shading) that can also be applied directly to objects, which can drastically change their appearance. (See phong shading).

LOD (Level of Detail). A model of a particular resolution among a series of models of the same object. Multiple LOD's are used to increase graphics performance by drawing simpler geometry when the object occupies fewer pixels on the screen. LOD selection can also be driven by graphics load, area-of-interest, gaze direction, and the relative distance of the participant from an object. Normally, the further a participant is from an object, less detail is required.

Mental Models. Mental models are the conceptual representations that humans (and perhaps other organisms create to give meaning to their experiences and knowledge. Metal models can be likened to large hierarchical and relational networks, whereby information is taken from the environment, and meaning is constructed in a manner that makes sense to the individual.

MOO - An object-oriented MUD.

Motion Parallax. Objects at different distance and fixation points move different amounts when the viewpoint is dollied along the x axis (left- right).

MUD. A multiuser dungeon; a place on the Internet where people can meet and browse (some of which are also a MOO).

Multimedia. Typically, a presentation blending of text, graphics, audio and video from various sources. May be computer augmented and/or controlled. A sub-set of Hypermedia.

Orientation. The orientation of a user (or an object) is how that user or object is aligned in Cartesian space. If the participant’s view is skewed off the normal (parallel) angle of the horizon, it will contribute to a sense of disorientation, as our proprioceptive and vestibular systems seek this normal angle of orientation.

Parallel Processors. Virtual reality, and other graphics-intensive presentations require very heavy processor power. Some developers have gone to linking processors together, so that they run in parallel, providing substantial additional power.

PC. Personal computer.

Phong Shading. A method for calculating the brightness of a surface pixel by linearly interpolating points on a polygon and using the cosine of the viewing angle. Produces realistic shading.

Photorealism. An attempt to create realistic appearing images using level of detail, color and texture to fool the eye.

Pitch. The angular displacement of a view along the lateral axis.

Pod. Capsule or cabin designed to hold one or more players in a VR-based game. Typically a pod includes connections for I/O devices such as HMD’s, headphones, joysticks, etc.

Polygon Mesh. A polygonal object where, for each object in a mesh, there is a common pool of points that are referenced by the polygons for that object. Transforming these shared points reduces the calculations needed to render the object. A point at the edge of a cube is only processed once, rather once for each of the three edge/polygons that reference it.

Polygons. Polygons are an ordered set of vertices connected by sides. These can be dynamically created and texture-mapped using various sources of image data. Various hardware platforms support different texturing methods and quantities. Rendering is performed in either wireframe, smooth-shaded or textured modes.

Presence; Telepresence. One of the defining characteristic of a good VR system, a feeling of being there, immersed in the environment, able to interact with other objects there.

Projected Reality. A VR system that uses projection screens rather than HMD’s or personal display monitors.

Proprioceptive System. Humans (and other organisms) have the capability to accurately judge where their bodies are in Cartesian space. For example, even though I may have my hand behind my back, I still know where it is located relative to the rest of my body and to the environment.

Real-time. A phrase used to describe computer graphics and interactions that appear to the user without lag or flicker (e.g. 60 cycles per second (cps) displays; highly interactive computation). Real-time graphics and interactions contribute to the participant’s sense of presence, in that the brain is not forced to wait for feedback from the system once an action or interaction has been initiated.

Render. The process of drawing a graphics object as pixels on a computer display.

Resolution. Usually the number of lines or pixels in a display, e.g. a VGA display has 640 by 480 pixels per screen.

Roll. The angular displacement of a view along the longitudinal axis.

Scaling. In the virtual environment, objects can be manipulated along any axis relative to each other, and relative to the user. This process allows the designer to change both the size and the relative dimensions of an object. In addition, the environment itself can also be changed in the same fashion, using multiplication or division, providing the user with the opportunity to ‘go inside’ microscopic organisms, or to manipulate ‘the universe’ with his or her hand. Using scale effectively is one of the most powerful aspects of virtual reality as it can change the participant’s perspective in a dramatic manner.

Sensors. Sensors are used in the virtual environment to react to changes in either the state of the participant, or objects in the virtual environment, or in response to multiple devices connected to lights, objects, viewpoints, etc., in the real world.

Shutter Glasses. LCD screens or physically rotating shutters used to see stereoscopically when linked to the frame rate of a monitor.

Simnet. A prototype networked simulation system built by BBN for training military skills in tanks, helicopters, and other vehicles. Using networked graphics and displays built into physical mock-ups, it has been called a vehicle-based VR or synthetic environment.

Simulator Sickness. The disturbances produced by simulators, ranging in degree from a feeling of unpleasantness, disorientation, and headaches to nausea and vomiting. Many factors may be involved, including sensory distortions such as abnormal movement of arms and heads because of the weight of equipment; long delays or lags in feedback, and missing visual cues from convergence and accommodation. Simulator sickness rarely occurs with displays less than 60 degrees visual angle.

Stereoscopic Viewing Device. A stereoscopic viewing device allows the participant to ‘see’ a slightly different view of an environment, just as our eyes do in the real world. Our brain recomposes the two images, giving the viewer a sense of depth, thereby adding the 3-D element to the experience. It can be a problem if the views presented to each eye are either too close together, or too far apart. This can be extremely disorienting for the viewer.

Synthetic Environments. VR displays used for simulation.

Tactile Displays. Devices like force feedback gloves, buzzers, and exoskeletons that provide tactile, kinesthetic, and joint sensations.

Tactile Feedback (TFB). Sensation applied to the skin, typically in response to contact or other actions in a virtual world. (Compare to Force Feedback.) Tactile Feedback can be used to produce a symbol, like Braille, or simply a sensation that indicates some condition.

Tactile Stimulation. Devices that can provide feedback to the user regarding haptic interactions. Examples include force feedback gloves, buzzers, and exoskeletons that provide tactile, kinesthetic, and joint sensations.

Telepresence. The ability to act and interact in a distant environment through cybernetic technology. The electronic analog to an out-of-body experience.

Texture Animation. The process of requesting that a texture be re-applied to a surface at a certain rate, giving the user the sensation that the texture is actually ‘moving’. This is a particularly useful technique for adding realism to objects who’s’ surfaces generally do move, such as water.

Texture Mapping. A bitmap added to an object to give added realism.

Three Dimensional (3D) Computer Environment. See Virtual Reality.

Tracker. A device that emits numeric coordinates that describe its changing position in Cartesian space. Typically, position trackers are attached to head mounted displays (see above) and to input gloves. Position trackers work via various technologies, including direct connection, magnetic sensing, acoustic or optical tracking. Manufacturers include Ascension Technology, Logitech, Polhemus, Shooting Star Technology, and others.

Vestibular System. Humans (and other organisms) have a complex system of inner-ear canals and very small bony structures which reflect our angle of orientation relative to the environment. Normally, it is the vestibular system that keeps our bodies upright in space, unless we choose otherwise. Individuals with vertigo have problems with their vestibular systems. Note, in a virtual environment, orientation is completely arbitrary, which can be confusing to the vestibular system, resulting in disorientation and Simulator Sickness.

Virtual Environments (VE). Realistic simulations of interactive scenes. See Virtual Reality.

Virtual Object. An object which is not physically tangible, but is perceptually tangible nonetheless. Holograms and objects found in virtual environments are two examples.

Virtual Prototyping. The use of VR for design and evaluation of new models.

Virtual Reality (VR), Virtual Environment (VE). 1. That sense of place and being which exists in cyberspace. Artificial Reality implies non-immersion technology, such as Myron Kreuger’s Video Place. Virtual Reality commonly implies full-immersion technologies using goggles and similar devices. Virtual Environment and Synthetic Environment are terms typically used by the US Defense Department and Space Agency and carrying the same essential meaning. See also Artificial Reality (AR), Synthetic Environment (SE). 2. An immersive, interactive simulation of realistic or imaginary environments.

Virtual World. Referencing the entire virtual environment or universe.

Visual Realism. See photorealism..

Visualization. Use of computer graphics to make visible numeric or other quantifiable relationships.

Workstation. Personal computing system optimized for high performance. Typically workstations include high performance, high resolution graphics display systems, and use the UNIX operating system. Workstations are typically considered to be more powerful than PCs, but that difference is fading quickly.

X, Y, and Z axes. The designated planes of origin, by which all locations in Cartesian space are designated. In the real world, Y represents height, X represents width, and Z represents depth. Depending upon the virtual system being used, these coordinate references may change.

Yaw. The angular displacement of a view around the vertical axis.