Date: Wed, 4 Aug 1993 14:16:08 CDT From: Greg Newby Subject: TERMS: A Complete Virtual Reality Glossary Summary: This is the best glossary seen yet! -- The Mods. VIRTU-L VIRTUAL REALITY TERMS Joe Psotka and Sharon Davison 6DOF - Six degrees of freedom: Yaw, pitch, roll, up-down, left-right, front-back (or pan, zoom, swivel). A-Buffering - Keeping track of the Z-depth of pixels to cull them before rendering. Accelerator - specialized hardware to increase speed of graphics manipulation. Accommodation - Change in the focal length of the eye's lens. Actors - CAD representations of players performing actions for them, as in the Mandala system (see Agent, Character). Accelerator - Specialized hardware to increase speed of graphics manipulation. Affine - Any transformation composed from rotations, translations, dilatations (expansions and contractions) and shears. Agents - CAD representations of human forms capable of guiding (Guides) navigators through a VR (see Actor, Character). Aliasing - An undesirable jagged edge on many 3D renderings on bitmapped displays. Creates jaggies along the sides of objects and flickering of objects smaller than a pixel. (see Anti- Aliasing ) Allocentric - Other than egocentric, such as a bird's eye view, or adopting another person's viewpoint. Ambient light - General non-directional illumination. Anti- Aliasing removes jagged edges on bitmapped displays by interpolating neutral colors or intermediate intensities. Articulation - Objects composed of several parts that are separably moveable. Artificial Intelligence - The attempt to mimic and automate human cognitive skills through rules and knowledge representation techniques (e.g., understanding visual images, recognizing speech and written text, solving problems, making medical diagnoses, heuristic knowledge, etc.). Artificial Reality - Introduced by arts and computer visualization scholar Myron Krueger in the mid-1970s to describe his computer- generated responsive environments. Krueger has emphasized the non-intrusive (Second - Person VR) systems that track people with pattern recognition techniques and display them and the surround on projection systems (see CAVE). As realized in his VIDEOPLACE and the Vivid Group's Mandala system, it is a computer display system that perceives and captures "a participant's action in terms of the body's relationship to a graphic world and generates responses (usually imagery) that maintain the illusion that his actions are taking place within that world." (M. Krueger, Artificial Reality, 1992) (See Virtual Reality and Cyberspace) Aspect ratio - Ratio of width to height of the field of view. Augmented Reality - This is the use of transparent displays worn as glasses on which data can be projected. This allows someone to repair a radar, for example, and have the needed data displayed on the glasses while walking around the radar. Back clipping plane - A distance beyond which objects are not shown. Backface Removal - The elimination of those polygons that are facing away from the viewer. Backward raytracing - From the eye to the object (currently how most raytracing is done). Binaural - Stereo sound incorporating information about the shadows at human ears and heads. Biosensors - Special glasses or bracelets containing electrodes to monitor muscle electrical activity. One interesting VR use is for tracking eye movements by measuring muscle movements. BOOM - A 3-D display device suspended from a weighted boom that can swivel freely about so the viewer doesn't have to wear an HMD; instead, it steps up to the viewer like a pair of binoculars. The boom's position communicates the user's point of view to the computer. Browser - Overviews such as indexes, lists or animated maps to provide a means of navigating through the physical, temporal, and conceptual elements of a VR. CAVE - A VR using projection devices on the walls and ceiling to give the illusion of immersion. Character - A being with a virtual body in virtual reality. (Walser, 1991) (see Agent, Actor).. Concept Map - A browser or terms, definitions, or icons arranged in semantic proximity. Convergence - The angle between the two eyes at a fixation point. This changes for objects at varying depths in the real world and on 3-D displays. Convolvotron - A system for controlling binaural sound production in a VR. Consensual Reality - The world, or a simulation of a world, as viewed and comprehended by a society. (Walser, 1991). Culling - Removing invisible pieces of geometry and only sending potentially visible geometry to the graphics subsystem. Simple culling involves rejecting objects not in the view frustum. more complex systems take into account occlusion of some objects by others, e.g. a building hiding trees behind it. Cybernetic Simulation - Dynamic model of a world filled with objects that exhibit lesser or greater degrees of intelligence. Cyberspace - 1. A place filled with virtual "stuff" populated by people with virtual bodies. A special kind of virtual space which promotes experiences involving the whole body. (Walser, 1991). 2. A term coined by William Gibson in his book Neuromancer (1984 a coincidental date!) to describe a shared virtual universe operating within the sum total of all the world's computer networks. (See Artificial Reality and Virtual Reality) Cyberspace Playhouse - Social center or place where people go to play roles in simulations. (Walser, 1991). Cyberia - see Cyberspace and a pun on Siberia; an Autodesk project and the first VR project by a CAD company. DataGlove - A glove wired with sensors and connected to a computer system for gesture recognition. It is used for tactile feedback and it often enables navigation through a virtual environment and interaction with 3-D objects within it. DataSpace - A visualized representation of complex information. DataSuit - Same as a DataGlove, but designed for the entire body. Only one DataSuit has yet been built, with limited capabilities. Deck - A physical space containing an array of instruments which enable a player to act within, and feel a part of, a virtual space. (Walser, 1991). De-rez - Techniques to make pixels less visible in a display. Depth Cuing - Using shading, texture, color, interposition (or many other visual characteristics) to provide a cue for the z-coordinates or distance of an object. Direct Manipulation - A term coined by Shneiderman to reflect the use of computer icons or text as if they were real objects. Disorientation - Confusion about distances and directions for navigation. Dreaming - A state of mind during sleep where vivid colored imagery becomes realistic and immersive. A natural counterpart to VR. Droid - Puppet that embodies a human intellect (as in android). (Walser, 1991). Dynamics - The way that objects interact and move. The rules that govern all actions and behaviors within the environment. Dynamic Lighting: Changes in lighting effects on objects as they and the observer move. Force Feedback - Representations of the inertia or resistance objects have when they are moved or touched. Effectors - The output techniques that communicate a user's movements or commands to the computer and to the VR. Egocenter - The sense of self and personal viewpoint that determines one's location in a VR. See projection point. Electromagnetic Forces - Effects of emf on human tissues are poorly understood and may constitute an important hazard from tracking and display devices. Endoscopic - Part of a family of new surgical procedures that avoid cutting open major portions of the patient in favor of making small holes through which tools and sensors are inserted and the surgery performed. In a VR or telepresence application, the surgeon manipulates the tools by observing the surgery site on a monitor via optical fibers and a tiny video camera. Environment - This a computer-generated model that can be experienced from the "inside" as if it were a place. Eyeball in the Hand - A metaphor for visualized tracking where the tracker is held in the hand and is connected to motion of the projection point of the display. Eyephone - A HMD made by VPL that combines visual and auditory displays. Eye Tracking - Devices that measure direction of gaze. Most HMDs do not currently support eye tracking directly. Exoskeletal Devices - In order to provide force feedback designers have added rigid external supports to gloves and arm motion systems. Field of View - The angle in degrees of the visual field. Most HMDs offer 60 to 90 degrees FOV. Since our two eyes have overlapping 140 degree FOV, binocular or total FOV is roughly 180 degrees in most people. A feeling of immersion seems to arise with FOV greater than 60 degrees. Finite element modelling - Decomposition of complex structures into small, simple elements so that engineering computations are manageable. Fish Tank VR - With stereographic display systems attached to a monitor and the scene's virtual image behind the screen, the egocentric projection is called a fish tank. Flat Shading - A uniform shading in which one value is applied to each facet of a polygon. Force Feedback - The computer guides a machine to offer just the degree of resistance to motion or pressure a situation would offer in real life. Fractal - Any function that contains elements of self-similarity (after the work of Benoit Mandelbrot). Frustum of Vision - 3-D field of view in which all modelled objects are visible. Gesture - Hand motion that can be interpreted as a sign or signal or symbol. Goggles - Often used to refer to HMD or other displays. Gouraud - Shading polygons smoothly with bilinear interpolation. Haptic Interfaces - 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. Head-coupled - Displays or robotic actions that are activated by head motion through a head tracking device. Head Tracking - Monitoring the position of the head through various devices. Head-related transfer function - A mathematical transformation of sound spectrum that modifies the amplitude and phase of acoustic signals to take into account the shape effects of the listener's head. Heads Up Display - (HUD) A display device that lets users see graphics superimposed on their view of the world. (Created for aviators to see symbols and dials while looking out the window.) Hidden Surface - Parts of a graphics object occluded by intervening objects. Holodeck - Virtual reality simulation system and place used primarily for entertainment by the crew of the Enterprise in Star Trek: The Next Generation television series. HMD (Head Mounted display) - 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 HMDs they sell as Eyephones. Hypermedia - The combination of digital text, video, and sound with navigation techniques like buttons, links, and hotspots into one system. HyperSpace - The space of hypertext or hypermedia documents. Immersion - The feeling of presence, of "being there", surrounded by space and capable of interacting with all available objects that is the hallmark of good VR. Impressionists - A 19th century group of artists whose paintings were directed at capturing color and mood, rather than exact perspective outlines. Interactive Fiction - Dramatic creations that encourage user and viewer participation through computer technology, e.g. hypertext, group feedback, or VR. Interaural Amplitude - Differences between a person's two ears in the intensity of sound. Interaural Time - Differences between a person's two ears in the phase of sound. Interface - A set of devices, software, and techniques that connect computers with people to make it easier to perform useful activities. Inverse kinematics - A specification of the motion of dynamic systems from properties of their joints and extensions. Internet - A world wide digital network. Jack - To connect to the matrix of virtual space. (see Gibson). Joysticks - Graphic interface devices. Kinaesthetic Dissonance - Mismatch between feedback or its absence from touch or motion during VR experiences.. 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. Laparoscopy (also laparoscopic surgery) - Less invasive forms of surgery that operate through small optics and instruments; lending themselves to robotic manipulation and VR training. 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. 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, Magic Wand - A 3D interface device used for pointing and interaction; an elongated 3D mouse. Metaball - A kind of "equipotential surface" around a point. You specify a point, a radius, and an "intensity" for each ball; when balls come close, their shapes blend to form a smooth equipotential surface. They seem to be very useful for modelling shapes like animals and humans. They can be rendered by most raytracing packages ( also "blobs" or "soft spheres" or "fuzzy spheres"). Microsurgery - A form of surgery that lends itself to robotics and VR. See also Laparoscopy. MIDI - A digital sound standard for music. MOO - A MUD, object-oriented. Monitor - Display, HMD, Goggles, HUD, LCD Motion parallax - Objects at different distance and fixation points move different amounts when the viewpoint is dollied along the x axis (left- right). Motion Platform - A controlled system that provides real motion to simulate the displayed motion in a VR. Motivation - A psychological need, drive, or feeling that raises the intensity of an action. MRI - Magnetic Resonance Imaging; a way of making internal organs and structures visible by analyzing radio frequency emissions of atoms in a strong magnetic field. Can be made 3D with rendering of large amounts of data. MUD - A multiuser dungeon; a place on the internet where people can meet and browse (also a MOO). Multiperson Space - 1. Multiplayer space involving 2 or more human players. 2. A type of interactive simulation which gives every user a sense that he/she, personally, has a body in a virtual space. (Walser, 1991). Multiplayer Space - Cyberspace that emerges from simulation that is generated simultaneously by two or more decks. Players can be made up of one human and the rest AI. (Walser, 1991). Nanomanipulation - Ability to visualize and affect objects in the nanometer range. Navigation - Moving through virtual space without losing one's way. Objects: Graphical entities that can be dynamically created or loaded from model files. Many functions act upon them... Tasks: each object performs a task per frame Hierarchies: objects can be "linked" together Sensors: objects can be connected to sensors Modify: color, texture, scale, etc. Collision Detection: between objects and polygons Vertices: these can be dynamically created along with the definition of a vector normal for Gouraud-shading. Occipital Cortex - The back of the brain receiving retinotopic projections of visual displays. Occlusion - Hiding objects from sight by interposition of other objects. Pan - The angular displacement of a view along any axis or direction in a 3D world; or a move through translation in a 2D world. Parietal Cortex - An area of the brain adjacent and above the occipital cortex, thought to process spatial location and direction. Paths: objects or viewpoints can follow predefined paths that can be dynamically created and interpolated. Perspective - The rules that determine the relative size of objects on a flat page to give the impression of 3D distance. 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 with much detail and texture. Pitch - The angular displacement of a view along the lateral axis (front - back). Pixel - The smallest element of a display that can be adjusted in intensity. Polygons - 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. Pop. When an object's visible appearance suddenly changes or an object appears out of nowhere. Usually an undesired artifact of poor LOD. Portals - Polygons that once passed thru, automatically load a new world or execute a user-defined function. Position trigger - A hotspot, or sensitive spot, or button, that begins a computation when touched in some way. Presence - A 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 HMDs or personal display monitors. Radiosity - A diffuse illumination calculation system for graphics based on energy balancing that takes into account the multiple reflectances off many walls. Raytracing - A rendering system that traces the path of light from objects to light sources (see Backward Raytracing). Real projection - A VR projection system ( a pun on rear projection). Real-time - Appearing to be without lag or flicker (e.g. 60 cps displays; highly interactive computation). Renaissance - A period of art dominated by the exploration of perspective. Render - Convert a graphics object into pixels. Resolution - Usually the number of lines or pixels in a display, e.g. a VGA display has 640 by 480 pixels. Roll - The angular displacement of a view along the longitudinal axis (left- right). Scan Conversion - The change of video signals from one form (e.g. RGB) to another (e.g. NTSC). Scintillation. The "sparkling" of textures or small objects. Usually undesirable and caused by aliasing. Second Person VR - The use of computational medium to portray a representation of you that is not realistic, but still identifiable. E.G. In the Mandala system a video camera allows you to see yourself as another object over which you have control by your own bodily movement. Sensor Lagtime - Delays in the feedback or representation of your actions caused by computation in the tracker or sensor. Sensors - Mechanisms or Functions that act to change objects in response to multiple devices connected to lights, objects, viewpoints, etc., in the real world. Sensory Substitution - The conversion of sensory information from one sense to another; e.g. the use of auditory echoes and cues to "see" the shape of your surroundings. Sequence (keyframe animation) - Interpolate images between stored frames (tweening). Shaded Surface - [BLANK] Shared Worlds - Virtual environments that are shared by multiple participants at the same location or across long distance networks. 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. Sound - Accurate localization of sounds without individualized head transfer functions remains a problem. Spatial superposition - In augmented reality displays, accurate spatial registration of real and virtual images remains difficult. Spatial navigation - Accurate self localization and orientation in virtual spaces is not as easy as real world navigation. Techniques for embedding navigational assists in complex dataspaces remain important research goals. Spatial Representation System - The cortical structures and functions that maintain spatial orientation and recognition. Spreadsheets - Early spreadsheets made the computer a valuable tool for accounting, and helped spread computers throughout industry. What is the "spreadsheet" or commercial application that will make VR a success? Star Trek - The fantasy rich series offers a widely known example of a VR in its "Holodeck". Plans are also underway to use VR in a Star Trek LBE (location based entertainment). Stereopsis - Binocular vision of images with horizontal disparities. The importance of stereopsis for immersion is not established. Striate Cortex - Visual cortex (see Occipital, Parietal). Supercockpit - An Air Force project led by Tom Furness that advanced the engineering and human factors of HMDs and VR. It used digital displays of instruments and terrain. Synthetic Environments - VR displays used for simulation. Tactile displays - Devices like force feedback gloves, buzzers, and exoskeletons that provide tactile, kinaesthetic, and joint sensations. Tactile stimulation - Devices like force feedback gloves, buzzers, and exoskeletons that provide tactile, kinaesthetic, and joint sensations. Tele-existence - Remote VR. Telemanipulation - Robotic control of distant objects. Teleoperation - see Telemanipulation. Telepresence - VR with displays of real, remote scenes. Telerobotic - Robotic control of distant objects (see Telemanipulation, Teleoperation). Telesurgery - Surgery using Teleoperation. Terrain - Geographical information and models that can be either randomly generated or based on actual data. Dynamic terrain is an important goal for current SIMNET applications. Texture mapping: A bitmap added to an object to give added realism. Detail Texture. A texture superimposed on another texture to increase the apparent resolution of the original texture image. Used when the eyepoint is so close to the textured object that the base texture is being magnified (i.e. one texel in the texture image being mapped to many pixels on the screen). A detail texture, typically a noise image, is blended into the image at a higher resolution adding a gritty realism to the appearance of the object. Texture Swimming - Unnatural motion of static textures on the surfaces of objects as they are rotated. Caused by quick and dirty texture interpolation in screen coordinates. Correctable by subdividing polygons sufficiently or by doing perspective correction. Theater - VR opens new metaphors to explore with interactive theater. Tracker - A device that emits numeric coordinates for its the changing position in space. Transparency - How invisible and unobtrusive a VR system is. Trompe l'Oeil - Perspective paintings that deceive viewers into believing they are real (e.g. a painting of the sky and clouds on the inside of a dome). Universe - This is the "container" of all entities in a VR. Entities can be temporarily added or removed from consideration by the simulation manager. The sequence of events in the simulation loop can be user-defined. VRactors - Virtual actors, either autonomous or telerobotic in a VR theater. Viewpoints - Points from which raytracing and geometry creation occurs. The geometric eye point of the simulation. You can have multiple viewpoints. They can be attached to multiple sensors. Virtual Cadaver - A current NIH project to slice and digitize a complete human body. Virtual patient - Telerobotic or digitized animations of humans with accurate disease models. Virtual Prototyping - The use of VR for design and evaluation of new models. Virtual Reality - An immersive, interactive simulation of realistic or imaginary environments. (Jaron Lanier) Virtual Environments - Realistic simulations of interactive scenes. Visualization - Use of computer graphics to make visible numeric or other quantifiable relationships. Voxel - A cubic volume pixel for quantizing 3D space. Waldo - A remotely controlled mechanical puppet (Heinlein). Windows - On some hardware platforms, you can have multiple windows and viewpoints into the same virtual world. Wire Frame Outlines - Displays of the outlines of polygons, not filled in. World - Whole environment or universe. World in the hand - A metaphor for visualized tracking where the tracker is held in the hand and is connected to motion of the object located at that position in the display. Yaw - The angular displacement of a view around the vertical, y axis (up - down). ------------------------------------------------------------------ We thank many people for their help and input, particularly all the users of virtu-l and sci.virtual.worlds. Latham's dictionary was particularly useful. Latham, R. (1991) The dictionary of Computer Graphics Technology and Applications. New York: Springer - Verlag. ------------------------------------------------------------------ Benedikt, M. (Ed.), (1991) Cyberspace: First Steps. Cambridge, MA: The MIT Press. Earnshaw, R. A., Gigante, M. A., Jones, H. Virtual Reality Systems, New York: Academic Press. Ellis, S. R. (Ed.), (1991) Pictorial Communication in Virtual and Real Environments. London: Taylor and Francis. Kalawsky , R. (1993) The Science of Virtual Reality and Virtual Environments New York: Addison-Wesley. Laurel, B. (1991) Computers as theater. New York: Addison-Wesley Publishing Co. Pimentel and Teixeira (1992) Through the looking glass. Intel. Rheingold, H. (1991 ) Virtual Reality. New York, Simon & Schuster. I thank many people for their help and input, particularly all the users of virtu-l and sci.virtual.worlds.