Virtual Reality Zone/VRZONE.ISO/mac/TEXT/MISC/VRTERMS.TXT

Internet Message Format | 1994-11-28 | 28KB

From: Greg Newby <[e-mail]>
Subject: TERMS: A Complete Virtual Reality Glossary
Date: Wed, 4 Aug 1993 14:16:08 CDT


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.