T-1: Data communications service that supports 1.544 megabits per second operation.

T-2: Data communications service that supports 45 megabits per second operation.

tabular model: A symbolic model whose properties are expressed in tabular form; for example, a truth table that represents a Boolean logic "OR" function. Contrast with: graphical model; mathematical model; narrative model; software model.

taction: Is the sense of touch that comes from sensitive nerve sensors at the surface of the skin.

target: Feature (i.e., object, landmark, human feature) to be localized by the tracking process.

taxonomy: A classification system. Provides the basis for organizing objects for identification, retrieval and research purposes.

technical data: Scientific or technical information recorded in any form or medium (e.g., manuals and drawings). Computer programs, related software, financial data and other information related to contract administration are not technical data where documentation of computer programs and related software are.

technical infrastructure: The internal framework that must be built to implement an operational service.

telecommunications: Any transmission; emission; reception of signs, signals, writings, images, sounds; or information of any nature by wire, radio, visual, or other electromagnetic systems.

telepresence: The ability to directly interact (often via computer mediation) with a physically real, remote environment from the first person point of view; there are no restrictions on the location of the remote environment, and there are no restrictions on the size of the device used to carry out the user's commands at the remote location.

tempest: An unclassified term referring to technical investigations for compromising emanations from electrically operated information processing equipment; these investigations are conducted in support of emanations and emissions security.

Test and Evaluation: The act of generating empirical data during the research, development or sustainment of systems, and the creation of information through analysis that is useful to technical personnel and decision makers for reducing design and acquisition risks. The process by which systems are measured against requirements and specifications, and the results analyzed so as to gauge progress and provide feedback.

Test and Training Enabling Architecture: The Test and Training Enabling Architecture (TENA) is designed to bring affordable interoperability to US live simulation test and training ranges and their customers. The TENA program was established in 2002 for developing the foundation that will allow DoD ranges, labs and facilities to be interoperable by 2010. TENA integrates testing, training, simulation, and a high-performance computing technology, distributed across many facilities, and ties them together with a common architecture.

texturing: A technique performed in the rasterizing stage of the graphics pipeline in order to modify the object model's surface properties such as color, specular reflection, or pixel normals.

tightly coupled: A condition that exists when simulation entities are involved in very close interaction such that every action of an entity must be immediately accounted for by the other entities in real-time.

time: The measurable aspect of duration. Time makes use of scales based upon the occurrence of periodic events. These are: the day, depending on the rotation of the Earth; the month, depending on the revolution of the Moon around the Earth; and the year, depending upon the revolution of the Earth around the Sun. Time is expressed as a length on a duration scale measured from an index on that scale. For example: 4 p.m. local mean solar time means that 4 mean solar hours have elapsed since the mean Sun was on the meridian of the observer.

time-dependent event: An event that occurs at a predetermined point in time or after a predetermined period of time has elapsed. See: conditional event.

time management: 1. A collection of High Level Architecture (HLA) services that support controlled message ordering and delivery to the cooperating joined federates within a federation execution in a way that is consistent with federation requirements. 2. Maintains a common sense of time among all federates, either based on real time clock or based on an event based clock.

time redundancy: Use of extra processing when time is available to perform the same computation multiple times with a single hardware and software combination and then compare the results.

time-slice simulation: A discrete simulation that is terminated after a specific amount of time has elapsed; for example, a model depicting the year-by-year forces affecting a volcanic eruption over a period of 100,000 years. Synonym: time-interval simulation. See: critical event simulation.

time stamp (of an event): A time stamp is used to indicate the time at which the data contained in the protocol data unit were generated. For simulations using absolute timestamps, this time is the exact UTC. For simulations using relative timestamps, this time is the time that the simulation application assumes the event or state occurred in the synthetic environment relative to its own host clock. By example this timestamp can be specified using a 32-bit unsigned integer representing units of time passed since the beginning of the current hour. The least significant bit indicates whether the timestamp is absolute or relative.

timestamp order: An ordering of messages provided by a runtime infrastructure for joined federates making use of time management services and messages containing time stamps. Messages having different time stamps are said to be delivered in timestamp order if for any two messages M1 and M2 (time stamped with T1 and T2, respectively) that are delivered to a single joined federate where T1 < T2, then M1 is acted upon before M2.

time step models: Dynamic models in which time is advanced by a fixed or independently determined amount to a new point in time, and the states or status of some or all resources are updated as of that new point in time. Typically these time steps are of constant size, but they need not be.

time variable: A variable whose value represents simulated time or the state of the simulation clock.

Topographic Map of the United States: The recommended designation for the topographic map of the United States prepared of the quadrangle areas in atlas sheet form, chiefly by the U.S. Geological Survey. This map portrays all basic information about location, elevation, and extent of physical and cultural features that are required for preliminary economic and engineering studies and for incorporation in maps prepared for special purposes.

touch feedback: Conveys real-time information on contact surface geometry, virtual object surface roughness, slippage, and temperature. It does not actively resist the user's contact motion and does not stop the user from moving through virtual surfaces.

tracked munition: 1. A munition for which position data is required over time. By necessity, a tracked munition becomes a simulation entity during its flight; its flight path is represented, therefore, by Entity State Protocol Data Units. 2. A munition for which tracking data is required. A tracked munition's flight path is represented by Entity State Protocol Data Units.

tracker: The special-purpose hardware used in VR to measure the real-time change in a 3D object position and orientation.

tracker accuracy: Represents the difference between the object's actual 3D position and that reported by tracker measurements.

tracker drift: The steady increase in tracker error with time.

tracker jitter: Represents the change in tracker output over time when the tracked object is stationary.

traditional warfare: A form of warfare between the regulated militaries of states, or alliances of states, in which the objective is to defeat an adversary's armed forces, destroy an adversary's war-making capacity, or seize or retain territory in order to force a change in an adversary's government or policies.

transmission security: The component of communications security that results from all measures designed to protect transmissions from interception and exploitation by means other than cryptanalysis.

transmit management: The control of the transmission rate to match the transmission media. The transmission rate is selected to reduce total network traffic.

transverse Mercator map projection: A conformal cylindrical map projection, being in principle equivalent to the regular Mercator map projection turned (transverse) 90 in azimuth. In this projection, the central meridian is represented by a straight line, corresponding to the line which represents the Equator on the regular Mercator map projection. Neither the geographic meridians (except the central meridian) nor the geodetic parallels (except the Equator) are represented by straight lines. Also called Inverse cylindrical orthomorphic map projection; Inverse Mercator map projection; transverse cylindrical orthomorphic map projection.

trial: Represents a single instance of an experiment to be performed as part of a human factor study.

Turing test: An informal validation method well suited for validating models of human behavior first proposed as a means to evaluate the intelligence of a computer system.

typing: The enforcement of the software class of an object, such that objects of different types may not be interchanged, or may be interchanged only in restricted ways.

U

ultrasound tracker: A noncontact position measurement device that uses an ultrasonic signal produced by a stationary transmitter to determine the real-time position of a movable receiver element.

unbundling: The process of unpacking a set of protocol data units into multiple separate protocol data units. Contrast with: bundling.

unconventional warfare: A broad spectrum of military and paramilitary operations, normally of long duration, predominantly conducted through, with, or by indigenous or surrogate forces who are organized, trained, equipped, supported, and directed in varying degrees by an external source. It includes, but is not limited to, guerrilla warfare, subversion, sabotage, intelligence activities, and unconventional assisted recovery.

unicast: A transmission mode in which a single message is sent to a single network destination; i.e., one-to-one.

Unified Modeling Language (UML): A general purpose, standardized specification (modeling) language for object modeling that includes a graphical notation used to create an abstract model of a system.

unit: A basis of measurement.

unit conversion: A system of converting measurement from one basis to another; for example, English/metric, knots/feet per second, etc.

Universal Space Rectangular Coordinate System: A right-handed orthogonal coordinate system with its origin at the center of the Earth, positive x-axis in the equatorial plane and passing through the zero degree meridian, positive y-axis in the equatorial plane and passing through the ninety degree east meridian, and positive z-axis passing through the North Pole.

universal time: A measure of time that conforms, within a close approximation, to the mean diurnal rotation of the Earth and serves as the basis of civil time-keeping. Universal time (UT1) is determined from observations of the stars, radio sources, and also from ranging observations of the Moon and artificial Earth satellites. The scale determined directly from such observations is designated Universal Time Observed (UTO); it is slightly dependent on the place of observation. When UTO is corrected for the shift in longitude of the observing station caused by polar motion, the time scale UT1 is obtained. When an accuracy better than one second is not required, Universal Time can be used to mean Coordinated Universal Time (UTC). Also called "Zulu Time". See: Greenwich Mean Time.

universal transverse Mercator (UTM): A military grid system based on the transverse Mercator projection, applied to maps of the Earth's surface extending to 84 N and 80 S latitudes.

update rate: Maximum frequency of report of position, orientation, or other regularly occurring event.

user: The organization that accredits and uses the results or products from a specific application of a model or simulation.

V

validation: 1. The process of determining the degree to which a model or simulation and its associated data are an accurate representation of the real world from the perspective of the intended uses of the model. 2. The process of evaluating a model, simulation, or federation of models and simulations throughout the development and execution process to determine how well it satisfies the acceptability criteria within the context of the referent. 3. Data validation is the documented assessment of data by subject area experts and its comparison to known or best-estimate values. Data producer validation is that documented assessment within stated criteria and assumptions. Data user validation is that documented assessment of data as appropriate for use in an intended M&S. 4. Distributed simulation validation is the process of determining the degree to which a distributed simulation is an accurate representation of the real world from the perspective of its intended use(s) as defined by the requirements. 5. Face validation is the process of determining whether a model or simulation based on performance seems reasonable to people knowledgeable about the system under study. The process does not review software code or logic, but rather reviews the inputs and outputs to assure that they appear realistic or representative. 6. Model/simulation validation is the process of determining the degree to which a model is an accurate representation of the real world from the perspective of the intended use(s) of the model.

validity: 1. The quality of maintained data that is found on an adequate system of classification (e.g., data model) that is rigorous enough to compel acceptance for a specific use. 2. The quality of being inferred, deduced or calculated correctly enough to suit a specific application.

variable: A quantity or data item whose value can change. See: dependent variable; independent variable; state variable. Contrast with: constant.

variance reduction: Procedure used to increase the precision of the estimates that can be obtained for a given number of iterations.

vector: The vector structure, in contrast to the single pixel value of raster features, describes features objectively and subjectively in great detail. Vector features are points, lines, or areas defined by polygons. The vector structure is more flexible because at any magnification it preserves feature content and retains maximum digitized positional accuracy. Vector is not a simple data structure like raster; it requires sophisticated data manipulation software at an additional significant storage cost.

verification: 1. The process of determining that a model or simulation implementation accurately represents the developer's conceptual description and specification. 2. The process of determining that a model or simulation implementation and its associated data accurately represent the developer's conceptual description and specifications. 3. The process of evaluating a model, simulation, or federation of models and simulations and its intermediate products to determine whether the products from a given development phase satisfy the conditions imposed at the start of that phase and, ultimately, determining that an implementation of a model, simulation, or federation of models and simulations correctly and completely represents the developer's conceptual description and specifications. 4. Data verification is the use of techniques and procedures to ensure that data meets specified constraints defined by data standards and business rules. Data producer verification is the use of techniques and procedures to ensure that data meets constraints defined by data standards and business rules derived from process and data modeling. Data user verification is the use of techniques and procedures to ensure that data meets user specified constraints defined by data standards and business rules derived from process and data modeling and to ensure that data are transformed and formatted properly. 5. Distributed simulation verification is the process of determining that an implementation of a distributed simulation accurately represents the developer's conceptual description and specifications. 6. Model/simulation verification is the process of determining that a model implementation accurately represents the developer's conceptual description and specifications.

verification agent: 1. The person or organization designated to perform verification of a model, simulation, or federation of models and/or simulations and the associated data. 2. The organization designated by the M&S sponsor to perform verification of a model, simulation, or federation of M&S.

verification and validation agent: The person or organization designated to perform the verification, validation, or both, of a model, simulation, or federation of models and simulations, and their associated data.

verification and validation proponent: The agency responsible for ensuring verification and validation is performed on a specific model or simulation.

Verification, Validation & Accreditation (VV&A): Verification is the process of determining that a model implementation and its associated data accurately represent the developer's conceptual description and specifications. Validation is the process of determining the degree to which a model and its associated data are an accurate representation of the real world from the perspective of the intended uses of the model. Accreditation is the official certification that a model, simulation, or federation of models and simulations and its associated data are fit for a specific purpose. The VV&A area encompasses three main components: the thing to be simulated, i.e., the real world referent; the simulation model; and a bounding principle, i.e., the accuracy required for the intended use.

video game: A virtual experience carefully designed to be entertaining (among other things).

video see through: Work by combining a closed-view head mounted display with one or two head-mounted video cameras. The video cameras provide the user's view of the real world. Video from these cameras is combined with the graphic images created by the scene generator, blending the real and virtual.

vignette: A self-contained portion of a scenario.

virtual: Refers to the essence or effect of something, not the fact.

virtual battlespace: The illusion resulting from simulating the actual battlespace.

virtual images: Visual, auditory, and tactile stimuli that are transmitted to the sensory end organs so they appear to originate from within the three-dimensional space surrounding the user.

virtual network: The interconnection of Distributed Interactive Simulation cells by any communications means that provide the necessary network services to conduct an exercise.

virtual prototype: A model or simulation of a system placed in a synthetic environment, and used to investigate and evaluate requirements, concepts, system design, testing, production, and sustainment of the system throughout its life cycle.

virtual reality: The effect created by generating an environment that does not exist in the real world. Usually, a stereoscopic display and computer-generated three-dimensional environment gives the immersion effect. The environment is interactive, allowing the participant to look and navigate about the environment, enhancing the immersion effect. Virtual environment and virtual world are synonyms for virtual reality.

virtual simulation: A simulation involving real people operating simulated systems. Virtual simulations inject human-in-the-loop in a central role by exercising motor control skills (i.e., flying an airplane), decision skills (i.e., committing fire control resources to action), or communication skills (i.e., as members of a C4I team).

virtual time: See: simulated time.

virtual training domain: A simulator-based training environment that trains real people using virtual simulators that physically replicate the working environments of real mission systems operating within realistically simulated operational battlespace environments and scenarios.

virtual world: 1. An imaginary space often manifested through a medium. 2. A description of a collection of objects in a space and the rules and relationships governing those objects.

visualization: The formation of an artificial image that cannot be seen otherwise.

visualization pipeline: Process of creating visual representation from simulation data. The pipeline describes a step-wise process involving four phases, namely: 1. Data analysis: preparation of raw simulation data for visualization (i.e., by applying a smoothing filter or interpolating missing values). This step is computer centered, with little or no user interaction. 2. Filtering: Selection of data portions to be visualized, this step is usually user-centered. 3. Mapping or transformation: Focus data are mapped to geometric primitives (i.e., points, lines) and their attributes (color, position, size). This is the most critical step for achieving effective visual representation. 4. Rendering: Geometric data are transformed into visuals (i.e., pixel-based image in 2D, or a 3D model.

visual stealth: A component that provides the capabilities for visually observing a simulation exercise without participating in the simulation exercise interaction.

W

warfare simulation: A model of warfare or any part of warfare for any purpose (such as analysis or training).

war game: A simulation game in which participants seek to achieve a specified military objective given preestablished resources and constraints; for example, a simulation in which participants make battlefield decisions and a computer determines the results of those decisions. Synonym: constructive simulation; higher order model. See: management game.

wargaming: Simulating, by whatever means, a military operation involving two or more opposing forces, using rules, data and procedures designed to depict an actual or assumed live situation.

web mapping service: Produces maps of spatially referenced data dynamically from geographic information.

white box model: A model whose internal implementation is known and fully visible; for example, a model of a computerized change-return mechanism in a vending machine, in the form of a diagram of the circuits and gears that make the change. Synonym: glass box model. Contrast with: black box model.

white box testing: Inner workings of the module are examined as part of the testing to ensure proper functioning.

wide area network: A communications network designed to support interactions across large geographic areas.

world coordinate system: The right-handed geocentric Cartesian system. The shape of the world is described by the World Geodetic System 1984 standard. The origin of the world coordinate system is the centroid of the earth. The axes of this system are labeled X, Y, and Z, with: the positive X-axis passing through the Prime Meridian at the Equator; the positive Y-axis passing through 90 degrees East longitude at the Equator; and the positive Z-axis passing through the North Pole.

World Geodetic System 1984 (WGS 84): A geocentric coordinate system which describes a basic frame of reference and geometric figure for the Earth, and which models the Earth from a geometric, geodetic, and gravitational standpoint. The WGS 84 coordinate system origin and axes also serve as the x, y, and z axes of the WGS 84 ellipsoid, the z axis being the rotational axis.

world view: The view each simulation entity maintains of the simulated world from its own vantage point, based on the results of its own simulation and its processing of event messages received from all external entities. For computer generated forces and for manned simulators or real vehicles, the world view is the perceptions of the participating humans.

X

XTERM: A terminal emulator that functions as a standard terminal for X Window System. It allows the user to work with multiple programs simultaneously, each in a separate window.

X Window System: Called X for short, is a network-based graphics window system that was developed at MIT in 1984.

Y

yaw: Rotation around the Z axis.

yoked variable: One of two or more variables that are dependent on each other in such a manner that a change in one automatically causes a change in the others.

Z

Z-buffer: The management of image depth coordinates in three-dimensional (3-D) graphics, usually done in hardware, sometimes in software. Also known as depth buffering.