-- G -- | ||
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Term |
Definition/Description |
Source |

gal |
A unit of acceleration equal to 1 centimeter per second per second, or 1000 milligals, used in measuring the acceleration of gravity. | HDBK-850 |

galactic circle |
See galactic equator. |
HDBK-850 |

galactic equator |
A great circle of the celestial sphere, inclined 62° to the celestial equator and coinciding approximately with the center line of the Milky Way, constituting the primary great circle for the galactic system of coordinates. It is everywhere 90° from the galactic poles. Also called galactic circle. |
HDBK-850 |

galactic latitude |
Angular distance north or south of the galactic equator; the arc of a great circle through the galactic poles, between the galactic equator and a point on the celestial sphere, measured northward or southward from the galactic equator through 90° and labeled "N" or "S" to indicate the direction of measurement. |
HDBK-850 |

galactic longitude |
Angular distance east of sidereal hour angle (SHA) 94.4° along the galactic equator; the arc of the galactic equator or the angle at the galactic pole between the great circle through the intersection of the galactic equator and the celestial equator in Sagittarius (SHA 94.4°) and a great circle through the galactic poles measured eastward from the great circle through SHA 94.4° through 360°. | HDBK-850 |

galactic pole |
On the celestial sphere, either of the two points 90° from the galactic equator. | HDBK-850 |

galactic system of coordinates |
An astronomic coordinate system using latitude measured north and south from the galactic equator and longitude measured in the sense of increasing right ascension from 0° to 360°. The system was originally defined such that the pole was at RA = 12h40m, Dec = + 28°; however, in 1958 the International Astronomical Union (IAU) introduced the IAU galactic system which defined the pole at RA = 12h49m, Dec = 27°24'. | HDBK-850 |

galley proof |
A proof from type on a galley before it is made up in pages; also, such proofs. | HDBK-850 |

gamma |
1. (photography) The tangent of the angle which the straight-line portion of the characteristic curve makes with the log-exposure axis. It indicates the slope of the straight-line portion of the curve and is a measure of the extent of development and the contrast of the photographic material. 2. (geomagnetism) A small unit of magnetic field intensity sometimes used in describing the Earth's magnetic field. Lt is defined as being equal to l0-5 oersted. See also nanotesla. |
HDBK-850 |

gap |
(JCS) (imagery) Any space where imagery fails to meet minimum coverage requirements. This might be a space not covered by imagery or a space where the minimum specified overlap was not obtained. See also holiday. |
HDBK-850 |

gateway |
A device for converting one network's message protocol to the format used by another network's protocol. It can be implemented in hardware or software. | TAFIM 3.0 |

gauss |
A centimeter-gram-second electro- magnetic unit of magnetic induction equal to 104 tesla. See also tesla. |
HDBK-850 |

Gauss-Kruger grid |
See transverse Mercator grid. |
HDBK-850 |

gazetteer |
A directory of geographic objects and their location. EXAMPLE: a gazetteer of streets in a municipality. | CEN/TC 287 |

gazetteer |
An alphabetical list of place names giving feature identification and geographic and/or grid coordinates. | HDBK-850 |

general chart |
A nautical chart intended for offshore coastwise navigation. A general chart is of smaller scale than a coast chart, but of larger scale than a sailing chart. | HDBK-850 |

General Defense Intelligence Program |
A DoD budgetary program encompassing expenditures for DoD-related intelligence programs and infrastructure. | USIS 95 |

General Imagery Intelligence Training System |
A DIA-administered system for coordinating DoD General Military Intelligence (GMI) training. | USIS 95 |

general intelligence production |
Intelligence information/finished intelligence concerning the (1) military capabilities of foreign countries/organizations or (2) topics affecting potential U. S./allied military operations, relating to armed force capabilities such as; order of battle, tactics, doctrine, area and terrain intelligence, transportation and military support industries, military C3, or (3) other topics to include overall industrial capacity; the location and assessment of energy capacity; and a distribution network, country demographics, and environmental and economic assessments. | USIS 95 |

general map |
(JCS) A map of small scale used for general planning purposes. See also map. |
HDBK-850 |

general military intelligence |
Intelligence information and/or finished intelligence concerning the (1) military capabilities of foreign countries and/or organizations, or (2) topics affecting potential US/allied military operations, relating to the following subjects: armed forces capabilities, including order of battle, organization, training, tactics, doctrine, strategy, and other factors bearing on military strength and effectiveness; area and terrain intelligence, including urban areas, coasts and landing beaches, and medical, meteorological, oceanographic, and geological intelligence; transportation in all modes; military materiel production and support industries; military and civilian C3 systems; military economics, including foreign military assistance; insurgency and terrorism; military-political and/or sociological intelligence; location, identification , and description of military-related installations; government control; escape and evasion; and threats and forecasts. Excludes scientific and technical intelligence. | USIS 95 |

General Navigation Chart |
Small scale (1:1,000,000 or smaller) chart designed for open sea surface navigation. Depicted information supports voyage planning, ocean navigation, and military operations. | HDBK-850 |

general precession |
The motion of the equinoxes westward along the ecliptic at the rate of about 50.13" per year. See also lunisolar precession; planetary precession; precession in declination; precession in right ascension; precession of the equinoxes. |
HDBK-850 |

General Service |
A non-Sensitive Compartmented Information (SCI) DoD message system. | USIS 95 |

GENeral SERvice (GENSER) |
A term that applies to collateral (non-SCI) communications traffic handled by the common-user networks at security classification levels from Unclassified to Top Secret. [Joint Pub 6-02.1] | DISA CFS |

generalization |
1. The processes of reducing raw data for transformation into a data base or map. Generalization involves aggregation, agglomeration (combination), selection, resolution feature elimination (omission), classification, smoothing, resampling, simplification, exaggeration, displacement, compacting variables, measurement level reduction, dimensionality change, and symbolization. 2. (line generalization) Commonly refers to coordinate thinning or line thinning and/or smoothing. See also line thinning. |
HDBK-850 |

generalization |
The geometric and conceptual transformation of the attributes of a feature to make the feature less detailed. | ISO/TC 211 |

generalization relationship |
A subtype of feature relationship describing supertype/subtype relationship between features. | ISO/TC 211 |

general-purpose map |
A map which provides a broad range of information and which satisfies the needs of a broad range of users. | HDBK-850 |

generation |
(photography) The preparation of successive positive/negative reproductions from an original negative (first generation). The first positive produced is a second-generation product; the negative made from this positive is a third-generation product, and the next positive or print from that negative is a fourth-generation product. With each successive generation, quality deteriorates. | HDBK-850 |

Generic Application Environment (GAE) |
A term used to describe the set of architecture components that describe the different possible types of IT applications. | TAFIM 3.0 |

Generic Technology Environment (GTE) |
A term used to describe the set of architecture components that describe the different types of services required to support a Generic Application Environment (GAE). |
TAFIM 3.0 |

Generic Technology Platform (GTP) |
A term used to describe the different types of delivery components that can be used to support IT applications. | TAFIM 3.0 |

generic term |
That part of a name which describes the kind of feature to which the name is applied, and which has the same meaning in current local usage. For example, the generic term "wah" in "Tokyo-wah" means "bay". | HDBK-850 |

Geoceiver |
Trade name for an antenna-receiver capable of receiving signals from the Navy navigation satellites, from which three-dimensional positions can be computed for the antenna location. See also Doppler navigation, definition 2. |
HDBK-850 |

geocentric |
Relative to the Earth as a center; measured from the center of the Earth. | HDBK-850 |

geocentric cartesian datum |
A 3-dimensional cartesian coordinate system with origin based on a definition of the Earth's centre, Z-axis parallel to the direction of the CTS pole, and the X-axis in the direction of the zero meridian plane. | CEN/TC 287 |

geocentric coordinate system |
See geocentric coordinates. |
HDBK-850 |

geocentric coordinates |
(terrestrial) Coordinates that define the position of a point with respect to the center of the Earth. Geocentric coordinates can be either Cartesian (x,y,z) or spherical (geocentric latitude and longitude, and radial distance). Also called geocentric coordinate system; geocentric position. |
HDBK-850 |

geocentric diameter |
The diameter of a celestial body measured in seconds of arc as viewed from the Earth's center. | HDBK-850 |

geocentric ellipsoidal datum |
A geodetic ellipsoid linked to a geocentric cartesian datum. The centre of the ellipsoid being the origin and the minor axis of the ellipsoid being the polar axis. | CEN/TC 287 |

geocentric geodetic coordinates |
Geodetic coordinates referred to a geocentric reference ellipsoid. | HDBK-850 |

geocentric gravitational constant |
The product of the Earth's mass and the gravitational constant. This product is known to a far greater precision than either factor. | HDBK-850 |

geocentric horizon |
The plane through the center of the Earth, parallel to the topocentric horizon. | HDBK-850 |

geocentric latitude |
The angle at the center of the Earth between the plane of the celestial equator and a line to a point on the surface of the Earth. Geocentric latitude is used as an auxiliary latitude in some computations in astronomy, geodesy, and cartography, in which connection it is defined as the angle formed with the major axis of the ellipse (meridional section of the spheroid) by the radius vector from the center of the ellipse to the given point. In astronomic work, geocentric latitude is also called reduced latitude, a term that is sometimes applied to parametric latitude in geodesy and cartography. The geocentric and isometric latitudes are approximately equal. |
HDBK-850 |

geocentric longitude |
See geodetic longitude. |
HDBK-850 |

geocentric parallax |
The difference in the apparent direction or position of a celestial body as observed from the center of the Earth and a point on its surface. This varies with the body's altitude and distance from the Earth. Also called diurnal parallax. |
HDBK-850 |

geocentric position |
See geocentric coordinates. |
HDBK-850 |

geocentric radius vector |
The vector from the center of the Earth to the point in question. See also geocentric coordinates. |
HDBK-850 |

geocentric station position |
The location of a station defined in terms of geocentric coordinates. | HDBK-850 |

geocentric zenith |
The point where a line from the center of the Earth through a point on its surface meets the celestial sphere. | HDBK-850 |

geocode |
An encoded non-geodetic reference for a geographic object that gives a unique identifier to each object in a set. EXAMPLE: the NUTS codes. | CEN/TC 287 |

geocoding |
The assignment of a geographic value to a pixel of an image/air photo via the placement on a desired datum and map projection. | OGC RFI |

geodata |
Information that identifies the geographical location and characteristics of natural or man-made features and boundaries of the Earth. Geodata represent abstractions of real-world entities, such as roads, buildings, vehicles, lakes, forests and countries. | OpenGIS Guide |

geodata model |
A formalized system for representing geodata. OpenGIS Specification defines geographic data types in the Open Geodata Model. |
OpenGIS Guide |

geodesic |
See geodesic line. |
HDBK-850 |

geodesic line |
A line of shortest distance between any two points on any mathematically defined surface. A geodesic line for an ellipsoid, in general, is a line of double curvature, and usually lies between the two normal section lines which the two points determine. If the two terminal points are in nearly the same latitude, the geodesic line may cross one of the normal section lines. It should be noted that, except along the Equator and along the meridians, the geodesic line is not a plane curve and cannot be sighted over directly. However, for conventional triangulation the lengths and directions of geodesic lines differ inappreciably from corresponding pairs of normal section lines. Also called geodesic; geodetic line. |
HDBK-850 |

geodesy |
The science which deals with the determination of the size and figure of the Earth. | HDBK-850 |

geodetic and geophysical data (G&G) |
Information or earth data, pertaining to the sciences of geodesy and geophysics. Typically includes gravity information, geodetic point positioning data, datum definition, etc. | HDBK-850 |

geodetic and geophysical data reduction |
The process of enhancing the value of geodetic and geophysical data by analysis, evaluation, computation, and adjustment. The process includes (1) transforming unadjusted survey data and observations into an adjusted form with reliability statements; (2) establishing basic frameworks of horizontal and vertical control in advance of map, chart, and target materials production, and publishing of trig lists; and (3) analysis, evaluation, and computation of geodetic and geophysical data obtained by surface, airborne, or satellite techniques to establish, extend, connect, and transform datums and to relate datums to the Department of Defense World Geodetic System. | HDBK-850 |

geodetic anomaly |
See anomaly, definition 2. |
HDBK-850 |

geodetic astronomy |
The branch of geodesy which utilizes astronomic observations to extract geodetic information. | HDBK-850 |

geodetic azimuth |
The angle between the geodetic meridian and the tangent to the geodesic line at the observer, measured in the plane perpendicular to the ellipsoid normal of the observer; preferably clockwise from north. Although older surveys, particularly by the Coast and Geodetic Survey (now National Geodetic Survey), used south, the Department of Defense now uses north. | HDBK-850 |

geodetic azimuth mark |
A marked point established in connection with a triangulation (or traverse) station to provide a starting azimuth for dependent surveys. | HDBK-850 |

geodetic control |
A system of horizontal and/or vertical control stations that have been established and adjusted by geodetic methods and in which the shape and size of the Earth (geoid) have been considered in position computations. | HDBK-850 |

geodetic control data |
Information concerning the precise horizontal and vertical geodetic location of points on the surface of the Earth and celestial bodies, including points obtained by photogrammetric techniques. | HDBK-850 |

geodetic coordinate system |
(A&D LDM Entity: "GEODETIC-COORDINTE-SYSTEM") Information about the quantities of latitude, longitude, and height (ellipsoid), which define the position of a point on the surface of the earth with respect to the reference spheroid. | A&D LDM |

geodetic coordinates |
The quantities of latitude, longitude, and height (ellipsoid), which define the position of a point on the surface of the Earth with respect to the reference spheroid. Also imprecisely called geographic coordinates. |
HDBK-850 |

geodetic data sheet |
See control data card. |
HDBK-850 |

geodetic datum |
An ellipsoid fixed in reference to the earth so that the polar axis, the central point, and the zero meridian plane are all fixed. NOTE - There are two types. (1) local geodetic datum; the ellipsoid has been chosen and fixed to fit a region. (2) geocentric datum; the ellipsoid has been chosen to fit the earth as a whole and its central point is based on a definition of earth's center of mass. See also datum, tridimensional datum, bidimensional datum and unidimensional datum. |
ISO/TC 211 |

geodetic ellipsoid |
A flattened ellipsoid of rotation, usually chosen to fit the geoid as closely as possible, either locally or globally. | CEN/TC 287 |

geodetic equator |
The line of zero geodetic latitude; the great circle described by the semimajor axis of the reference ellipsoid as it is rotated about the minor axis. See also astronomic equator. |
HDBK-850 |

geodetic height |
See ellipsoidal height. |
HDBK-850 |

geodetic latitude |
Angle from the equatorial plane to the direction of the perpendicular to the ellipsoid through the given point, northwards treated as positive. | CEN/TC 287 |

geodetic leveling |
Spirit leveling of a high order of accuracy, usually extended over large areas, to furnish accurate vertical control as a basis for the control in the vertical dimension for all surveying and mapping operations. Spirit leveling follows the geoid and its associated level surfaces which are irregular, rather than any mathematically determined spheroid or ellipsoid and associated regular level surfaces. |
HDBK-850 |

geodetic line |
See geodesic line. |
HDBK-850 |

geodetic longitude |
Angle from the zero meridian plane to the meridian plane of the given point, eastward treated as positive. | CEN/TC 287 |

geodetic meridian |
A line on a reference ellipsoid which has the same geodetic longitude at every point. Also called geographic meridian. |
HDBK-850 |

geodetic meridian plane |
A plane that contains the normal to the reference ellipsoid at a given point and the rotation axis of the reference ellipsoid. | HDBK-850 |

geodetic parallel |
A line on the reference spheroid which has the same geodetic latitude at every point. A geodetic parallel, other than the Equator, is not a geodesic (geodetic) line. In form, it is a small circle whose plane is parallel with the plane of the geodetic equator. | HDBK-850 |

geodetic position |
A position of a point on the surface of the Earth expressed in terms of geodetic latitude, geodetic longitude, and geodetic height A geodetic position implies an adopted geodetic datum. |
HDBK-850 |

geodetic positioning |
See geopositioning. |
USIS 95 |

geodetic reference |
A spatial reference that takes the form of a set of coordinates in a geodetic reference system. EXAMPLE: latitude and longitude. | CEN/TC 287 |

Geodetic Reference System 1980 (GRS 80) |
This geodetic reference system was adopted by the XVII General Assembly of the International Union of Geodesy and Geophysics at Canberra, Australia in 1979. The GRS 80 is defined by the four fundamental constants: semi-major axis 6,378,137m, gravitational constant of the Earth (including the atmosphere) 3,986,005 x 108 m3 s-2, second degree zonal coefficient 108,263 x 10-8, and angular rotational velocity 7,292,115 x 10-11 radians. | HDBK-850 |

geodetic satellite |
Any satellite whose orbit and payload render it useful for geodetic purposes. | HDBK-850 |

geodetic stellar camera |
A precision terrestrial camera, usually employing glass plates, used to photograph elevated illuminated objects against a star background. | HDBK-850 |

geodetic survey |
A survey in which the figure and size of the Earth is considered. It is applicable for large areas and long lines and is used for the precise location of basic points suitable for controlling other surveys. | HDBK-850 |

geodetic zenith |
The point where the normal (to the reference spheroid) extended upward, meets the celestial sphere. | HDBK-850 |

Geodimeter |
A trade name for an instrument that measures distance by precise electronic phase comparison of modulated light waves which travel to a reflector and return. | HDBK-850 |

geoelectric survey |
A survey to determine the electricity or resistivity potential of the Earth rocks. | HDBK-850 |

geographic (geographical) |
Signifying basic relationship to the Earth considered as a globe-shaped body. The term geographic is applied alike to data based on the geoid and on other spheroids. |
HDBK-850 |

geographic application |
Applications which pertain to the Earth and Earth phenomena, with known spatial and temporal reference systems. Expressed in a human context versus computer context. | OpenGIS Guide |

geographic area |
The area defined according to an indirect spatial reference system. Examples for geographic area are country or municipality. | CEN/TC 287 |

Geographic Base File/Dual Independent-Map-Encoding (GBF/DIME) |
Topologically structured files developed by the Bureau of the Census which serve as a relatively inexpensive geographic information data source. GBF/DIME files include street networks, street addresses, political boundaries, and major hydrographic features. Each street segment is represented as a straight line regardless of its real world shape. | HDBK-850 |

geographic coordinates |
(JCS) The quantities of latitude and longitude which define the position of a point on the surface of the Earth with respect to the reference spheroid. Also called astronomic coordinates; gravimetric coordinates; terrestrial coordinates. See also coordinates; geodetic coordinates. |
HDBK-850 |

geographic data |
Data concerning phenomena directly or indirectly associated with a location relative to the surface of the Earth. | CEN/TC 287 |

geographic dataset |
A structured collection of geographic data according to a conceptual schema and collected for transfer. | CEN/TC 287 |

geographic feature |
An identifiable object relative to the earth's surface. See also geospatial-feature. |
ISO/TC 211 |

geographic information |
1. The knowledge obtained as a result of the synthesis, analysis, or interpretation of geographic data. 2. Information concerning phenomena implicitly or explicitly associated with a location relative to the Earth. |
ISO/TC 211 |

Geographic Information System |
An automated system for spatially managing and analyzing geographic information. | USIS 95 |

Geographic Information System (GIS) |
The generic term used for a system of computer software programs and equipment that is used to acquire, store, manipulate, analyze, and display spatial data. | HDBK-850 |

geographic information system (GIS) |
GIS are special-purpose digital databases in which a common spatial coordinate system is the primary means of reference. GIS contain subsystems for: 1) data input; 2) data storage, retrieval, and representation; 3) data management, transformation, and analysis; and 4) data reporting and product generation. It is useful to view GIS as a process rather than a thing. A GIS supports data collection, analysis, and decision making and is far more than a software or hardware product. Other terms for GIS, and special-purpose GIS, include: Land-Base Information System, Land Record System, Land Information System, Land Management System, Multipurpose Cadastre, and AM/FM System. | OpenGIS Guide |

geographic intelligence |
Intelligence dealing with the location, description, and analysis of physical and cultural factors of the world, (e.g., terrain, climate, natural resources, transportation, boundaries, population distribution) and their changes through time. | USIS 95 |

geographic latitude |
A generic term for geodetic or astronomical latitude. More often geodetic. | CEN/TC 287 |

geographic limits |
The lines having latitude and longitude values bounding the area of a map or chart; that area exclusive of overlap areas. See also neatlines. |
HDBK-850 |

geographic location |
See geographic position. |
HDBK-850 |

geographic longitude |
A generic term for geodetic or astronomical longitude. More often geodetic. | CEN/TC 287 |

geographic meridian |
A general term, applying alike to an astronomic or geodetic meridian. | HDBK-850 |

geographic name |
Also called place name and toponym. See also Board of Geographic Names. |
HDBK-850 |

Geographic Names Processing System (GNPS) |
The DMA [NIMA] system which includes the hardware, software and procedures to maintain the geographic names data required for digital maps and gazetteers. | HDBK-850 |

geographic nonlinearity |
The error introduced by digitization and subsequent processing to the total error of both absolute and relative positioning of any feature on the graphic. | HDBK-850 |

geographic object |
A real-world object that has a permanent geographic location. EXAMPLE: the Eiffel Tower. | CEN/TC 287 |

geographic parallel |
A general term, applying alike to an astronomic parallel or a geodetic parallel . | HDBK-850 |

geographic position |
The position of a point on the surface of the Earth expressed in terms of latitude and longitude, either geodetic or astronomic. | HDBK-850 |

geographic positioning |
See geopositioning. |
USIS 95 |

Geographic Region |
One of the 34 regional subdivisions into which the world is divided. Each subdivision includes one or more countries or, in the case of the larger countries such as China, a portion of a country. The regions are identified by a two-letter code; the first, an alphabetic character (A-Z) and the second, a numeric (0- 9). Geographic regions and their member countries are listed in a staff-defined table in the Requirements Management System (RMS). | USIS 95 |

geographic subset |
A set of data within a geographic dataset, possibly limited by some constraints such as spatial extent, class, property, time, etc. A geographic subset may be as big as the whole geographic dataset, or as small as a single object value of a single object for some property. | CEN/TC 287 |

geographic survey |
A general term, not susceptible of defined limitation, covering a wide range of surveys lying between and merging into exploratory surveys on the one hand and basic topographic surveys on the other. Geographic surveys usually cover large areas, are based on coordinated control, and are used to record physical and statistical characteristics of the area surveyed. | HDBK-850 |

geographic vertical |
See vertical. |
HDBK-850 |

geographical area classification system |
A logical and orderly geographical division of the world using numbers, letters, and combinations of the same for the designation of areas and subareas. | HDBK-850 |

geographical exploration traverse |
A route followed across some parts of the Earth, approximate positions along which are determined by surveying or navigational methods. | HDBK-850 |

geographical mile |
The length of 1 minute of arc at the Equator, or 6,087.08 feet (on the Clarke spheroid of 1866). | HDBK-850 |

geographical pole |
Either of the two points of intersection of the surface of the Earth with its axis, where all meridians meet. | HDBK-850 |

geoid |
The equipotential surface in the gravity field of the Earth which approximates the undisturbed mean sea level extended continuously through the continents. The geoid is the surface of reference for astronomic observations and for geodetic leveling. See also compensated geoid; equilibrium theory; equipotential surface; geoidal horizon; gravimetric geoid; isostatic geoid; reference spheroid. |
HDBK-850 |

geoid |
(UCDM Entity: "GEOID") The equipotential surface of the gravity field of the Earth. | USIGS/CDM-A |

geoid model |
A mathematical function defining a surface to represent the geoid either locally or globally. EXAMPLE: MSL Marseille, MSL. | CEN/TC 287 |

geoidal contour |
A line on the surface of the geoid of constant elevation with reference to the surface of the spheroid of reference. Geoidal contours depend on the surface of reference as well as on the shape of the geoid. The same geoid referred to different surfaces of reference will give different sets of geoidal contours. | HDBK-850 |

geoidal height |
The distance of the geoid above (positive) or below (negative) the mathematical reference spheroid. Also called geoid separation; undulation of the geoid. See also astrogeodetic undulations. |
HDBK-850 |

geoidal height profile |
See astrogeodetic leveling. |
HDBK-850 |

geoidal horizon |
That circle of the celestial sphere formed by the intersection of the celestial sphere and a plane tangent to the sea level surface of the Earth at the zenith nadir line. | HDBK-850 |

geoidal separation |
See geoidal height. |
HDBK-850 |

geokinetics |
Local and global motion of the Earth or sea, its measurement, isolation from, and effect upon precision equipment and measuring instruments. Usually applied to the design and test of inertial instruments and systems and stable platforms. | HDBK-850 |

geologic survey |
A survey or investigation of the Earth, of the physical changes which the Earth's crust has undergone or is undergoing, and of the causes producing those changes. | HDBK-850 |

Geological Long Range Inclined Asdic (GLORIA) |
A low resolution side scan sonar used for reconnaissance surveys of the ocean floor. | HDBK-850 |

geological map |
A map showing the structure and composition of the Earth's crust. | HDBK-850 |

geomagnetic coordinates |
A system of spherical coordinates based on the best fit of a centered dipole to the actual magnetic field of the Earth. | HDBK-850 |

geomagnetic equator |
The terrestrial great circle everywhere 90° from the geomagnetic poles. Geomagnetic equator should not be confused with magnetic equator, the line connecting all points of zero magnetic dip. |
HDBK-850 |

geomagnetic latitude |
Angular distance from the geomagnetic equator, measured northward or southward through 90° and labeled "N" or "S" to indicate the direction of measurement. Geomagnetic latitude should not be confused with magnetic latitude. See also dip. |
HDBK-850 |

geomagnetic meridian |
The meridional lines of a geomagnetic coordinate system. Not to be confused with magnetic meridian. |
HDBK-850 |

geomagnetic pole |
Either of two antipodal points marking the intersection of the Earth's surface with the extended axis of a powerful bar magnet assumed to be located at the center of the Earth and approximating the source of the actual magnetic field of the Earth. The expression geomagnetic pole should not be confused with magnetic pole, which relates to the actual magnetic field of the Earth. |
HDBK-850 |

geomagnetism |
1. The magnetic phenomenon, collectively considered, exhibited by the Earth and its atmosphere, and by extension the magnetic phenomena in interplanetary space. 2. The study of the magnetic field of the Earth. Also called terrestrial magnetism. |
HDBK-850 |

geomatics |
Discipline concerned with the collection, distribution, storage, analysis, processing, presentation of geographic data or geographic information. | ISO/TC 211 |

geometric latitude |
See parametric latitude. |
HDBK-850 |

geometric map projection |
See perspective map projection. |
HDBK-850 |

geometric nonlinearity |
Any distortion introduced by digitization and subsequent processing of a mathematically-correct reference system or grid, other than simple rotation, translation, or scale change. | HDBK-850 |

geometric primitive |
The basic geometric units of representation; specifically, nodes, edges, and faces. | VPF Glossary |

geometric primitive type |
A class of geometric primitives. | CEN/TC 287 |

geometric transformation |
The re-sampling, relocation or re-sizing of image pixels. | OGC RFI |

geometrical dip |
The vertical angle, at the eye of an observer, between the horizontal and a straight line tangent to the surface of the Earth. It is larger than dip by the amount of terrestrial refraction. | HDBK-850 |

geometrical horizon |
Originally, the celestial horizon; now more commonly the intersection of the celestial sphere and an infinite number of straight lines tangent to the Earth's surface, and radiating from the eye of the observer. If there were no terrestrial refraction, geometrical and visible horizons would coincide. | HDBK-850 |

geometry sub-schema |
A conceptual schema defining the spatial characteristics of the object types included in the application schema. | CEN/TC 287 |

geomorphic |
Pertaining to land forms. | HDBK-850 |

geomorphic data |
A set of model coordinates defining the trace of a geomorphic feature. These consist of ridgelines, valleys, drainage and lakes which are used to refine the elevation data group during the production process. | HDBK-850 |

geop |
An equipotential surface in the gravity field of the Earth. Also called geopotential surface. |
HDBK-850 |

geophysics |
The science of the Earth with respect to its structure, composition, and development. Geophysics is a branch of experimental physics dealing with the Earth, including its atmosphere and hydrosphere. It includes the sciences of dynamical geology and physical geography, and makes use of geology, seismology, meteorology, oceanography, magnetism, and other Earth sciences in collecting and interpreting Earth data. | HDBK-850 |

geopositioning |
The photogrammetric adjustment of one or more images relative to each other and to an absolute (fixed) ground reference system. Also refered to as geodetic positioning or geographic positioning. |
OGC RFI |

geopositioning |
The process of accurately locating a target relative to the Earth's surface. Also refered to as geodetic positioning or geographic positioning. |
USIS 95 |

geopotential |
The gravity potential of the actual Earth. The sum of the gravitational (attraction) potential and the potential of the centrifugal force. A function describing the variation of the geopotential in space. The function whose partial derivative in any direction gives the gravity component in that direction. |
HDBK-850 |

geopotential number |
The difference between the geopotential on the geoid and the geopotential at a point. |
HDBK-850 |

geopotential surface |
See geop. |
HDBK-850 |

geoprocessing application |
Computer applications which model, interpret and use Earth information. The implementation of a Geographic Application on a computer. The terms "geoprocessing", "geomatics", and "geotechnology" mean approximately the same thing, though some groups make minor distinctions between them. | OpenGIS Guide |

GEOREF |
(JCS) A worldwide position reference system that may be applied to any map or chart graduated in latitude and longitude [with Greenwich as prime meridian] regardless of projection. It is a method of expressing latitude and longitude in a form suitable for rapid reporting and plotting. This term is derived from the words "The World Geographic Reference System". | HDBK-850 |

geo-referenced data |
Spatial data that pertain to a location on the earth's surface. | HDBK-850 |

georeferencing |
The assignment of a geographic coordinate to a reference pixel in a geo-coded image. | OGC RFI |

geospatial |
Refers to the geographic location and characteristics of natural or constructed features and boundaries on the Earth. | USGS SP |

geospatial data |
Information that identifies the geographic location and characteristics of natural or constructed features and boundaries on the earth. This information may be derived from, among other things, remote sensing, mapping, and surveying technologies. (U.S. Executive Office of the President, 1994) | FGDC |

geospatial function (or process) |
Any function or process which handles or operates on geodata. | OpenGIS Guide |

geospatial information (GI) |
Any information that has associated with it some geographical and temporal reference (includes what is referred to as Mapping, Charting, Geodesy, Imagery and Intelligence). [GI IPT ToR, w/ 6/13/96 Integration Team mods] | GI IPT |

geospatial information framework |
The subset of geospatial information used to establish the reference for the integration and exploitation of other spatially and temporally tagged data. [GI IPT ToR, w/ 6/13/96 and 6/17/96 Integration Team mods] | GI IPT |

Geospatial Information Infrastructure (GII) |
The collection of technology, policies, standards, doctrine, systems, processes and services necessary to generate, manage and utilize geospatial information in the Geospatial Information Framework. [GI IPT ToR, w/ 6/13/96 Integration Team mods] | GI IPT |

geospatial information services |
The enabling capabilities provided to generate, manage and utilize geospatial information. [6/17/96 Integration Team working session] | GI IPT |

geospatial-feature |
A feature which is fixed relative to the earth's surface. | USIGS/CDM-A |

geospatial-feature-representation |
A descriptive and geometric model of a geospatial-feature. | USIGS/CDM-A |

geosphere |
The solid and liquid portions of the Earth; the lithosphere plus the hydrosphere. | HDBK-850 |

Geostationary Operational Environmental Satellites (GOES) |
The National Oceanic and Atmospheric Administration operates the geostationary GOES environmental satellite system for the purpose of providing synoptic visible, infrared imaging and infrared thermal sounding for atmospheric temperature sounding profiles. | USIS 95 |

geosynchronous orbit |
A near-circular, low-inclined orbit with a 23.93447 hour period. The satellite stays over a fixed longitude above the equator. | USIS 95 |

German Industrial Standard |
See Deutsche Industrie-Norm (DIN). |
HDBK-850 |

Gestion et Etude des Informations Spectrocopiques Atmospheriques (GEISA) |
The GEISA (Management and Study of Atmospheric Spectroscopic Information) data bank (GEISA-93) includes the data on spectral transitions of 40 molecules and 86 isotopic species from 0 to 22656 cm-1, the infrared absorption cross sections data on cholorfluorocarbons, N2O5, and CIONOO2. Recently the IBM personal computer compatible version of the software (GEISA-PC) has been created. | USIS 95 |

giant planets |
See major planets. |
HDBK-850 |

gisement |
See grid declination. |
HDBK-850 |

glide bomb |
A bomb, fitted with airfoils to provide lift, that is carried and released in the direction of a target by an airplane. | USIS 95 |

Global Broadcast Service (GBS) |
A government owned Ka band satellite-based system that will provide rapid, one-way distribution of large volumes of data to highly-mobile warfighters. When it achieves operational status, GBS will provide worldwide coverage and will be able to disseminate information such as weather, imagery, video, and multimedia files provided by national and theater sources into small portable receivers. Information will be transported via commercial protocols, such as Motion Picture Experts Group Standard 2 (MPEG-2) and Asynchronous Transfer Mode (ATM), with suitable government security services. Phase One of this program will be a test bed broadcast management center. |
DII MP |

Global Combat Support System (GCSS) |
A demand driven, joint Warfighter focused initiative to accelerate delivery of improved combat support capabilities. GCSS is not an acquisition program, it is an initiative for interfacing and integrating DOD-wide Service/Agency sponsored Combat Support Systems. The GCSS builds on the technical developments and products, procedures and integrtion strategies which have been employed in GCCS to provide interoperability across combat support functions and between combat support and Command and Control functions. In a broad strategy, GCSS will build a little, test a little, and field a lot. [GCSS Implementation Plan, Sect 1 & App B] | DII MP |

Global Command and Control System (GCCS) |
A highly mobile, deployable command, control, communications, computers, and intelligence (C4I) system that supports forces for joint and combined operations throughout the spectrum of conflict anytime and anywhere in the world with compatible, interoperable, and integrated C4I systems. [GCCS COE] | DISA CFS |

Global Navigation Chart (GNC) |
A 1:5,000,000 scale series of multicolored charts designed for general planning purposes for operations involving long distances or large areas of in-flight navigation in long range, high altitude, high speed aircraft. | HDBK-850 |

Global Positioning System (GPS) |
See Navstar Global Positioning System (GPS). |
SPACECOM Web Site |

globular map projection |
A map projection representing a hemisphere, on which the equator and a central geographic meridian are represented by straight lines intersecting at right angles; these lines are divided into equal parts. All meridians, except the central one, are represented by circular arcs connecting points of equal division on the equator with the poles. Excepting the equator, the parallels are circular arcs dividing the central and extreme outer meridians into equal parts. The extreme outer meridian limits the projection and is a full circle . | HDBK-850 |

gnomonic chart |
A chart on the gnomonic projection. Also called great circle chart. |
HDBK-850 |

gnomonic map projection |
A perspective map projection on a plane tangent to the surface of a sphere having the point of projection at the center of the sphere. The projection is neither conformal nor equal-area. It is the only projection on which great circles on the sphere are represented as straight lines. | HDBK-850 |

Goddard Space Flight Center (GSFC) |
NASA established the Goddard Space Flight Center in 1959 as its first major laboratory devouted entirely to the exploration of Earth and space. This NASA field center is a major U.S. laboratory for developing and operating unmanned scientific spacecraft. The Center manages many of NASA's Earth Observation, Astronomy, and Space Physics missions. Goddard Space Flight Center also oversees operations at the Wallops Flight Facility near Chincoteague, Virginia. A primary function of that facility is the launching of rockets carrying suborbital and low-Earth orbit space probes. Also, Goddard is the lead Center in NASA's Mission to Planet Earth program, NASA's long term, coordinated research effort to study the Earth as a global environmental system. The Goddard Space Flight Center is located in Greenbelt, MD. | GSFC Web Site |

goldenrod paper |
A paper, usually a shade of yellow or red, for blocking out nonprinting areas of negatives or film layouts. Also called masking paper. |
HDBK-850 |

goniometer |
An instrument for measuring angles. See also photogoniometer. |
HDBK-850 |

Goode's Interrupted Homolosine projection |
An equal-area projection, based on the Mollweide and sinusoidal projections, using the sinusoidal from the Equator to 40° N and 40° S, and the Mollweide in higher latitudes. The oceans are "interrupted" to allow the continents to be recentered on several meridians, so as to attain good overall shape. It is used widely for maps of economic distributions. | HDBK-850 |

gore |
1. (surveying) An irregularly shaped tract of land, generally triangular, left between two adjoining surveyed tracts, because of inaccuracies in the boundary surveys or as a remnant of a systematic survey. 2. (globe) A lune-shaped map which may be fitted to the surface of a globe with a negligible amount of distortion. |
HDBK-850 |

Government Open Systems Interconnection Profile (GOSIP) |
A government (e.g., U.S. or U.K.) profile of functional applications that outlines a national policy and strategy for converting to a communications system based on OSI. Use of GOSIP is no longer mandatory. | TAFIM 3.0 |

government-off-the-shelf (GOTS) |
Software products that have been developed by the government and distributed throughout the government for use. | DII MP |

gradation |
The range of tones from the brightest highlights to the deepest shadows. | HDBK-850 |

grade |
The rate of slope or degree of inclination. See also gradient. |
HDBK-850 |

grade correction |
(land surveying) A correction applied to a distance measured on a slope to reduce it to a horizontal distance between the vertical lines through its end points. Also called correction for inclination of tape; inclination correction; slope correction. |
HDBK-850 |

gradient |
1. A rate of rise or fall of a quantity against horizontal distance expressed as a ratio, decimal, fraction, percentage, or the tangent of the angle of inclination. Also called percent of slope; slope. 2. The rate of increase or decrease of one quantity with respect to another. |
HDBK-850 |

gradient speed |
The speed of a photographic material determined on the basis of the exposure corresponding to a particular gradient of the characteristic curve. | HDBK-850 |

gradient tints |
See hypsometric tinting. |
HDBK-850 |

gradienter |
An attachment to an engineer's transit with which an angle of inclination is measured in terms of the tangent of the angle rather than in degrees and minutes. It may be used as a telemeter in measuring horizontal distances. | HDBK-850 |

gradiometer |
An instrument used to measure gravity gradients. | HDBK-850 |

graduation error |
Inaccuracy in the graduations of the scale of an instrument | HDBK-850 |

Graf sea gravimeter |
A balance-type gravity meter designed for ocean surveys which consists of a mass at the end of a horizontal arm that is supported by a torsion spring rotational axis. | HDBK-850 |

grain |
1. (photography) One of the discrete silver particles resulting from the development of an exposed light-sensitive material. The random distribution of these particles in an area of uniform exposure gives rise to the appearance known as "graininess" 2. (paper) See grain direction. 3. (lithography) See grained surface. |
HDBK-850 |

grain direction |
The alignment of paper fibers parallel to the movement on the paper machine during manufacture. | HDBK-850 |

grained surface |
The roughened or irregular surface of an offset printing plate. | HDBK-850 |

graining |
The mechanical roughening or grinding of an abrasive into the surface of a metal press plate to increase the surface area and improve the water receptiveness of the surface. | HDBK-850 |

granularity |
The graininess of a developed photographic image, evident particularly on enlargements, that is due either to agglomerations of developed grains or to an overlapping pattern of grains. | HDBK-850 |

Graphic Kernal System (GKS) |
An ISO standard for computer graphics programming which contains functions for outputting graphical primitives, controlling the appearance of graphical primitives with attributes, controlling graphical workstations, controlling transformations and coordinate systems, generating and controlling groups of primitives called segments, obtaining graphical input, manipulating groups of device-independent instructions called metafiles, inquiring the capabilities and states of the graphics system, and handling errors. | HDBK-850 |

graphic products |
A graphic product may be a paper copy of a map or chart, or the repro-material used to produce the map or chart. | HDBK-850 |

graphic scale |
(JCS) A graduated line by means of which distances on the map, chart, or photograph may be measured in terms of ground distances. Also called bar scale. See also scale. |
HDBK-850 |

graphical notation |
A ormal language using graphical symbols. Graphical notations can be used to present conceptual schemata. | CEN/TC 287 |

graphical radial triangulation |
A radial triangulation performed by other than analytical means. A radial triangulation is assumed to be made with principal points as radial centers unless the definitive term designates otherwise (as, for example, nadir-point triangulation or nadir-point plot and isocenter triangulation or isocenter plot, and nadir-point slotted-template plot, etc.). | HDBK-850 |

graphical rectification |
Any rectification technique employing a graphic method for determining the solution as contrasted with mechanical techniques. See also paper-strip method. |
HDBK-850 |

graphical user interface (GUI) |
A computer program or environment that displays options on the screen as icons, i.e., picture symbols, by which users enter commands by selecting an icon. Note: Icons may be selected, e.g. , by pressing the <ENTER> key on the keyboard, by "clicking" a computer mouse button, or by touching the icon on a touch pad. | FED STD 1037C |

graphics |
The art or science of conveying information through the use of display media, such as graphs, letters, lines, drawings, and pictures. Note: Graphics includes the transmission of coded images such as facsimile | FED STD 1037C |

graphics |
A product based on the results of imagery exploitation. A wide variety of products including briefing boards, annotated prints, line drawings, sketches, etc., and can be either hardcopy or softcopy. | USIS 95 |

graticule |
1. A network of lines representing parallels of latitude and meridians of longitude forming a map projection. See also fictitious graticule. 2. A scale at the focal plane of an optical instrument to aid in the measurement of objects. See also reticle. |
HDBK-850 |

Gravatt level |
A dumpy level with the spirit level mounted on top of a short telescope tube having a large object glass. Later made with wyes. See wye level. |
HDBK-850 |

Gravatt leveling rod |
A speaking rod, marked with rectangles each 0.01 foot high, the rectangles at the 0.1 of foot being longer and those at the 0.5 being identified by dots. |
HDBK-850 |

graver |
See scriber. |
HDBK-850 |

gravimeter (gravity meter) |
An accelerometer designed to measure relative differences in the acceleration due to gravity at different locations. | HDBK-850 |

gravimetric coordinates |
See astronomic coordinates. |
HDBK-850 |

gravimetric datum orientation |
Adjustment of the ellipsoid of reference for a particular geodetic datum so that the differences between the gravimetric and astrogeodetic deflection components and geoidal undulations are minimized. |
HDBK-850 |

gravimetric deflection |
A deflection of the vertical determined by methods of gravimetric geodesy. | HDBK-850 |

gravimetric geodesy |
The science that utilizes measurements and characteristics of the Earth's gravity field as well as theories regarding this field to deduce the shape of the Earth and in combination with arc measurements, the Earth's size. Also called physical geodesy. |
HDBK-850 |

gravimetric geoid |
An approximation to the geoid as determined from gravity observation. | HDBK-850 |

gravimetric map |
A map on which contour lines are used to represent points at which the acceleration of gravity is equal. | HDBK-850 |

gravimetric survey |
A survey made to determine the acceleration of gravity at various places on the Earth's surface. | HDBK-850 |

gravimetric undulations |
Separations between a gravimetrically determined geoid and a reference ellipsoid of specified flattening. | HDBK-850 |

gravitation |
The mutual interaction of two masses producing a force between them acting along the line joining their centers of mass. The force is proportional to the product of the two masses divided by the square of the distance between the two centers of mass. | HDBK-850 |

gravitational constant |
See constant of gravitation. |
HDBK-850 |

gravitational disturbance |
See gravity disturbance. |
HDBK-850 |

gravitational flattening |
The ratio of the difference between the polar and equatorial normal gravities to the equatorial normal gravity. Also called gravity flattening. |
HDBK-850 |

gravitational gradient |
The change in the gravity per unit distance. | HDBK-850 |

gravitational harmonics |
The spherical harmonics used in approximating the gravitational field of the Earth. See also gravity field of the Earth; sectorial harmonics; spherical harmonics; tesseral harmonics; zonal harmonics. |
HDBK-850 |

gravitational perturbations |
Perturbations caused by body forces due to nonspherical terrestrial effects, lunisolar effect, tides, and the effect of relativity . | HDBK-850 |

gravitational potential |
1. The potential associated with the force of gravitation arising from the attraction between mass points, e.g., the Earth's center and a particle in space. 2. At any point, the work needed to remove an object from that point to infinity. |
HDBK-850 |

gravity |
Viewed from a frame of reference fixed in the Earth, acceleration imparted by the Earth to a mass which is rotating with the Earth. Since the Earth is rotating, the acceleration observed as gravity is the resultant of the acceleration of gravitation and the centrifugal acceleration arising from this rotation and the use of an earthbound rotating frame of reference. It is directed normal to sea level and to its geopotential surfaces. See also absolute gravity; center of gravity; Clairaut's theorem; constant of gravitation; direction of the force of gravity; equatorial gravity value; equipotential surface; formula for theoretical gravity; gravitation; Hayford deflection templets; Hayford effect; Helmert's gravity formula of 1901; Helmert's gravity formula of 1915; intensity of gravity; international gravity formula; isostasy; longitude term gravity formula; normal gravity; observed gravity; reduced gravity; regional gravity; relative gravity; residual gravity; resolution; resolution limit; standard gravity; subgravity; theoretical gravity; virtual gravity. |
HDBK-850 |

gravity anomaly |
The difference between the observed gravity value properly reduced to sea level, and the theoretical gravity obtained from gravity formula. Also called observed gravity anomaly. See also Bouguer anomaly; free-air anomaly; gravity disturbance; Hayford gravity anomalies/Hayford anomalies; isostatic anomaly. |
HDBK-850 |

gravity anomaly map |
A map showing the positions and magnitudes of gravity anomalies. Also, a map on which contour lines are used to represent points at which the gravity anomalies are equal. | HDBK-850 |

gravity corer |
Any type of corer that achieves bottom penetration solely as a result of gravity. | HDBK-850 |

gravity data |
Information concerning that acceleration which attracts bodies and is expressed as observations or in the form of gravity anomaly charts or spherical harmonics for spatial representation of the Earth and other celestial bodies. | HDBK-850 |

gravity disturbance |
The difference between the observed gravity and the normal gravity at the same point (the vertical gradient of the disturbing potential) as opposed to gravity anomaly which uses corresponding points on two different surfaces. Because the centrifugal force is the same when both are taken at the same point, it can also be called gravitational disturbance. |
HDBK-850 |

gravity field of the Earth |
The field of force arising from a combination of the mass attraction and rotation of the Earth. The field is normally expressed in terms of point values, mean area values, and/or series expansion for the potential of the field. | HDBK-850 |

gravity flattening |
See gravitational flattening. |
HDBK-850 |

gravity instrument |
A device for measuring the acceleration due to gravity (absolute) or gravity differences between two or more points (relative). See also astatized gravimeter; Brown gravity apparatus; dynamic gravity meter; Graf sea gravimeter; gravimeter; La Coste-Romberg gravimeter; stable gravimeter; stable-type gravimeter; static gravity meter; torsion balance; unstable-type gravimeter. |
HDBK-850 |

gravity network |
A network of gravity stations. | HDBK-850 |

gravity reduction |
A combination of gravity corrections to obtain reduced gravity on the geoid. See also Bouguer correction; free-air correction; isostatic correction; terrain correction. |
HDBK-850 |

gravity reference stations |
Stations which serve as reference values for a gravity survey, i.e., with respect to which the differences at the other stations are determined in a relative survey. The absolute value of gravity may or may not be known at the reference stations. | HDBK-850 |

gravity station |
A station at which observations are made to determine the value of gravity. | HDBK-850 |

gray level |
The quantified brightness value assigned to a pixel. A value may correspond to graytones ranging from black, through the grays, to white. | USIS 95 |

gray scale |
See step wedge. |
HDBK-850 |

gray scale |
A calibrated sequence of gray tones ranging from black to white. A measure of the number of discrete levels of gray intensity available in an image processing system. For instance, a linear eight bit system includes the values 0-255. | USIS 95 |

grazing angle |
The angle between the line of sight from the target to the imaging vehicle and the local tangent plane at the target. A vehicle at nadir over the target has a grazing angle of 90 degrees. Also known as slope. | USIS 95 |

great circle |
A circle defined by the intersection of the surface of the Earth and any plane that passes through the center of the Earth. Note: On the idealized surface of the Earth, the shortest distance between two points lies along a great circle. | Fed STD 1037C |

great circle |
A circle on the surface of the Earth, the plane of which passes through the center of the Earth. Also called orthodrome. |
HDBK-850 |

great elliptic arc |
An arc defined by a plane which contains the two points and the center of the reference spheroid. | HDBK-850 |

great year |
The period of one complete cycle of the equinoxes around the ecliptic, about 25,800 years. Also called platonic year. |
HDBK-850 |

great-circle bearing |
The initial direction of a great circle through two terrestrial points, expressed as angular distance from a reference direction. It is usually measured from 0° at the reference direction clockwise to 360°. |
HDBK-850 |

great-circle chart |
A chart on which a great circle appears as a straight line; a chart on the gnomonic projection. | HDBK-850 |

great-circle direction |
Horizontal direction of a great circle, expressed as angular distance from a reference direction. | HDBK-850 |

great-circle distance |
The length of the shorter arc of the great circle joining two points. It is usually expressed in nautical miles. | HDBK-850 |

great-circle line |
In land surveying, the line of intersection of the surface of the Earth and the plane of a great circle of the celestial sphere. | HDBK-850 |

great-circle route |
(JCS) The route which follows the shortest arc of a great circle between two points. | HDBK-850 |

greatest elongation |
The maximum angular distance of a body of the solar system from the Sun, as observed from the Earth. The direction of the body east or west of the Sun is usually specified, as the greatest elongation west. | HDBK-850 |

Greenwich apparent time (GAT) |
Local apparent time at the Greenwich meridian. | HDBK-850 |

Greenwich civil time (GCT) |
See Universal Time (UT1). |
HDBK-850 |

Greenwich hour angle (GHA) |
Angular distance west of the Greenwich celestial meridian; the arc of the celestial equator, or the angle at the celestial equator, or the angle at the celestial pole, between the upper branch of the Greenwich celestial meridian and the hour circle of a point on the celestial sphere, measured westward from the Greenwich celestial meridian through 360°; local hour angle at the Greenwich meridian. | HDBK-850 |

Greenwich interval |
An interval based on the Moon's transit of the Greenwich celestial meridian, as distinguished from a local interval based on the Moon's transit of the local celestial meridian. | HDBK-850 |

Greenwich lunar time |
Local lunar time at the Greenwich meridian; the arc of the celestial equator or the angle, at the celestial pole, between the lower branch of the Greenwich celestial meridian and the hour circle of the Moon, measured westward from the lower branch of the Greenwich celestial meridian through 24 hours; Greenwich hour angle of the Moon, expressed in time units, plus 12 hours. | HDBK-850 |

Greenwich Mean Time (GMT) |
See Universal Time (UT1). |
JPUB 1-02 |

Greenwich meridian |
The meridian through Greenwich, England, serving as the reference for Greenwich time, in contrast with local meridians. It is accepted almost universally as the prime meridian, or the origin of measurement of longitude. | HDBK-850 |

Greenwich meridian plane |
The meridian plane passing through Greenwich, England, widely used as the zero meridian plane. This is actually only a half-plane, on the European side of the polar axis. | CEN/TC 287 |

Greenwich sidereal date |
The number of mean sidereal days that have elapsed on the Greenwich meridian since the beginning of the sidereal day that was in progress at Greenwich mean noon on January 1, 4713 B.C. See also Greenwich sidereal day number. |
HDBK-850 |

Greenwich sidereal day number |
The integral part of the Greenwich sidereal date. It is a means of numbering consecutively successive sidereal days beginning at the instants of upper transit of the mean vernal equinox over the Greenwich meridian. See also Greenwich sidereal date. |
HDBK-850 |

Greenwich Sidereal Time (GST) |
Local sidereal time at the Greenwich meridian. The arc of the celestial equator, or the angle at the celestial pole, between the upper branch of the Greenwich celestial meridian and the hour circle of the vernal equinox, measured westward from the upper branch of the Greenwich celestial meridian through 24 hours; Greenwich hour angle of the vernal equinox, expressed in time units. | HDBK-850 |

Greenwich time |
Time based upon the Greenwich meridian as reference, as contrasted with that based upon a local or zone meridian. | HDBK-850 |

Gregorian calendar |
A calendar in general use introduced in 1582 to correct an error in the Julian calendar. NOTE - In the Gregorian calendar common years have 365 days and leap years 366 days divided into 12 sequential months. [ISO 8601:1988] | ISO/TC 211 |

grid |
1. (geodesy) Two sets of parallel lines intersecting at right angles and forming squares; a rectangular Cartesian coordinate system that is superimposed on maps, charts, and other similar representations of the earth's surface in an accurate and consistent manner to permit identification of ground locations with respect to other locations and the computation of direction and distance to other points. 2. A type of Digital Elevation Model (DEM) that is derived from interpolating elevation values from irregularly or regularly spaced points that have X, Y, Z values. 3 A network composed of two families of lines such that a pair of lines, one from each family, intersects in no more than two points. 4. (GIS) Program developed at Harvard in the early 1970s which contained all the standard Boolean operations that today's GIS have. See also arbitrary grid; atlas grid; British grid reference system; GEOREF; Lambert grid; major grid; military grid; military grid reference system; National grid; overlapping grid; parallactic grid; perspective grid; point-designation grid; polar grid; secondary grid; tangent plane grid system; transverse Mercator grid; Universal Polar Stereographic (UPS) grid; Universal Transverse Mercator (UTM) grid; world polyconic grid, preferred grid, primary grid, and prime grid meridian. |
HDBK-850 |

grid |
A set of points arrayed in a pattern or area elements forming a regular, or nearly regular, tessellation of a surface. | ISO/TC 211 |

grid amplitude |
Amplitude relative to grid east or west. See also amplitude. |
HDBK-850 |

grid azimuth |
The angle in the plane of projection measured clockwise between a straight line and the central meridian of a plane rectangular coordinate system. | HDBK-850 |

grid bearing |
(JCS) Bearing measured from grid north. | HDBK-850 |

grid cell |
A two-dimensional object that represents the smallest nondivisible data element of a grid. | ISO/TC 211 |

grid computation |
The determination, from a set of tables derived from formulas, of the true shape and dimensions of a grid, for the purpose of constructing such a grid. The grid is mathematically coordinated with its related map projection; they are usually computed concurrently . | HDBK-850 |

grid convergence |
(JCS) The horizontal angle at a place between true north and grid north. It is proportional to the longitude difference between the place and the central meridian. See also convergence. |
HDBK-850 |

grid coordinate |
A system of point-positioning on a plane, arising from a system mathematical projection of points on a specific geodetic datum to that plane. | ISO/TC 211 |

grid coordinate system |
(JCS) A plane rectangular coordinate system usually based on, and mathematically adjusted to, a map projection in order that geographic positions (latitudes and longitudes) may be readily transformed into plane coordinates and the computations relating to them may be made by the ordinary methods of plane surveying. | HDBK-850 |

grid coordinates |
(JCS) Coordinates of a grid coordinate system to which numbers and/or letters are assigned for use in designating a point on a gridded map, photograph, or chart. See also coordinates. |
HDBK-850 |

grid declination |
The angular difference in direction between grid north and true north. It is measured east or west from true north. Also called declination of grid north; gisement. |
HDBK-850 |

grid direction |
Horizontal direction expressed as angular distance from grid north. | HDBK-850 |

grid distance |
See grid length. |
HDBK-850 |

grid equator |
A line perpendicular to a prime grid meridian, at the origin. | HDBK-850 |

grid interval |
(JCS) The distance represented between the lines of a grid. |
HDBK-850 |

grid inverse |
The computation of grid length and grid azimuths from grid coordinates. | HDBK-850 |

grid junctions |
Those lines delineating the joining of two or more grid systems on a map or chart. | HDBK-850 |

grid latitude |
Angular distance from a grid equator. See also fictitious latitude. |
HDBK-850 |

grid length |
The distance between two points obtained by computation from grid coordinates of the points. It differs from the geodetic length by the amount of a small correction based on the scale factor for the line. Also called grid distance. |
HDBK-850 |

grid line |
One of the lines of a grid. | HDBK-850 |

grid longitude |
Angular distance between a prime grid meridian and any given grid meridian. See also fictitious longitude. |
HDBK-850 |

grid magnetic angle |
(JCS) Angular difference in direction between grid north and magnetic north. It is measured east or west from grid north. Also called grivation; grid variation. |
HDBK-850 |

grid meridian |
One of the grid lines extending in a grid north-south direction. The reference grid meridian is called prime grid meridian. In polar regions the prime grid meridian is usually the 180° - 0° geographic meridian. See also fictitious meridian. |
HDBK-850 |

grid method |
(photogrammetry) A method of plotting detail from oblique photographs by superimposing a perspective of a map grid on a photograph and transferring the detail by eye, that is, by using the corresponding lines of the map grid and its perspective as placement guides. See also perspective grid. |
HDBK-850 |

grid north |
(JCS) The northerly or zero direction indicated by the grid datum of directional reference. | HDBK-850 |

grid number |
The numerical value of a grid line indicating the distance of that line from the false origin of the grid. See also grid coordinates. |
HDBK-850 |

grid origin |
The point, usually near the center of a grid zone, where a parallel intersects a north-south grid line coincident to a meridian. See also false origin. |
HDBK-850 |

grid parallel |
A line parallel to a grid equator, connecting all points of equal grid latitude. See also fictitious parallel. |
HDBK-850 |

grid plate |
1. (cartography) See color separation drawing. 2. (photogrammetry) See reseau. |
HDBK-850 |

grid prime vertical |
The vertical through the grid east and west points of the horizon. | HDBK-850 |

grid rhumb line |
A line making the same oblique angle with all grid meridians. Grid parallels and meridians may be considered special cases of the grid rhumb line. See also fictitious rhumb line. |
HDBK-850 |

grid ticks |
(JCS) Small marks on the neatline of a map or chart indicating additional grid reference systems included on that sheet. Grid ticks are sometimes shown on the interior grid lines of some maps for ease of referencing. | HDBK-850 |

grid variation |
See grid magnetic angle. |
HDBK-850 |

grid zone |
An arbitrary division of the Earth's surface designated for identification without reference to latitude or longitude. | HDBK-850 |

gridded oblique |
An oblique aerial photograph printed with a superimposed grid to assist in the identification of a particular area within the photograph; used chiefly for artillery spotting. | HDBK-850 |

gridded photograph (GP) |
A photograph with a precise geographic grid. Used for manual measurement of precise coordinates where elevation is not required. Provides acceptable aircraft inertial navigation system fixpoint derivation as a substitute for survey or other point positioning data. | HDBK-850 |

Gridded Reference Graphic |
A product with an overprinted grid. May be either a non rectified image with a common reference grid or a rectified image with a precise metric grid. | USIS 95 |

gripper edge |
(JCS)The edge by which paper or other printing material is drawn into the printing machine. | HDBK-850 |

gripper margin |
See gripper edge. |
HDBK-850 |

grivation |
See grid magnetic angle. |
HDBK-850 |

gross error |
The result of carelessness or a mistake. May be detected through repetition of the measurements. | HDBK-850 |

gross model |
The total overlap area of a pair of aerial photographs. See also neat model. |
HDBK-850 |

Ground Attack Control Center |
Part of the Joint Surveillance Targeting and Attack Radar System (JSTARS) program. It is being designed to receive and provide for the exploitation of data from JSTARS in support of Air Force tactical requirements. | USIS 95 |

ground camera |
See terrestrial camera. |
HDBK-850 |

ground combat element (GCE) |
The Marine air-ground task force (MAGTF) element that is task organized to conduct ground operations. The GCE is constructed around an infantry unit and varies in size from a reinforced infantry battalion to one or more reinforced Marine division(s). The GCE also includes appropriate combat support and combat service support units. Normally, there is only one GCE in a MAGTF. |
JPUB 1-02 |

ground control |
(JCS) A system of accurate measurements used to determine the distances and directions or differences in elevation between points on the Earth. See also common control; control point; field control; traverse. |
HDBK-850 |

ground control point |
See control station. |
HDBK-850 |

ground data |
See ground truth. |
HDBK-850 |

ground distance |
The great-circle distance between two ground positions, as contrasted with slant ranger the straight-line distance between two points. Also called ground range. |
HDBK-850 |

ground gained forward (GGF) |
(aerial photography) The net gain per photograph in the direction of flight for a specified overlap. The GGF is used to compute the number of exposures in a strip of aerial photography. | HDBK-850 |

ground gained sideways (GGS) |
(aerial photography) The net lateral gain per flight for a specified sidelap. The GGS is used to compute the number of flight lines for an area to be photographed. | HDBK-850 |

ground information |
See ground truth. |
HDBK-850 |

ground nadir |
(JCS) The point on the ground vertically beneath the perspective center of the camera lens. On a true vertical photograph this coincides with the principal point. Also called ground plumb point. |
HDBK-850 |

Ground Order-of-Battle |
A compilation of data which provides the identification, strength, command structure, and disposition of the personnel, facilities, units and equipment of any military ground force. | USIS 95 |

ground parallel |
The intersection of the plane of the photograph with the plane of reference of the ground. See also axis of homology. |
HDBK-850 |

ground photogrammetry |
See terrestrial photogrammetry. |
HDBK-850 |

ground photograph |
See terrestrial photograph. |
HDBK-850 |

ground plane |
The horizontal plane passing through the ground nadir of a camera station. | HDBK-850 |

ground plumb point |
See ground nadir. |
HDBK-850 |

ground pyramid |
A component of an analytical method for determining the precise degree of photographic tilt, representing a specific spatial configuration from three ground control points (forming a triangle) on the ground to the exposure station of the photograph containing the identical points. When used with the photo pyramid, the ground pyramid permits the exact analytical determination of tilt in the photograph. See also photo pyramid. |
HDBK-850 |

ground range |
See ground distance. |
HDBK-850 |

ground range |
The distance from the ground trace of the satellite to the target, measured in nautical miles. | USIS 95 |

ground resolution |
The minimum distance which can be detected between two adjacent features, or the minimum size of a feature expressed in size of objects or distances on the ground. | HDBK-850 |

ground resolved distance |
The smallest detail that can be seen in a given image. | USIS 95 |

ground return |
(JCS) The reflection from the terrain as displayed and/or recorded as an image. | HDBK-850 |

ground sample distance (GSD) |
The center to center distance between two adjacent pixels on the ground. The projected size of the detector onto the ground, equal to linear dimension of pixel in the image plane times altitude divided by focal length of lens. | USIS 95 |

ground speed |
(JCS) The horizontal component of the speed of an aircraft relative to the earth's surface. | HDBK-850 |

ground station |
A monumented station, established by field survey methods, which is used as a base for ground station equipment for the procurement of shoran or shiran controlled photography or control data. | HDBK-850 |

ground station module |
The system will be the down-link ground station for JSTARS. | USIS 95 |

ground survey |
A survey made by ground methods, as distinguished from an aerial survey. A ground survey may or may not include the use of photographs. | HDBK-850 |

ground swing |
An error-causing condition in electronic distance measuring which is brought about by the reflection of the microwave beam from the ground or water surface. The reflected beam mixes with the direct beam at the receiving antenna, thereby changing the phase of the direct beam and causing an error in the distance measured. By varying the carrier frequency, the error becomes cyclic, making possible mean instrument readings that are substantially accurate. | HDBK-850 |

ground trace |
See ground parallel. |
HDBK-850 |

ground track |
The plot of the satellite nadir points. The vertical projection of the actual flight path of an aerial or space vehicle onto the surface of the Earth. | USIS 95 |

ground truth |
A term coined for data/information obtained from actual ground measurement of surface/subsurface features to aid in the interpretation of remotely sensed data. Also called ground data; ground information. |
HDBK-850 |

ground-space coordinate system |
A scheme by which positions of triangulation stations, control points, and other ground features are related by distance and azimuth or by x- and y-coordinates. | HDBK-850 |

groupware |
1. A generic term for real-time data sharing programs that support team projects. 2. A collaborative technology that uses multimedia. 3. An information system that lets multiple users work on a single application simultaneously. |
Multimedia |

guard stake |
(surveying) A stake driven near a hub, usually sloped with the top of the guard stake over the hub. The guard stake protects, and its markings identify, the hub. | HDBK-850 |

guide |
A drafting or scribing surface bearing a map image to be traced by drafting or scribing for reproduction. Also called color separation guide; drafting guide; scribing guide. |
HDBK-850 |

guide meridian |
An auxiliary governing line projected north along an astronomic meridian, from points established on the base line or a standard parallel, usually at intervals of 24 miles east or west of the principal meridian, on which township, section, and quarter section corners are established. See also auxiliary guide meridian; principal meridian. |
HDBK-850 |

Gunter's chain |
A measuring device used in land surveying, composed of 100 metal links fastened together with rings, the length of the chain being 66 feet. Also called four-pole chain; four-rod chain. See also chain. |
HDBK-850 |

gyroazimuth theodolite |
See gyrotheodolite. |
HDBK-850 |

gyrocompass |
A compass which functions by virtue of the couples generated in a rotor when the latter's axis is displaced from parallelism with that of the Earth. A gyrocompass is independent of magnetism and will automatically align itself in the celestial meridian. However, it requires a steady source of motive power and is subject to dynamic error under certain conditions. Certain aircraft compasses also use gyroscopes to gain stability, while relying basically on the magnetic meridian; these are to be distinguished from the true gyrocompass. |
HDBK-850 |

gyromagnetic compass |
(JCS) A directional gyroscope whose azimuth scale is maintained in alignment with the magnetic meridian by a magnetic detector unit. |
HDBK-850 |

gyromeridian indicating instrument |
See gyrotheodolite. |
HDBK-850 |

gyroscope |
A device consisting of a spinning rotor and associated supporting readouts which makes use of Newton's Law of Rotation to give an indication of the angular velocity of the instrument's case with respect to an inertial reference frame. This instrument is used as the basic sensor in many direction-seeking, direction-keeping, and attitude stabilization systems. | HDBK-850 |

gyroscopic stabilization |
Equilibrium in the attitude and/or course of a ship or airborne vehicle maintained by the use of gyroscopes. Also, the maintenance (by the use of gyroscopes) of a camera in a desired attitude within an airborne vehicle. | HDBK-850 |

gyrotheodolite |
A theodolite with a gyrocompass attached or built in, whereby a true azimuth reference can be established in any weather, day or night, without the aid of stars, landmarks, or other visible stations. The azimuth obtained from the gyro or inertial theodolite is essentially the astronomic azimuth at the point of observation. This azimuth will differ from the corresponding geodetic azimuth by the amount of the Laplace correction. | HDBK-850 |

*Last Updated by Mark Owens 17 February 1999.*