1 - NGA

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glvlng the posltbn of the origin (two elements),
the otiw’rtalbn of the network (one element),
and the parameters of a reference elllpsokf (two
efamants). More racenf definitions express lfre
position and orientation as Iunclbtts of the
deviations In the matian and in the prima
vertical, the gaoid-ellipedd separafiin, ane the
parameters of a refererwe ellipsoid. The Wortd
Gaodatk System (WGS) is a gsocarrtrfc system
that provides a bask reference trarne and
(faomatrk figure for the earth, models the earlh
grevlmatrically, and provides the means for
ratallrtg positions on varioue datums to en earth.
cantered, earth fkad coordinate system. Atso
called horizontal detum; horizontal
gaodetlc datum. See also horizontal
control datum. 3. (leveling) A fevaf surface to
wtrich efavatfons are referred, usually, mean sea
level Imt may also include mean low water,
mean bwer bcw waler, or an arbttra~ etarffrrg
elevation(s). Also called vertlcel datum. See
also allltude datum; Cape Canaverel
datum; Department O! Da fenee World
Geodetic Syetem; Europeen datum;
hydrographlc datum; Indfan datum;
Internatfonaf low water; local datum; low
water datum; low water epringa datum;
lower low watar dstum; Mercury datum;
model drmrm; National Geodetic
Vertical datum of 1929; North American
datum o! 1927; North American detum
of 1983; pfrotographlc datum; prefarred
datum; Pulkovo 1932 datum; reference
datum; eoundlng detum; tidal datum;
Tokyo datum; vertical control datum:
World Geodetic Syetem.
day—The duratioir of one rotation of the Esrth,
or occasionally another celestial body, on its
axis. It is measured by successive transits of a
reference point on the celestial sphere over the
meridan, and esch type takes its name trom
the reference used. See also apparent eoler
dey; eetronomlc dey; calendar day; clvlf
day; constituent day; Julian day; lunar
day: mean eolar day; modiflad Julian
day; Sidereal day; aotar day.
de-integration—Definition of feafure or
tfremafic singles or sets from an Infegraled data
base.
deadbeat compaas—See eperlodlc
cortlpaee.
OECCa chaI1-A cffan showing Oecca IInes of
position.
Decca-A trade name for a radio phase
comparison ayatem which uses master and
slave stations to establish a hyperbolic fettice
arxt provide auxmte position fixing facifiilee.
December ●aletlce-see wlnlar aolstlce.
declination dlfferencs-The difference
between two dactinatione, patikufariy between
the declination of a cdestial body and the value
used ae an argument for entering a table.
decfinaflon of grid notih-see. grid
declination.
declfnaf Ion of the Moon-See lunar
declination.
declination of the Sun-See eolar
declination.
declination—1. In a syetem of polar or
spherical coordinates, the angle at the origin
between a iine to a point and the equafortal
plane, meesured in a plane perpendicular to the
equatorial plane. 2. me arc between the
Equator and the point measured on a great
citie parpendicuiar 10 the Equator. 3. (JCS)
(astronomy) The snguiar distance to e body on
the celestial sphere measured north or south
through 90” from the ceiestial equstor along Ihe
hour circle of the body. Comparable to latitude
on the terrestrial sphere. 4. Dtten used as a
shortened term for magnetic dacllnatlon
although this uee is not prefemd. sea also grid
decllnatlon; Orid magnetfc angle; lunar
decfinatlon; parailei of decflnetion: solar
cfeclinaflon.
decllnatoire—A combined magnetic compass
arvd afraighl-edge, suiiabla for use on a
plantable 10 martr the magnetic merfdian. Also
called box compase; trough compaas.
decllnometer-A magnetic instrument similar
to a surveyors compass, but arranged so that
the line of sight can be rotated to conform with
fhe needle or to any dasfred setting on the
horizontal circle. Used in determining the
magnetic declination.
decompraaa-The process by which
compressed dats is expanded to Its former file
size.
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defltrltlon-in imaoery Irrterpretetion, the
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