1 - NGA

1’
I
between the times 01 lransm’Rfing and receiving
a signai by Ihe ranging instruments,
electronic sketchmaster—See universal
●nalog photographic rectlflcatlon
system.
.Iacfronlc survey-Any survey utilizing
eledronic equipment.
electronic telemeler—An electronic device
that measures the phase difference or tranail
fhna between a transmitted electromagnetic
~~~,e of known frequancy am speed and tts
tilL-HtiBK-850
Elecfrotapa-A trade mme for a precise
electronic surveying device which fransmffs a
radio frequency signal to a responder unil which
in turn retransmits the signal baCk to the
imerrogalor unit. The time Iapsa between
original transmission and receipt of return signal
is maasurad and displayed in a direct digital
readout for eventual reduction into a precise
finear distance. f! operatea on the same
principal as the Tellurometer.
elaments of a fix—The sDecific values Of the
coordinates used to define ‘a positim.
alevatad pola-The celestial pole above the
horizon, Oppaile of depreaaed pole.
alevatlon angle-See anale of elavatlon.
efevetlon denelty category-A term used
thmugfmut sizing of digital elevation data
transactions within the MARK 90 system.
Elevation density category 1 represents
elevation post spacing at 3 arc second imervals.
A pmducf having a scale smaller !han 1:50,000
woufd typically be represented by this density.
Elevation density category 2 represents
alevation post spacing at 1 arc second intervals,
A prockmf having a scale of 1:50,000 or larger
would typically be represented by this density,
elevatlon matrfx-A series 01 height values
for points spaced at regular intervals and usually
expressad In the form of a two-dimensional
array of numbers.
efevallon meter-A mechanical or
eiecfromechanical davice on wheels that
measures slopa and distance, and automatically
and cominuousty klfegrales their product into
dMferenca of elevation.
82
efevatlon Poata-A point with a known
horizontal and vetliml poaifbn with respad to
some defined referense system. Poaf pints
are cmnrrmn elevation pints between two
different digital terrain files. Dgifsti Ter@n
Elavalion Data are eievatkon posts in dffifal
form. A dqffal alevation matrfx consfata of
elavallon posts evenfy distributed in a
rectangular pattern.
elevation tints—See hypsomatrlc tlntlng.
elevation-VerfW dkifance horn a datum,
usually mean sea level, to a ~inf or object on
the Earlh’s aurlace; nol to be contused wtfh
altlludo whfch refers to pofnts or ok+scts above
the Earfha surface. In geodetic formulas,
elevatkms ara heighls: h is height above
ellipsoid, His height above lhe geoid or local
datum. Occasionally the h and H may be
reversed. See alsa adjusted elevetlon;
assumed ground elevrstlon: barometric
elSWe!lOn: CfIaCkfJd apd eleve;lon;
crftlcal elavatlon; dfffarence of
elevatlon; dynamic elevatlon; flald
alevation; fkad elevation; frlghaaf
elevallon; mean ground elevation;
optimum ground eievation; orfhometrlc
elevation; preilmlnary elevation; spot
elevallon; standard elavellon;
Supplemental elevatlon; unchecked
spot aievation.
ellipsold of revolution—See elflpsold of
rotation.
ellipsoid of roletion-The surface generated
by an ellipse rotating about one of ifs axes. Also
called allipsoid of revoluflon. See also
obiafe epharold; prolate epharold.
alllpsoldal height—The height above fhe
reference ellipsoid, measured along the
ellipsoidal outer normal through the point in
question. Also called geodetic height.
ellipsoidal reflacfor-A mirmr rjurlaca which
Cunforms fo a portion of an ellfpsold of
revolution, Principally employed in several types
of slereoploner pmjecfora such as tha ER-55
ellipsold-An t3111paoldIs a mathamalical figure
genarated by the revolution of an ellipse about
one ffs axes. The ellipsoid that approximates the
geoid is an ellipse rotaled about its minor axis,
or an oblate spheroid. See also datumcentered
elflpaoid; Earth-cantered