1 - NGA

MIL-HDBK-850
which have been previously determined by
COwlation or by graphical melhods, or by
desrmption obtained from data supptied by
documents O( record. such as deeds,
maps, or other sources.
locators hand levef-A hand IWld type of
tavel used to measure approximate
ditferencee in elevation
Iocklng angla-in tilt analysis of oblique
photographs, the complement of the
interloc+ring angle. The depression angle 01
the oblique when the lilt of the WMllCal
photograph is zero.
Ioglcal conalatancy-(digilal mapping) The
correctness 01 the relationships encoded In
the data Wrmfure of Ihe daIa sel.
Ioglcel contouring—A procedure, based on
the Iacta that contours are spaced equally
along a untform slope, which permits the
sketching of contours from field notes with
considerable ascuracy arrd without Ihe
need of running a ievel line for every
mntour. Contour lines are interpolated by
spaciW them proportionately between spot
elevations established af every poinl where
there is a change in slope.
lonQ chord+ roule surveying) On a Simple
wrve, the chord, or straight line, that
extends from me poin\ of curvature to the
poirrf ot Iangerwy; on a compound curve,
the chord Ihat extends from lhe pint of
compound curvature to the point of
wrvature or to the point of tangency. In a
description of a circular land boundary, the
iengfh arrd bearing of fhe long chord is an
important factor.
long Ilne ezlmuth (LOLA) surveye— A
measurement by use of phoforecording
thaodolites and airborne strobe lights of
bng azimuth lines nol visible between
ground afafions.
long rud-A level rod, usually a Philadelphia
md, permitting readings of 13 teet when
fully extended. Also called high rod. See
also ahorr rod.
Iong-parlod constltuant—A tide or tidal
current constituent with a period fhat IS
independem of the rotation of the Earth but
whfch depends upon !he orbital movement
of the Moon or of the Earth. The period is
146
usually longer than a day and in general a
halt-month or larger.
Iong-period perturbations-Periodic
perturbations in Ihe orbft of a plane! or
satellite which require more than one orbital
period to execute one completa periodic
veriation.
Iong-renge chaft-See long-range
navlgallon chart.
long-range navigation chart-Any one of
a series of small scale, 1:3,000,000 or
smaller, aeronautical charls designed for
long fllghls using dead reckoning ar’d
celestial navigation as the principal means
of navigation. Also called Iong-ranga
chart.
Iongltude difference—See departura.
definition 1.
Iongltude equation—A condition equation
which expresses the r.elalkmshiP beween
the fixed longitudes of two points which are
connected by triangulation or traverse.
Iangitu”de tactor—The’ “change in Iongltude
along a celestial line of posilion par one
minule change in latitude.
Iongltuda of the Moon% nodes—The
angular distances along the ecliptic of the
Moon% nodes from the vemat equinox; the
nodes hava a retrograde r’r’miion, and
complete a cycle of 360” in approximalety
19 years.
Iongltude signal—A sign indicating a time
event, observable al different stations, and
used in comparing local times 01 those
stations, end determining the dtiererrce of
their longitudes.
Iongltude term gravity formula—A n
additional term in the formula tor theoretical
gravity which expresses the variation with
bngitude due to a triezial ellipsoid of
reference. See afso Halmert% gravity
formula of 1915.
longltude—A linear or angular distame
measured east or west Irom a reference
meridian (usually Greenwich) on a sphere
or spheroid. See also assumed
longltude; asironomlc Iongltude;
Celeetlal longitude; circle of