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I
dlroction ●rgla-in lra~ing, the angle
between the mtenna base line and an
hrre@rary line cixmecfing the cenler 01 the base
line with the target .
dlractlon Instrument theodollte-A
tha@oiiie In which the graduated horizontal
C4rcle remains fixed during a 6erfaa of
obaervatbna, the telesco~ being poinlad on a
nurrtiar of signals or objjcfs In succession, and
the cfirectbn of each read on the circle, usual~
by mearra of mlciumeler mlcroecopas. Direction
krstrumenf lhaodoliles are used abrrost
excbaively In first- and eacorxkrrder
Irirmgulafion. Atao called dlrectlon
theodollte; triangulation theodollte.
dlrsctlon method of adjustment—
(trlarrgufstfon and traverse) A melfrod 01
adjustment of observations which determines
Corrections to obsenred directions. The direction
method Is used in the adjustment of first- and
eecxmkrder suwey obsewalions.
dlrecflon method of dotermlnlng
astronomic aslmuth-The determination of
the astronomic azimuth of a line by measuring,
with a dkection theodolite, the horizontal angle”.
between a selecled star and e suitable mark
and applying that ar@e to the azimuth of the
star computed for the epoch 01 the observation.
direction method of meeaurlng
horizontal anQlee—See dlrectlon metfSOd
of obatsrvatlon.
dlrectlon method of obaarvatlon-A
melhod of obsewing angular relationships
wherein fhe graduated circle is hetd in a fixed
position, and the directions of the various
signals are observed around the hortzon. Thus,
directions are poimings whereby angles are
found by the differences in directions. Also
called sflractlon method of maaaurhrg
horizontal anglea.
dlrectlon ot grevlty-See dlrectlon of the
Iorco of gravity.
dlrectlon of relallve movement—The
direction of motion relative to a reference pcint,
Ifeeff uaualfy In motion.
dlrectlon of the force of gravity—Th e
direction indiiated by a plumb line. It is
perpendicular to the surface 01 the geoid. Also
called dlrectlon of gravity.
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dlractlon Ot tilt—The direction (azimuth) of
the prtncfpal plane of a phoksgraph. Also, the
direction of Ihe principal line on a photograph.
dlrectlon theodollte-See dlrectlon
Instrument theodollta.
directional radar prediction-(JCS) A
prectktion made for a particular heading.
dlrectlonel reflectance-Reflectance
measured for a specific mode of Irradmtbn and
collecfbn.
dlrectlorr-1. (JCS) A term used by a spotter
Or ObSaWEr In a call tor fire to Indiie the
bearing of the spotting line. 2. The poaftiorr of
one point relative to another without reference
to the dk.lance between them. Direction may be
either twodimensional or three-dimenskwral, the
horizontal being the usual plane 01 the latter.
Direction is usually incketed In terms of Ifs
angular distance tmm a reference diiectlon. See
also gteat-circle direction; grid dlrectlon;
horizontal direction; magnetic direction;
Mercator dlrectlon; reference dlrfrctlon;
reletlve direction; true direction; x.
dlreclion.
discrepancy—A difference betwean results ot
dupliia!e or comparable measures of a quantity.
The difference in computed values of a quantity
obtained by different processes using data from
the same suwey.
diek oparatlng system (DOS)-One of
many operating ayaleme tor computers which
act as an interface between e user end the
computer hardware. DOS was ap.acMcally
designed lor personal comrnstem (PCs).
dlapereton—(oplice) The separetiin 0! tight
Inlo its component cobm by its passage through
a diffraction grating or by refraakm such es that
provided by a prism.
displacement—l. (cartography) The
hortzomal shift of the plotted position of a
topographic feature from Ifs true position,
caused by required adherence to prescribed line
weights and symbol sizes. 2. Any shii in the
position of an image on a photograph which
does not alter the perspective characteristics of
the photograph (I.e., shill due to lilt of the
photograph, scale change in the photograph,
and relief 0! the objects photogrephedj. See
also refraction displacement; relle?