1 - NGA

horizontal conirol survey net-See
survey net, delinifkm 1.
horizontal controf-A network o/ stations of
known geographic or grid fmsitions referred to a
cvmn horizontal datum, wh”ch control the
horizontal posirbns of mapped features with
respect to parallels and mariduns, or northirrg
and casting grid Iirrae ehown on lhe map.
HOdXOntal control Irwtudes basic (marked) and
Supplemanrary @nnsrrtsed) stallona.
horizontal copiane-See baeal coplane.
horizontal datum—See datum, definition 2.
horizontal deformation—in relative
ortenfalion, the cumulative model warpage
atfecfing the horizontal datum from z-motion
error, brldglng error, and swing error.
lIOrlZOntal dlrectlon—Obse Ned frorlzorrtal
angles at a triangulation station reduced to a
common iniiial direction.
horizontal extension—See extension,
definition 2.
hortzontel geodetic datum—See
horizontal control datum.
horizontal lntenelly—The intensity of the
horizontal component of the magnetic field in
the plane of the msgneilc meridian.
horizontal lhw-A line perpendicular to the
veriic.al.
horizontal parellax—1. (astronomy) The
geocentric parallax of a body on the observer’s
trorfzon. This is equal 10 the angular
semidiameter of the Earlh as seen Irom the
body. 2. (phologrammelry) See absolute
stereoscopic parallaz.
horizontal pase point—See supplemental
poaltlon.
horlzorttal photo~raph—A photograph
taken with the axis of the camere horizontal.
horlzontaf plane-1. A plane perpendicular
10 tha diradion of gravity: and plane tangent to
the gsoki or parallel to euch a plana, 2.
(surveying) A plane perpendicular 10 the plumb
line wittsjn which, or on which, angles and
MIL-HC)BK-850
distances are observed. For any plenknatric
survey il is assumed that all plumb fines therein
are parallel, and all horizontal pfanas therein are
parallel
horizontal retraction—A natural error In
SUweYiW which is the raautt of the horizontal
bending of fighl rays berween a target and en
obsewing Instrument. Usually cauaed by the
dttterences In density of the air along the path of
the light rays, reauffing from temperature
variations. See also terreatrlal refraction.
horizontal stadla—A method of measuring
dk4aWeS wherein the stadia rod is held in a
horizontal position and the stadia hairs of the
irratrurrrenl are vertical during obsarvatkms.
horizontal taping and plumbhrg—A
method whereby the tape is field horizontally,
and the posilione of M pertinent ~raduations are
projected to the ground with plumb bobs.
horizontal/vertical brldglng—See
brldglng.
horizontal/vertical exIenalon—See
eXtenSIOn del,ini.,on 2.
horlzontallzlng tha model—See leVellhg,
definition 2.
horizontally comrolled photography—
Cartographic aerial photography obtained
simultaneously with racardlng of distanca
measurements between the taking aircratf and
aach of Iwo or more geodetically positioned
ground stations. Shoran or ehiran are normally
used as lhe dklance measuring equipment.
The resuft is precise relative horizontal
positioning o! each photograph which has
associated recorded distances. This positioning
information is used as horizontal control data in
Ihe mapping process.
horizon—(JCS) fn general, rhe apparent or
visible junction of the earlh and sky, ae seen
Irom any specffic positbn. Also called the
aPParent, vlslble, or local horizon. A
horizontal plane passing through a point of
vision or perapectlve center. [me apparent or
visible hor”uon approximates the true horizon
only whan the poim of vision is very cbse to eee
level,] See also apparent horizon; attltuda
Indlcaror; calestlal horizon; felee
horizon; geocentric horizon; geoldal
horizon; geometrical horizon; radar
horizon; eenslble horizon; trua horizon.
121