1 - NGA

length corracflon-(taping) The difference
bahveen the nominal length of a laps and
ils effective length under conditions of
afandardiiafion, The standard length of a
fape is usually expressed by a number o!
whole units (the nominal length) plus or
minus a small distance which is tha length
correction defined above.
MIL-HDBK-850
Lenolr laval—An krsfwmerrf which has the
telescope passing through steel blocks,
one near each end, whose upper and lower
tamrs are plane and closely parallal; me
bwer faces real upn a brass circle; the
UPPar facas SUPPOII a apiril level, which is
reversed in tavelirrg the instrument.
lens axis—See optical axla.
tans calibration-See camera
calibration.
Iarrs component—See lens element.
Ians dlaforliorr+JCS) Image displacement
caused by lens irregularities and
aberrations.
lens alemenl—One lens 01 a complex lens
system. In a photographic lens, the Ierms
from element and rear element are
often used. Also called lens component.
Ians epaed—See relative aperture.
Ianaatlc compaas—A type of compass
equipped wfih a lens which permits the
observer to read the far aide of the
movable dial.
lens-A disk of optical glass, or plastic, or a
combination of (WO or more such disks, by
which rays of fight may be made to
Kvrverge or to diverge. Such disks have
two surtacas, which may both be spherical,
one Plane and ona spherical, or various
other cmnbinallons [cyfirrdrical, paraboloid,
or hyperboloid). See also achromatic
lens; anastigmailc lens; aplanatlc
Iena; apochromatlc lens; aapherlcal
Iana; aallgmatlzer; coated lens;
Compensating lasts; converflble
Ians; cylindrical Iena; eyepiece:
Freanel Iena; Metrogon Iena:
narrow-angle Iana; negative Iene;
normal-angle Iene; objective lens;
po.sitlve lens; process lens:
142
apherlcal lens; auperwide-angle
Iene; thick Iena; tfrln Iana; wldean@e
Iene.
Level O topology—A topological surface
which comains a set ot entily points and
edges. Edges mnrain onty coordinate and
aftritrute information.
Level 1 topology—A topological aUIfaC8
which Cunsiars of a eel of entity poinfs and
edges that meet at nodes. Edges contain
stan node, end node, next edga, and
previous edge information,
Lavel 2 lopology—A topological surface
which consists of a set of edges and entity
points, when projected on a planar surface,
the edges maet only at nodes. Edges
contain start node, end node, and next and
previous edge information, Edges meet
only at nodes.
Level 3 topolog y—A IopoloQical surf aca
which is partitioned by a set ot mutually
exclusive and coliecfively exhaustive facea.
Edges conlain left tace, right face, start and
end noda, and next and previous edge
information. Edges meet oniy at nodes.
level constant—The amount by which the
actual line 0! sight lhrough a leveling
instrument (when the bubble ia centerad in
ils vial) departs from the tmfy horizontal line
through the center of the instrument,
computed in millimeters per millimeter of
siadia interval. When leveling rods
graduated in yards instead 01 meters are
used, the level constant, C. woutd be
expressed in milliyards per milfiyard of
stadia interval. Also called C-conetant.
Iavellng—1. (survaying) The operations of
measuring vertical distances, diraclly or
indirectly, 10 determine elevations. See also
aatrogeodetlc Ievellng;
astrogravlmetric Ievellng; barometric
Ievellng; dltterentlal Ievellng; direct
Ievellrrg; firs!-ordar Ievellrrg; flylrrg
Ievela; geodetic leveling; profile
levallng; reciprocal Ievellng;
aacond-ordar Iavellng; aplrlt
Ievellrsg; atadla trigonometric
Ievellng; thermometric Iavellng;
third-ordar Ievellng; fhree-wire
Ievellng; trigonometric Ievaflng;
verrlcef engulatlon; water Ievellng.
2. (photogrammetry) In absolute