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material.
floetlng mark+ photograrnmelry) A mark
Sean as occupying a pxition in the lhreedlmensbnal
apace formed by the stereoscopic
fueion ot a pair of phonographs and used as a
relerenca mark in examining or measuring the
stereoscopic model.
fbrsflng-(cartography) The technique of
making mlntrr adjwstmenfs of delail In order to
maintain fheir proper relative position.
flood control mep-A special map, or set ot
maps, designed for study and planning the
control of areas subject to inundation.
ftood lld~The porlion of the tide cycle
between low water and the following high water
Also called rlelng tide.
flowllna-The slope axfandino from the
heights abng the neatline to the model datum,
at an angle no greater than 45°, to preclude
forming the ptastic Sheet al a 90- angle al the
nealline of a plastlc reliaf map.
fluorescent maD-A Mao raoroducact wllh
IIuorescem Ink or’ on fluorescern paper, “which”
enables the user to read the map in darkness
under uftraviole! light.
flux-gato magnatomaler-An instrument
desfgned 10 measure the Earth’s magnelic field,
Also called saturabte raactor.
ttuxmeter—An instrument for measuring the
Intensify of a magnetic fiakf.
fly levettng-Sae ftylng levels.
fly-by mathod+aurveytng) A fechrdque 01
dalerminlng approximate elevations where
exlremefy rugged terrain is anmuntered. The
principle Is tdenfical to the two-base method
axcepf the roving barometers are air transpcmed
and raad In tha aircraft as II passes on a level
wtth the topographic feature whose elevIJtiOn is
raquired.
flylng Ievai.s-l. A Ieval line run at the close
of a working day to check the resuffs of an
extended line run In ona direction onfy. Longer
etghts and fewer setups are used as Iha
WfPoee ia Io delect We mislakes. Also Mlted
fly levellng. 2. Level Ihras run with the
engineer’s ordinary ieveling equlpmant but with
MIL-HDBK-850
a dislinctty bw order of accuracy. Enor of cbsure
may be perhaps one fcmt (or mora) times the
square rool of the diilarwe in miles.
total langfh-A general term for the distance
between the canter, vertex, or rear node of a
lens (or tha vetiax of a mirror) ard fhe poinf al
which the hnaga of an Inflnttefy distanf ob)act
comas into critical focus. The term must be
praceded by an adjective such ae “equlvatentor
“calibrate~ 10 have a precise meanfng. Saa
also back focal length; callbretad focal
length; effacttve focat length;
equivalent total length; nominal focal
length.
focal plane-(phonography) Tha plane,
perpendicular to the axis of the lens in tijch
images of points in the object fiekf of the tens
are focused.
focat point—See focus.
focal range—See depth of focus.
focal-plane ptala-A glass plate sat in Iha
camera so that the surface away from tha lens
.@incides with Jhe focal plane. Its purpose is 10
posilwn the emulsion of the film in the focal
plane when the film is physkelly pressed tnto
contact with the glaas plala. Atso catled
contact gtaaa; contact plate.
focus-The point toward which rays of light
converge 10 form an image after passinp
through a fens. Ateo defined as the condition of
sharpest imagery. Also called focal point;
prlnclpal tocus. Sae also hyparfocat
distance; eldereal focus.
foldad opllcs—(phologrammetry) Any optical
or Ians system containing rattecling cemponenfa
which reducas Ihe physical length of a
phonographic or sensing system, or changes the
path of an optical sxis.
foldlng vernier—A single vernier so
conshucred and numbered that it may be read
In aither dhection.
fool-meter rod—A sladia rod, marked in fact
and tanths on one side, and metara and
hundredths on the other side, used to
determina distances and elevations in one unit
of measuramem and to check tham by readings
in a difterent unit.
force tunctlon-See potential.
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