1 - NGA

MIL-HDBK-850
foresight—l, An Observation of the distance irectel-A family of mafhematicel fumtione
arsl direclion to the nest instrument station, 2. which are somatimss uaad to describe natural
(trarralt traverse) A peint set ahead 10 be used phenomena and shapes such as coastlines.
tor reference wfren resetting the transil on line or irrountains, river pafk%s, etc.
when verifying the alignment. 3. (leveling) The
reading on e rod that is Ireti at a point whose
etevation Is to be determined. Also called
mlnue ●ight. See also backsight.
forestry map-A map prepared principally to
shcw the s)ze, ctarrsj)y, kiml, ard value of Iraes
on a given area.
form llnaa+JCS) Lines resembling contours,
but representing no actual elevations, which
have been sketched from visual observation or
from inadequate or unreliable map sources, to
show collectively the configuration of the terrain
lormat-Predetermined arrangement of
characters, fields, tines, punctuation, page
numbar, etc.
forming machlrra-The equipment Ior
forming, by heat and vacuum, preprinted plastic
maps over a mold representing the Ierrain of Ih(
area.
formule for theoratlcal grevlty—A Iormula
expressing gravily on the spheroid of reference
in terms of geographic posilion, it being
assumed the! the spheroid of relerence is a
level surface.
forward azimuth—See azimuth, definition
1.
forward lap-See ovarlep, definition 1.
found cornar—A term adopted by the U.S.
Geological Survey to designate an exislent
I cametiof the pubiic-land sinweys which has
been recovered by field investigation.
four.pole chain—See Gunter% chein.
four-rod chalrr-See Gunter’s chain.
fourth-order trssversbA survey traverse of
an accuracy less than third-order travarse or
which fails to meet third-order official atandarda
In tourth-order traverse, angles are observact
with a tranah or sezfant ‘or are determined
grephicalty, and distances are measured wilh
taoe or stadia
fractional seals-See representative
frectlon.
fractional aectlon— A sectbn containing an
arsa appreciably different from 640 sores,
usually as a reautt ot an invasion by a
segregated body of water, or by other land
which cannot properjy be surveyed or disposed .
of as part of that section. See also sractlorr.
frecflonal township- A township Conlairrlng
less than 36 normal sections, uaualfy lv3Gause
ot invasion by a segragaled body of water, or by
other Iansf which cannot property be surveyed as
parl 01 lhat township, or by closing the public
tand surveys on State boundadss, or other
limiting lines. Half ranges and half
Iownshlps are fraclbnal townships by
definition. See ab.o township.
trame camera—A camera in which an entire
frame or format is exposed through a lens that
is fixed relative to the tocel plane, See atSo
panoramic camera.
framework of conlrol—See survey nat.
frema-(JCS) In photography, any single
exposure centained whhin e continuous
sequence of phonographs.
free-air enomaly—(JCS) The ditlerance
between obsewed gravity and theoretical gravity
which has been computed for Iatltude and
corrected for ejevalion of the atatlon above or
below the gaoid, by appfbatbn of the normal
rate of chenge of gravity for change of
elevatlon, as in free air. Also called Faye
anomaly.
free-ok correctlorr-Correction factor, usually
expressed as milligals per reeler, which Is
appflad 10 obsawed gravity to reduce the value
to sea level. Also called Faye correction.
free-swlnglng pendulum—A pendulum
moving wholly under the influence of gravjty and
an initial momsrrfum imparled to it by
mechanical or olher means. In gravity work, the
initial momentum may be imparled by drawing
the pendulum slightly out of plumb and Ihen
releasing il.