1 - NGA

auccasswe returns of the Sun to a sidereal hour
angle of 80” (about Jatwary 1). The length of
tha Wfltkxrs year Is the aama as thal 01 the
tropical yaar, since both are based upon Iha
position of the Sun with respacl to the vernal
equinox. Aleo called Beaaellan year.
flctitloue-in cartography, pertaining to or
measured from an arbitrary reference line.
fldellty—Tha degree with which a eystem
arxarralely reproduces the dala input into il.
fiducial asrea-The lines joining opposite
fiducial msrlca on a photograph, The x-asis is
generally considered 10 be the one nearfy
parallel with the line of ffiiht.
fldr.rclel mark(e+l. (surveying) An index line
or point. A line or point used SS a basis of
reference. 2. (JCS) (pholegrammetry) See
Colilmatlng marke. 3. Also, markers in any
instrument which detine the axes wfrose
infarsecfion fixes the principal point of a
photograph and tulfills the requirements of
interior orfemation.
field callbratlorr-A term generally applied
where only a corrrbhalion of fietd and office
wmputar techniques are available 10 check
instrument accuracy. Adjustments, other than
normal operator adjustments, cannot be made
during field calibration.
field check-The operation of checking a map
compilation manuscript on the ground. See also
field clesalficstlon.
field claeelflcatlon-Field inspection and
idenfifiition of faaturas which a map compiler b
unable to delineate: identification and
deiinaatlon of pofitical boundary lines, place
namaa, road ciassitications, buildings hidden by
trees, and so forth. Fietd classification may be
Included aa pan of Iha comrol survey efiort snd
Mrmslly la wmplemd prior to tha actual
stereocompilation phasa. See SISO field
Inapectlon.
flald comparator-A shori Iina whose length
is measured with accuracy and precision, and is
used to check tha lengths of apparatus (tapes)
used in tha actual Siald operations. Also callad
calibration couraa; comparator base.
fiald completion-A combination of field
Inspections or surveys, either bafore or arter
armpilation, to classify and mmplete the map
MIL-HDBK-850
content, correct erroneous data, and add
intormetion such es names, civil boundaries,
and similar classifiialion data. its Wrpxe is to
till in or confirm that portion of a map manuscript
prepared by atareocompilstion.
tleld contouring-Contourirrg a topography
map by field methods accomptishad by
planeteble surveys on a prepared base or by
stadla survey. Ganerally, this operation applies
to tarrain unsuitable for contouring by
phologrammetric methods. Also used in limited
areae when engineering dasign (drainage)
raquiras 1-foot contours. Sea also contour
aketchlng.
field control-(JCS) A series of points whose
relalive positions and elevalbns are kmwn.
These ~sifions are used in basic data in
mapping and charting. Normal~, these positions
ara established by sufvay mathods and are
sometimes referred to as trig control or
trlgonomatrlcal net (work). See also
common control (srsllleW); control
point; ground control.
flald corractlon copy—A map or lracing
prepared in the field, delineating CU@C@rS for
subsequent reproduction of a’ tip.
Ilald correction—Adjustments made to field
measuramenls, such as angies or distances, 10
correct for geometric or iength dkcrapancias.
field elevatlon—An elevation taken trom the
fiaid computation of a Iina of Ievals.
flald lnspecllon—The process of comparing
aerial photographs with conditions ae lhay exist
on the ground, and of obtaining informatbn to
supplement or Clartiy that which is not raadily
discernible on the photographs themselves.
Also catted classlflcatlon aunrey.
field lntenalty—See field strength.
flald of view—(JCS) In photography, lhe
angla between two rays passing lhrough Ihe
perspective center (rear nodal point) Or a
camera ians to the two opposite sides of the
Iormal. Not to be cxmlusad with angla of
viaw. See also engia of view.
Ileld poaitlon—A position computed while
field work is in progress to determine the
acceplabliily of the observations or 10 prov”kkea
preliminary poshion for other purpsee,
94