1 - NGA

successive returns of the Sun 10 a sidereal hour
angle 0180” (about January 1). The length of
the Iicflfkssa year Is the same as that of the
tropisxsl year, since tmlh are based upm the
posffiin ot \ha Sun whh respect to lha vernal
equinox. Also called Beaeellan year.
flcfltlouts-in cartography, pertaining to or
measured from an arbdrary referetwe fine.
fldellty-Tha degrea with which a system
acxxrralely reproduces the data inpul into it.
flduclssl exea-The lines pkrlng opposite
fiducial martss on a photograph. The x-axis Is
generally rmnaidered 10 lx the one nearfy
parallel wifh the line of fflght.
flduclal merk(s>l. (surveying) An index line
or point. A line or point used as a basis of
reference. 2. (JCS) (photogrammetry) See
Collimetlng marks. 3. Also, markers in any
instrument which deline the axes whose
intersection fixes Ihe principal point of a
phofogreph arsl fuffills the requirements of
interfor orientation.
field csrllbratlon-A term aenerallv aozdied
where only e corrridrration of-field in-d Ott’ice
computer techniques are available to check
insfnsment accuracy. Adjustments, other than
normal operator edius!ments, cannot be made
during field calibration.
field chack-lhe operation of checking a map
compilation manuscript on the ground. See also
flehl cleeslflcatlon.
MIL-HDBK-850
field claeelflcntlon-Field Inspection and
idenfffiiation of features which a map compiler is
unable to de fineate; identification and
delineation of pofitcal lxsundary lines, place
names, road classfficatkrns, buildings hidden by
lrees, and so forth. Field classification may be
Included aa parf of the OJnfrol survey efiorf and
normally Ls completed prior to the actual
slereocompilation phase, See also field
Inapectlon.
field comparator-A short line whose Iengfh
b measured wiih accuracy and precision, and Is
used to check the iengths of apparatus (tapes)
used in the actual fieid operations. Also called
calibration course; comparator beaa.
field complation—A combination of fiefd
inspections or surveys, either before or after
compilation, to classify and fnmplefe the map
content, correct erroneous date, end add
Information such es names, civil boundaries,
and similar classifiifion data. Its purpose is to
fill in or confirm that portion of a map manuscript
prepared by alareocompilation.
Ileid contouring-Corrtouring a topographic
map by field methods accomplished by
planateble surveys on a prepared base or by
stadia survey. Generaliy, this operation applies
to Ierrain unsuitable for contouring by
photogrammelric methods. Also used in limited
areas when engineering design (drainage)
requires 1-toot contours. See also contour
aketchlng.
field control-(JC S) A series of points whose
relafive positions and efevatbns are known.
These positions are usad in basic data in
mapping and chariing. Normally, these positions
ara established by survey malhods and are
sometimes referred to as trig control or
trigonometrical net (work). See also
common control (arflllary); control
pohrt; ground control.
fiafd correction copy—A map or tracing
prepared in the field, delineating corrections fOr
subsequent reproduction of a map.
field correcIlon—Adjustments made to field
measurements, such as angles or distances, to
correcl lor geometric or length discrepancies.
field alevaUon-An elevation taken from the
field computation of a line of levels,
field lnapectlon—The process of comparing
asrial photographs with condMcms as lhey exist
on the grourxl, and of obtaining informatbn to
supplement or clarity that which Is not readily
discernible on the photographs themselves.
Also called classlftcatlon survey.
field lntenslty—See field strength.
field of view—(JCS) in photography, the
angle between two rays peasing through the
perspective center (rear nodal palm) of a
camera lens to the IWO oppmite sides of the
format. Not to be can fused with angle of
view. See also angla of view.
field posltlon—A position computed while
lie!d work is in progress to determine lhe
acceplabifity of the observations or to provide a
preliminary position for othar purposes.
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