1 - NGA

flrot polnf of Cancer-See summer
eoleflce, definition 1.
flref point of Ceprtcornus-See winter
eolstlce, definition 1.
first point of Llbre-See autumnal
equinox.
flraf.ordar bench mark-A bench mark
mnneded to [ha datum (Usually mean saa
Ievef) by continuous first-order levell~.
flret-order lovellng—Spirit Ievatlng
Conforming to the speciilcstlona of the current
‘Cleeaifkafiin, Standards of Accuracy and
General Specifications of Geodetic Control
Surveys; Formerly known as preclae Ievallng
and Iavellng of high preCISlOn.
Recommended lor primaty Nationsl Nerworlm,
as a basis for all subordinate elevation
determlnafions, scientific studies such as cruslal
movemanf over large regions, extensive
engineering projects such as hydroelectric
dams. Such leveling generally includes the
determination of geopotenlial values through
simu!4ane0us gravity measurements.
flrsd-order level—A leveling inatrumenl which
meate the folbwing Crfterta: (1) tha Sensilivit y 01
the level bubble vial must be 10“ of arc or less
per division of 2 mm: (2) the instrument must be
wnstrucfed of bw expsnsbn metal 10 minjmlze
lhe effect of unequal heating; (3) the objective
lens must have an effective opening of at least
40 mm and a magnification of 40X,
first.ordar travarse-A survey traverse which
extends between ad@sted positions of olher
first-order control surveys and conforms to the
crmenf spesiflzafions of first-order traverse, per
“Cfessifiition, Standamb of Amuracy and
General Specffbstions of Geodetic Control
Surveys. -
flraf-order triangulation—First-order
trianguladcn was at one time known as primery
trlangutatlon: changed in 1921 to preciee
triangulation; and In 1925 to first-order
Irfangulalion. Theee surveys contorm to the
current ‘Claeetfiition, Standards of Accuracy
and Ganeral Specifications of GecdeW Cormol
Surveys.” Racummended for primary National
Networks, aa a basis for all subotilnate surveys;
metropolitan area survey:, where high value is
attached 10 land and Ifs hne of communication
frontage; and in scientific etudies, such as
MIL-HDBK-850
crustal movement and space expiration.
flraf-ofdar wotk-The designation given
survey work 01 the Nlgheet prescribed order 01
precision and accuracy. Such eurveya were
formerly called primary.
Fischer allipeold of 1960-A reference
ellipsoid wtih fwu primary uses. In tha Mercury
datum if has the approximate dhmsnsions of
semima]or axis-6 .378,166.0 meters, and the
flattening or ellipticlly-1/296,3. in the South
ASa datum the sarnlmajor axis is 6,378,155.0
meters, and the flattening or eliipficffy Is 1/238.3.
Fischer laval-A dumpy level capable of fimtorder
leveling.
flxad alavatlon—An elevatlon which has
been adopted, either as a resutf of tide
observations or pravious adjustment of spirit
leveling, and which is held at its accepted value
in any subsequent adjustment.
fixed posltlon—See adjueted posltlon.
fixed salelllte—See aynchronosse
aatelllle.
flxad-length recora*A computer data
element format, in which all recorde have the
same length, These remrds allow direct access
without searching or indices. See also
variable-length records.
fixed-ratio pantograph—See pantograph.
fixed-rstlo projection prfntar-A dlaposnlve
prinler hsvinQ an optical ayslem in whiih a lens
is placed between the negative and the
dispositive plate, Ihe object and image
distances being set al nominal values according
to the laws of optics, but with freedom of
adjustment within narrow Ilmlts, to produce
diapc.silives whose Scala is al a predetermined
rafio to the negative scale.
tixer nerwoti+JCS) A combination of redb
or radar dkectlon firdng installations whkh,
operating in mnjuncfiorr, are capable of plotting
the positon relative to fhe ground of an aircraft
in flight.
flxlng—The process of rendering a devatoped
photographic image permanent by removing the
unaffected light-sensitive material.
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