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besis for compsrkn of other duact”ms.
rekwsnco ●lllpsold—See reference
sphorold.
rofermtcrn frama-See coordlnrstoe.
rm?mrwsco grid-See grid.
rsrforanco lovol—See datum Iovol.
MIL-HDBK-850
mfomnco Ilne-Any line whiih csn serve as s
mfemnce or base fer the masauremant of other
qusntitiea. Alae celled datum line.
reference mark—A permanent
suppfamantary msrk cbas to a survey atetiin to
which it is relstsd by an accumtety measured
dktence end direction, andfor a difference in
elevetion.
rofarsmco maridlmr—See local meridian.
reference monument+% iron post or rock
csp eczxssory used where the peint for a comer
rncmumsrrt is such that, for prectiial purposes, a
permsnent comer rrmnumant cannot be
eclab%hed, or If mooumentad, a full
=m@emsnt of bearing trees or bsering ti)acts
are not obtainable.
mfarenca plane-See datum level.
mforonce point—See detum point.
reference clgnaf-in telemetry, the signel
against whiih data carrying signsls are
mmperd to measure dtierenceg in timrj,
phsae, frequency, or other veluas or quantities.
reforenco spheroid—A Iheore!ical figure
whoaa d!msnsione cfosafy approach the
dimensions of fhe E@@ the exact dimensions
are delenninad by various consideretiona of the
section of the Eenh’e surfeca concerned. Also
cdlad reference .Ilipsold: sphorold of
roferonco. See al- World Geodetic
Syetem.
referonco statlo*A place where tide or tidsl
current ocmstants have bean determined from
observations, end whloh are used as a standard
for the comparison of simuftrmseus
observations at a subordinate station. Ako, a
piece fer whkh Independent daily predictions
are obtahad for other locations by means of
dfierencas or fectors. Also cslled stenderd
214
po~, standard ●tstlon.
rafarenclng—?he process of measuring the
Iwizontsl diaiemee and dradioms from a
survey station to nearby Iandmsrka, refarame
rnsrka, and other ob@cfe whfi can be uafxf in .
the ~ary of the station.
mttactad ray-A my extending outward from
e point of mfktii.
ratlactlng prlsrrt+i prism thst devietee a fiiht
besm by interrsd reflection, Practkslty all prisms
used in photogremntatric” instruments ❑re of fhia
type.
reflecting pro]ector-An instrument whmh is
used to projsct the imege of photographs,
~1% ~ et~r gmphik= enio e copying tsble.
Ths scsle of the projected irrmge can be varied
by raising or bwering the pro@bar or, In some
models, the copy bosrd, Thsae fatter models
sko ellow the tilling of the copy besrd in x- and
ydiractions in order to compensate For tip and
tilf dktortbn in aerial phetogrephs.
refloctlon—The return or change in the
direction of travel of psrtidae or mdmnt energy ~---~ ~ -- ,
vhkh irrpinges on a surfaca bui does not enter
the substance providing the reflecting aurfaca.
See also dlffractlon; dlffuso rafloctlon;
refraction; specular reflection.
reflector constant—The emourd thsl a
distance measurement must be reduced *en
using glass reflectors bcause the velocity of
light is sbwer in glass thsn it is in air. The
constant wili also include the distence difference
between the reflector housing plumbing pOim
and the effective reflecthg plane of the prism.
refiight-lmother flight over the same crmree
to xure photographs to fill in for those missing
or dsf ective.
refrected ray—A ray extending onward fmm
the pint of refrect’bn.
refracting prlsrn-A prism lhst deviates a
beem of fight by refrsctiom The angular
deviation is e functien of the wavelength of light;
therefore, if the baem is composed ef while
light, the prism will aprasd the beam into a
spectrum. Refracting prisms can be used in
opticel instruments onty for small Cieviitkrna.
See also wadgo.
mfractlon ●@a-That poti~on of an