1 - NGA

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escape and evasion graphic—A map,
chart or other graphc, usually produced on a
l@rtweighl durabla material, apaciikally
designed to @fe personnel to safety from
enemy trefd tsirrilory.
●atabllahmsmt of tha port-Tfre average
Iraervel between uppar and bwer kmar franail
naar tiie of new and full Moon and the next
hfgh water. Also called common
esrtabllshment; high watar tull and
change: vulgar eatabllshmant. See also
Iunltidal Interval.
eatabllshment—See Iunltidal Interval.
etch ellp-A pencil-shaped abrasive used in
removiq unwanted marks on a metal
preaaplate. Also called anakeallp.
etchad zinc plata-An etched copy 01 Ihe
mntour drawing of the base map, used aa Ihe
guide in cutting the stepped Ierrain base of a
model for making relief models.
Mli-HDBK~650
tstckl. To remove selected areas of the
emulsion eiihpr che,micalty or manually. 2.
Chemical treatment of a lithographic plate to
make ncrnprfntlng areas grease-repellent and
water-receptive or 10 produce the image on
deep etch plates. 3. An acid solution mixed with
the dampening fountain water on an offset
press to help control ink on tha pressplale.
Euler”a equation-A relation in a parebolic
orbit Involvlng IWO radius vectors, their chord,
and the time Interval between tham.
Euler% thaoram-A mathematical expression
to obtain the radius of curvature of a normal
section in any azimuth on the reference
ellipsoid. The czlrnulh angle, and the radius of
curvature in the meridian and in the prime
vertlml must be known,
EulerIan anglea-A system of three angles
which uniqualy dafkses wllh reference to one
coordinate system (e.g. Earth axis) the
orientation of a secand coordinate system (e.g.
the axis of an orbff).
Europaan datum-The Initial point of this
system Is located at Potadam, Germany.
Numerous national systams have been joined
Info a large dalum based upon the International
elllpsold which was ortented by fhe
astrogaodelic method. The European and
88
African triangulation chains have bean
connected and the gap of the Afrfcan am
rnaasuremem from Csiro to Cape Town has
been filled. Thus, all of Eurupa, south Afrka,
and North Africa are rmaldad into one system.
Through comrrmn survey stations, If wae also
possible to convert data from the Russian
Pulkovo 1932 system 10 the Europaan datum
and, ae a result, tha Eumpaan dafum irvSudea
triangulation as far aast as the 84ih mer’tiin.
Adddbflal lies Suross the Middle Eaat heva
permitted connedlon of the Itilan and
Europaan datums. Sea also prefarred
datum.
evectlon—A perturbation of the Moon in its
orbu due to the attraction of the Sun. This
reaufte in an increase in the eccentricity of the
Moon’s orbii when the Sun passes the Moon’s
Ilne of apsldas and a decrease when
perpendicular to it. See alee lunar Inaquellt y,
definition 1.
Evereai spheroid (elllpaold)—A referance
ellipsoid having the following approximate
dimensions: semimajor axis-6,377,276.3
meters: flattening or etlipticity—1/300 .80. Used
in India, Burma, Pakistan, Laos, Cambodia,
Thailand, and Vietnam,
exaggerated aterao—See hyperatareoscopy.
exlatent corner—A corner whose position
can be identified by verifyi~ the evic!emce of Ihe
monument or its accessories, by refereffie to
the description that k conlalned in the field
notes; or whare the point can be bcated by an
acceptable supplemental survey remrd, some
physical evidence, or Ieslimony.
extstlng data-Source material antior
krforrnatwn assumed or krrewn to be in the
possession of a gtien source ard subject to
“elf-shel~ collection, as In mntraal to data
obtained by operational field surveys.
exit puplf-The image of the aperture @op
Iorrnad by all the lens elaments on the image
side of the aptmure stop.
exit window—The image of fhe field stop
formed by ali the lens elements on the image
side of fhe field slop.
exmarldlan altitude-An altltude of a
celestial body near the celestial meridian of the
observer to which a cerrect!!n is to be applied to