NavCom SF-2040 Rev.C - Manual (Page 153)

LAND-PAK™ User Guide – Rev. C
6-149
formula is h=H+N; (He=Eo + Ug in Carlson
documentation). The geoid models are essenti
geoid height difference models in a grid format.
ally
X-Port has two geoid models available covering
the United States at 1 minute grid intervals
(Geoid03 and Geoid99); and EGM96 covering the
entire globe at 15 minute intervals. These geoid
models are huge and take a lot of disk space.
X-Port applies the geoid model by subtracting the
geoid undulation from the GPS measured
ellipsoid height. The result is then used and
displayed. In practice, the geoid model is most
applicable to two types of scenarios. One of these
types is when setting up the base over a known
poin
on
e
Units ne of
thre
Inte
• Sca
G
fro
e
t and an elevation is known or assume
the best relative orthometric heights are de
d and
sired at
g multiple
vertical control points in a three dimensional
solution. The geoid model is a good check and
can be better than solving for a 3D transformati
because the local control points can have mor
ertical error than the geoid model.
other points. Be cautious when usin
v
•
: Coordinates can be converted into o
e available units, Metric, US Feet or
rnational Feet.
le Factor: After converting the LAT/LON
m the GPS records to state plane coordinates
applying the coordinate alignment
calization, a.k.a. transformation) file, the
Project Scale Factor
and
(Lo
is applied as the final
adjustment to the coordinates. This adjustment is
used on the X, Y and not the Z. The Project Scal
Factor is applied by dividing the distance between
the coordinate and a base point by the Project
Scale Factor. The coordinate is then set by
starting from the base point and moving in the
direction of the coordinate for the adjusted