NavCom SurveCE Integration Rev.A User Manual
Page 131
SurvCE ™ Integration User Guide – Rev. A
4-129
Coordinates. Select which north to use. For this
alignment method, the state plane coordinate is
translated to the local coordinate. Then the
rotation can use either the state plane grid or the
geodetic as north. No scale is applied in this
transformation. The state plane and geodetic true
north diverge east and west of the state plane
zone central meridian.
• Geoid To Apply: This option will account for the
geoid undulation in determining the orthometric
heights (elevation) of the measurement.
Orthometric heights or elevation measurements
are used in survey calculations. In order to
convert ellipsoid heights h (
He
in Carlson
documentation) as measured by GPS into
orthometric elevations H (
Eo
in Carlson
documentation), a correction must be provided for
between the GPS measured ellipsoid heights
(called
GPS elevations
by Carlson) referenced to
the ellipsoid and the geoid (equal potential
surface approximating global sea level). This
correction is the geoid undulation N (
Ug
in Carlson
documentation). The conventional formula is
h=H+N; (
He=Eo + Ug
in Carlson documentation).
The geoid models are essentially geoid height
difference models in a grid format.
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
point and an elevation is known or assumed and