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13.2
Description
Transformation
Geoid model
Manage...\Coordinate Systems
Terminology
This chapter describes technical terms related to coordinate system management.
Refer to "39.1 Overview" for information on transformations.
Description
GPS operates on the WGS 1984 ellipsoid and all heights obtained by measuring baselines
are ellipsoidal heights. Existing heights are usually orthometric heights, also called height
above the geoid, height above mean sea level or levelled height. The mean sea level corre-
sponds to a surface known as the geoid. The relation between ellipsoidal height and ortho-
metric height is
Orthometric Height = Ellipsoidal Height - Geoid Separation N
P0
d1
d2
GPS12_076
a
a) WGS 1984 ellipsoid
b
b) Geoid
P0 Measured point
d1
d2
GPS1200+
Ellipsoidal height
Geoid separation N, is negative when the
geoid is below the ellipsoid
284
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