Reference Ellipsoid and the Geodetic Coordinate System - Geodesy: Introduction to Geodetic Datum and Geodetic Systems - page 168

Fig. 5.4 Intersection line
between the geoid and the
meridian plane (L ﾼ 90 )
Fig. 5.5 Intersection line
between the geoid and the
equatorial plane
complicated and inconvenient to perform geodetic surveying computations on this
pear-shaped surface. On the other hand, the rotational ellipsoid on which compu-
tations are performed provides a tradeoff between computational precision and
simplicity and convenience in calculations. Therefore, the ellipsoid of rotation is
always chosen as the preferred reference surface for geodetic computations.
When a set of ellipsoidal parameters or an Earth ellipsoid is selected, its location
relative to the geoid should be determined, namely to complete the orientation of
the ellipsoid. Therefore, the corresponding relationship between the Earth's surface
and the ellipsoid can be established to reduce the observations from the terrestrial
geodetic control network to the ellipsoid.
The reference ellipsoid is the Earth ellipsoid with defined parameters and
orientation. The terrestrial observations in the geodetic control network need to
be reduced to the reference ellipsoid and computations are to be performed on this