Figure 1-16. Single Astronomic Station Datum Orientation
(2) Astronomic-Geodetic Method. When comparing the geodetic and astronomic coordinates of
a point, discrepancies will normally be found between the two sets of values. The deflection of the
vertical angle, formed by the intersection of the ellipsoid and geoid normals, is usually expressed in
terms of north-south and east-west. The north-south component, frequently called the meridional
component is proportional to the difference between the geodetic and the astronomic longitude and
proportional to the difference between the geodetic and the astronomic azimuth. Consequently, the east-
west component can be found in two ways. From the two ways of expressing the east-west component,
we derive what is known as the Laplace equation.
(a) Since the Laplace equation is derived from certain mathematical relationships which
involve the components of the deflection of the vertical along with astronomical and geodetic latitude,
longitude, and azimuth, the following equations shown in Table 1-2, page 1-28, may be more
enlightening:
EN0593
1-26
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