(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: