The correction to be applied to the relative deflection of the vertical at the initial point
is determined by the mean of the differences between the absolute gravimetric and
relative astro-geodetic deflection components (Figure 1-20).
Figure 1-20. Gravimetric Datum Orientation
Due to this correction at the origin, the relative deflections of the vertical components
at the other Laplace stations are corrected. The relation between the corrections at the
initial point and those of the other Laplace stations can then be computed.
Readjusting the triangulation stations of the net, by holding fixed the corrected
Laplace stations, provides the correct position of the net.
(b) Before such a gravimetric adjustment is possible, a general study of the earth's gravity
field is required. A detailed study of the gravity field is required in the area of the points where the
gravimetric deflection of the vertical is to be computed.