The Use and Abuse of Vertical Deflections

This paper reviews the deflection of the vertical and its use and abuse in geodetic surveying. ‘Importantly, the deflection of the vertical in Australia will change by around 6” upon the implementation of the Geocentric Datum of Australia (GDA94). Therefore, for some applications, the deflection of the vertical may no longer simply be neglected in survey computations and adjustments. With the release of AUSGeoid98, absolute deflections of the vertical with respect to the GRSSO ellipsoid are now available for this purpose. The improvements made when using these deflections of the vertical in a terrestrial network adjustment on the GDA94 will be demonstrated for a case study in Western Australia.