The Importance of Using Deviations of the Vertical for the Reduction of Survey Data to a Geocentric Datum

This paper reviews the deviation of vertical and its use in the reduction of terrestrial survey data such as directions, azimuths, zenith angles and slope distances. The deviations of the vertical over Australia will change by an average of 6.8” due to the implementation of the Geocentric Datum of Australia. Therefore, for most applications, the deviation of the vertical may no longer be neglected in survey computations and adjustments. With the release of the AUSGeoid98, absolute deviations of the vertical at the geoid and with respect to the GRS80 ellipsoid are now available for these purposes. The improvements made when using deviations of the vertical are demonstrated for several worked examples. The exception is that the deviation of the vertical should not be applied when computing height differences from zenith angles and slope distances for use on the Australian Height Datum (AHD).