No abstract

No abstract

With the adoption of the Geocentric Datum of Australia or GDA94 (eg. Featherstone, 1996), these simplifying assumptions will not necessarily remain valid (Featherstone, 1997). This is because the geocentric GRS80 ellipsoid (Moritz, 1980), used with the GDA94, is a best fit to the level surfaces and plumblines of the Earth's gravity field on a global scale, and does not provide a best fit over Australia. Importantly, survey measurements made with respect to the gravity vector do not change with a change of datum (Heiskanen and Moritz, 1967), notwithstanding temporal variations due to geophysical phenomena. Terrestrial surveys conducted on a geocentric datum are more likely to require that the separation between the geoid and ellipsoid and the angular differences between the plumbline and the ellipsoidal normal are taken into account during the reduction of survey data. This also applies to the adjustment of existing terrestrial geodetic networks onto a geocentric datum, such as those undertaken by national and State/Territory mapping agencies to implement the GDA94.

In the past, EDM-height traversing was rarely considered as an alternative to geodetic leveling. This paper outlines the theory of the method and investigates the attainable accuracy. In flat terrain, EDM-height traversing is capable of achieving third-order leveling specifications, while in mountainous areas it can compete even with first-order leveling, if systematic errors of the latter are taken into account. Published results are summarized, and a list of recommended practices is given.

No abstract