Dynamic Datum Transformations in Australia and New Zealand

Dynamic datums, which account for crustal dynamics, are widely used in Australia and New Zealand, although in many cases users may not be aware that they are using such a datum. The most widely-used global dynamic datums in Australia and New Zealand are the International Terrestrial Reference Frame (ITRF) and the World Geodetic System 1984 (WGS84). The use of WGS84 presents particular challenges, as it cannot be directly accessed at the sub-metre level by most spatial professionals. The relationship between WGS84 and ITRF is explored in detail, leading to recommendations on how users should deal with WGS84 datasets. New Zealand and Australia have taken different approaches to modelling the relationship between global dynamic datums and their local geodetic datums. Australia has calculated a set of local transformation parameters, which incorporate tectonic movements. New Zealand has adopted a set of global parameters, and uses a deformation model to account for crustal dynamics. As both countries seek to modernise their geodetic datums, the availability of simple yet accurate transformations will be critical to the success of the modernisation process. This paper outlines the options for dynamic datum transformations within a modernised datum, discussing the strengths and weaknesses of each approach.