The Practical Implications and Limitations of the Introduction of a Semi-Dynamic Datum - A New Zealand Case Study

In 1998 Land Information New Zealand introduced New Zealand Geodetic Datum 2000 (NZGD2000) as its new national datum. It is defined as a semi-dynamic datum and incorporates a national deformation model to ensure that the accuracy of the datum is maintained. The deformation model allows observations made at an epoch other than the datum reference epoch of 2000.0 to be modeled so that coordinates at the reference epoch can be generated. From a geodetic perspective its implementation is relatively straight forward. In New Zealand the geodetic system and datum also underpin the cadastre and spatial positioning. Cadastral surveys are made in terms of NZGD2000 and about 70% of parcels have NZGD2000 survey accurate coordinates. Many users of the geodetic system are non-technical users, for whom managing the dynamics of the datum presents a potential annoyance and complexity. LINZ manages the dynamics of the geodetic system which enables other spatial datasets connected to it to be updated. The implementation of a Continuously Operating Reference Station (CORS) network in New Zealand also presents a set of issues that need to be considered when CORS stations are incorporated as part of a semi-dynamic datum. This paper presents some of the implications and limitations for users of geodetic and related datasets when implementing a semi-dynamic datum and discusses solutions based on New Zealand experiences.