Proposal for a Dynamic National Geodetic Datum for New Zealand

New Zealand's current geodetic datum (New Zealand Geodetic Datum 1949) has been subjected to earth deformation of between 2 to 3 metres since the observations were performed but still the original coordinates of 1st order trig stations are held fixed. Trig stations, cadastral boundaries and the "fixed" assets of landowners are slowly moving relative to each other. Any future datum, if it also has fixed coordinates, will be measurably distorted within months and may need to be discarded within a decade. A "dynamic" datum is one of the options being considered as a possible solution. Such a datum could maintain a defined relationship to the dynamic IERS Terrestrial Reference System. By including station velocity models along with periodic readjustments, the spatial accuracy of the datum could be maintained in the face of wide spread earth deformation; improvements in survey technology; and changing demands of geodetic density and accuracy. The implications for geodetic, cadastral and topographic databases and for the users of a dynamic datum are addressed.