Abstract
PositioNZ-PP is an on-line GPS processing utility for New Zealand that is currently being developed by Land Information New Zealand (LINZ). The system was developed to process user supplied static GPS data using New Zealand's PositioNZ CORS network as reference stations. There are already many services like this around the world; however LINZ decided to create its own system to utilize the PositioNZ CORS network and to allow the calculation of coordinates in terms of the NZGD2000 datum. The GPS processing engine incorporates components that check the input RINEX file, identify and acquire RINEX data for the three best PositioNZ stations to act as control, acquire appropriate International GNSS Service (IGS) orbit files and initiate GPS processing. This step generates a set of International Terrestrial Reference Frame (ITRF) coordinates at the epoch of observation, which still must be transformed to the reference epoch of NZGD2000. Because of New Zealand's location on the Pacific Australian plate boundary, current day models of tectonic deformation are necessary to correct coordinates for tectonic motion that has occurred between the epoch of observation and the reference epoch (2000.0). The PositioNZ-PP system makes use of two subroutines for this purpose. The first (the Station Coordinate Prediction Model) uses parameters determined from a least square analysis of the time series from PositioNZ CORS network to correct coordinates for changes associated with the secular velocity, seasonal (annual and semi-annual) cycles, offsets caused by equipment changes and co-seismic displacements, decaying post-seismic signals and slow-slip events. This subroutine estimates accurate coordinates for the PositioNZ CORS network at the epoch of observation. The second subroutine (the New Zealand Deformation Model) uses a gridded model of the secular velocity field and the co-seismic displacement associated with any relevant earthquakes to transform the coordinates associated with the user data to NZGD2000 at epoch 2000.0.