Frequently Asked Questions
What is the South Island Coordinate Update?
We have updated the deformation model in NZGD2000 to account for movements that occurred in the four major Canterbury and four major Fiordland earthquakes since 2000.
This has resulted in the coordinates of all control and cadastral marks in the South Island and Stewart Island/Rakiura moving to some extent (see the map below).
How have you updated this information?
Extensive control surveys have been carried out in Canterbury to provide accurate control for cadastral and other survey work. The technical implications of this are:
- new control mark coordinates based on recent GNSS surveys are now available via the geodetic database
- all cadastral marks have been re-adjusted to be in terms of the updated control network
- the deformation model is not accurate enough to depict the effects of extensive localised ground movement, such as that caused by liquefaction, so in these areas the accuracy of all cadastral and control mark coordinates that have not been re-surveyed have been downgraded.
We have also updated the Canterbury vertical control network:
- all existing published heights were downgraded following the earthquakes
- extensive precise levelling has been carried out to enable new heights to be published on marks across the Canterbury Plains. These heights are now available via the geodetic database.
- heights will be published in terms of the Lyttelton Vertical Datum 1937
- the offset between NZVD2009 and Lyttelton 1937 remains +0.47 metres
Why did you update this information?
The New Zealand Geodetic Datum 2000 (NZGD2000) includes a horizontal deformation model to account for predicted crustal movements.
The original deformation model was based on GNSS data collected prior to 1998, and as a result it:
- could not represent seismic deformation events that have occurred since its definition (e.g. Fiordland and Canterbury earthquakes)
- did not utilise the extensive GNSS data collected by LINZ since 1998.
The Canterbury earthquakes were also the first significant earthquake-induced deformation to affect a developed region of New Zealand since Landonline was implemented in 2000. Fortunately Landonline was developed in a way that permits an updated deformation model to be incorporated, and we have leveraged this capability to apply the updates. This was the first time this has been undertaken however.
Changing the coordinates of most survey marks in Canterbury was an essential activity that is necessary to support the re-build process and will be of benefit to all users.
Why hadn't you updated the coordinates sooner?
The surveys to determine the magnitude of the movements took some time to complete, and each major after-shock meant that they needed to be restarted. Because of this, we had to wait until the likelihood of after-shocks had decreased enough for us to start the survey work.
Surveyors have had access to updated coordinates on control marks for some time, and this information was made available soon after the measurements, which followed each after-shock, had been completed.
Updating all coordinates in the South Island was a significant undertaking, both for LINZ and for users who need to incorporate the updated information into their databases and systems. We chose to carry out a single (large) update rather than successive smaller updates – this has meant that we needed to wait until the chances of another significant after-shock had reduced to an acceptable level.
Who can I contact for more information?
If you have questions, please contact our Customer Support team in the first instance:
Phone: 0800 665 463 (New Zealand callfree only)
Email: customersupport@linz.govt.nz