On 8 May 2010, 5a control marks were reclassified from order 5 to order 6 to better reflected their accuracy. The coordinates of these marks did not change. They have now been tested against the Standard for the Geospatial Accuracy Framework (LINZS25005) and Standard for Tiers, Classes and Orders of LINZ Data (LINZS25006), and the appropriate orders assigned.
Today all order 5 and better geodetic marks are coordinated using the National Geodetic Adjustment. This means that all of the order 5 marks in the Geodetic Database will comply with the order 5 accuracy standards and have ellipsoidal heights.
About trig stations and geodetic marks
The National Geodetic Adjustment
What were order 5a marks?
When the New Zealand Geodetic Datum 2000 (NZGD2000) was implemented, order 5 marks were established to provide the ‘street-level’ control for cadastral surveying and other applications.
New Zealand Geodetic Datum 2000
When the order 5 marks were established there was also a need to provide control marks to support the survey conversion process that preceded the rollout of Landonline.
Accuracy of the digital cadastre
To enable this, order 5 coordinates were generated using 2 distinct processes:
- Existing traverse data from control surveys was captured and adjusted in terms of NZGD2000, producing 5a marks.
- Existing cadastral marks were surveyed with GPS to assign them order 5 coordinates, producing 5b marks.
Until the reclassification in 2010, the survey control system had 72,000 order 5 marks, 56,000 5a marks and 16,000 5b marks.
Failure of 5a marks to comply with order 5 accuracy standard
Although coordinates were initially assigned order 5 accuracy, subsequent analysis showed that a majority of 5a marks did not comply with all aspects of the accuracy standard. Most achieved the order 6 standard, so the 2010 re-classification better reflected the accuracy of the coordinates.
Re-establishment order 5 control
As part of the geodetic annual programme, order 5 control marks have been re-established in areas where the control marks have been changed to order 6.