Supply of Data to the Geodetic System

With the increasing use of GNSS technology, it is now commonplace for surveyors to collect geodetic-quality data. In many cases this data meets the accuracy requirements for order 5 making it suitable for inclusion in the geodetic system.

LINZ has recently worked with several surveyors to include their data in the geodetic system, leading to the upgrading of nearly 100 marks to order 5 in Landonline and the Geodetic Database.

The example figure below shows order 5 survey control derived from data supplied by a cadastral surveyor. The marks are in a forested area where control density was previously very low.

The benefits of inclusion of surveyors’ data into the geodetic system for surveyors include:

• a greater level of control in an area where they frequently work
• official ellipsoidal heights assigned, which with use of the geoid model enables heights to be derived in terms of the official vertical datum, NZVD2009, or the local levelling datum, and
• the preparation of multiple Cadastral Survey Datasets for large land development projects is simplified.

The advantages for LINZ and the wider spatial community include:

• the rate of provision of control is increased
• marks are likely to be in locations where their long-term viability is assured, as the surveyor submitting the data should have a good knowledge of future development in the area (especially relevant where construction works are planned), and
• marks are provided in remote rural locations that might otherwise not have dense survey control.

To help you submit data, LINZ can carry out the required least squares analysis of the data to determine whether it meets order 5 accuracy standards. We can also dispense with many of the usual formatting requirements for geodetic work and some of the supporting data requirements. For example, it is not essential to supply supporting documents such as mark photographs (although it is desirable).

Please note that the supplied data needs to comply with LINZ standards in areas such as accuracy, mark attributes and network design. An important factor to consider is order 5 marks must have an ellipsoidal height. Care must be taken to ensure the vertical accuracy of the data by following standard survey practices such as making multiple antenna height measurements and changing the antenna height between observation sessions.

If you are interested in having your data included in the geodetic system, please contact the National Geodetic Office at CRM_Geodetic@linz.govt.nz.