New Zealand Quasigeoid 2009 (NZGeoid2009)

A datum is a reference framework that determines how points are referenced. This ensures that locations are consistently positioned, which allows spatial data to be exchanged between users. A datum needs to have a reference surface that heights and depths can be referenced against. This is a geoid, a shape like a slightly squashed ball that gives a hypothetical global sea level surface, or a quasigeoid that provides a simplified version that is suitable for most applications. For New Zealand Vertical Datum 2009 (NZVD2009) the reference surface is New Zealand Quasigeoid 2009 (NZGeoid2009). In 2009, NZVD2009 aligned with Mean-Sea Level (MSL) within several decimetres, however this value varies around the coastline.

New Zealand Vertical Datum 2009

NZGeoid2009 was calculated by enhancing a global gravity model (EGM2008) using a combination of land and satellite-based gravity observations, along with a Digital Elevation model (DEM). GNSS (Global Navigation Satellite System) and levelling survey observations were not used to compute NZGeoid2009.  

Global gravity model (EGM2008) 

Find out more about about gravity data collection and the computation of geoids and quasigeoids

NZGeoid2009 can be used to transform height data between NZVD2009 and NZGD2000 heights, as well as using published offsets to covert to and from the 13 Local Vertical Datums. 

Vertical Datum Relationship Grids

Local mean sea level datums

Use our online coordinate converter

Note: NZGeoid2009 is not a datum, heights should not be referenced to the geoid surface directly.

Parameters of Zealand Quasigeoid 2009 (NZGeoid2009)

Coverage area: 160° E to 170° W, 25° S to 60° S. This area corresponds to mainland New Zealand, its offshore islands, and the New Zealand continental shelf. This is the same area of coverage as New Zealand Geodetic Datum 2000 (NZGD2000).

Resolution: gridded at a resolution of one arc-minute, which is approximately 1.8 kilometres.

Expected accuracy: approximately 6 centimetres, throughout New Zealand. This accuracy is based on comparisons with geodetic control marks that have both GNSS (Global Navigation Satellite System) and levelling survey observations.  

The image below displays the NZGeod2009 model across its defined area, indicating the expected spatial variation of NZGeod2009.