New Zealand Quasigeoid 2009 (NZGeoid09)

The New Zealand Quasigeoid 2009 (NZGeoid09) is the reference surface for the New Zealand Vertical Datum 2009 (NZVD2009).

The geoid is an undulating surface that is related to the Earth's gravitational field that approximates level of the seas over the entire Earth within a few metres. Because it is related to gravity, it is a more intuitive reference surface than the ellipsoid.

NZGeoid09 was calculated for LINZ to provide a national geoid model with a higher resolution and accuracy than is available from the EGM08 global model. A description of how NZGeoid09 was computed is available in the technical report Computation of a New Gravimetric Quasigeoid Model for New Zealand (PDF 2MB).

NZGeoid09 can be used with the published offsets to transform heights from the 13 mean sea level datums to NZVD2009.

NZGeoid09 is published on a one arc-minute grid (approximately 1.8 kilometres) over the New Zealand continental shelf (160° E to 170° W, 25° S to 60° S). It has an expected accuracy of 6 centimetres based on comparisons with GPS-levelling derived geoid values in New Zealand. It was calculated by enhancing a global geopotential model using a combination of land and satellite based gravity observations. GPS-levelling observations were not used to compute NZGeoid09.

The NZGeoid09 model is available for download as either an ASCII grid or coordinate triplets over several spatial extents. It can also be interpolated using the online coordinate conversion utility.

Area	ASCII grid	Coordinate triplets
Full computation area (160° E - 170° W; 25°S - 60°S)	zip 9.2MB	zip 20.2MB
New Zealand (165° E - 180° E; 34°S - 48°S)	zip 1.8MB	zip 3.6MB
North Island (172° E - 179° E; 34°S – 42°S)	zip 495KB	zip 964KB
South Island, Stewart Island/Rakiura (166° E - 175° E; 41°S - 48°S)	zip 553KB	zip 1.1MB