NZGeoid05 Datum Offsets

The 13 mean sea level (MSL) datums used in New Zealand are offset from the NZGeoid05 and each other. This is because the datums are defined in terms of mean sea level at their respective standard ports. Also, rather than distorting NZGeoid05 with the effect of the offsets it was defined independently of them. The relationship of the different height surfaces is shown in the figure below

The offsets from NZGeoid05 to each of the MSL datums are provided below. The offset is positive when NZGeoid05 is above the levelling datum.

MSL Datum	NZGeoid05 Offset (metres)	Standard Deviation (metres)
One Tree Point 1964	0.26	0.06
Auckland 1946	0.50	0.07
Moturiki 1953	0.32	0.07
Gisborne 1926	0.59	0.09
Napier 1962	0.32	0.05
Taranaki 1970	0.45	0.07
Wellington 1953	0.51	0.04
Nelson 1955	0.26	0.08
Lyttelton 1937	0.35	0.10
Dunedin 1958	0.48	0.16
Dunedin-Bluff 1960	0.26	0.08
Bluff 1955	0.37	0.05
Stewart Island 1977	0.40	0.12

These offsets can be used in conjunction with NZGeoid05 to transform NZGD2000 ellipsoidal heights to normal-orthometric heights in terms of the MSL datums.