Transformations from CIGD1979 to NZGD2000

The official method used to transform Chatham Islands Geodetic Datum 1979 (CIGD1979) coordinates (latitude and longitude) to New Zealand Geodetic Datum 2000 (NZGD2000), is a 7-parameter similarity transformation. This method is described on the Geodetic datum conversions page.

Chatham Islands Geodetic Datum 1979 (CIGD1979) 

New Zealand Geodetic Datum 2000 (NZGD2000)

Geodetic datum conversions

Similarity transformations convert the coordinate of a point from one ellipsoid to another. Similarity transformations account for the difference between the ellipsoids of different geodetic datums but do not account for distortions within the datums themselves. Internal distortions of a datum are better modelled using a distortion grid. The formula used to calculate similarity transformation can be found on the Equations used for datum transformations page.

Coordinate systems used in New Zealand

Reference ellipsoids

Geodetic datums

NZGD1949-NZGD2000 distortion grid

Equations used for datum transformations

This transformation is defined in the Standard for New Zealand Geodetic Datum 2000, and summarised in the NZGD2000 LINZG25700 Fact sheet.

Standard for New Zealand Geodetic Datum 2000 (LINZS25000)

NZGD2000 fact sheet (LINZG25700)

Note that the 2 common conventions used to define similarity transformations, Helmert and Bursa-Wolf, use different signs to describe the rotation components. The transformations used in New Zealand follow the Helmert convention. Always check that your transformation software is applying the correct rotation directions.

Seven-parameter transformation

The 7-parameter transformation calculates the differences between using an X,Y,Z system. It defines one datum with its centre at 0,0,0, and the centre of the other datum at a distance (Tx, Ty, TZ) metres away, as well as rotations around each axis (Rx,Ry,Rz), and a scale factor.

The 7-parameter transformation from CIGD1979 to NZGD2000 has an estimated accuracy of +/- 2m. The transformation parameters are:

This transformation can be reversed (to convert from NZGD2000 to CIGD1979) by reversing the signs of the listed parameters.