Geodetic Datum Conversions

A geographic coordinate (latitude, longitude and ellipsoidal height) is in terms of a geodetic datum (eg NZGD2000, NZGD1949). The two main ways to transform geographic coordinates between geodetic datums are to use a transformation grid or a similarity transformation. These are shown diagram below.

Transformation grids directly transform geographic coordinates between two specified datums (eg the NZGD2000 distortion grid converts from NZGD1949).

Similarity transformations (3 or 7 parameter) are performed on Cartesian ( X , Y , Z ) coordinates. This transformation is a three-step process because the geographic coordinates first needs to be changed to a Cartesian value, converted between datums and then changed back to a geographic coordinate.

Additional information and examples of specific transformations is provided in the pages described below.

NZGD1949 to NZGD2000

Overview and details of the 3 and 7 parameter similarity transformations and the distortion grid for converting between NZGD1949 and NZGD2000. more...

WGS84 to NZGD2000

Description of how GPS derived coordinates relate to NZGD2000. more...

CIGD1979 to NZGD2000

Overview and details of the 7 parameter similarity transformation to convert between CIGD1979 and NZGD2000. more ...

Equations used for datum transformations

Description of the formulas that are necessary to implement the similarity transformations described above. more...

Datum transformation examples

Example computations using the above formulas and parameters. more...