Projection Conversions

A projection coordinate (northing and easting) is in terms of a specific projection (e.g. NZTM2000). Every projection is defined in terms of a geodetic datum. When comparing coordinates it is critical that they are in terms of the same projection or else errors will be introduced.

The general conversion process is outlined in the diagram below. Projection coordinates are first transformed to their geographic equivalents and then to the new projection if it is in terms of the same datum. If the target projection is in terms of a different datum then the geographic coordinate must be converted to this using a datum transformation then to the new projection.

 

Flow diagram of the projection conversion process.
 

Coordinates can be converted between projections using the formulae described in the section below if the parameters defining them are known. These formulas are also implemented in the online coordinate conversion utility that is available on this site.

Transverse Mercator transformation formulae

Formulae and description for converting coordinates to and from Transverse Mercator projections. This is the most commonly used type of projection in New Zealand and includes NZTM2000. more...

Lambert Conformal Conic formulae

Formulae and description for converting coordinates to and from Lambert Conformal Conic projections. This type of projection is used for the New Zealand Continental Shelf and in the Ross Sea region of Antarctica. more...

New Zealand Map Grid transformation formulae

New Zealand Map Grid (NZMG) is a special projection only used in New Zealand. This page provides the formulae and coefficients that define it. more...

Converting from NZMG to NZTM2000

The conversion of coordinates from New Zealand Map Grid (NZMG) to New Zealand Transverse Mercator 2000 (NZTM2000) is a three-stage process. more...

Projection transformation examples

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