Reference Ellipsoids
An ellipsoid is a mathematical approximation of the shape of the Earth formed by rotating an ellipse about an axis. An oblate ellipsoid (where the ellipsoid is formed by rotation along the minor ellipsoid axis) is the best fit to the Earth, although it can still depart by up to 100 metres from its actual shape.
The following parameters define ellipsoids commonly used in New Zealand geodetic datums:
| Ellipsoid | Semi-major axis ( a ) | Inverse flattening ( 1 / f ) |
|---|---|---|
| GRS80 | 6 378 137 m | 298.257 222 101 |
| International 1924 | 6 378 388 m | 297 |
| WGS84 | 6 378 137 m | 298.257 223 563 |
Find out more...
For geodetic system
- Geodesy in New Zealand
- About trig stations & geodetic marks
- Understanding datums & projections
- Using maps with different projections
- GPS in New Zealand
