Historical Earth Ellipsoids
Currently the most common reference ellipsoid used, and that used in the context of the Global Positioning System, is the one defined by WGS 84.
Traditional reference ellipsoids or geodetic datums are defined regionally and therefore non-geocentric, e.g., ED50. Modern geodetic datums are established with the aid of GPS and will therefore be geocentric, e.g., WGS 84.
The following table lists some of the most common ellipsoids:
| Name | Equatorial axis (m) | Polar axis (m) | Inverse flattening, |
|---|---|---|---|
| Airy 1830 | 6 377 563.4 | 6 356 256.9 | 299.324 975 3 |
| Clarke 1866 | 6 378 206.4 | 6 356 583.8 | 294.978 698 2 |
| Bessel 1841 | 6 377 397.155 | 6 356 078.965 | 299.152 843 4 |
| International 1924 | 6 378 388 | 6 356 911.9 | 297 |
| Krasovsky 1940 | 6 378 245 | 6 356 863 | 298.299 738 1 |
| GRS 1980 | 6 378 137 | 6 356 752.3141 | 298.257 222 101 |
| WGS 1984 | 6 378 137 | 6 356 752.3142 | 298.257 223 563 |
| Sphere (6371 km) | 6 371 000 | 6 371 000 |
Read more about this topic: Reference Ellipsoid
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