Valid proj ellipse specifications:
| MERIT | a=6378137.0 rf=298.257 MERIT 1983 |
| SGS85 | a=6378136.0 rf=298.257 Soviet Geodetic System 85 |
| GRS80 | a=6378137.0 rf=298.257222101 GRS 1980(IUGG, 1980) |
| IAU76 | a=6378140.0 rf=298.257 IAU 1976 |
| airy | a=6377563.396 b=6356256.910 Airy 1830 |
| APL4.9 | a=6378137.0. rf=298.25 Appl. Physics. 1965 |
| NWL9D | a=6378145.0. rf=298.25 Naval Weapons Lab., 1965 |
| mod_airy | a=6377340.189 b=6356034.446 Modified Airy |
| andrae | a=6377104.43 rf=300.0 Andrae 1876 (Den., Iclnd.) |
| aust_SA | a=6378160.0 rf=298.25 Australian Natl & S. Amer. 1969 |
| GRS67 | a=6378160.0 rf=298.2471674270 GRS 67(IUGG 1967) |
| bessel | a=6377397.155 rf=299.1528128 Bessel 1841 |
| bess_nam | a=6377483.865 rf=299.1528128 Bessel 1841 (Namibia) |
| clrk66 | a=6378206.4 b=6356583.8 Clarke 1866 |
| clrk80 | a=6378249.145 rf=293.4663 Clarke 1880 mod. |
| CPM | a=6375738.7 rf=334.29 Comm. des Poids et Mesures 1799 |
| delmbr | a=6376428. rf=311.5 Delambre 1810 (Belgium) |
| engelis | a=6378136.05 rf=298.2566 Engelis 1985 |
| evrst30 | a=6377276.345 rf=300.8017 Everest 1830 |
| evrst48 | a=6377304.063 rf=300.8017 Everest 1948 |
| evrst56 | a=6377301.243 rf=300.8017 Everest 1956 |
| evrst69 | a=6377295.664 rf=300.8017 Everest 1969 |
| evrstSS | a=6377298.556 rf=300.8017 Everest (Sabah & Sarawak) |
| fschr60 | a=6378166. rf=298.3 Fischer (Mercury Datum) 1960 |
| fschr60m | a=6378155. rf=298.3 Modified Fischer 1960 |
| fschr68 | a=6378150. rf=298.3 Fischer 1968 |
| helmert | a=6378200. rf=298.3 Helmert 1906 |
| hough | a=6378270.0 rf=297. Hough |
| intl | a=6378388.0 rf=297. International 1909 (Hayford) |
| krass | a=6378245.0 rf=298.3 Krassovsky, 1942 |
| kaula | a=6378163. rf=298.24 Kaula 1961 |
| lerch | a=6378139. rf=298.257 Lerch 1979 |
| mprts | a=6397300. rf=191. Maupertius 1738 |
| new_intl | a=6378157.5 b=6356772.2 New International 1967 |
| plessis | a=6376523. b=6355863. Plessis 1817 (France) |
| SEasia | a=6378155.0 b=6356773.3205 Southeast Asia |
| walbeck | a=6376896.0 b=6355834.8467 Walbeck |
| WGS60 | a=6378165.0 rf=298.3 WGS 60 |
| WGS66 | a=6378145.0 rf=298.25 WGS 66 |
| WGS72 | a=6378135.0 rf=298.26 WGS 72 |
| WGS84 | a=6378137.0 rf=298.257223563 WGS 84 |