Length of a degree(km) |
Year |
Observer |
Country |
Latitude of Middle arc(Deg/Sec) |
111.49 |
1738 |
Maupertius - re-examined by Svanberg |
Lapland |
1.31.08 N |
111.23 |
1802 |
Roy & Kater |
England |
52.35.45 N |
111.11 |
1790 |
Delambre & Mecham |
France |
44.51.2 N |
111.03 |
1755 |
Ruscovich |
Rome |
42.59.0 N |
110.87 |
1750 |
Abb Lacaille |
Cape of Good Hope |
33.18.30 S |
110.66 |
1835 |
Everest |
India |
16.7.22 N |
110.64 |
1808 |
Lambton |
India |
2.32.21 N |
110.58 |
1735 |
Condamine & Bouguer |
Peru |
1.31.08 N |
|
|
Table 2: Official Ellipsoids Equatorial (Source: J. Snyder, Map Projections - A Working Manual). The Everest spheroid is still used in India, as well
as in Pakistan, Nepal, Burma, Sri Lanka, Bangladesh, Bhutan, and other Southeast Asian countries. The Clarke (1866) ellipsoid was used for mapping in North America until recently. Many countries are now switching to WGS84, the datum used as a reference by the GPS.
|
Name |
Date |
Radius a (M) |
Radius b (M) |
Polar Flattening |
WGS 84 |
1984 |
6,378,137 |
6,356,752.3 |
1/298.257 |
WGS 72 |
1972 |
6,378,135 |
6,356,750.5 |
1/298.26 |
Australian |
1965 |
6,378,160 |
6,356,774.7 |
1/298.25 |
Krasovsky |
1940 |
6,378,245 |
6,356,863 |
1/298.3 |
International |
1924 |
6,378,388 |
6,356,911.9 |
1/297 |
Clarke |
1880 |
6,378.249.1 |
6,356,514.9 |
1/293.46 |
Clarke |
1866 |
6,378,206.4 |
6,356,583.8 |
1/294.98 |
Bessel |
1841 |
6,377,397.2 |
6,356,079.0 |
1/299.15 |
Airy |
1830 |
6,377,563.4 |
6,356,256.9 |
1/299.32 |
Everest |
1830 |
6,377,276.3 |
6,356,075.4 |
1/300.8 |
| |