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Ellipsoids

The Math

The "flattening factor" measures the compression of a sphere. The notation of f is used for flattening.

Official Ellipsoids

The following ellipsoids come from Map Projections - A Working Manual (Snyder, 1987)and other sources. Radii may be specified more precisely than the 0.1 meter shown here.

Name Year Equatorial Radius, RM meters Polar Radius, Rm meters Flattening factor, f Users
Airy 1830 6,377,563.4 6,356,256.9 1/299.32 Great Britain
Bessel 1841 6,377,397.2 6,356,079.0 1/299.15

Central Europe; Chile; Indonesia

Clarke 1866 6,378,206.4 6,356,583.8 1/294.98 North America; Philippines
Clarke 1880 6,378,249.1 6,356,514.9 1/293.46 Most of Africa; France
International 1924 6,378,388.0 6,356,911.9 1/297.00 Much of the world
Australian 1965 6,378,160.0 6,356,774.7 1/298.25 Australia
WGS72 1972 6,378,135.0 6,356,750.5 1/298.26 NASA, US Dept. of Defense
GRS80 1980 6,378,137.0 6,356,752.3 1/298.26 Worldwide
WGS84 1984 - current 6,378,137.0 6,356,752.3 1/298.26 Worldwide

Additional Resources

Wikipedia page on Flattening

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