{{short description|Earth-approximating ellipsoid introduced in 1910}} {{nofootnotes|date=November 2009}} {{one source|date=November 2009}}
In [[geodesy]], the '''Hayford ellipsoid''' is a [[reference ellipsoid]] named after the American [[geodesist]] [[John Fillmore Hayford]] (1868–1925), which was introduced in 1910. The Hayford ellipsoid was also referred to as the '''International ellipsoid 1924''' after it had been adopted by the [[International Union of Geodesy and Geophysics]] IUGG in 1924, and was recommended for use all over the world. Many countries retained their previous ellipsoids.
The Hayford ellipsoid is defined by its [[semi-major axis]] {{mvar|a}} = {{val|6378388.000|u=m}} and its [[flattening]] {{mvar|f}} = 1:297.00. Unlike some of its predecessors, such as the [[Bessel ellipsoid]] ({{mvar|a}} = {{val|6377397|u=m}}, {{mvar|f}} = 1:299.15), which was a European ellipsoid, the Hayford ellipsoid also included measurements from [[North America]], as well as other continents (to a lesser extent). It also included [[Statically indeterminate|isostatic]] measurements to reduce [[plumbline]] divergences. Hayfords ellipsoid did not reach the accuracy of [[Friedrich Robert Helmert|Helmert's]] ellipsoid published 1906 ({{mvar|a}} = {{val|6378200|u=m}}, {{mvar|f}} = 1:298.3).
It has since been replaced as the "International ellipsoid" by the newer [[Lucerne ellipsoid]] (1967) and [[GRS 80]] (1980).
==See also== *[[Earth ellipsoid]]
==Sources== *[[Defense Mapping Agency]]: ''Geodesy for the layman'', 1983, p. 8 [http://www.ngs.noaa.gov/PUBS_LIB/Geodesy4Layman/geo4lay.pdf]
[[Category:Geodesy]] [[Category:Geophysics]] [[Category:Ellipsoids]]
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