Hayford ellipsoid
The Hayford ellipsoid is the earth's ellipsoid that John Fillmore Hayford (1868-1925), an American geodesist , calculated from 1905 to 1909 from global survey data. Hayford's Earth Dimensions
- Equator half-axis a = 6,378,388 m, flattening of the earth f = 1: 297.0
can be found in the table of important reference ellipsoids compared to other ellipsoids, such as the Bessel ellipsoid from 1841 . They were adopted by the international geoscientific umbrella organization IUGG in 1924 as the International Ellipsoid 1924 .
In contrast to the older Bessel ellipsoid, which is optimal for Eurasia , the data from numerous surveying networks in North America are included, and to a lesser extent also from other continents and some island groups . In addition, the data were subjected to a geophysical reduction according to the isostasis hypothesis in such a way that the vertical deviation effects of the deeper earth's crust could be reduced. As a result, Hayford's ellipsoid axes are largely cleared of a continental geological effect, which in the Bessel and other early ellipsoids led to an axis shortening compared to an ideal earth ellipsoid with global data distribution.
Since a more precise "international ellipsoid" was defined in 1967 with the Lucerne ellipsoid and in 1980 with the GRS 80 , it became common to simply use the "Hayford ellipsoid" instead of "International ellipsoid (1924)".
According to more modern results, Hayford's equator axis is 251 m too long and its flattening at the poles is 90 m too shallow. One of the reasons for this is that the great mountains in Eurasia are mainly east-west, whereas in America they are north-south.