The Hayford ellipsoid is a

geodetic Geodesy ( ) is the Earth science of accurately measuring and understanding Earth's figure (geometric shape and size), orientation in space, and gravity. The field also incorporates studies of how these properties change over time and equivale ...

reference ellipsoid An Earth ellipsoid or Earth spheroid is a mathematical figure approximating the Earth's form, used as a reference frame for computations in geodesy, astronomy, and the geosciences. Various different ellipsoids have been used as approximatio ...

, named after the US geodesist

John Fillmore Hayford John Fillmore Hayford (May 19, 1868 – March 10, 1925) was an eminent United States geodesist. His work involved the study of isostasy and the construction of a reference ellipsoid for approximating the figure of the Earth. The crater Hayford o ...

(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 The International Union of Geodesy and Geophysics (IUGG; french: Union géodésique et géophysique internationale, UGGI) is an international non-governmental organization dedicated to the scientific study of Earth and its space environment usi ...

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 In geometry, the major axis of an ellipse is its longest diameter: a line segment that runs through the center and both foci, with ends at the two most widely separated points of the perimeter. The semi-major axis (major semiaxis) is the lo ...

= and its

flattening Flattening is a measure of the compression of a circle or sphere A sphere () is a Geometry, geometrical object that is a solid geometry, three-dimensional analogue to a two-dimensional circle. A sphere is the Locus (mathematics), set o ...

= 1:297.00. Unlike some of its predecessors, such as the

Bessel ellipsoid The Bessel ellipsoid (or Bessel 1841) is an important reference ellipsoid of geodesy. It is currently used by several countries for their national geodetic surveys, but will be replaced in the next decades by modern ellipsoids of satellite geode ...

( = , = 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 isostatic measurements to reduce

plumbline A plumb bob, plumb bob level, or plummet, is a weight, usually with a pointed tip on the bottom, suspended from a string and used as a vertical reference line, or plumb-line. It is a precursor to the spirit level and used to establish a verti ...

divergences. Hayfords ellipsoid did not reach the accuracy of Helmerts ellipsoid published 1906 ( = , = 1:298.3). It has since been replaced as the "International ellipsoid" by the newer Lucerne ellipsoid (1967) and GRS 80 (1980).

Sources

Defense Mapping Agency The National Geospatial-Intelligence Agency (NGA) is a combat support agency within the United States Department of Defense whose primary mission is collecting, analyzing, and distributing geospatial intelligence (GEOINT) in support of national ...

: ''Geodesy for the layman'', 1983, p.

Geodesy Geophysics {{geodesy-stub

See also

Sources