Next ellipsoid
A reference ellipsoid derived from geodetic measurements , which best fits the regional curvature of the earth of a national territory or a continent, is referred to as the closest ellipsoid . The parameters of this regional ellipsoid (mostly equator axis a and flattening f ) are calculated by minimizing the perpendicular deviations by means of an adjustment .
The best connection attribute refers to the fact that a system of the smallest possible vertical deviations is equivalent to an optimal adaptation of the ellipsoid to the geoid in the area covered by measurements (see figure). If one extends the project area over a whole continent or even further, then the results come closer to the axes of the central earth ellipsoid , the larger the calculation area.
The method of vertical deviation adjustment was developed in Europe and the USA around the turn of the century and is related to astro-geodetic network adjustment ; Additional parameters to the latter are improvements in the ellipsoid parameters ( da, df ), a possible small twist dA and a scale factor of a few mm per km.
While older ellipsoids such as that by Bessel (1841) could only achieve perpendicular deviation minimization through approximate adjustment, the Hayford ellipsoid of 1909 or 1924 was the first to emerge from a strict adjustment. Hayford called it the area method and also used an isostasis correction of the underlying astro-geodetic measurement data.
See also
- Earth figure , geoid determination , international earth measurement
- Land surveying , network adjustment , geodetic datum
- Karl Ledersteger , Helmut Wolf
literature
- Karl Ledersteger : Astronomical and Physical Geodesy ( Earth Measurement ) , Chapter II: The derivation of best-connected ellipsoids. JEK volume V, chap. II, IV and XIII, JB Metzler-Verlag, Stuttgart 1968.
- Bernhard Heck : Calculation methods and evaluation models for national surveying . Wichmann-Verlag, Karlsruhe 1987, ISBN 387907-173X .