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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, in Europe and on other continents, but will be replaced in the next decades by modern ellipsoids of satellite geodesy. The Bessel ellipsoid was derived 1841 by Friedrich Wilhelm Bessel, based on several meridian arcs and other data of continental geodetic networks of Europe, Russia and the British Survey of India. It is based on 10 meridional arcs and 38 precise measurements of the astro—geographic latitude and longitude (see also astro geodesy). The dimensions of the ellipsoid axes were defined by logarithms in keeping with former calculation methods. == The Bessel and GPS ellipsoids == The Bessel ellipsoid fits especially well to the geoid curvature of Europe and Eurasia. Therefore it is optimal for National survey networks in these regions, despite of the fact that its axes are about 700 m shorter than that of the mean Earth ellipsoid derived by satellites. Below there are the two axes ''a'', ''b'' and the flattening ''ƒ'' = (''a'' − ''b'')/''a''. For comparison, the data of the modern ''World Geodetic System'' WGS84 are shown, which is mainly used for modern surveys and the GPS system. * Bessel ellipsoid 1841 (defined by log ''a'' and ''ƒ''): * * ''a'' = 6,377,397.155 m * * ''ƒ'' = 1 / 299.1528153513233 (0.003342 773154 ± 0.000005) * * ''b'' = 6,356,078.963 m. * Earth ellipsoid WGS84 (defined directly by ''a'' and ''ƒ''): * * ''a'' = 6,378,137.0 m * * ''ƒ'' = 1 / 298.257223563 * * ''b'' = 6,356,752.30 m. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Bessel ellipsoid」の詳細全文を読む スポンサード リンク
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