测量基准 Geodetic datum
（重定向自Geodesic datum）
测量基准，又称大地原点，是测量的参照点。在大地测量学及测量中，大地原点是一组用来对照测量点的地球坐标，往往与地理测量体系的参考椭球体模型有关。
在机械工程方面，测量基准就是设计或者加工时作为基准或参考的面等，例如基座的底面一般都会加工，可以作为基准面
Geodesic datum
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Geodetic datum 测量基准
（重定向自Geodesic datum）
A Geodetic datum or geodetic system is a coordinate system, and a set of reference points, used to locate places on the Earth (or similar objects). An approximate definition of sea level is the datum WGS 84, an ellipsoid, whereas a more accurate definition is Earth Gravitational Model 2008 (EGM2008), using at least 2,159 spherical harmonics. Other datums are defined for other areas or at other times; ED50 was defined in 1950 over Europe and differs from WGS 84 by a few hundred meters depending on where in Europe you look. Mars has no oceans and so no sea level, but at least two martian datums have been used to locate places there.
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