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geodetic datum Geodetic Reference System
A geodetic datum definition has a change of semantics and meaning.
  • at the beginning, a geodetic datum was the astronomic and geodetic determination of size, position and orientation of a local, regional or national reference system. Mainly, they had no relationship to other reference systems
    • in geomatics a geodetic datum often means the datum transformation parameters from a national to a global geodetic reference system.
  • modern geodetic reference systems are determinded in a combination of many geodetic and astronomic measurements like Global Satelite Navigation System (GNSS), Very Long Baseline Interferometry (VBLI) etc. They are positionned earth centered.