4.9.2011A 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.
