[Proj] converting WGS84/ETRS89 to ITM/OSGM15

[Even Rouault]

Alain,

> Doing the same way you try
> this (with proj program) I can’t get the correct use of the GeoidGrid.
> Why???? 

proj is the historical command line utility at the time where the library only 
handled cartographic projections, but not datum transformations hence it 
ignores +towgs84, +nadgrids, +geoidgrids. For the later, you need to use cs2s

Even

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