[Proj] +towgs84 approximation error

[Jochem]

Hello Antoine,

My coordinates in the old frame have precision of a few cm (obtained by
triangulation a hundred years ago) and the coordinates in the new frame 1 cm
(obtained by static GPS measurements 15 years ago). Both networks are tied
to WGS84 with an precision of a few metres. 

However the two frames are tied to each other far more precisely. The
relative transformation parameters have a precision of a few cm, since these
are based on the measurements. However these parameters have been in use for
some time now in software with strict formulas, and by that they have become
more or less official. Therefore, I need Proj.4 to produce the exact same
result (+/- 1 mm) as the other software with the strict formulas.

Regards, Jochem





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