[Proj] +towgs84 approximation error

Martin Desruisseaux martin.desruisseaux at geomatys.com
Thu Mar 23 06:41:16 EST 2017

Le 23/03/2017 à 11:52, Jochem a écrit :

> Therefore, I need Proj.4 to produce the exact same result (+/- 1 mm)
> as the other software with the strict formulas.
I would have a different approach. To me, the problem is that Proj.4 and
other software are used as black boxes: there is nothing telling the
user that the coordinate transformation (s)he is using has an accuracy
of 5 cm, or 10 metres, or 25 metres, etc. I think that this information
should be made easily available. Again, this can be done with access to
a more complete EPSG dataset than the current CSV files.

I could even relate this issue to wider thoughts about the importance of
metadata in this "post-truth" era, for making easier to evaluate our
confidence in data or statement, but this is out of scope for this thread.


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