[PROJ] Some (probably dumb) questions about cs2cs and projinfo

[Even Rouault]

Le 24/02/2026 à 14:00, Andrea Giudiceandrea via PROJ a écrit :
> Il 24/02/2026 13:23, Andrea Giudiceandrea ha scritto:
>> Thank you very much, Even. Your explanation clarifies all my doubts!
>
> Actually, not exactly all...
>
> I wonder why In QGIS the listed transformations available for 
> EPSG:23033 -> EPSG:3065 are only 2 (1 grid, 1 ballpark, corresponding 
> to projinfo without "--grid-check discard_missing") instead of the 6 
> (5 Helmert, 1 ballpark) listed by projinfo with "--grid-check 
> discard_missing" or a union of both (1 grid shift, 5 Helmert and 1 
> ballpark).
>
> This creates a discrepancy, making QGIS use a ballpark transformation 
> whereas a better one could be used.
>
> Maybe it would be useful if QGIS could list and let the user choose 
> among all the available transformations, wouldn't it?

This is a case where one could argue which one is the best between the 
ballpark ED50 -> IGM95 or going through WGS 84 by using a likely poorly 
conditionned Helmert transformation. Both results are right and wrong to 
some accuracy requirements...

Why IGM is still not releasing freely their grids ? (I remember doing 
them some education in Firenze in 2022 ...)

Even

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