Hi,

I get the expected 4070327.25 166078.93 4891298.61 result with proj 6.0.0, 7.2.1, 9.2.0 and master

There's no grid involved in this operation, just inverse LCC projection on the RGF93 datum

I also tried to reproduce your issue if the PROJ < 6 IGNF file is found in the PROJ resource path(s) (non nominal situation - this file is not needed any more, and will generally lead to suboptimal results. Its content is included in the proj.db file), but even with that I get the expected result. So no idea why you get wrong results

Even


Le 26/05/2023 à 20:54, Nicolas Bellaiche a écrit :
Hi all,

I'm migrating my C++ code from PROJ4 to PROJ9 and I meet a worrying issue with the computation. Some of my regress tests don't pass so I've tested with cs2cs and gets the same difference:

PROJ4

echo652760.73700000 <callto:652760.73700000>7033791.24300000 43 <callto:7033791.24300000 43>.64200000 | cs2cs +init=IGNF:LAMB93 +to +init=IGNF:RGF93:

4070327.25166078.93 4891298.61 <callto:166078.93 4891298.61>


PROJ7 or PROJ9

echo652760.73700000 <callto:652760.73700000>7033791.24300000 43 <callto:7033791.24300000 43>.64200000 | cs2cs +init=IGNF:LAMB93 +to +init=IGNF:RGF93:

4070355.05166080.07 4891332.24 <callto:166080.07 4891332.24>




I suspect that PROJ7 and PROJ9 don't read properly the geoid file but I'm not sure. Someone can help me tracking and fixing this problem?

Thanks,

Nicolas Bellaiche
Institut Géographique National France

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