[PROJ] PROJ 9 & old syntax +init=

[Nicolas Bellaiche]

I compare with the results given by CIRCE which is the official software developed by the National Geographic Institute of France, these coordinates are official datasets distributed with the application. 


De: "Alain Orsoni" <Alain.Orsoni at ign.fr> 
À: "Nicolas Bellaiche" <nicolas.bellaiche at ign.fr> 
Cc: "proj" <PROJ at lists.osgeo.org> 
Envoyé: Jeudi 1 Juin 2023 16:27:23 
Objet: Re: [PROJ] PROJ 9 & old syntax +init= 

For me LAMB1 and UTM31RGF93 are both considered as being on Geoid in the new database. 
So the altitude from input is just transferred to the output. 

So I think the result from 9.2 version is correct in terms of Z management. 

But it’s only from my understanding… 

Alain 






Le 1 juin 2023 à 15:54, Nicolas Bellaiche < [ mailto:nicolas.bellaiche at ign.fr | nicolas.bellaiche at ign.fr ] > a écrit : 

Hi all, 


I am still puzzled by the difference between the old syntax +init= and the new syntax. I just rebuilt the last release 9.2.1 and tested with it to make sure it's not a bug already fixed. 

1) Example where the grid shift is not taken into account with the new syntax. (it's correct with +init=) 

1.a) NEW SYNTAX: z not correct (grid shift not used) 

echo 600000.00000000 300097.53400000 0.00000000 | ./bin/cs2cs IGNF:LAMB1 +to IGNF:UTM31RGF93 
452845.19 5583309.40 0.00 

1.b) OLD SYNTAX: z correct: 

echo 600000.00000000 300097.53400000 0.00000000 | ./bin/cs2cs +init=IGNF:LAMB1 +to +init=IGNF:UTM31RGF93 
452845.19 5583309.40 43.64 



2) Example where the old syntax gives a wrong result while the new syntax works: 

2.a) OLD SYNTAX from cartographic to geocentric coordinates / result is wrong 

echo 652760.737 7033791.243 43.642 | PROJ_DEBUG=3 ./bin/cs2cs +init=IGNF:LAMB93 +to +init=IGNF:RGF93 
4070355.05 166080.07 4891332.24 


2.b) NEW SYNTAX from cartographic to geocentric coordinates / result is correct 

echo 652760.737 7033791.243 43.642 | PROJ_DEBUG=3 ./bin/cs2cs IGNF:LAMB93 +to IGNF:RGF93 
4070327.25 166078.93 4891298.61 




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