Cct, proj_create_crs_to_crs and towgs84 parameters

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Cct, proj_create_crs_to_crs and towgs84 parameters

Olli Räisä
Hello,

Proj-5.0.0RC2 cct outputs appear to differ from cs2cs outputs, when a coordinate reference system has non-zero towgs84 parameters.

An example:

bin\cs2cs +init=epsg:2393 +to +init=epsg:3879
3500000 6650000 0
25611546.42     6651551.63 25.30

bin\cct -t0 +proj=pipeline +step +init=epsg:2393 +inv +step +init=epsg:3879
3500000 6650000 0
25611608.8193   6651462.4308      340.2153        0.0000 

Looking at proj_create_crs_to_crs function code, I assumed that these commands produce the same results (within some tolerance).

Regards,
Olli Räisä


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Re: Cct, proj_create_crs_to_crs and towgs84 parameters

Kristian Evers-2

Hi Olli,

 

Thanks for reporting this. You assume correct. The issue has already been reported and mostly fixed. See the discussion here: https://github.com/OSGeo/proj.4/issues/783.

 

This should be fixed in RC3.

 

/Kristian

 

Fra: [hidden email] [mailto:[hidden email]] På vegne af Olli Räisä
Sendt: 12. februar 2018 09:36
Til: [hidden email]
Emne: [Proj] Cct, proj_create_crs_to_crs and towgs84 parameters

 

Hello,

 

Proj-5.0.0RC2 cct outputs appear to differ from cs2cs outputs, when a coordinate reference system has non-zero towgs84 parameters.

 

An example:

 

bin\cs2cs +init=epsg:2393 +to +init=epsg:3879

3500000 6650000 0

25611546.42     6651551.63 25.30

 

bin\cct -t0 +proj=pipeline +step +init=epsg:2393 +inv +step +init=epsg:3879

3500000 6650000 0

25611608.8193   6651462.4308      340.2153        0.0000 

 

Looking at proj_create_crs_to_crs function code, I assumed that these commands produce the same results (within some tolerance).

 

Regards,

Olli Räisä

 


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Re: Cct, proj_create_crs_to_crs and towgs84 parameters

Thomas Knudsen
In reply to this post by Olli Räisä
Hello Olli,

Thanks for testing and reporting! Your report probably relates to a bug which has been fixed
in pull request #793 over at https://github.com/OSGeo/proj.4/pull/793

Unfortunately, the build fails, due to something which *may* be a bug in cppcheck (the code
compiles cleanly on all platforms, but cppcheck reports a syntax error). I'll have to look into
this before merging the PR.

Running locally, my current build reports the following on your test material:

$ echo 3500000 6650000 0 | bin\Debug\cs2cs_d +init=epsg:2393 +to +init=epsg:3879
25611546.42     6651551.63 25.30

$ echo 3500000 6650000 0 | bin\Debug\cct_d -t0 +proj=pipeline +step +init=epsg:2393 +inv +step +init=epsg:3879
25611546.4190   6651551.6301       25.2952        0.0000

/Thomas


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