CMake: add option EMBED_PROJ_DATA_PATH

[WangWeiLin-MV]

Add an option EMBED_PROJ_DATA_PATH to allow PROJ_DATA_PATH not to be hardcoded. Defaults to ON, does not change existing behavior.

There are many ways to get the path, and the existing code allows macros not to be defined, for example src/filemanager.cpp#L1390-L1394.

There are many situations where you have to concern about hard coding path which might be fragile and breaks easily, or just want file path independent in build time. So, the option is added.

[kbevers]

Could you please explain why this is desirable to you?

[rouault]

Could you please explain why this is desirable to you?

Besides original reporter's own needs, I see this could be of value for example for conda-forge builds, where PROJ is relocated in a arbitrary location on the user machine, and thus hardcoding PROJ_DATA makes little sense.

[kbevers]

I'm sure there's a benefit, I just think it is good form to explain why we should consider a pull request.

This needs adding to the docs as well, by the way. Under CMake configure options in https://github.com/OSGeo/PROJ/blob/master/docs/source/install.rst

[jjimenezshaw]

Could you please explain why this is desirable to you?

Besides original reporter's own needs, I see this could be of value for example for conda-forge builds, where PROJ is relocated in a arbitrary location on the user machine, and thus hardcoding PROJ_DATA makes little sense.

That would be useful for me too. When you do not know where your proj is going to be located, it makes no sense. Even worse, it could be that there is an older version installed there, and just takes the wrong proj.db

[jjimenezshaw]

9.4.1 is already released. Should it be 9.5, the next release?

[kbevers]

Yes

[kbevers]

Also, I think the description below this needs a bit more work. When I'm reading this it only clear to my that this hardcodes the PROJ_DATA_PATH into the binaries because I've read the discussion in this PR. A short explanation of why you might want to turn this off would be very helpful

[WangWeiLin-MV]

Hi, I have made the changes, please review this PR and if you have any questions, please let me know.

[jjimenezshaw]

Could you please explain why this is desirable to you?

Besides original reporter's own needs, I see this could be of value for example for conda-forge builds, where PROJ is relocated in a arbitrary location on the user machine, and thus hardcoding PROJ_DATA makes little sense.

That would be useful for me too. When you do not know where your proj is going to be located, it makes no sense. Even worse, it could be that there is an older version installed there, and just takes the wrong proj.db

Another use case that happened to me (just in case it is happening to anybody else): "it works in my (developer's) computer"

I am using PROJ in an application that can be located anywhere in the filesystem. PROJ_DATA had to be set accordingly at the beginning (or right before) of the process. However it was working (in my computer) without setting it... because magically it was using the proj.db from my compilation folder, not the distribution folder. Even if the CI computer, because it was first compiling PROJ and then the application. We noticed it later when we tested manually somewhere else that never compiled PROJ. We changed the CI workflow to build and run in different instances.

[rouault]

Actually, I stand corrected regarding conda-forge. Conda has magic to patch strings !

Hard-coded path (with placeholder padding) in the "raw" package downloaded from the forge:

$ strings /home/even/miniconda3/pkgs/proj-9.4.1-hb784bbd_0/lib/libproj.so.25.9.4.1 | grep share/proj
../share/proj
/home/conda/feedstock_root/build_artifacts/proj_1718272424126/_h_env_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placeh/share/proj

vs substituted paths in the package installed in the conda env:

$ strings /home/even/miniconda3/envs/gdal_3.9.1/lib/libproj.so.25.9.4.1 | grep share/proj
../share/proj
/home/even/miniconda3/envs/gdal_3.9.1/share/proj

[jjimenezshaw]

Conda has magic to patch strings !

I am a bit scared. How is it doing that?

[rouault]

I am a bit scared. How is it doing that?

https://docs.conda.io/projects/conda-build/en/stable/resources/make-relocatable.html