[gdal-dev] Properly reinitializing PROJ_LIB search paths after supplementary file download

Tue Oct 7 14:26:33 PDT 2025

All,

I just wanted to give a quick update. I have switched to using PROJ_DATA.
Though I did not expect this to fix my original issue, I can confirm that
it has not. Is there perhaps a cache that I need to clear or something like
that? Or, is there some component of GDAL/Proj that I need to reset?

On Tue, Oct 7, 2025 at 1:10 PM David Klaus <dklaus at carlsonsw.com> wrote:

> Jeff,
>
> Thank you for that information. I wasn't aware that had changed. I will
> update our code,
>
> On Tue, Oct 7, 2025 at 1:07 PM Jeff McKenna via gdal-dev <
> gdal-dev at lists.osgeo.org> wrote:
>
>> Hi David, be careful that the former PROJ_LIB environment variable was
>> changed to PROJ_DATA since the PROJ 9.1.0 release (the former may work
>> for you now, but, you should change your packaging process to the
>> correct name, depending on what PROJ version you have).
>>
>> Also, you can follow the PROJ_DATA releases at
>>
>> https://github.com/OSGeo/PROJ-data/releases
>>
>> Thanks,
>>
>> -jeff
>>
>>
>>
>>
>> --
>> Jeff McKenna
>> GatewayGeo: Developers of MS4W, & offering MapServer Consulting/Dev
>> co-founder of FOSS4G
>>
>> http://gatewaygeo.com
>>
>>
>>
>>
>> On 2025-10-07 12:00 p.m., David Klaus via gdal-dev wrote:
>> > Hello GDAL community,
>> >
>> > The product that I work on uses the CPP GDAL library for a number of
>> > routines. Occasionally, this requires supplementary files -- Currently,
>> > we supply proj-data 1.20 <
>> https://github.com/OSGeo/PROJ-data/releases/
>> > tag/1.20.0> -- which we download when we detect that the dataset is
>> > needed. Here's the problem, often GDALRegisterAll() is called before
>> the
>> > proj-data 1.20 files are downloaded. From my testing, it appears that
>> if
>> > the proj-data 1.20 files are not available when GDALRegisterAll() is
>> > called, GDAL will not use them regardless of whether or not these files
>> > are available later.
>> >
>> > Now, what I think might be a good solution is appropriately updating
>> > GDAL's state after proj-data is downloaded s.t. it is able to detect
>> the
>> > proj-data files. But, I'm not sure how to do this. Calling the
>> following
>> > seems to produce correct results:
>> >
>> > GDALDestroy()
>> > GDALAllRegister()
>> >
>> > However, the documentation says the following:
>> >
>> >
>> ///////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////FROM
>> DOCUMENTATION///////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
>> > Finalize GDAL/OGR library.
>> >
>> > This function calls GDALDestroyDriverManager() and OGRCleanupAll() and
>> > finalize Thread Local Storage variables.
>> >
>> > Prior to GDAL 2.4.0, this function should normally be explicitly called
>> > by application code if GDAL is dynamically linked (but that does not
>> > hurt), since it was automatically called through the unregistration
>> > mechanisms of dynamic library loading.
>> >
>> > Since GDAL 2.4.0, this function may be called by application code,
>> since
>> > it is no longer called automatically, on non-MSVC builds, due to
>> > ordering problems with respect to automatic destruction of global C++
>> > objects.
>> >
>> > *Note: no GDAL/OGR code should be called after this call!*
>> >
>> ///////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////FROM
>> DOCUMENTATION///////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
>> >
>> > So, this doesn't seem like the correct way to address this problem. How
>> > should I go about updating GDAL's state s.t. it will detect and read
>> the
>> > downloaded supplementary proj-data files? Or, is there something more I
>> > should be doing before GDALAllRegister() is called?
>> >
>> > GDAL Version: GDAL 3.10.3, released 2025/04/01
>> > Proj Version: 9.6.0
>> >
>> > P.S. To get out in front of what I expect to be the first question, yes
>> > I am setting the PROJ_LIB environmental variable at runtime to the
>> > correct folder. Further, I have tried creating an empty proj-data
>> folder
>> > available to GDAL when GDALRegisterAll() is called. This did not change
>> > GDAL's behavior. Here is the code I use for setting PROJ_LIB:
>> >
>> > SetEnvironmentVariable("PROJ_LIB", "c:/path/to/proj-data/folder");
>> > _putenv_s("PROJ_LIB", "c:/path/to/proj-data/folder"); // (See:
>> GETENV_NOTE)
>> >
>> > P.P.S Here is the GETENV_NOTE:
>> > // GETENV_NOTE:
>> > // _putenv_s() is used to ensure compatibility with getenv(). getenv()
>> > operates on environment variables loaded into  the _environ global
>> > variable (loaded at "process startup.")
>> > // SetEnvironmentVariable() affects the environment variables set for
>> > this process but does not change _environ. _putenv_s() updates _environ
>> > and ensures compatibility w/
>> > // genenv().
>> >
>> > P.P.P.S I do know that there is a more current proj-data dataset
>> > available. We may update to this dataset in the future. But unless that
>> > will fix the current issue, I'd rather not do that now.
>> >
>> >
>> > --
>> > David Klaus
>> > Carlson Software
>> >
>> >
>> > *Disclaimer*
>> >
>> > The information contained in this communication from the sender is
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>> > authorized to receive it. If you are not the recipient, you are hereby
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>> > relation of the contents of this information is strictly prohibited and
>> > may be unlawful.
>> >
>> >
>> > _______________________________________________
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>> >
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>>
>>
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>
> --
> David Klaus
> Carlson Software
>

-- 
David Klaus
Carlson Software

Disclaimer

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