[PROJ] specifying the search paths

[Roger Bivand]

Even,

On Wed, 1 Jul 2020, Even Rouault wrote:

> Roger,
>
>> I have a question about the use of
>> proj_context_set_search_paths(PJ_DEFAULT_CTX, ...). On initiating PRØJ, I
>> see from proj_info().searchpath that (now 7.1.0) I have three paths, the
>> last two identical /usr/local/share/proj, and the first
>> $HOME/.local/share/proj - which contains a cache.db.
>>
>> For testing on other platforms than my own, I need to change the first
>> path to a temporary directory with write access, so that I do not write in
>> the user space of the test platform. So I use
>> proj_context_set_search_paths(PJ_DEFAULT_CTX, ...), providing the correct
>> length of the vector of paths, and the paths themselves. The
>> user-writeable path is first, as at startup. It, however, does not contain
>> a cache.db file, even of zero length. After finding a coordinate operation
>> (using a grid cached in $HOME/.local/share/proj), the temporary directory
>> remains empty, $HOME/.local/share/proj is used despite not being on the
>> active path list, and the operation completes successfully.
>>
>> This is, however, not what I need - I need the download to occur to the
>> temporary directory, so that I can demonstrate that cache.db gets
>> populated.
>>
>> May libproj be caching paths so that even if the path to the use-writeable
>> directory has been set, it still uses the one determined on load, even if
>> it had been renamed and is not on the this of search paths? I find the
>> default use-writeable directory being re-created even when it is not on
>> the declared list of search paths. I'm only using PJ_DEFAULT_CTX - is that
>> the problem?
>
> The location of the user writable directory for cache.db is not controlled through
> proj_context_set_search_paths(). You can get the location with
> proj_context_get_user_writable_directory()
>

Thanks for a rapid and full reply. My context is that in order to include 
runnable code examples in R packages, they need to meet a requirement not 
to cause data to be written outside the R temporary directory for the 
running instance irrespective of platform. So I need to control the 
address of the user-writeable directory completely in order to show users 
what is going on, and to permit the package to meet test requirements. I 
can try pj_context_set_user_writable_directory() understanding that it is 
not part of the public API, and will report back.

Best wishes,

Roger

> In the non-public API (proj_internal.h), there's a 
> pj_context_set_user_writable_directory() function to modify it. It is 
> actually PROJ_DLL exported because used by the projsync utility, but do 
> not rely on it for production code, as this might change in the future, 
> if the function was promoted to the public API.
>
> On Unix, you can also modify it by setting the XDG_DATA_HOME environment variable (the
> actually directory will then be ${XDG_DATA_HOME}/proj)
> A non-documented feature used by PROJ tests is also to use
> the PROJ_USER_WRITABLE_DIRECTORY environment variable: this will have precedence on
> XDG_DATA_HOME
>
> See
> https://github.com/OSGeo/PROJ/blob/b66798a8f3d559b5fe28c22973241e97d191a053/src/
> filemanager.cpp#L1190
>
> Even
>
>

-- 
Roger Bivand
Department of Economics, Norwegian School of Economics,
Helleveien 30, N-5045 Bergen, Norway.
voice: +47 55 95 93 55; e-mail: Roger.Bivand at nhh.no
https://orcid.org/0000-0003-2392-6140
https://scholar.google.no/citations?user=AWeghB0AAAAJ&hl=en