[PROJ] Obtaining possible transformation pipelines

[Nyall Dawson]

On Tue, 28 May 2019 at 03:23, Even Rouault <even.rouault at spatialys.com> wrote:
>
> > If I have a proj string representing a coordinate operation, is there
> > any way to determine what grids are required for using it when those
> > grids are NOT available for use on the system?
>
> I don't think so. As you find out, PROJ will refuse to instanciate a
> coordinate operation from a PROJ string that has a grids not present on the
> system.
>
> Asthere are not so many ways of expressing grids in PROJ grids, basically you
> could look for +grids=xxxxx

That's what I was originally thinking could be a fallback option. But
then, I can't see any way to get the detailed metadata relating to a
grid except for proj_coordoperation_get_grid_used. So even if I
captured the grid name from the proj string, I still can't determine
the url and package name, etc relating to that grid. (or can I?)

What I'm aiming to do is take a proj coordinate operation string
stored in a project file, and show a nice warning to users if it can't
be used locally, along with the links to download the missing grid
files.

Nyall