[PROJ] Obtaining possible transformation pipelines

[Nyall Dawson]

On Fri, 31 May 2019 at 19:06, Even Rouault <even.rouault at spatialys.com> wrote:
>
> On vendredi 31 mai 2019 14:05:38 CEST Nyall Dawson wrote:
> > 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?)
>
> In the C++ API, you have DatabaseContext::lookForGridInfo() that would cover
> this. Would need to be exposed in the C API.

Thanks, PR at https://github.com/OSGeo/proj.4/pull/1494

Nyall