[PROJ] Obtaining possible transformation pipelines

[Even Rouault]

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.

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