[PROJ] Proj6 Docs

[Even Rouault]

> Hum. Right now I’m creating and caching the result of
> proj_create_crs_to_crs(). If I get two PJ from proj_create() is there a way
> to create an “optimum pipeline” ala proj_create_crs_to_crs() using two PJ
> as the start/end points, instead of two strings?

2 options:
- you export your PJ objects as wkt with proj_as_wkt() and feed that to 
proj_create_crs_to_crs()
- or you emulate most of what proj_create_crs_to_crs() does, which is 
essentially using proj_create_operations() which takes 2 PJ objects (of type 
CRS):
https://github.com/OSGeo/proj.4/blob/master/src/4D_api.cpp#L1010


> > Or, after the commit I just pushed, you can extract the source CRS from
> > the
> > pipeline with proj_get_source_crs() (but only if you've created the
> > pipeline with proj_create_crs_to_crs(). Not if you created it with
> > proj_create("+proj=pipeline ...") )
> 
> Any chance you could also add proj_get_dest_crs() to pick the CRS off the
> end of a pipeline? 

Ah, that was implied that my changeset also fixes the dest part of course.

Even

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