[PROJ] Converting coordinates between different ellipsoids... possible? valid?

[Nyall Dawson]

On Mon, 20 May 2019 at 17:45, Even Rouault <even.rouault at spatialys.com> wrote:
>
> On lundi 20 mai 2019 13:15:55 CEST Nyall Dawson wrote:
> > Hey list,
> >
> > If I attempt to create a transform using proj_create_crs_to_crs, with
> > the source proj string "+proj=longlat +datum=WGS84 +no_defs" and dest
> > proj string "+proj=longlat +a=2632345 +no_defs", I get the error
> > "internal_proj_create_operations: Source and target ellipsoid do not
> > belong to the same celestial body".
> >
> > My question is -- should this be allowed? It worked ok in previous
> > proj versions, and it's a common situation in QGIS
>
> Not for real world use cases, but for some artificial unit cases, right ?
>
> > Or is it violating some rule of transformation? How can I reproduce
> > the proj 4 behaviour here?
>
> I think we discussed this before. Basically there's a new check that prevents
> doing non sensical transformations. No workaround than disabling the check in
> code

Thanks for the direction (not being sarcastic, you definitely pointed
fingers back at the non-proj code being at fault, which it was).  This
invalid transform was the result of some no-longer-correct assumptions
that crs objects can always be represented by a proj string or unique
auth/code combo.

Nyall

>
> Even
>
> --
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