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

[Even Rouault]

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

Even

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