[PROJ] 7.2.1 RC1 ob_tran changes break existing logic

[Even Rouault]

On lundi 28 décembre 2020 16:41:09 CET Kristian Evers wrote:
> Thanks for clearing this up, Even. The workflow is a bit cumbersome but with
> the knowledge you’ve provided here it should be possible for Roger to adapt
> the code to work around this.
> 
> I agree that a function to determine if a CRS is derived would be a nice
> addition.

Queued in https://github.com/OSGeo/PROJ/pull/2496 . I've targetted it for 8.0 
. Could be easily backported if deemed necessary.

> 
> I guess this problem mostly shows up because ob_tran is a bit of a weird
> projection. It is often the cause of problems. I wonder if it is time to
> get rid of it

Although I concur it is an annoyance, I can't see how we could get rid of it. 
There are definitely use cases where people want a CRS object expressing such 
rotation.

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