[PROJ] Intermediate steps due same datum transformation

[Even Rouault]

Le 19/07/2022 à 17:02, Oleg Bizin a écrit :
> Even,
>
> Thank you for the detailed answer!
>
> I have a couple more clarifying questions.
>
>     More generally PROJ >= 6 will not use WGS 84 as a compulsory pivot
>     in coordinate transformations
>
> 1. Is it correct that the  PROJ < 6 definitely uses WGS84 as a 
> compulsory pivot?
When there was a datum indication in the PROJ.4 string, yes, since 
+towgs84 or +nadgrids implied the WGS84 pivot. When source and 
transformation CRS PROJ.4 strings used the same +towgs84 terms, that was 
skipped as an optimization (what newer PROJ does too)
>
> 2. Currently, before your fix, for custom crs transformation to WGS84 
> may perform, but  without significant impact on accuracy?

For most uses yes, it shouldn't have significant impact. Unless you 
transformation coordinates back and forth many many times.


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