[PROJ] Intermediate steps due same datum transformation

[Oleg Bizin]

Ok, now everything is clear.
Thanks!

вт, 19 июл. 2022 г. в 18:10, Even Rouault <even.rouault at spatialys.com>:

>
> 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.
>
> -- http://www.spatialys.com
> My software is free, but my time generally not.
>
>
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