[PROJ] How to not take the direct transformation

[Even Rouault]

No there's no such option but you could easily add one to the coordinate 
operation factory context

and when set relax checks about res.empty() likely at

https://github.com/OSGeo/PROJ/blob/8072ad6aae7a11f605c04a7068bd295404705fe0/src/iso19111/operation/coordinateoperationfactory.cpp#L4161 
,

https://github.com/OSGeo/PROJ/blob/8072ad6aae7a11f605c04a7068bd295404705fe0/src/iso19111/operation/coordinateoperationfactory.cpp#L4207 
and

https://github.com/OSGeo/PROJ/blob/8072ad6aae7a11f605c04a7068bd295404705fe0/src/iso19111/operation/coordinateoperationfactory.cpp#L4228

Le 19/03/2026 à 21:31, Javier Jimenez Shaw via PROJ a écrit :
> Hi
>
> There is a "feature" in PROJ that is sometimes inconvenient: if there 
> is a direct transformation from A to B, it is not searching for better 
> options.
>
> That can be really annoying in some cases, and confusing as well.
>
> Is there any way to "disable" it? something in the context? an 
> environment variable?
>
> Example:
> If I transform from WGS84 to NAD83(2011) it is going to use the 
> transformation 
> https://epsg.org/transformation_9774/NAD83-2011-to-WGS-84-1.html, that 
> is a no-op, with 2m accuracy.
> However from WGS84 to NAD83(2011)+NAVD88 it is taking a more 
> complicated transformation for the horizontal values. That is very 
> confusing. It happens in other situations (that of course I cannot 
> remember now).
>
> I understand that changing the current behaviour could be to big (we 
> can discuss if it makes sense or not), but having a way to disable 
> that "optimization" would be great.
>
> Thank you
>
> Cheers
> Javier.
>
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