[PROJ] Consistency of Proj and Esri transformations

[Martin Desruisseaux]

Hello

I think that in case of difference, neither PROJ or ESRI should be 
adopted as practical reference. The cause of the difference needs to be 
analyzed in order to see if there is a bug, which may happen sometime in 
a software and sometime in another.

Many CRS are defined by national map agencies (USGS in USA I think, IGN 
in France, etc.). Those agencies sometime publish example of points 
transformed from an old CRS defined by the agency to a newer CRS. The 
example points published by those agencies are the closest match to an 
"official" reference I can think to. But we have to search for examples 
provided by the agency of each country instead of having a central place 
providing examples for many CRS.

Alternatively, for the convenience of a single source of points that can 
be used as practical references for many CRS, the most trustable source 
I'm aware of is https://gigs.iogp.org/.

     Martin

Le 17/12/2021 à 18:08, Dave Knopp a écrit :

> Does anyone have pointers to systematic comparisons, evaluations, or any
> consistency efforts re: numeric consistency between Proj transformation
> results and those produced via Esri projection engine?
>
> A second question: in the case of differences, any thoughts which should
> be adopted as a practical reference?