[PROJ] EPSG v10 update status

[Nyall Dawson]

> And possibly also try #2371, but if your code inspects the details of objects, like accessing the datum of a CRS, be prepared for the dreaded datum ensemble concept to show up (for anything based on WGS84 and ETRS89), in which case you may need to use new functions added in the C API.

Hi Even,

I've been trying to get my head around how the introduction of datum
ensembles will impact downstream projects, and specifically how things
will/should change for users of these applications.

Am I correct in my understanding that a ensemble is (at this stage) a
"metadata only" concept, which indicates that the datum is only
suitable for approximate spatial referencing? Or does a datum being
flagged as an ensemble also influence the operations determined by
PROJ and their order of precedence?

How would you imagine a downstream project like QGIS should respond to
this concept? Should we add a user-visible flag on any CRS definitions
associated with a datum ensemble to say "Warning: ensemble datum, not
for use in accurate spatial referencing"? What other user-facing
changes do you think should be introduced?

Nyall






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