[PROJ] EPSG v10 update status

[Greg Troxel]

I am glad to see progress in this area as I find datum ensembles to be a
major source of trouble, especially in the US.  A few questions:

> for dynamic datum & CRS (like "WGS 84 (Gxxxx)", "ITRFxxxx"), ingest the
> frame reference epoch from the database and emit it in WKT. No/little
> backward compatibility issue foreseen.

Sorry if this is dragging you off topic, but I continue to have a hard
time following exactly what people mean by "dynamic datum".  Sometimes
it seems to mean "defined relative to ITRFxxxx via a velocity model, so
that coordinates of crust-fixed stations are stable".  And sometimes it
seems to mean "a datum that we ackknowledge is not crust-fixed".

Here, I wonder if you are referring the to progression of realizations,
or one of the above, or something else?

> datum ensembles... This is the most annoying part. The "World Geodetic
> System 1984" and "European Terrestrial Reference System 1989" datum
> have now in EPSG 10 a " ensemble" suffix in their names to reflect the
> new nature of those objects.

I understand the issue with WGS84, and am guessing ETRS89 is similar.
I don't follow why NAD83 isn't listed here, and I wonder if you think
there's a good reason, or just 'it ought to be but nobody has done the
work yet'.

From my US-centric perspective, NAD83 and WGS84 are the preeminent
examples of datum ensembles.


Also, I wonder if ITRFxxxx is going to be treated as datum ensemble.  As
I understand it, ITRFxxxx are successive realizations for ITRS (which is
itself not a datum).


I also wonder if there is a code for WGS84(TRANSIT) or whatever it's
called, so that this is nameable separately from the ensemble.

Thanks,
Greg
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