[PROJ] EPSG v10 update status

[Nyall Dawson]

On Sat, 10 Oct 2020 at 01:36, Even Rouault <even.rouault at spatialys.com> wrote:

> Here's the extensive list of what is considered in EPSG as a dynamic datum:
>
>
>
> $ sqlite3 data/proj.db "select 'EPSG:' || code || ', ' || name from geodetic_datum where frame_reference_epoch is not null order by name"
>
snip
>
> EPSG:1166, World Geodetic System 1984 (Transit)

Is there any proj c api which can be used to determine whether or not
a particular datum is dynamic? (i.e. to obtain this list without
direct database querying).

> 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.

My interpretation of your PRs is that the answer is no, but just to
confirm: does proj now have the capability to ingest coordinate
metadata from a WKT string? If so, is there any api in proj yet to
retrieve the coordinate epoch from this metadata for a dynamic datum
CRS?

Nyall


>
>
>
> From a quick look, at least for the datums with which I've some familiarity, it looks like they are datums which are not crust-fixed.
>
>
>
> For example, Australia's GDA2020 which is crust-fixed is not there, altough it has a time-dependent Helmert transformation to ATRF2014 and ITRF2014 (both listed above)
>
>
>
> > 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 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'.
>
>
>
> I don't know why the NAD83 family isn't there. Probably depends on NOAA deciding on how it wants to deal with that.
>
>
>
> > 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 don't know. But given the below definition taken again from 18-005r4, I'm wondering if someone who bothers enough to express coordinates in a ITRFxxxx datum would be really keen in seeing them degraded in a coarser ITRS ensemble. You could just use the WGS 84 ensemble for the same purpose I guess.
>
>
>
> """
>
> A Datum Ensemble is a construct to facilitate the merging of realizations of the same Terrestrial Reference System or Vertical Reference System for lower accuracy spatial manipulation. In this document, datum ensemble is a collection of two or more reference frames that are realizations of one Terrestrial or Vertical Reference System and which for all but the highest accuracy requirements may be considered to be insignificantly different from each other. Datasets referenced to the various realizations may be merged without change of coordinates.
>
> """
>
>
>
> > 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.
>
>
>
> With epsg10_part2:
>
>
>
> $ projinfo -k ensemble EPSG:6326
>
>
>
> WKT2:2019 string:
>
> ENSEMBLE["World Geodetic System 1984 ensemble",
>
> MEMBER["World Geodetic System 1984 (Transit)",
>
> ID["EPSG",1166]],
>
> MEMBER["World Geodetic System 1984 (G730)",
>
> ID["EPSG",1152]],
>
> MEMBER["World Geodetic System 1984 (G873)",
>
> ID["EPSG",1153]],
>
> MEMBER["World Geodetic System 1984 (G1150)",
>
> ID["EPSG",1154]],
>
> MEMBER["World Geodetic System 1984 (G1674)",
>
> ID["EPSG",1155]],
>
> MEMBER["World Geodetic System 1984 (G1762)",
>
> ID["EPSG",1156]],
>
> ELLIPSOID["WGS 84",6378137,298.257223563,
>
> LENGTHUNIT["metre",1],
>
> ID["EPSG",7030]],
>
> ENSEMBLEACCURACY[2.0],
>
> ID["EPSG",6326]]
>
>
>
> Even
>
>
>
> --
>
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>
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>
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