[PROJ] Inconsistent WKT1 output

[Even Rouault]

Javier,

yes the conventions are different. PROJ follows (mostly) 
https://docs.ogc.org/is/18-010r7/18-010r7.html#37:

"""

Identifier is an optional attribute which references an external 
description of the object and which may be applied to a coordinate 
reference system, a coordinate operation or a bound CRS. It may also be 
utilised for components of these objects although this is recommended 
only for the following circumstances:

  * coordinate operation methods and parameters;
  * source and target CRSs when embedded within a coordinate
    transformation or a concatenated coordinate operation;
  * source CRS when embedded within a point motion operation;
  * individual coordinate operations embedded within a concatenated
    coordinate operation;
  * base CRS when embedded within a derived CRS (including projected CRS);
  * source CRS, target CRS and abridged transformation when embedded
    within a bound CRS;
  * individual members of a datum ensemble.

"""

So if the top object has an ID, generally its sub-objects won't have 
their IDs emitted, except the above exceptions (I see we don't emit ids 
for individual members of a datum ensemble. I remember that those 
exceptions have been in flux, so probably this was changed after this 
was implemented in PROJ. anyway I would be inclined to to change that 
now, as datum ensemble are sufficiently verbose as they are)

See 
https://github.com/OSGeo/PROJ/blob/bafe3a91901b4515a8017a6b019e43edb74a0764/src/iso19111/io.cpp#L485 
for the logic. It could be tuned to whatever people fancy for their WKT 
(there's actually a predefined WKT2_SIMPLIFIED variant where there are 
no ids on projection methods and parameters), since the omission of id 
is a convention, and not a hard rule

There's always a bit of "tension" about the appropriate verbosity of 
WKT: should it be a full dump of the (extract of) the underlying 
geodetic database or just a summary with the appropriate level of detail.

Even

Le 29/03/2023 à 18:46, Javier Jimenez Shaw a écrit :
> Hi
>
> Comparing some WKT1 strings I found something strange. If I ask for 
> WKT1_GDAL based on an EPSG code, I get the authorities of the 
> spheroid, prime and the datum. However, If I use an WKT2 as the input, 
> they are not there.
>
> Is that expected?
>
> > projinfo -o wkt1_gdal EPSG:6318
> WKT1:GDAL string:
> GEOGCS["NAD83(2011)",
>     DATUM["NAD83_National_Spatial_Reference_System_2011",
>         SPHEROID["GRS 1980",6378137,298.257222101,
>             AUTHORITY["EPSG","7019"]],
>         AUTHORITY["EPSG","1116"]],
>     PRIMEM["Greenwich",0,
>         AUTHORITY["EPSG","8901"]],
>     UNIT["degree",0.0174532925199433,
>         AUTHORITY["EPSG","9122"]],
>     AUTHORITY["EPSG","6318"]]
>
> > projinfo -o wkt1_gdal "$(projinfo EPSG:6318 -o wkt2_2019 -q)"
> WKT1:GDAL string:
> GEOGCS["NAD83(2011)",
>     DATUM["NAD83_National_Spatial_Reference_System_2011",
>         SPHEROID["GRS 1980",6378137,298.257222101]],
>     PRIMEM["Greenwich",0],
>     UNIT["degree",0.0174532925199433,
>         AUTHORITY["EPSG","9122"]],
> AUTHORITY["EPSG","6318"]]
>
> Thank
>
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