[PROJ] Problems with EPSG:1236 - (AGD84 to WGS 84 (2))

[Torill Kjøsnes Gabrielsen]

Hi,

I´m developing a transformation api using PROJ9 and pyproj. We´ve done a
broad test of different transformations, and we have some issues which I´m
not able to understand.

Going from AGD to WGS 84, I find 5 available transformations in the
"coordinate_operation_view" in proj.db internal database:
EPSG:15785, AGD84 to WGS 84 (9)
EPSG:1236, AGD84 to WGS 84 (2)
EPSG:1109, AGD84 to WGS 84 (1)
EPSG:1669, AGD84 to WGS 84 (7)
EPSG:15789, AGD84 to WGS 84 (8)

Asking for the available transformations using 'projinfo -s EPSG:4203 -t
EPSG:4326 -o PROJ --spatial-test intersects' i get only 4:
DERIVED_FROM(EPSG):15785, AGD84 to WGS 84 (9), 2.9 m, Australia -
Queensland, South Australia, Western Australia, federal areas offshore west
of 129°E.
EPSG:1669, AGD84 to WGS 84 (7), 3.0 m, Australia - Queensland, South
Australia, Western Australia, federal areas offshore west of 129°E.
EPSG:1109, AGD84 to WGS 84 (1), 4.0 m, Australia - Queensland, South
Australia, Western Australia, federal areas offshore west of 129°E.
EPSG:15789, AGD84 to WGS 84 (8), 5.0 m, Australia - Queensland, South
Australia, Western Australia, federal areas offshore west of 129°E.

EPSG:1236, AGD84 to WGS 84 (2) is missing. This has an accuracy of  5, same
as EPSG:15789.

We use  transformer.TransformerGroup to fetch the available transformations
in our code, and I get the same results even If l set minimum accuracy to 5
or 10.
I´ve also tried to set the AreaOfInterest to the transformation Extent, but
still the same result.

Question 1:
Is this to be considered as a bug, or is it a logical explanation? I have a
couple of more similar examples.

Question 2:
On the other side, I am able to get the pipeline going from 4203 to 4326
(AGD84 to WGS 84 (2)). by using:
Transformer.from_pipeline(f"urn:ogc:def:coordinateOperation:EPSG::1236")

As the API I develop delivers transformation pipelines in both directions,
where coordinates are not always given(optional), It's easy to get the
pipeline in both directions using TransformerGroup.

I am considering using the urn definition + Transformer.from_pipeline
instead, but struggle to find a way to get the reverse pipeline (from
EPSG:4326 to EPSG:4203 (EPSG:1236)).
Someone who can help on how this can be done?

Thanks and regards,
Torill Kjøsnes Gabrielsen
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