[PROJ] Synthetic Coordinate System

[Martin Desruisseaux]

Hello Ben

Le 23/03/2026 à 21:21, Ben Griffin via PROJ a écrit :
> As I understand it - and I am happy to be corrected,  it appears that you are confirming that there is not (yet) an
> agreed standard as to what a DGGS should be in ISO terms.

There is an ISO standard for DGGS, which is ISO 19170-1 at 
https://www.iso.org/standard/32588.html. The same standard is available 
for free on the OGC web site at 
https://docs.ogc.org/as/20-040r3/20-040r3.html. This is a joint OGC/ISO 
standard, like ISO 19111 which is identical to "OGC Topic 2" except for 
the cover and formatting.

However, PROJ's C++ API is derived from ISO 19111, and that standard has 
not been designed for DGGS. There is no plan to adapt ISO 19111 to DGGS, 
at least in the current ISO 19111 revision work. If PROJ wanted to 
introduce an API for the referencing part of DGGS, ISO 19112 may be a 
better model. I just saw that ISO 19170 references ISO 19112 in its list 
of normative references, so it seems that there is some agreement about 
its pertinence. We have used ISO 19112 years ago as an API for Military 
Grid Reference System (MGRS) and it worked well. My impression is that 
the use of ISO 19112 for modelling an API for DGGS during the OGC 
Testbed this year gave good results as well.


> My work - Hex9 - straddles both standards cleanly:
>    - The projection (continuous CRS) — ISO 19111
>    - The addressing system (H9 cell hierarchy) — ISO 19112

Yes, I think that this is the way that it has been implemented in at 
least part of the OGC Testbed. The Testbed reports should be published 
later this year normally, maybe in autumn.

     Martin

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