[PROJ] Synthetic Coordinate System

[Even Rouault]

ah ok I jumped too far to conclusion seeing DGGS mentionned. I read too 
quickly and am not familiar with HEX9.

Do you plan to submit your work to PROJ upstream?

I don't think it would make sense in the PROJ API to report the octant 
number in PROJ_COORD or in WKT, since it isn't needed to unambiguously 
qualify a location: just X and Y are sufficient, right ? So I don't 
really have a good suggestion to propose to you to be able to output the 
octant number. Perhaps there should be a way in the API to be able to 
report extra information, specific to a given projection, but that 
infrastructure doesn't exist.

Even

Le 22/03/2026 à 18:00, Ben Griffin via PROJ a écrit :
> Hi Even,
> Thank-you for your thoughts.
>
> As mentioned in my OP, the CRS isn’t a DGGS. It is a continuous CRS 
> that acts as the backbone for a DGGS.
> Consider, please, the net projections that are run using the current 
> system (albeit via the python module).
>
> https://raw.githubusercontent.com/MrBenGriffin/hex9/refs/heads/main/images/rhombus.jpg 
>
>
> Or
>
> https://raw.githubusercontent.com/MrBenGriffin/hex9/refs/heads/main/images/butterfly.jpg
>
> Those are projections under the CRS declared in the OP - they are not 
> representative of a DGGS.
> I’m not denying that the CRS is related to (and supports) DGGS - but 
> it is not a DGGS.
>
> The query concerned how best to capture a global coordinate that 
> involves an octahedral scheme - It feels like you picked up on 
> something else.
> One of the aspects of this, which to me feels the most obvious, is 
> that a CRS is continuous, while a DGGS is not.
>
> I feel that my position on this is defensible.
>
> Best regards
> Ben.
>
>> On 22 Mar 2026, at 16:47, Even Rouault <even.rouault at spatialys.com> 
>> wrote:
>>
>> Hi Ben,
>> I don't think PROJ API is the best fit for DGGS implementations. 
>> Probably https://github.com/ecere/dggal would be a better host (I 
>> haven't used it myself)
>> And AFAIK, WKT / ISO-19111 hasn't been designed with DGGS use cases 
>> in mind either.
>>
>> Even
>
>
>
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