null EPSG codes for complex coordinate systems

[hobu]

Current version of the extension states that proj:epsg is REQUIRED. I'm indexing a bunch of elevation content that is in compound coordinate systems for which there isn't a simple EPSG code. I can definitely provide a very complex proj:projjson object for the item, but boiling that down to a simple EPSG code that represents the entire thing is a fools' errand.

null for proj:epsg is allowed, but that section of the text doesn't tell the consumer what they should do if it is null.

Could that section also include something like:

For data with a null proj:epsg for which there is a coordinate definition, it can be provided in proj::wkt2 OR proj::projjson. Clients can prefer to take either, although there may be discrepancies in how each might be interpreted.

[m-mohr]

That makes sense and I think that is indeed what was meant originally. Do you agree, @matthewhanson ?

[emmanuelmathot]

Indeed, that the initial. Typically satellite imagery data in their own acquisition reference.