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Hi Ron,I agree that a URN should only be an identifier. And one could argue that since they are URNs that all OGC URNs really are only identifiers. However, since the OGC CRS URN "naming" scheme is so detailed, parameterizable, and even compoundable, I think that if one cared (dared?) to parse the URNs one could figure out the definition of the CRS. So, I think for OGC CRS URNs, the line between identify and define is pretty fuzzy.
I also agree that it would be good to have a way to easily register commonly used, parameterized CRS. And a grammar in which the CRS can be defined. (Is GML up to this task? Or will it be once ISO 19111-1 and -2 are folded in?)
On the other hand, for less commonly used or somewhat unique CRS, making the definition available at some URL and using that URL to reference the CRS may be enough.
Ethan Ron Lake wrote:
I don't see how a URN can define a CRS - URN's are to be identifiers of resources and should resolve to the definition of a CRS. I think from this discussion it seems that there is a need to register a "CRS with parameters" (somewhat like a function signature) and then define a grammar by which this CRS' parameters are passed.R
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