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
