hi IMHO WKT or SRID's are fine. I appreciate the principle of self-description, so WKT would do be better suited.
http://en.wikipedia.org/wiki/SRID http://en.wikipedia.org/wiki/Well-known_text#Spatial_reference_systems I see this as well worn ground. EPSG, GDAL, Proj, ESRI and others can use WKT. Adopting an existing framework for this meta-data would seem to be a good option. regards pk -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Bentley, Philip Sent: Monday, 3 October 2011 7:50 PM To: Ethan Davis; CF metadata Subject: Re: [CF-metadata] Question on WKT representation of CRS Hi Ethan, All good questions! I've provided some brief - and probably inadequate - responses inline. I've been working up an initial (reasonably concise) proposal covering this topic, which potentially I could upload to the CF trac site later this week. I guess it depends on whether folks would prefer discussions to happen against a dedicated trac ticket, or else here on the mailing list? Obviously if the preliminary sentiment is that use of WKT is a non-starter, then that'll save me the trouble of submitting the proposal :-) Cheers, Phil > -----Original Message----- > From: [email protected] > [mailto:[email protected]] On Behalf Of Ethan Davis > Sent: 01 October 2011 07:49 > To: CF metadata > Subject: [CF-metadata] Question on WKT representation of CRS > > Hi Phil, all, > > This latest round of discussion around using CRS WKT reminded > me of a few questions: > > 1) How easy is it to form a WKT that has good > interoperability between different client libraries? Not being familiar with the internals of the various libraries I'm not well placed to judge. The authors of those libraries may wish to chime in with their 2c worth. > 2) Are there good specification documents for WKT? > > I believe the relevant OGC document is OGC 06-103r4 which can be found > here: http://portal.opengeospatial.org/files/?artifact_id=25355 There's that definition. And also a more recent one in OGC document 01-009 -- Coordinate Transformation Services (at which point it became known as CS WKT). As yet I've haven't really been able to establish exactly who - if anyone - owns/maintains the WKT specification. From my former days in the oil and gas exploration industry I recall it first appearing under the (proprietary) auspices of POSC, long before open source was de rigeur! But that consortium no longer exists AFAICT. Hence it [the WKT syntax] seems to have just drifted into the public domain. > But in the wild, there seem to be lots of variations in > projection names and parameter names. There's even variation > between them in the OGC spec mentioned above and the EPSG data base. IMHO, some of the WKT examples in the OGC specs (and elsewhere) contain errors, or at least deviations from the spec. Personally I consider the EPSG (now OGP) registry to be the source of truth for CS/CRS entity names and, where relevant, values. There is no other viable alternative that I am aware of. > 3) Given that, is CRS as WKT well enough defined so that > providing a place for it in CF get us the interoperability we want? I don't think anyone would claim that WKT, on it's own, represents an interoperability silver bullet. But the received wisdom (as disseminated on the CF mailing list!) seems to be that it would offer a very handy adjunct to existing metadata descriptors. > Or, Phil, would the proposal you have in mind go into more > detail (or add to) the OGC spec? That wasn't my intent. > 4) One last question. The OGC CRS WKT specification is less > than two pages of EBNF (without a lot of explanation). How > far is the current CF grid mapping spec from complete > coverage of the CRS WKT? Prime meridian and some units? That I can't answer I'm afraid. As you know, there have been a number of posts to the CF mailing list over recent months where people have stated that having a WKT attribute would allow them to provide a more complete/accurate definition of the coordinate system(s) used in their netCDF files. I would hope that those same people would be able to provide those examples as support for a putative CF proposal regarding use of a WKT attribute. Regards, Phil _______________________________________________ CF-metadata mailing list [email protected] http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata _______________________________________________ CF-metadata mailing list [email protected] http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
