Hi, not so short mail about a question that some people have been posing me lately, on why GeoServer is not using the urn:ogc:... form for srsName (and it's using the old experimental urn:x-ogc one instead).
When WFS 1.1.0 specification came out, May 3 2005, they said (citing from page 36): --------------------------------------------------------------------------------------------------------------- Any valid URI value can be assigned to the srsName attribute. However, in order to enhance interoperability, a web feature service must be able to process srsName attribute values with the following format models: • EPSG:<EPSG code> • http://www.opengis.net/gml/srs/epsg.xml#<EPSG code> • urn:EPSG:geographicCRC:<epsg code> ---------------------------------------------------------------------------------------------------------------- When it was time to create the cite tests and the reference implementation they however made us implement the urn form following the syntax of the time: urn:x-ogc:def:crs:EPSG:4326 where the x standard for "experimental" as IANA still did not have the occasion to approve its official usage. A June 2008 newsletter from OGC reports the IANA approving the "ogc" NID as news, meaning "ogc" has been valid form for the past 2.5 years. The most recent document from OGC talking about the urn syntax is: http://portal.opengeospatial.org/files/?artifact_id=30575 from January 2009 which reports the following syntax (mind the double column), page 39: ----------------------------------------------------------------------------------------------------------------- Specializing the above, the URN value for an anyURI that references one object in the European Petroleum Survey Group (EPSG) database should have the form: urn:ogc:def:objectType:EPSG::code ... The URN value for CRS 2984 is: urn:ogc:def:crs:EPSG::2984. ---------------------------------------------------------------------------------------------------------------- Now, in my opinion even today someone should be able to read the WFS spec and implement it as is (standards should not morph over time, shouldn't they), however I don't think any server implements WFS 1.1.0 as originally mandated. Most use the urn:x-ogc form. Some use urn:ogc. What about us, what shall we do? Eventually we'll have to switch to the urn:ogc form as we implement newer versions of the standards which, hopefully, are going to be a tad more explicit about it, and even more hopefully, a tad more stable. In fact WFS 2.0 says (page 33): ------------------------------------------------------------------------------------------------------------- Servers that implement this International Standard shall be able to process srsName attribute values using the following format model: • urn:ogc:def:crs:EPSG::<EPSG code> [(see OGC OGC 07-092r1)] In this format model, the value <EPSG code> is a placeholders for actual EPSG code values. EXAMPLE srsName="urn:ogc:def:crs:EPSG::26986” -------------------------------------------------------------------------------------------------------------- Finally a bit of clarity. So, for WFS 2.0, when and if we implement it, we're going to use the form suggested by the latest urn best practice. Cool. What are we going to do with WFS 1.1 then? Make it a special case so that we continue to use urn:x-ogc, to avoid changing our syntax below the client feet, or should we follow suit, use urn:ogc:def:crs:EPSG::<EPSG code> also in WFS 1.1, get simpler code, and redirect complaints about the change to OGC? Cheers Andrea ----------------------------------------------------- Ing. Andrea Aime Senior Software Engineer GeoSolutions S.A.S. Via Poggio alle Viti 1187 55054 Massarosa (LU) Italy phone: +39 0584962313 fax: +39 0584962313 http://www.geo-solutions.it http://geo-solutions.blogspot.com/ http://www.linkedin.com/in/andreaaime http://twitter.com/geowolf ----------------------------------------------------- ------------------------------------------------------------------------------ Centralized Desktop Delivery: Dell and VMware Reference Architecture Simplifying enterprise desktop deployment and management using Dell EqualLogic storage and VMware View: A highly scalable, end-to-end client virtualization framework. Read more! http://p.sf.net/sfu/dell-eql-dev2dev _______________________________________________ Geoserver-devel mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/geoserver-devel
