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By following the links on http://www.opengis.net/def/crs/ one can download identifiers/IRIs for various CRSes minted by the OGC. For many CRSes, there seem to be multiple identifiers, differing in what looks like a version number. E.g., for EPSG:2000:

http://www.opengis.net/def/crs/EPSG/0/2000
http://www.opengis.net/def/crs/EPSG/8.5/2000
http://www.opengis.net/def/crs/EPSG/8.9.2/2000
http://www.opengis.net/def/crs/EPSG/9.4.2/2000
http://www.opengis.net/def/crs/EPSG/9.5/2000
http://www.opengis.net/def/crs/EPSG/9.5.3/2000

Does anybody know what these version-like numbers refer to? The OGC GeoSPARQL standard uses IRIs with 0 (i.e., the first IRI in the above list), but does not explain what the 0 stands for.

  • 1
    It is the version number of the EPSG database. The newest one is 9.5.4 epsg.org – user30184 Oct 14 '18 at 19:16
  • @user30184 make that the answer – Ian Turton Oct 14 '18 at 19:57
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As commented by @user30184 the numbers in the resolver URL refer to the version number of the CRS family (EPSG, OGC or IAU). A special version indicator is written as "0". It indicates "no particular version" in general.

Source:

The resolver provides versioning of all definitions. To this end, CRS URLs - following common OGC policy - contain a version indicator. For example, in the following URL the "0" is such a version indicator:

http://www.opengis.net/def/crs/EPSG/0/4326

Version identification adheres to the following rules:

  • a concrete version number has a syntax of n.n.n where n is a nonnegative integer number following OGC versioning semantics (first digit change = possible backwards incompatibility; second digit change = backwards-compatible change; third-digit change = bug fix). For EPSG definitions, OGC adopts the IOGP version number unaltered (note that EPSG does not necessarily adhere to the OGC versioning semantics).
    • Example: http://www.opengis.net/def/crs/EPSG/8.9.2/4326
  • a special version indicator is written as "0". It indicates "no particular version" in general
    • Example: http://www.opengis.net/def/crs/EPSG/0/4326

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