OGC requests comment on candidate standard: Geographic Information

4 October 2018: The Open Geospatial Consortium (OGC) seeks public comment on the candidate standard jointly developed by the International Organization for Standardization (ISO) and the Open Geospatial Consortium: “Geographic Information - Well-Known Text representation of coordinate reference systems” (CRS WKT).

Well-Known Text (WKT) is used as a compact machine- and human-readable representation of geometric objects and coordinate reference information, as specified two decades ago in the OGC and ISO standard “Geographic information – Simple feature access – Part 1: Common architecture.” This standard included a capability for describing coordinate reference systems as text. The original CRS WKT was subsequently extended in numerous incompatible ways, and had thus become non-interoperable.

In 2015, OGC and ISO adopted a major revision of the CRS WKT specification that allowed a rigorous description of coordinate reference systems and coordinate operations in WKT, following the data model described in OGC Abstract Specification, Topic 2, which is also published as ISO 19111:2007 - Spatial referencing by coordinates. However, OGC AS Topic 2 and ISO 19111:2007 have recently been revised. The revision of CRS WKT tracks the changes made to the CRS data model.

The new edition of the CRS WKT standard aligns with the coordinate reference system model described in ISO 19111:2018. Specifically the changes from the 2015 edition are:

• Extension to describe dynamic geodetic and dynamic vertical coordinate reference systems - coordinate reference systems in which coordinate values on the surface of the earth change with time due to tectonic deformation including a time reference (coordinate epoch) for coordinates referenced to a dynamic CRS;
• Extension to describe geoid-based vertical coordinate reference systems;
• Extension for the description of datum ensembles, groups of realizations of one terrestrial or vertical reference system that for low accuracy purposes may be merged ignoring coordinate transformation;
• A rigorous description of temporal coordinate reference systems;
• The removal (deprecation) of image coordinate reference systems; and
• The remodelling of scope and extent information.

This latest edition of CRS WKT cancels and replaces the 2015 version (also published as ISO 19162:2015), which has been technically revised. The candidate CRS WKT standard was prepared by the OGC CRS Standards Working Group and Technical Committee ISO/TC 211 Geographic information/Geomatics.

The candidate Well Known Text Representation of Coordinate Reference Systems standard is available for review and comment on the OGC Portal. Comments are due by 5th November 2018 and should be submitted via the method outlined on the CRS WKT Standard’s request page.