Using OGC and W3C standards

Since its publication in 2016, RSM has a "Positioning" package dealing with spatial data. The Positioning package handles:

• Geographic reference systems;
• Linear reference systems (in the sense of ISO 19148);
• Coordinates expressed in the above reference systems.

The UML package "Positioning" was, from the beginning, aligned on OGC works. Given the intense activity of OGC on GeoSPARQL, it seems advisable to reference the current state of the OGC works and benefit from evolutions fuelled by the geographer community.

Overall guidelines for handling spatial data can be found in Spatial Data on the Web, a W3C publication.

GeoSPARQL status

Current version is 1.1. W3C offers a RDF data validator (SHACL file) matching that version.

Necessary adaptations?

In the railway context, we particularly need:

• slopes (hence: altitudes)
• linear positioning

GeoSPARQL might ultimately support 6 coordinates (X,Y,Z,M,T,L), as per issues published in version 2 milestones repository. Z stands for altitude, M for [linear] measure, and L for detail level which might be welcome in our case (facilitating the representation of networks at different levels of detail).

These general orientations should make us feel comfortable in embracing GeoSPARQL as the standard for spatial data representation in the context of the CDM. However, "quick fixes" or provisional choices from our side might be needed for:

• representation of coordinate reference systems: in the OGC community, the debate goes on about integrating the CRS reference in the string representing the coordinate value, or referencing it explicitly (so it can be exploited by reasoners), etc.;
• representation of linear coordinates matching kilometric points in the way they are currently used by railways, a subject covered by RSM Positioning package;
• ...