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opengeospatial / ogc-geosparql

Public Repository for the OGC GeoSPARQL Standards Working Group
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SpatialObject with local CRS #500

Open situx opened 8 months ago

situx commented 8 months ago

In GeoSPARQL, we can define WKT Literals not only for instances of Geometry, but also for instances of SpatialObjects.

For annotations on 3D objects which are not georeferenced we cannot point to a CRS using a URI in the WKT literal, because the EPSG registry or any other CRS registry does not include the coordinate (reference) system of the 3D model we are describing.

If we do not add a CRS URI to the WKT literal, GeoSPARQL assumes that the WKT Literal is encoded in the world coordinate system.

In the future, we can describe such a local CRS using a CRS ontology.

Currently, it would be a good way if we could define a URI that we could use to indicate that the WKT Literal includes local, non-georeferenced coordinates, for example:

"<http://www.opengis.net/ont/geosparql/localCRS> POINT(1 1)"^^geo:wktLiteral

What do people think about this?

situx commented 7 months ago

Use Case for this issue: https://situx.github.io/ars-lod/feat_e7fca8c2-4cde-42ce-ad27-3929df461a3e_target/index.html

situx commented 7 months ago

We could probably find an EPSG URL that describes a local SRS, that would solve this issue. I will post a fitting URL if I find one.

situx commented 7 months ago

@paulc-dstl There are cartesian coordinate systems in epsg.io, but none of the EPSG definitions provide axis units in millimetres, which is what we use in our models. So maybe that is not a solution here.

gatemezing commented 7 months ago

It would make sense. Some years ago, we defined a small ontology for geometric primitives with a use case in France. We used a property http://data.ign.fr/def/geometrie#crs to point to a specific local CRS, and in the case of the French IGN, it was http://data.ign.fr/id/ignf/crs/RGF93LAMB93. I am happy to realize that the data is still available and this query gives the list of the local CRS available for our use case.

mperry455 commented 7 months ago

Oracle Spatial predefines a set of local coordinate reference systems in various units of measurement. I assume other spatial databases do something similar. It would be good to have something standardized though.

gatemezing commented 6 months ago

Thank you @mperry455! We could create a page of such databases specific predefined list to better show the need of a standardized approach.

situx commented 6 months ago

As discussed in the group on 3rd April, the solution might be:

How does this sound to people? @gatemezing ?