Triply Use Case 3: Applying a 3D CRS

[wouterbeek]

Triply Use Case 3: Applying a 3D CRS

Description

In GeoSPARQL, I can specify the CRS for my geometry serializations in GML or WKT literals. For WKT, GeoSPARQL specifically extended the serialization format, to be able to include a CRS IRI at the start of the literal. If GeoSPARQL will include 3D objects (see #583), it will depend on the serialization format whether it will be possible to specify the CRS in that format. If the format does not yet provide support for specifying the CRS, a modification of the serialization format -- similar to what was done for WKT -- may be necessary.

Actor

• Data Expert (who may not be a Geodata Expert)

Preconditions

• I have 3D data, but not yet in GeoSPARQL.
• I know how to store 2D data in GeoSPARQL.
• I have found a CRS IRI that works for my 3D data (see Triply Use Case 13: Finding a 3D CRS #599).

Postconditions

• I have stored all 3D data as GeoSPARQL in my triple store, with the CRS IRI that supports 3D, as recognized by other triple stores.

Steps

1. I have 3D data about buildings in The Netherlands.
2. By using the approach described in Triply Use Case 13: Finding a 3D CRS #599, I have found CRS IRI http://www.opengis.net/def/crs/EPSG/0/7415 that I can use for my data.
3. By using the approach described in Triply Use Case 1: Support for GLTF and other 3D formats #583, I can serialize my 3D object in a literal.
4. By using the approach described in this current issue (see the "Description" section), I can include the CRS IRI from step 2 into the literal from step 3.
5. My 3D data is now represented with the correct CRS. When somebody else queries my dataset, they are able to interpret my CRS IRI.

Related issues

An alternative to moving the CRS IRI into the 3D object literal, is to have a dedicates CRS property. This alternative CRS specification approach is not specific to 3D support, and is independently addressed in #82 and #419.

[FransKnibbe]

I read this use case as illustrating the need for a CRS ontology, and through that, an official Linked Data based CRS registry. This is the topic of https://github.com/opengeospatial/ontology-crs. 3D CRSs do exist. For official data in the Netherlands, that would be RD+NAP, with its OGC IRI being http://www.opengis.net/def/crs/EPSG/0/7415. But if you don't know this beforehand, it is difficult to find applicable 3D CRSs for 3D models.

Another aspect is applying the CRS IRI, once it is found. I think that does call for a inCRS or hasCRS property (see issue #82 and issue #419). For 3D geometry this is especially needed, because 3D geometry formats typically are not geographical, and have no built-in way of referencing a CRS.

[situx]

Agreed. This is a CRS ontology need and pertains to the issues @FransKnibbe mentioned

[wouterbeek]

@FransKnibbe and @situx Thank you for your feedback. I have now split this issue into applying a 3D CRS IRI (this issue), and finding a CRS IRI (issue #599). Let me know in case I can make additional improvements to either issue.