Discussion item: disjoint theoretical model / encodings cityGML

One of the key challenges around JSON encoding of CityGML v3 (like CityJSON might be) is the apparent disjoint in the development of the theoretical model and its physical encoding(s). Good practice suggests that validation of a theoretical data model through implementation and physical encoding can have a positive impact; making the model better. However, according to the current development plan of CityGML 3.0, the theoretical model will be going through the standards approval process before work starts on the creation of a physical encoding. As the SDW IG, do we have an opinion on whether implementation evidence is 100% essential in the standards process - even for conceptual models?

I raise the question here because this is relevant to CityJSON - one of the potential standardization candidates we're sheparding through it's incubation phase. Currently, CityJSON is being developed as an alternative encoding for CityGML 2.0. Basing it on version 3.0 has been considered, but @hugoledoux has concerns about the complexity of the proposed CityGML 3.0 data model from a developer's perspective. Wouldn't it be good to experience this by implementing an encoding, before the theoretical model is approved?

The CityGML SWG is an OGC entity, and will have their own discussion and resolution on this. However, as the SDWIG we could reach out to the CityGML SWG - if we think it's warranted and think having CityJSON is a good idea - to express our opinion. The SDWIG was created by OGC and W3C together to be a kind of intermediary between our communities - so it would fit our role.

For example, we could express to them that we see a need to define a web-friendly JSON encoding of the CityGML data model, that theoretical data models need implementations to challenge the design, and point out that we are in favour of an interactive process where data model and encoding of CityGML would be developed hand in hand instead of one after the other.

It would be good if we can get a conclusion (i.e. do we want to make such a statement as a group) ahead of the OGC TC in Stuttgart (mid-September). That way, we could communicate this to the SWG before they have their next face to face meeting.

Read the CityGML 3.0 development plan and the CityJSON incubation context described in the issue, then review the CityGML SWG’s position. No repository files or tests are identified. Done means reaching an SDWIG conclusion on whether to make a statement and, if so, agreeing on its message for the SWG.