type and version easier to identify that a file is a CityJSON file

[hugoledoux]

{
  "type": "CityModel",
  "version": "http://www.cityjson.org/version/0.2",
}

-->

{
  "type": "CityJSON",
  "version": "0.2",
  "schema": "http://www.cityjson.org/en/0.2/_downloads/cityjson-v02.schema.json"
}

[kenohori]

This fixes a big problem with CityGML, which is that a program can't know if a file is a CityGML file easily.

• Fetching schemas in URLs -> needs internet access, messy to program, takes time and links are often broken (or down), and for the truly paranoid, http links can be hijacked
• Comparing namespace strings with known URLs -> schema can be hosted somewhere else and have any filename
• Assuming that CityModel means CityGML -> non-CityGML files can use that name too

[clausnagel]

@kenohori The CityGML namespaces are fix and independent from a server location. So in fact it's quite simple to understand and check if a XML dataset contains CityGML elements.

[kenohori]

@clausnagel You are right. I was assuming that the namespace URIs were pointing to actual locations...

That being said, I still feel like this is a chance to correct a part of CityGML that doesn't make much sense. I've been trying to go to the addresses of various CityGML namespaces and many of them just point to 404 errors.

[clausnagel]

Namespace URIs are purely formal identifiers. They are not the addresses of a page, and they are not meant to be followed as links. (O'Reilly XML in a nutshell)

With that said, I agree that there nevertheless could be some content at the CityGML namespace URIs, such as the corresponding XML schema document. I can bring that into the CityGML group at OGC.

[hugoledoux]

done 032d46c0bb7d51f2848a0c04401e5fe6c49ef2af