GML CodeList questions

[VladimirAlexiev]

@rob-metalinkage @avillar, and @pzaborowski @FrancescaNoardo, cc @nataschake I'm looking at an example and trying to figure out how to decode CodeList values

https://github.com/opengeospatial/CityGML3.0-GML-Encoding/blob/main/resources/examples/Building/Building_CityGML3.0_LOD2_with_several_attributes.gml#L269 has this:

      <bldg:function>31001_9998</bldg:function>
      <bldg:roofType>3100</bldg:roofType>

• GML Conceptual Model https://docs.ogc.org/is/20-010/20-010.html#RoofTypeValue-section just says there is a codelist RoofTypeValue
• GML Encoding Standard https://docs.ogc.org/is/21-006r2/21-006r2.html has 25 occurences of "rooftype", including
  1. <bldg:roofType>3100</bldg:roofType>, <bldg:roofType>1030</bldg:roofType>
  2. <bldg:roofType>Flat</bldg:roofType>, <bldg:roofType>Saddle</bldg:roofType>: I think that it's inconsistent to use both codes and English words in the same element!
  3. https://docs.ogc.org/is/21-006r2/21-006r2.html#_gml gives example of defining 1000->flat roof, 3100->saddle roof in XML
     1. And refers to https://www.ogc.org/citygml/3.0/codelists/gml/rooftypes, which is Page not found
  4. https://docs.ogc.org/is/21-006r2/21-006r2.html#_comma_separated_values_csv_structure gives a simple understandable CSV, but only as an example

Does that mean there's no registry of the 130 or so GML codelists, and so each CityGML file uses codes that are not standardized anywhere?

[VladimirAlexiev]

Similar for bldg:function: the Encoding standard gives some examples that use code vs English (inconsistent). There's also a hierarchical nomenclature. It doesn't give any global URL where this codelist could be looked up.

• <bldg:function>Office</bldg:function>
• <bldg:function>Living</bldg:function>
• <bldg:function>1000</bldg:function>
• <bldg:function>99999_1001</bldg:function>

[rob-metalinkage]

"<> enumerates the valid attribute values. In contrast to Enumeration, the list of values is open and, thus, not given inline the CityGML schema. The allowed values can be provided within an external code list. It is recommended that code lists are implemented as simple dictionaries following the GML 3.1.1 Simple Dictionary Profile (cf. chapter 6.6 and chapter 10.14). "

So yes - there is a requirement for some governance of this to achieve interoperability! We need to explore practices deeper