Carsten Roensdorf of the Ordnance Survey in Great Britain, and Others, Answer Questions about the OGC’s CityGML Standard

By Nora Parker

Question (Q): Are there explicitly defined criteria for qualifying city 3D models?

Answer (A): The standards document suggests a number of quality criteria. We are working on more, particularly template tender documents, though these are probably more useful in a national rather than international context.

Q: Will advertising be incorporated into the city modeling?

A: Not through the standard as such, as this doesn't make sense or at least I can't see this right now.

However, every owner/publisher of a CityGML city model can decide if they want to include advertising into their front-end solution. Most of the CityGML applications to date have been more on the professional use side, such as environmental analysis, though we have also seen a lot of use in promoting events such as marathons, and there is probably a lot of potential in this.

Q: How were CityGML XSDs derived from the shown UML model? Is the UML model available to the public?

A: The UML was done in Visual Paradigm, though we want to move to Enterprise Architect. If you are interested in the Visual Paradigm files I can see if we make these available - they are currently used as tools to generate the diagrams only.
We are working on the automated derivation of the XSDs from the UML and have tentatively planned to discuss the issues around this at a workshop, which is most likely to be held in Bonn, Germany in April or May this year. Please get back to me if you would like to be involved in the discussion.

Q: How does CityGML relate to the new IndoorGML initiative in OGC?

A: IndoorGML is a separate development. It has been designed to work very well with CityGML as one of the inputs/constrains that go into the dual-graph that is used for routing. IndoorGML has been developed by the same people who developed CityGML, but the drivers were different, as IndoorGML also had to allow a number of other data inputs. Apparently you can feed room information into IndoorGML in other ways than CityGML.

You don't have to start with 2D GIS data such as building footprints, though since a lot of this data exists, a lot of municipalities have decided to use this as a starting point. It seems that the geospatial data is much more strongly defined in the datasets in Europe. I realize that this doesn't help you directly, but there is huge potential in utilizing CityGML to build better datasets on the geospatial side in the U.S. as well.


Q: I work for the GSA and we are standardizing on IFC. I would love to hear some of the challenges faced with conversion of data from IFC to CityGML. Also, it seems that one should start with 2D GIS to build CityGML, but what if we want to bring together IFC converted BIMs on a very weakly-defined geospatial data subset?

A: If one searches “ifc citygml conversion,” there are many presentations and articles on this topic See

Also, check out Carl Reed's delicious references:

A whole book chapter is dedicated to the topic of IFC to CityGML conversion.


Q: Can the generics module be extended?

A: I would be interested in what your use case is for extending the generics module as an ADE. As I said in the webinar, this is possible, but I would only go this way if you have a lot of disparate information that you want to easily include but where you want to give some additional structure. Generics was intended as a very easy extension mechanism and I would generally advise to use it as this. We will happily consider any suggestions you may have in the OGC CityGML Standards Working Group (SWG).

Q: Can you please show how it actually works? Give a demo?

A: Have a look at the CGB thread in OWS4 – a demo is available there.

Published Wednesday, March 14th, 2012

Written by Nora Parker

Published in


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