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I’m exporting LoD 3 models from FME to CityGML and the files blow up in size. FME writes every Appearance on each triangle and also makes a separate position list for each triangle, everything becomes separate XML elements, so the markup absolutely dominates the file. I think CityGML should be able to store things more compactly at the object level, but I don’t see a way to make FME do that automatically. Every triangle whould not need its own position list right? I have thome different thoughts on the matter:

  • Can FME group or merge geometries/appearances to cut down the markup?

  • Can ImplicitGeometry be used effectively without creating a complex monster workspace?

  • Is CityJSON fundamentally a better route? (I’ve heard numbers around ≈ 1/6 of the file size.)

  • Are there external tools that post-optimize a CityGML without losing semantics?

Concrete tips, transformer setups, or example workspaces are very welcome.

​@virtualcitymatt 

Hello ​@karnil, texturing requires a link from a face to the appropriate appearance. There might be a transformer-based solution where we merge those into a single appearance before writing to CityGML. Suspect the SharedItem transformer set would be needed to do this. The writer should support shared instances, but there is often some configuration required to set that up before writing. I've found an article where a similar process is demonstrated for Sketchup. A workflow for CityGML would be similar, but you would need to write the to the correct geometry structure. Hope this helps, Kailin.

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