I am using FME to convert my CityGML data into GeoJSON format to import it my 3D mapbox application.

Mapbox uses extrusions to visualize 2D GeoJSON objects in 3D with their height values. (https://docs.mapbox.com/mapbox-gl-js/example/3d-extrusion-floorplan/)

However when I convert my CityGML data in FME ( CityGML reader > GeoJSON writer ), it results me a multiline object.

enter image description here

Is there any way to export the data in multipolygon format, maybe with a transformer in FME?

  • use the 2DForcer to remove the lines with z values.
    – Mapperz
    Oct 24, 2023 at 21:19
  • Then AreaBuilder to build the polygons.
    – Mapperz
    Oct 24, 2023 at 21:22
  • Thanks for the answer. It worked however this time I lost LoD2 features. When I import the data into MapBox and to visualize, buildings do not have the roof features now... Oct 25, 2023 at 13:01
  • you have to ask another question, your changing the end goal of the question. you will need to keep 3d values? have a look a mapbox vector tiles docs.safe.com/fme/2020.1/html/FME_Desktop_Documentation/…
    – Mapperz
    Oct 25, 2023 at 13:28

1 Answer 1


In FME Form Workbench, use the 2DForcer Transformer to convert the 3D objects to 2D. More information about the transformer is available here. Then add the AreaBuilder transformer to build polygons from the line. See picture below:

enter image description here

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