CityGML (OGC 3D City Model)

CityGML is an OGC standard for semantic 3D city models. It differs from an ordinary 3D mesh in that a building here is not just a set of triangles but an object with meaning: it has walls, a roof, a height, a floor count and a function. That is exactly why the format took root in urban planning and city computations rather than in visualization.

A map is exported to CityGML when a 3D city is needed for analysis: calculating insolation and solar panel potential, modeling noise, assessing density and building volumes, loading into a city database. Such tasks need attributes, not a pretty picture.

The output is a single CityGML 2.0 XML file: buildings at LOD1 detail, that is, as closed volumes extruded from OSM outlines by height or floor count, with correctly oriented floor, wall and roof faces. Every building records its measured height, the number of floors and a function code derived from OSM tags. Coordinates are WGS84 (EPSG:4326) by default, and the coordinate system is stated in the file itself.

Pitched roofs, facade details and interior rooms are absent from LOD1 by definition — this is the level of boxes. More detailed models require source data that simply does not exist in OpenStreetMap.