STEP (ISO 10303 CAD Exchange)

STEP (ISO 10303) is the international standard for model exchange and the common language of heavy CAD: SolidWorks, CATIA, Inventor, Creo and the free FreeCAD read and write it as standard. Unlike mesh formats, STEP stores real solids with faces and edges, so the model can be cut, merged and measured like an ordinary part.

Buildings from OpenStreetMap in STEP are needed where the city ends up in an engineering assembly: a stand or a model for milling, tooling, fitting equipment into existing development, a three-dimensional site scheme in an environment where everything else already lives in STEP.

What you get: a file with an assembly of solids where each building is extruded into a prism by its height (the height tag, otherwise the number of floors, otherwise 9 meters by default). The roofs are flat — this is volumetric massing, not an architectural model. The origin is the center of the chosen area and the coordinates are metric; after the import check the units in your CAD so that the assembly scale matches what you expect.

The default schema is AP214, the most compatible one; if needed, the file is built to the newer AP242. Roads, water and other flat layers do not get into STEP: the export is volumetric and takes only the buildings.