Context massing — Task

Used in: Urban Design Visualisation (Example). Depends on: Building heights from elevation models (Task). Implementation: Context massing (Recipe - Blender).

Context massing is the Task of turning 2D building footprints with height attributes into a simple 3D model of the surrounding city: a 2.5D-to-3D extrusion (see 2.5D geometries, 3D geometries) at a deliberately chosen Level of Detail:

• LOD1 — each footprint extruded to its height as a flat-topped block.
• LOD2 — each footprint extruded to its eave height, with a roof form added on top.

Task Schema (tool-agnostic)

1. Decide the Level of Detail per building (decision point) — typically LOD2 only for the buildings that frame the subject and appear in close views, and LOD1 for the rest. Record the choice as an ordinal lod attribute.
2. Place the terrain (Operator, optional) — import the DTM as a surface, so the buildings stand on real ground. Worth it wherever the site slopes.
3. Extrude (Operator) — LOD1 buildings to height; LOD2 buildings to eave; each standing at ground.
4. Model the roof forms (decision point + Operator) — for each LOD2 building, choose the roof form (gable, hipped, pyramid, mansard, flat with parapet) from photographs or the site visit, and raise the ridge by roof_rise. About half a metre of accuracy is enough.
5. Apply one neutral material (decision point) — the context is the ground of the image, not the figure; see Visual hierarchy and figure-ground.
6. Clean the geometry (Operator) — merge duplicate vertices and make all faces point outwards, so the model survives export.

Output: a 3D context model, georeferenced, with the LOD of every building known.

Task Recipes (tool-bound)

• Blender + BlenderGIS: Context massing (Recipe - Blender)
• QGIS 3D view (LOD1 only, for a quick check): extrude the footprints by the height field in the layer’s 3D View properties.