Generalisation of 3d Building Models by Cell Decomposition and Primitive Instancing

The article presents a cartographic generalisation approach for 3D building models with regard to the thematic visualisation of urban landscapes. Based on our earlier work to utilise approximating planes for generating simplified cell decompositions of the input objects, a new extension is introduced that guarantees well-formed roof structures. This is accomplished by first creating a simplified 2D decomposition of the ground plan polygon and interpreting the original roof geometry in the area of the cell. A matching roof shape is then selected from a pre-defined set of primitives and the 2D cells are transformed into 3D accordingly. This kind of template matching allows for operators other than simplification. By modifying the primitives’ parameters, it is possible to alter the roof shapes in order to accentuate certain features or to reduce the number of repetitive features like shed, gabled and hipped roof parts. However, to avoid the combination of roof types that lead to inconsistent roof structures, a restriction of possible shapes based on neighbour cell information is applied. We also demonstrate how the described techniques can be used to simplify curved building elements which can be commonly found in important landmarks like churches and castles.