The article presents a novel approach for the automatic generalisation of 3D building models with regard to the cartographic visualisation of urban landscapes. Building objects are geometrically simplified for the purpose of levels of detail generation to speed up rendering and to improve the perceptibility on small displays commonly found in mobile devices. Generalisation is realised in a process similar to half space modelling. Approximating planes are determined from the original building model. These are then used as space dividing primitives to remodel the object with a façade and roof structure of simpler shape.