Modelling of partly touching buildings

Especially in densly populated city centers, it often occurs that neighboring buildings partly or fully touch each other. In this case, the building's energetic behavior significantly differs from a free-standing building. Unfortunately, CityGML completely lacks a concept for "shared walls/roofs", and existing CityGML building models therefore do not represent closed building structures correcty. A single CityGML Building object is always bounded by exterior BoundarySurfaces (WallSurface, RoofSurface, GroundSurface).

In the Energy ADE, a ThermalBoundary object can be specified as "sharedWall". In reality, often only a part of a wall or roof surface is shared with a neighboring building, and the remaining part is facing the outside air. Thus, for transforming CityGML BoundarySurface into Energy ADE ThermalBoundary objects, a separation of the BoundarySurface geometry is needed, which is a time consuming and error-prone process. In most cases, it is much faster and much more robust only to calculate the size of the shared area. It is therefore proposed to add a numeric attribute to ThermalBoundary to either specify the absolute sharedAreaSize (type Area), or the ratio of shared area to total BoundarySurface area (sharedAreaRatio, type Scale).