CityGML Data Preparation for Thermal Building Simulation at District Level

More and more cities and countries around the world are providing CityGML LoD2 (Level of Detail) building models, either commercially or as open data. Although these models divide the outer shell of buildings into walls, roofs and floor areas, most of the input parameters required for thermal simulation are missing. In addition, CityGML allows different modeling approaches, so that the geometry of the models must also be checked, the neighborhood relationships analyzed and the models modified if necessary.The present article describes the analysis of CityGML models regarding the model structure and geometry. This includes checking the buildings geometry to be a closed volume, considering neighboring buildings as shading objects, and enriching building physics parameters depending on the year of construction. The geometry processing for buildings with several building parts, the calculation of shared surfaces in the case of closed constructions and the determination of neighboring buildings are described in detail. The enrichment of the building models with building physics and building usage parameters is introduced. All concepts are implemented in software and tested with the EnergyPlus simulation kernel. The software, which can be used to convert basic CityGML models into comprehensive CityGML Energy ADE models, will be available to the community as freeware.