LoD2BIM: A New Workflow for reconstructing and converting LoD2 Model to Information-rich IFC Model for Existing Building

Abstract. Numerous existing buildings in Germany lack corresponding BIM models. Advanced analysis and visualization purposes, including indoor navigation, energy demand simulations, and building materials recycling on these buildings presents significant challenges, as only Level of Detail 2 (LoD2) models provided by local housing authorities, along with architectural drawings and textual descriptions of the internal structures, are available. This paper proposes a semi-manual workflow, LoD2BIM, to facilitate the efficient reconstruction and conversion of existing building models, particularly transforming Germany's official 3D Building Models in LoD2 into comprehensive, information-rich IFC models using open-source software. Through the integration of BaseX and CesiumJS, the visualization, querying and extracting of one LoD2 model from CityGML file become easy and feasible. Central to the LoD2BIM workflow is Blender, it acts as the primary platform for model editing, reconstruction and conversion. Users can expediently rebuild and refine LoD2 models utilizing Blender’s visual interface and the tool floorplan to blender3d, based on floorplans or detailed written descriptions. New Blender add-ons are developed to streamline the model import and conversion process. The BlenderBIM add-on is also modified to facilitate the automatic batch assignment of mesh as IFC classes. This workflow not only showcases the reconstruction and subsequent conversion of CityGML models into IFC models but also illustrates the potential to act as an alternative to commercial software in Building Information Modeling (BIM) editing.