An algorithm to facet curved walls in IFC BIM for building energy analysis

The automatic transformation of a Building Information Model (BIM) in Industry Foundation Classes (IFC) to a building energy model (BEM) demonstrates significant benefits on the improvement of efficiency and accuracy in a building energy modeling process. However, so far, building objects with curved surfaces in IFC models are not supported by existing transformation approaches as they only handle polyhedral geometries. This study presents an algorithm to automatically facet curved walls and convert their geometries into polyhedrons, so that they can be further processed by existing transformation approaches. In the process of faceting curved walls, geometric connections between each target wall and adjacent walls are detected and handled to maintain the connections in the results. Furthermore, the algorithm updates the geometries of relevant building objects, including straight walls connected to curved walls, openings (i.e., windows and doors) on curved walls and spaces enclosed by curved walls, based on the faceted geometries. This removes curved surfaces of these objects on the one hand, and maintains their geometric relationships on the other. Moreover, slabs with the curved surfaces are also faceted. This algorithm takes an IFC BIM that pertains to the model view definition Concept Design BIM 2010 as an input. It generates a new IFC BIM, in which all curved walls and relevant building objects are represented as polyhedral geometries with correct geometric relationships. A prototype application that implements the algorithm was developed to evaluate the performance of the algorithm with a simple building model and a complex real-world building model. In the results, all the curved walls were faceted, and all relevant straight walls, openings, spaces and slabs were correctly updated, which indicated that the algorithm worked as intended.