Semantic Mapping: an Ontology Engineering Method for Integrating Building Models in Ifc and Citygml

One of the main problems facing 3D city modelling applications is lack of interoperability among various Building Information Models (BIM) and Geographic Information Systems (GIS) models. CityGML (representing a wide range of 3D urban objects) and IFC (representing a very detailed semantic model for buildings) are considered the most prominent semantic models in GIS and BIM, respectively, today. When integrating the two models, substantial difficulties may arise in transforming information from one to the other. Professionals from both domains have made significant efforts to integrate CityGML and IFC models for seeking useful common applications. However, most of these efforts use a unidirectional method (mostly from IFC to CityGML) for a conversion process. As a formal mapping between both domains is required, researchers have suggested that harmonising semantics is the best approach for such integration. In this paper, we focus on semantic integration of IFC and CityGML building models for bidirectional conversion. Both IFC and CityGML use different terminologies to describe the same domain. Additionally, there is a great heterogeneity in their semantics. This paper, therefore, propose more expressive reference ontology between IFC and CityGML semantic models and an intermediate Unified Building Modelled (UBM) is built. The result of the paper contributes, through the reference ontology, towards a formal mapping between IFC and CityGML ontologies that allows bidirectional conversion between them. It also contributes towards a design of meta-standard for 3D city modelling that can support applications on both domains.