The CityGML standard in GIS community and the IFC standard in BIM are popular in both industry and academic world, because they are composed of rich geometry and semantics representing a building from outdoor to indoor. Therefore, they are the solid foundation of the data model for IMM.
However, the two standards differ in many aspects such as the means of geometric representation and taxonomies. As the available datasets are surging, they have to be supported and integrated for IMM applications. Moreover, the spaces that are essential for IMM are not well defined in these models and it is not trivial to extract this information fully automatically because of the inconsistences during modelling, which is also to be tackled.
For example, BIM was proposed in the field of building design as the international industry semantic standard (NBIMS-1.0, 2007), being capable of providing an “authoritative semantic definition of building elements, spatial relationships, and quantities and properties of building components”. The insufficiencies of indoor navigation approaches caused by the existing GIS system can be overcome by making use of the advanced semantic and geometric information that are available in BIM. With the purpose of providing a successful 3D indoor navigation, it is necessary to transfer 3D geometric and semantic information from BIM into a 3D GIS environment (Isikdag, 2006). The challenge is to maintain the consistency of automatic change of LOD models