The integration of GIS and BIM can be achieved through various methods, mainly including data format conversion, data standard extension, and ontology development. Among these, data format conversion is the most widely applied in practice. IFC, a data standard designed for BIM, facilitates information sharing within buildings. It has become an ISO international standard, enabling multidisciplinary design and management integration.
Most BIM software today supports importing and exporting data in the IFC format, making it one of the most common standards for information sharing in the field. On the GIS side, CityGML is the prevalent format; it is an international standard developed by the Open Geospatial Consortium (OGC) to enable the sharing of 3D city model information. CityGML defines semantic information, 3D geometry, and topology for urban spatial objects.
IFC and CityGML share similarities—they are both object-oriented formats and define comparable entities. In practical applications, their models are generally interoperable. However, they also differ in various details, reflecting distinct information structures. IFC typically contains more detailed information. This complexity makes complete data mapping between the two formats challenging.
To tackle these challenges, researchers have explored various methods to integrate GIS and BIM, resulting in solutions tailored to meet application needs. Currently, conversion between IFC and CityGML primarily involves manual and semi-automatic approaches. However, fully automated conversion has yet to be realized due to speed and complexity constraints.
The manual conversion process generally involves four steps: ① semantic filtering, ② shell calculation, ③ installation, and ④ refinement. This approach leverages the semantic features of both models to filter information efficiently. Through this, a semantic mapping conversion framework can be established to support effective data sharing between IFC and CityGML.
More recently, semi-automatic conversion has been achieved using data warehouse technologies such as Extract, Transform, Load (ETL). This method extracts data of the same type from the source system, applies multi-level semantic filtering and geometric information extraction, and finally converts the data into the appropriate format for loading into the data warehouse. The ETL process allows flexible, complete, and customizable mapping between BIM and GIS data.
ETL tools are well-suited for batch processing, enabling the conversion of large datasets efficiently. However, this approach still has limitations. According to current research, data loss during conversion between IFC and CityGML remains inevitable. Therefore, future efforts will focus on minimizing information loss throughout the data conversion process.
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