Removing duplicated geometries in IFC models using rigid body transformation estimation and flyweight design pattern

Background: The digital process of Building Information Modeling (BIM) involves the creation and modification of CAD-based building models. The complexity of such models has been increasing steadily within the last few years. BIM Models are usually being exchanged using open and standardized data formats. In this context, the Industry Foundation Classes (IFC) are widely used. Therefore, software vendors provide interfaces for dealing with the IFC format. To obtain a high level of data integrity, however, IFC elements are often managed as completely distinct entities, which can result in the creation of multiple copies of identical pieces of information. Since the trend to provide web-based solutions for BIM applications is also becoming increasingly important, especially the conflict between available resource consumption and suitable response times must be considered. Although existing optimization algorithms can reduce the size of an IFC file by analyzing its structure syntactically, there is still the gap to detect identical pieces of geometries that are syntactically distinct. Also, when subsequently merging such geometries, the available sharing concepts must be questioned. Methods: The contribution of this paper is twofold. On the one hand, we propose an algorithm to retrospectively detect identical geometries by estimating the rigid body transformation. On the other hand, we outline and evaluate the available possibilities for sharing geometries within the IFC data model. The so-called flyweight pattern is applied to provide and maintain the appropriate reuse of identical information. Results: The methodologies are exemplary demonstrated by modeling and optimizing a typical tunnel lining structure, which contains many repetitive elements. As a result, a noticeable reduction of storage and processing time can be measured. Conclusions: Establishing BIM in large building projects, where complexity not only depends on variation and geometric detail, but also depends on enormous repetition of these elements, a significant benefit is expected.