# A Network Analysis-Based Approach for As-Built BIM Generation and Inspection
## 3 Methodology
### Network Analysis and Comparison  
The analysis of BIM networks can be approached from two distinct perspectives: global analysis and node matching. Each perspective provides unique insights and serves different purposes in the overall evaluation and comparison of as-designed and as-built BIM models. Global analysis focuses on the overall characteristics and structure of the BIM network, including:  
Global Parameters: These parameters give a holistic view of the network's structure. Examples include network density, average node degree, clustering coefficient, and path length. These metrics help in understanding the complexity, connectivity, and robustness of the network.  
Community Detection: This involves identifying groups of nodes that are more densely connected internally than with the rest of the network. Community detection can reveal functional modules or subsystems within the building, such as different floors, rooms, or structural components that work together. Comparing community structures in as-designed and as-built networks can highlight discrepancies and areas where the actual construction deviates from the original design.  
Node matching is the process of identifying corresponding nodes between two networks, which is crucial for the following:  
Accuracy of Corresponding Relationships: Ensuring that nodes representing the same physical element in the as-designed and as-built models are correctly matched is essential for accurate comparison and analysis. This involves comparing attributes like type, dimensions, and spatial relationships of nodes.  
Figure 3: Building element list and example of network establishment.  
Foundation for Future BIM Comparison: High accuracy in node matching provides a reliable basis for more detailed comparisons and analyses, such as detecting construction errors and deviations from the design and assessing the structural integrity of the built environment.  
However, the parameter and property selection needs to be adjusted and determined with an in-depth study in the future. Element identification and comparison in as-built and as-designed BIM models are target functions of the above analysis and comparison, which are illustrated in the examples below.  
The floor in a building structure typically has the most connections with other elements, which means the node with the highest degree in the network tends to be identified as the floor. For instance, in Figure 4, the floor is connected to most components.  
By comparing the number of nodes in the two networks, the number of structures in the two BIMs can be analysed and compared. In practice, multiple elements in as-designed BIM are easily recognised as one in as-built BIM, which means the number of nodes in the networks will be different. As shown in Figures 5 and 6, six walls in the as-designed model are reconstructed as one in the as-built model. Global comparison and community analysis in the proposal method are instrumental in addressing the identified problems. Due to scanning accuracy limitations, as-built BIMs generally have different nodes compared to as-designed BIMs. Therefore, evaluating the number of nodes and edges provides an in-depth assessment of the scanning process. In community analysis, discrepancies are observed as isolated nodes in as-built networks, whereas they appear as clusters of adjacent nodes in as-designed networks. Consequently, analysing and comparing these network differences facilitates the detection and identification of such issues.  
Figure 4: Floor element in Revit model.  
Figure 5: Elements in the as-built BIM.