# Automatic Bridge Design Parameter Extraction for Scan-to-BIM
## 2 System Development
### Design Parameter Extraction  
When the planar components of the bridge PCD are repeatedly extracted by applying the MSAC used in the 3D transformation process, they are decomposed, as shown in Figure 9, and demonstrate a pattern from the largest to the smallest plane. The design parameters can be extracted based on the distance between the planes because each decomposed plane has coordinates. However, bridge shapes and the design parameters requiring extraction differ based on the bridge type. Therefore, this study developed automatic design parameter extraction models for several common bridge types: beam girder, T-type girder, plate-type girder, steel box girder, and prestressed concrete box girder.  
Figure 8: Point cloud data before (**left**) and after (**right**) 3D coordinate transformation.  
Figure 7: Y-axis in the measurement coordinate system (\(\overrightarrow{y}\)) and bridge coordinate system (\(\overrightarrow{y^{\prime}}\)).  
The bridge type most widely used for railway bridges is the beam girder bridge, which has a more complex shape than other girder bridges. Further, the design parameter extraction using a constant decomposition pattern would not produce satisfactory results because the beam members all have the same shape. Therefore, this study added an algorithm to extract the design parameters from the beam members, which manually specifies the region of interest (ROI) in the area of the design parameter \(H_{2}\). The design parameters that can be extracted from the beam girder bridge model are \(H_{1}\), \(H_{2}\), \(H_{3}\), \(W_{1}\), \(W_{2}\), \(W_{3}\), \(W_{4}\), and \(W_{5}\), as shown in Figure 10, and the length \(L\).  
T-type girder bridges have relatively simple shapes and are not currently widely used for railway bridges. Therefore, the model for this bridge type was developed to only extract the basic design parameters. Completing the T-type girder model-based on the LiDAR PCD will be a subject for future work. The design parameters that can be extracted from the T-type girder bridge model are \(H_{1}\), \(H_{2}\), \(H_{3}\), \(W_{1}\), \(W_{2}\), \(W_{3}\), and \(W_{4}\), as shown in Figure 11, and the length \(L\).  
Figure 11: Design parameters for a T-type girder bridge.  
Figure 9: Bridge point cloud data decomposition.  
Although plate girder bridges were a popular bridge type selection in past decades, they are now rarely designed because of the large amount of steel that they require. Therefore, the model for this bridge type was developed to only extract the basic design parameters. Completing the plate girder model-based on the LiDAR PCD will be a subject for future work. The design parameters that can be extracted from the plate girder bridge model are \(H_{1},\,H_{2},\,H_{3},\,W_{1},\,W_{2},\,W_{3},\,\) and \(W_{4}\), as seen in Figure 12, and the length \(L\).  
While steel box girder bridges have been commonly applied as roadway structures, currently, they are rarely used for railway bridges. Therefore, the model for this bridge type was developed to only extract the basic design parameters. Completing the steel box girder model-based on the LiDAR PCD will be a subject for future work. The design parameters that can be extracted from the steel box girder bridge model are \(H_{1},\,H_{2},\,H_{3},\,W_{1},\,W_{2},\,\) and \(W_{3}\), as shown in Figure 13, and the length \(L\).  
Given the cross-sectional shape of prestressed concrete (PSC) box girder bridges, as shown in Figure 14, the shape inside the PSC box cannot be obtained or checked against an in-service bridge. Therefore, the model for this bridge type was developed to only extract the basic design parameters. Completing the PSC box girder model-based on the LiDAR PCD will be a subject for future work. The design parameters that can be extracted from the PSC box girder bridge model are \(H_{1},\,H_{2},\,H_{3},\,W_{1},\,W_{2},\,\) and \(W_{3}\), as seen in Figure 14, and the length \(L\).  
Figure 12: Design parameters for a plate girder bridge.  
Figure 13: Design parameters for a steel box girder bridge.