## 4 Case Study
### Capture of Point Cloud Data  
Selection of laser scanner: There are many types of laser scanners on the market. The selection of the laser scanner in the project was determined by factors such as the range and accuracy specifications of the scanner, the accuracy requirements of the project, the cost of the scanner, and the budget of the entire project. The location and the scanning parameters of the scan were crucial to maintaining a high level of accuracy. There are three key impact factors of the scanning accuracy: (1) distance to the object, (2) incident angle between the 3D laser scan and the installed anchor plates, and (3) angular resolution of the 3D laser scanner. After all of those factors were studied, the Leica P30 laser scanner, as shown in Figure 10, was selected to capture the data. Multiple scans were then performed to minimize the occlusion effect. The instrument specification is provided, as shown in Table 2. \begin{table}
\begin{tabular}{c c} \hline \hline \multicolumn{2}{c}{**Leica Scan Station P30**} \\ \hline Range accuracy & 1.2 mm + 10 ppm over full range \\ Angular accuracy & 8\({}^{\circ}\) horizontal; 8\({}^{\circ}\) vertical \\
3D(Three dimensional) position accuracy & 3 mm at 50 m; 6 mm at 100 m \\ Target acquisition & 2 mm standard deviation at 50 m \\ Range and reflectivity & 18\(\%\) at 120 m \\ Scan rate & Up to 1,000,000 points per second \\ Range noise & 0.4 mm rms at 10 m \\
0.5 mm rms at 50 m \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Leica P30 laser scanner specification. Figure 10: Leica P30 laser scanner. Figure 9: BIM model of anchor plates and end posts after pouring concrete. When the prefabricated parts were delivered on-site, quick scans of anchor plates were performed. Their dimensions were recorded to compare with the design requirement. Planning of the site layout and the installation alignment: After verifying the components' quality, the survey control and installation alignment were set up using laser scanning technology. A total of sixteen scans were performed along the riverbank. The scanning locations were carefully established before scanning was performed by evaluating three factors: (1) distance, (2) angle between the anchor plate and the scanner, and (3) angular and 3D position accuracy. Based on the range of the Leica P30, the researchers decided to scan every 200 m along with the project length of 3135 m, as shown in Figure 11 (this picture is for illustration purposes only). Due to the rural conditions in the construction environment, an ideal set-up is not always possible. The location of the scanner depended on the existing condition of the job site. The layout of the scanner's location is shown in Figure 11. In total, 16 scans were performed to define the installation alignment. The anchor plates were installed in a reinforced concrete foundation and embedded flush with the ground. The anchor plate is used to support the center posts. In non-operative mode, the anchor plates' internal threaded bushings are closed with dummy bolts. They protect the bushings from debris. In operative mode, the dummy bolts are removed, and service bolts are utilized to connect the center posts with the anchor plates. Figure 12 shows the anchor plates installed every 3 m (3000 mm, as shown in the figure) according to the plan and specification. Figure 11: Scan locations. Figure 12: Anchor plate positions. After an anchor plate was placed and levelled, it was permanently welded to the reinforcement to protect any movement during the cast-in-place process, as shown in Figure 13a. Multiple scans were performed to capture the point cloud data. Control targets were placed manually at the recommended optimal distance from the scanner and evenly throughout the scan at different elevations, according to the operating manual. Then, point clouds were tied into a single coordinate system, as shown in Figure 13b. After verifying the anchor plates' installation tolerance, end posts were welded to the reinforcement, as shown in Figure 14, and concrete was cast in place.