## 2 A Brief Introduction to Laser-Scanning 3D Model Reconstruction Technology
### Principle of 3D Laser-Scanning Technology  
The operational principle of 3D laser-scanning technology is depicted in Figure 1. The \(XY\) plane signifies the lateral scanning plane of the 3D laser scanner, and the \(Z\)-axis is perpendicular to the lateral scanning plane. During the scanning process, the laser emitter and laser receiver located in the middle of the scanner rotate rapidly around the \(Y\)-axis to achieve longitudinal scanning. Simultaneously, the entire scanner rotates around the \(Z\)-axis to achieve lateral scanning. In theory, the longitudinal scanning angle range and the lateral scanning angle range are both within 0\({}^{\circ}\) to 360\({}^{\circ}\). However, due to the presence of the support structure of the 3D laser scanner, there is a conical blind spot region beneath the scanner. In practical situations, the point cloud data in the blind spot region can be supplemented by employing a multi-station scanning approach. Through the observation of the distance measurement value \(S\) from the laser scanner's center point to \begin{table}
\begin{tabular}{c c c c} \hline \hline
**No.** & **Index** &
\begin{tabular}{c} **Laser-Scanning 3D Model** \\ **Reconstruction Technology** \\ \end{tabular} & **3D Software Modeling Technology** \\ \hline
1 & Costs & \
\begin{tabular}{c} The economic cost of the 3D \\ laser-scanning equipment is relatively \\ high, but at the same time it saves time. \\ The variety and level of skilled \\ manpower required is high. \\ High precision with multiple \\ presentation of results. \\ \end{tabular} &
\begin{tabular}{c} The economic cost is relatively low, while \\ the time cost of decommissioning \\ is increased. \\ The skilled manpower required are \\ relatively homogeneous. \\ General, not applicable to the modeling \\ of complex objects. \\ Drawings containing dimensional data of \\ modeled entities. \\ \end{tabular} \\
5 & Workloads & \
\begin{tabular}{c} The data acquisition and modeling \\ required for processing the point cloud \\ data is large. \\ \end{tabular} &
\begin{tabular}{c} The data acquisition and modeling \\ workload is large. \\ \end{tabular} \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Comparisons of laser-scanning 3D model reconstruction and 3D software modeling technology. the target object, the longitudinal scanning angle \(\theta\), and the lateral scanning angle \(\alpha\), the 3D coordinates (\(X_{\text{o}}\), \(Y_{\text{o}}\), \(Z_{\text{o}}\)) of the target object's spatial position can be computed, which result in the acquisition of point cloud data for the target object. The relationship between parameters \(S\), \(\theta\), and \(\alpha\) is demonstrated in Equation (1). The parameter \(S\) is determined by calculating the time difference between the laser emission and reflection (\(\Delta T\)), multiplied by the speed of laser propagation in air (C). Laser scanners are generally driven by servo motors; the two parameters \(\alpha\) and \(\theta\) can be measured according to the motor rotation angle and are usually recorded with the angle encoder that comes with the scanner. \[\left\{ \begin{array}{l}X_{\text{o}}=S\times\cos\theta\cos\alpha\\ Y_{\text{o}}=S\times\cos\theta\sin\alpha\\ Z_{\text{o}}=S\times\sin\theta\\ S=\frac{C\times\Delta T}{2}\end{array} \right. \tag{1}\]  
The interiors within the HWRR plant exhibit a diverse array of equipment and pipes with varying shapes. These components can be viewed as assemblies of numerous points, and the clarity of the equipment and pipe contours improves with an increased number of captured points. Through 3D scans performed from different positions and perspectives, extensive point cloud data with spatial coordinate information can be acquired. This facilitates the derivation of comprehensive point cloud data that encompass spatial details regarding the shapes and dimensions of internal equipment and pipes within the nuclear facility [27].