## 4 Results and Discussion
### Plan for Constructing and Renewing Digital Twin with Spatial Object Type  
#### 4.2.1 Linear Spatial Object Extraction Process  
Spatial objects encountered in underground utility tunnels can be primarily classified into three categories. The first type includes point objects, depicted in Figure 5, which encompass small objects such as fire extinguishers, CCTV systems, and lighting fixtures. The second type comprises line objects, represented in Figure 6, including items such as power cables, water conduits, gas pipes, and telecommunication lines. The third type consists of plane objects, illustrated in Figure 7, which include items like walls, floors, and staircases.  
Figure 5: BIM library of underground utility tunnel point objects.  
Figure 6: BIM library of underground utility tunnel line objects.  
In Table 1, objects in the underground utility tunnel were classified into points, lines, and planes, and detailed categories were set accordingly. Representative point-type objects include fire extinguishers, lights, and sensors, while representative linear objects include electric wires and drain pipes. Representative planar objects include walls, roofs, and floors. Accordingly, updates are set to be triggered by the movement of point-shaped 3D objects, with no updates for the remaining linear and planar shapes. In addition, updates to property information preservation are set to proceed, with some exceptions for point-type objects.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \multicolumn{1}{c}{**Major Category**} & \multicolumn{1}{c}{**Minor Category**} & \multicolumn{1}{c}{**Library**} & \multicolumn{1}{c}{\begin{tabular}{c} **3D Object** \\ **Update** \\ \end{tabular} } & \multicolumn{1}{c}{**Property Information Update**} \\ \hline \multirow{8}{*}{Point} & Fine extinguisher & \(\bigcirc\) & Yes & Yes \\  & Light & \(\bigcirc\) & Yes & Yes \\  & Sensor & \(\bigcirc\) & Yes & Yes \\  & & Sprinkler head & \(\bigcirc\) & Yes & Yes \\  & & Gate valve & \(\bigcirc\) & Yes & Yes \\  & & Air valve & \(\bigcirc\) & Yes & Yes \\  & & Notice sign & \(\bigcirc\) & Yes & Yes \\  & Point & Wire splitter & \(\bigcirc\) & Yes & Yes \\  & Facilities & Emergency exit sign & \(\bigcirc\) & Yes & Yes \\  & & Automatic fire extinguishing equipment & \(\bigcirc\) & Yes & Yes \\  & & Automatic fire detection equipment & \(\bigcirc\) & Yes & Yes \\  & & CCTV & \(\bigcirc\) & Yes & Yes \\  & & Flange & \(\bigcirc\) & No & Yes \\  & & Distribution panel & \(\bigcirc\) & No & Yes \\  & & Plumbing equipment & \(\bigcirc\) & No & Yes \\  & &... &... &... &... \\ \hline \multirow{8}{*}{Line} & \multirow{4}{*}{\begin{tabular}{c} Point \\ Structures \\ \end{tabular} } & Bracket & \(\bigcirc\) & No & Yes \\  & Support & \(\bigcirc\) & No & Yes \\  & Branch & \(\bigcirc\) & No & No \\  & Pipe protection & \(\bigcirc\) & No & No \\  & &... &... &... \\ \hline \multirow{4}{*}{\begin{tabular}{c} Line \\ Facilities \\ \end{tabular} } & \multirow{4}{*}{\begin{tabular}{c} Line \\ Facilities \\ \end{tabular} } & Power line & \(\bigcirc\) & No & Yes \\  & Water pipe & \(\bigcirc\) & No & Yes \\  & Communications line & \(\bigcirc\) & No & Yes \\  & &... &... &... \\ \hline \multirow{4}{*}{\
\begin{tabular}{c} Plane \\ Plane \\ Structures \\ \end{tabular} } & \multirow{4}{*}{
\begin{tabular}{c} Plane \\ Status \\ Enframe/Exit \\ \end{tabular} } & Wall & \(\bigcirc\) & No & Yes \\  & & Slab & \(\bigcirc\) & No & Yes \\  & Floor & \(\bigcirc\) & No & Yes \\  & & Ventilation opening & \(\bigcirc\) & No & Yes \\  & Stairs & \(\bigcirc\) & No & Yes \\  & & Entrance/Exit & \(\bigcirc\) & No & Yes \\  & &... &... &... \\ \hline \hline \multicolumn{1}{c}{Other} & Other & Random objects & X & Yes & No \\ \hline \hline \end{tabular}
\end{table}
Table 1: Classification and update information with object type.  
Figure 7: BIM library of underground tunnel plane objects.