# Research on the Symbolic 3D Route Scene Expression Method Based on the Importance of Objects
## 3 Results and Discussion
### Symbolised 3D Railway Scene Construction  
On the basis of the results of the object importance evaluation model, we classified and stratified the geographical elements of the 3D route scenes in the experimental area. Then, we modelled the 3D symbols. The current mainstream 3D symbol modelling tools are ArcGIS, SketchUp, AutoCAD, 3D Studio MAX, CityEngine, etc. The main process of 3D symbol modelling is divided into the following steps:  
1 The design of the three-dimensional symbol model. In the process of modelling three-dimensional symbols, it is necessary to consider both the artistic nature of the symbols and also the intuitive expressiveness of the symbols. As the expression environment of three-dimensional symbols and two-dimensional symbols is different, three-dimensional symbol modelling should take into account four modelling principles: simplicity, abstraction and image balance, coordination, and feasibility. 2 Modelling of three-dimensional symbolic models. According to the semantic information of the geographical entity objects and the two-dimensional topological spatial structure, we modelled the objects within the experimental scope separately. On the basis of the idea of symbolisation, we generated 3D models with a high degree of realism through the software for the models of objects with a high level of hierarchy in the region. For other object models with lower levels in the region, we were able to use a combination of simple three-dimensional geometries such as spheres, columns, and vertebrae to express them. Figure 7 shows the 3D symbol models of the tunnel, bridge, and signal machine. 3 Simplification of the three-dimensional symbol model. The three-dimensional symbols designed in this research had a multi-detail hierarchy. Therefore, when we browsed large-scale 3D scenes, the content information and colours should not be over-saturated. Priority should be given to expressing the geographical entity objects that the user focuses \begin{table}
\begin{tabular}{c c c} \hline \hline
**Level** & **Geographical Elements** & **Object Importance (Rounded)** \\ \hline \multirow{6}{*}{2} & Section 9 roadbed & 10 \\ \cline{2-3}  & Section 11 roadbed & 10 \\ \cline{2-3}  & Section 17 roadbed & 9 \\ \cline{2-3}  & Section 1 roadbed & 9 \\ \cline{2-3}  & Section 22 roadbed & 9 \\ \cline{2-3}  & Section 3 roadbed & 8 \\ \cline{2-3}  &...... &...... \\ \hline \multirow{6}{*}{1} & Huanian to Yuanjiang Section 1603 Signals & 4 \\ \cline{2-3}  & Signal Tower 1347 & 3 \\ \cline{2-3}  & Signal machine 3051 between Guangyao and Ning’er & 3 \\ \cline{2-3}  & Xishuangbanna 4392 signalling machine & 3 \\ \cline{2-3}  & Yuxi S8 signalling machine & 3 \\ \cline{2-3}  & Maohan S-issuing code point signal machine & 3 \\ \cline{2-3}  &...... &... \\ \hline \hline \end{tabular}
\end{table} 
Table 4: _Cont._  
Figure 7: Three-dimensional symbol modelling: (**a**) bridge model; (**b**) tunnel model; (**c**) signal machine model. on. We should simplify the process by combining the results of the classification while considering the overall 3D scene in the right level of detail. In small-scale scenes, the 3D symbols need to be simple, easy to read, and abstract while focusing on the more important objects. Therefore, we simplified the 3D symbols in five different layers of the model on the basis of the CityGML idea. This allows for more efficient loading and also provides more detailed content of the solid objects. According to the above steps, we generated 3D symbols of the geographical elements in the region in different levels according to the five LODs. We imported all the 3D symbols into the database for storage. Finally, we built the symbolic 3D high-speed railway scene platform. Different layers of 3D symbols were loaded at different scales by calling different 3D symbol services. One of the LOD0 contained important stations. As the scale level increased, geographical elements such as tunnels, bridges, roadbeds, and signalling machines appeared level by level.