## 3 Results and Discussion  
### Road DEM Construction with Morphological Expression Priority  
A typical road in the experimental area for the DEM construction experiment was selected. According to the technical process outlined in Section 2, the elevation of the road sideline and the road centerline were first assigned and adjusted. Then, the elevation  
Figure 6: Road DEM correction process. value of the road's elevation point was calculated by constructing the local shape control equation, and, finally, the road DEM was generated. Comparing (a) and (b) in Figure 7 revealed that the elevation value of the surface of the road DEM constructed by the traditional interpolation method (IDW) in the flat terrain area was too jitter. The road should be flat; however, due to the significant fluctuation, the road's surface was rough and uneven, and the surface smoothness was poor. At the same time, the modeling method ignored the spatial element combination level of the road cross section and did not consider road shape. The road DEM constructed in this paper clearly eliminated the abnormal jitter caused by the elevation value in the traditional method, and improved the surface smoothness of the road DEM. In (c) and (d) in Figure 7, in an area with great topographic relief, the contrast between the traditional interpolation method (IDW) and the road DEM constructed by this method was not obvious because the road itself had great relief, and the elevation difference was too large. In contrast, the layered color-matching method matched colors in a certain range. When the elevation difference was too large, since its distribution color was consistent, the difference was not obvious for the road DEM in the relief area. Figure 7: Road DEMs of different methods. The morphological characteristics of the road can be intuitively expressed through the road slope analysis diagram. The slope map extracted from the results of this study and the comparison method are shown in Figure 8. The slope classification standard in this paper is based on the Code for Design of Urban Road Engineering (Ministry of Housing and Urban-Rural Development, 2012). According to the road slope map, whether in flat terrain area or undulating terrain area, an area with a large gradient extracted from the road DEM constructed by the traditional interpolation method (IDW) was relatively scattered. This was caused by excessive jitter of the elevation value of the road DEM. Moreover, it is clear that the road surface was relatively rough and uneven, resulting in a road form distortion, which did not conform to the actual terrain characteristics of the road. The road DEM built in this paper reduced excessive jitter of the road elevation value. In the flat area, the road slope was essentially within \(3^{\circ}\). However, in the area with great topographic relief, although the slope was greater than \(3^{\circ}\), the road slope in some areas was the same throughout the road, allowing for a smooth transition, which is consistent with the semantic characteristics of a smooth road transition. Figure 8: Road extraction slope map. The road had the geometric and semantic characteristics of 'horizontal singularity, vertical undulation'. The intersection was an important aspect, as it connected roads with one another. It had slightly gradual elevation fluctuation in the longitudinal direction, but showed continuity overall. Therefore, in road modeling, it is necessary to consider the smooth connection of road intersections. The intersection slope map constructed by the modeling method, such as in (c) and (d) in Figure 8, shows that the gradient distribution of the traditional interpolation method (IDW) at the intersection is uneven and the difference is too great. This which indicates that the elevation difference was large on both sides of the road, making the modeling results insufficiently coherent at the intersection.