Urban road DEM construction based on geometric and semantic characteristics

The accurate expression of terrain morphology is the essence of the urban terrain model construction. As the skeleton of urban terrain, urban road has special geometric and semantic characteristics. The road is a strip-shaped feature, which is flat in the horizontal direction and gently undulating in the vertical direction, and the roads are interlinked and connected. This research takes Jianye District of Nanjing as the studied area to explore the digital elevation model (DEM) construction method of urban roads. Firstly, the 1:1000 digital topographic map(DTM) is used to extract the point, line and plane elements of urban roads. Secondly, a selection method of elevation points for urban road DEM (UR-DEM) construction is proposed, referring to the urban road engineering design specification. That’s the improved Douglas–Peucker (D–P) algorithm with elevation change rate. Thirdly, the bidirectional interpolation method is constructed to keep the directional characteristics and geometric features of the urban roads. Then, the intersection processing method based on semantic connectivity is used, so that the roads can be connected correctly. Finally, UR-DEM is generated by inverse distance weighting (IDW) interpolation model, and the construction results are also analyzed and evaluated in this paper. The experimental results show that: (1) the existence of abnormal elevation points seriously affects the geometric shape of urban road, and the removing abnormal elevation points method proposed in this paper can maintain gently undulating characteristics of road well and largely reduce the road jitter. (2) The UR-DEM construction method proposed in this paper can express the spatial geometric and semantic features of urban road well, the model accuracy is higher than that of classical methods and the RMSE is 0.0225 m. This study can provide reference for the DEM construction of other urban features, and can provide data support for the process simulation of urban surface confluence and urban construction planning.