Objectives Road network is the basis of various road traffic analysis and visualization. It is difficult to extract road centerlines automatically in analyzing the internal of complex polygonal road surface and difficult road surface segmentation.An algorithm of constructing road network is proposed to distinguish road sections and intersections, which can simplify data preprocessing based on the topological relationship among blocks.
Methods Firstly, through performing logical negation operation on road surface, complex polygons with holes are converted into independent and simple block polygons. Secondly, neighbor points among them are calculated, and neighboring blocks of each block can be obtained using the neighbor analysis. Consequently, the topological relationship among common road sections or common intersections is determined, and road sections and intersections are discriminated. Then, it is obtained that two common blocks on both sides of each section and all blocks which around each intersection, so the geometric positions of centerlines of road sections are calculated by means of applying the unit circle rolling tracking algorithm. Finally, according to the type of intersection, the positions of intersection associated with road sections are determined to complete the construction of the road network digital model.The algorithm is verified by developing experimental software which uses urban road surface data in a city topographic map with scale of 1∶1 000 as experimental data.
Results The experimental result shows that the topological relationship of the final road traffic network is accurate and the matching relationship among blocks is correct. The positions of road centerlines are accurate and every line shape is smooth. There are no excess centerlines or missing centerlines. The proposed method works well in dense and sparse neighborhoods. Compared with traditional algorithms, the algorithm for constructing road network by using street topology relationship doesn't need to perform manual segmentation or road surface edge line encryption. It simplifies complex graphics by negating the road surface and obtains road sections information according to topological relationship among polygons. The road centerlines are calculated by using unit circle rolling algorithm, so the geometric characteristic of the road centerlines and the accuracy of the topological relationship can be guaranteed. The experimental result shows that the method construct a road network with complete topology, accurate location and smooth shape.
Conclusions In the process of constructing the road section-block topology using the method, the road sections and intersections are distinguished. It solves the problems of segmentation of the road sections and provides a good basis for the extraction of road centerlines. It is suitable for the construction of geometric road networks in dense road networks and dense blocks.