A Reconstruction Method for Broken Contour Lines Based on Similar Contours

Abstract

The reconstruction of a broken contour line is a prerequisite for the automated processing of contour lines. When the situation with broken contour lines is severe or the terrain is more complex, incorrect and missing connections are most likely to occur using traditional methods. In this paper, a reconstruction method for broken contour lines based on similar and completely closed contours is proposed. First, node densification is conducted on broken contour lines to improve the identification accuracy of the reference line. Second, the discrete Fréchet distance is used to select a reference line and perform reconstruction. Finally, the actual data of Yunnan Province are utilized for verification. The results show that the method proposed in this paper can achieve better reconstruction of broken contour lines, especially for severe broken contour situations or complex terrains; the reconstruction accuracy is significantly improved over that of the traditional method, indicating good feasibility. Figure 1. Schematic diagram of the minimum point pair method for reconstruction.82 However, the reconstructed line created with this method is usually a straight line, and when 83 the contour line is complex, the reconstructed line is prone to cross dislocation. For this reason, some 84 scholars have put forward a method to add direction for auxiliary identification (based on the 85 extraction of the interbreakpoint Euclidean distance) and a direction angle [3]; the search window is 86 set to calculate the directions of all breakpoints in the window, which allows the appointed 87 breakpoint and alternative breakpoint in the neighborhood search window to extend in each 88 direction. If the extension lines intersect, the breakpoints are matched and connected; the effect is 89 shown in Figure 2. 90 91 Figure 2. Schematic diagram of the breakpoint extension intersection identification matching method 92 for reconstruction.93 Limitations in Existing Methods 94The method for the reconstruction of broken contour lines is easy to implement by using the 95 Euclidean distance with an auxiliary direction, making it suitable for the reconstruction of contour 96 lines with a better surface effect, smaller breakpoint distance, and flatter terrain, as shown in Figure 97 3 A. However, when the following cases occur due to only considering the individual characteristics 98 of a broken contour line for connection, it is difficult to accurately determine the original trend of the 99 broken contour line, making it prone to incorrect and missing connections. 100(1) The overall breaking of a contour line is severe, and only a small part of the break remains, as 101 shown in Figure 3 B; 102 (2) The topography of the broken contour line area is complex (e.g., ridges, valleys, and saddles), as 103 shown in Figure 3 C. 104According to the above two cases, some scholars have put forward the strategy of using 105 breakpoint classification and directional differences for the reconstruction of broken contour lines 106[10] to enhance the connection ...

Contour line simplification method based on the two‐level Bellman–Ford algorithm

“…One contour map contains many similar contour line groups (Li, Liu, Wu, & Hao, 2019). To maintain the main shapes of the simplified contour line groups, the similarity among simplified contour lines must be maintained.…”