L.D. Wu, X.D. Yin, L.H. Zhang, Z.J. Chen

Dalian Naval Academy,Department of Hydrography and Cartography, Dalian, China


Depth contour is the important geographic feature in a chart, and it is the effective graphical method to show the seafloor terrain. Depth contouring has been a hot topic in the hydrographic surveying and mapping for a long time. Effective and reasonable contouring can determine navigable area for a ship, and make navigation safer.

The key issue, in fast plotting depth contour, is efficient tracing nodes of equivalent depth. In this paper, the traditional algorithm tracing nodes based on Triangulated Irregular Network (TIN) is studied. The principle that the equivalent node is the exit of a certain triangle and the entrance of its adjacency is used to trace the equivalent node in this algorithm, and the adjacent triangle is determined by checking the superposition of nodes with equivalent depth among different triangles. The traditional algorithm need search every triangle, which is time-consuming in contour tracing.

To overcome the drawback of traditional algorithm, an efficient algorithm tracing nodes based on triangle topology in TIN is proposed. This algorithm uses the adjacent triangle numbers recorded in the triangle, which can quickly find the suitable adjacent triangle, and trace the next equivalent node in the adjacent triangle. The experiment result demonstrates that this proposed algorithm.