Automatic Sounding Generalization in Nautical Chart Considering Bathymetry Complexity Variations

ABSTRACT

Sounding acts as the main feature in a digital nautical chart as it describes the concerned marine topography for the safety of navigation. Unlike the geometry-oriented selection of point feature, the generalization of soundings for chart compiling is expected to be context-oriented, which means bathymetry complexity variations across the study region should be preserved in the sounding selection process. However, such variations are not explicitly accessible to automated systems. This paper proposes an approach that effectively analyzes and measures bathymetry complexity from sounding data, with a focus on topography variations among different regions. The presented approach first divides the exploring region into several subregions, by adopting techniques of computational geometry and graph theory. Then, the approach quantitatively measures the bathymetry complexity of the subregions from grid-based digital terrain model. Finally, a composite bathymetry complexity index integrating aspects of steepness and depth variation is developed to guide the operation of sounding selection in different subregions. Generally, when seafloor is rugged with steep slopes, the number of soundings is high. While in flatter areas, a smaller amount of soundings is retained. The potential of our approach is demonstrated by an application to a real data set.

KEYWORDS:

• Digital nautical chart
• map generalization
• point cluster generalization
• sounding selection

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Erratum

Acknowledgments

We are grateful to the editor and the anonymous reviewers for their valuable comments and suggestions.

Additional information

Funding

The project was supported by the National Natural Science Foundation of China (No. 41701440), and the Fundamental Research Funds for the Central Universities, China University of Geosciences (Wuhan) (No. CUG170640).