Based on the current quality detection methods and development direction of digital chart, a Chart quality detection method based on depth range constraints in isobath zones was proposed for a large number of water depth points and isobates on digital chart. Firstly, in view of the defects existing in the current quality detection method, the current different quality detection methods are compared and analyzed. Then, the logical error of the chart data is studied. Through experimental calculation, the weight of the depth range extraction is determined. The experimental results show that the proposed method can effectively improve the accuracy of logical detection.
In view of the current situation that most of the current isobaths automatic simplification algorithms are aimed at a single depth contour and it is difficult to unify the automatic simplification and merging process, we propose an automatic simplification and merging algorithm of isobaths based on surface simplification. Firstly, the basic principles of surface simplification and rolling ball synthesis of seafloor topography are analyzed, and then high-precision digital depth model (DDM) is constructed using nautical chart data as the original three-dimensional data; Then, on this basis, the high-precision DDM is simplified by using the rolling ball transform; Finally, based on the simplified DDM, the isobaths are extracted reversely to realize the purpose of automatic simplification and merging. The experimental results show that: in typical regions, the proposed method can automatically identify and process the regions to be simplified and merged, and our method also improves the automatic synthesis quality of isobaths.
In view of the current situation that the method for estimating the quality of the depth generalization in chart cartography is simple and extensive, a series of the quality quantitative indices and evaluation methods are proposed for evaluating the quality of the depth generalization. On the basis of “Specification for Chinese Nautical Charts”, three kinds of the quality indices, including the probability of adequate depth, the representativeness of depth and the distribution of depth, are proposed and designed for respectively evaluating the ship’s navigational safety, the available navigation resource and the arrangement of charted depth. Correspondingly, the quantitative evaluation methods of the comprehensive quality of nautical chart are proposed. The experimental results demonstrate that: (1) compared with the traditional method, the proposed method can accurately analyze and evaluate the quality of each depth for ensuring the navigational safety; (2) compared with the accuracy assessment method, the proposed method can accurately calculate the depth for representing the navigable resource such as in the sea channel, narrow channel; (3) compared with the average spacing method, the proposed method can quantitatively evaluate the location distribution of each depth annotation expressed on the chart, and accurately determine whether the distribution of each depth point is clear and reasonable.
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