On the Effective Validation of Charted Soundings and Depth Curves

TitleOn the Effective Validation of Charted Soundings and Depth Curves
Publication TypeConference Proceedings
AuthorsKastrisios, C, Calder, BR, Masetti, G, Holmberg, P
Conference NameU.S. Hydro 2019
Conference DatesMarch 18-21
Conference LocationBiloxi, MS
KeywordsAnalytical cartography, Computer cartography, Data Generalization, Delaunay Triangulation, depth interpolation, Nautical cartography, nautical surface test, Sounding Selection

Depth curves and charted soundings are two structural components of nautical charts, both derived from a more detailed dataset through generalization. Once depth curves are generated, the cartographer makes a selection of soundings that complements the depth curves and other features carrying bathymetric information in the adequate representation of the seabed morphology at the scale of the product. The selection of charted soundings – which is currently either performed fully manually, or partially manually using a computer-assisted solution – must meet the safety constraint, i.e., that no source sounding exists that is shoaler than what the mariner would expect by mentally interpolating the charted bathymetric information. According to International Hydrographic Organization S-4 publication, for well-surveyed areas that is achieved through the “triangular method of selection” and consists of two tests: the Triangle Test and the Edge Test. There are currently no fully automated solutions, so, with the ultimate goal of supporting “cartography at point of use”, we consider the problem of automating the validation of shoal-selected soundings. We discuss an implementation of the triangle test with improved performance near linear features, the first automated implementation of the edge test, and that the edge test may identify shoals that the triangle test fails to detect, confirming its significance in the validation process. We demonstrate an “intrinsic” limitation of the two tests that makes infeasible a fully automated solution based solely on the two tests. Finally, to overcome the intrinsic limitation, we propose a new validation test, named Nautical Surface Test, that captures the local morphology at the appropriate charting resolution as the solution for the automated validation of the charted bathymetric information.