Gradual Generalization of Nautical Chart Contours with a Cube B-Spline Snake Model

—B-spline snake methods have been used in cartographic generalization in the past decade, particularly in the generalization of navigational charts where this method yields good results with respect to the shoal-bias rules for generalization of chart contours. However, previous studies only show generalization results at particular generalization (or scale) levels, and the user can only see two conditions: before the generalization and after generalization, but nothing in between. This paper presents an improved method of using B-spline snakes for generalization in the context of nautical charts, where the generalization process is done gradually, and the user can see the complete process of the generalization

Feature-driven generalisation of isobaths on nautical charts : a multi-agent system approach

A nautical chart provides a schematic view of the seafloor where isobaths (contour lines joining points of same depth) and depth soundings are generalised to highlight undersea features that form navigational hazards and routes. Considering that the process is ultimately driven by features and their significance to navigation, this article proposes a generalisation strategy where isobath generalisation is controlled by undersea features directly. The seafloor is not perceived as a continuous depth field but as a set of discrete features composed by groups of isobaths. In this article, generalisation constraints and operators are defined at feature level and composed of constraints and operators applying to isobaths. In order to automate the process, a multi-agent system is designed where features are autonomous agents evaluating their environment in order to trigger operations. Interactions between agents are described and an example on a bathymetric database excerpt illustrates the feasibility of the approach

Gradual Generalization of Nautical Chart Contours with a B-Spline Snake Method

B-spline snake methods have been used in cartographic generalization in the past decade, particularly in the generalization of nautical charts where these methods yield good results with respect to the shoal-bias rules for the generalization of chart contours. However, previous studies only show generalization results at particular generalization (or scale) levels, and show only two states of the algorithm: before and after generalization, but nothing in between. This thesis presents an improved method of using B-spline snakes and other auxiliary functions and workflows for generalization in the context of nautical charts which can generalize multiple nautical chart features from large scale to small scale without creating any invalid intermediate features that require special processing to resolve. This process allows users to generate charts at any intermediate scale without cartographic irregularities, and is capable of extension to include more specialized generalization operators

Controlled Line Smoothing by Snakes

A major focus of research in recent years has been the development of algorithms for automated line smoothing. However, combination of the algorithms with other generalization operators is a challenging problem. In this research a key aim was to extend a snakes optimization approach, allowing displacement of lines, to also be used for line smoothing. Furthermore, automated selection of control parameters is important for fully automated solutions. An existing approach based on line segmentation was used to control the selection of smoothing parameters dependent on object characteristics. Additionally a new typification routine is presented, which uses the same preprocessed analysis for the segmentation of lines to find suitable candidates from curve bends. The typification is realized by deleting undersized bends and emphasizing the remaining curve bends. The main results of this research are two new algorithms for line generalization, where the importance of the line smoothing algorithm lies in the usage of a optimization approach which can also be used for line displacemen

Generalisation of submarine features on nautical charts

2012-2013 > Academic research: refereed > Refereed conference paperVersion of RecordPublishe

An Ontology of the Submarine Relief for Analysis and Representation on Nautical Charts

A nautical chart is a kind of map used to describe the seafloor morphology and shoreline of adjacent lands. One of its main purposes is to guaranty safety of navigation. As a consequence, construction of a nautical chart follows very specific rules. The cartographer has to select and highlight undersea features according to their relevance to navigation. In an automated process, the system must be able to identify and classify these features from the terrain model. This paper aims therefore at defining ontologies of the submarine relief and nautical chart that will be at the root of a model-oriented generalisation process. To the best of our knowledge, no ontology has been defined to formalize the geographical and cartographic objects for nautical chart representation. Thus, a bottom-up approach was developed to extract and model knowledge derived from standards established by the International Hydrographic Organization (IHO) and cartographers’ expertise. The submarine relief ontology formalizes undersea features describing the submarine relief. Four concepts (composition, morphometric class, shape value and depth value) are introduced to describe properties and relationships between undersea features. The cartographic representation ontology of nautical chart will define several concepts (chart, features, isobathymetric lines and soundings) for the representation of undersea features on the chart.We are grateful to the Service Hydrographique et Oceno-graphique de la Marine (Brest, France) for their nautical documents and for their assistance and expertise in this study. This work was funded by the Research Grant Council of Hong Kong (grant PolyU 5172/08E), the Consulate General of France in Hong Kong and the Region Bretagne in France under grant 0211/ARE 09011/0002610

Preliminary Analysis of Quality of Contour Lines Using Smoothing Algorithms

In this paper several well-known filtering techniques were compared in the purpose of automatic line generalization. The used methods for line simplification are digital first order low-pass filter, Savitzky-Golay (SG) filter and Whittaker filter. Two versions of the algorithm for line feature generalization were tested, from source scale 1:25 000 towards target scale of 1:100 000 and from source scale 1:25 000 towards scale of 1:50 000. Also, GPS data filtering for the target scale 1:50 000 was tested. The first version of the algorithm considers that there are no control data, and the filtering parameter is dictated by the desired accuracy for the target scale. The second version involves control data in the target scale. This means that the optimal value for the filtering parameter is the value for which the difference between input and control data is the smallest. Analysis showed that the SG filter yielded the best results in general. The proposed filters can be considered as a new solution for automated cartographic line simplification

International Journal of Geographical Information Science

Prikaz časopisa International Journal of Geographical Information Science

International Journal of Geographical Information Science

Prikaz časopisa International Journal of Geographical Information Science