b-spline curve smoothing under position constraints for line generalisation
Currently, most of the operations performed for the construction of marine charts are still done manually. However, with the development of more and more powerful techniques, new processing methods must be developed in order to deal with the increasing amount of data and to achieve automatic construction. For that purpose, a new method for line smoothing is introduced in this paper and is applied to the generalisation of isobathymetric lines (lines connecting points at a same depth). The lines are modelled by B-spline curves which maintain their smooth feature. Smoothing is performed by reducing the curvature using a snake model. The generalisation constraint of navigation safety is satisfied by applying position constraints on the line. Spatial conflicts are also taken into consideration and are removed during the process. Parameters are automatically defined so that the method can be applied to large sets without user intervention. The method has been applied on real data sets and examples are provided and discussed for scale reduction of lines.
b-spline curve smoothing snake cartographic generalisation