Eliminating contour line artefacts by using constrained edges

Contour lines are an important means of cartographical visualization. If computed automatically on a triangulation, they contain many artefacts. This paper shows the results of their elimination by using constrained edges in the triangulation. Constrained edges can be inserted either manually by an editor – which enables all kinds of detected artefacts to be improved manually – or automatically for some kinds of artefacts only. We present a survey of detected artefacts, evaluation of the Delaunay and greedy triangulations as to the number and kind of contour line artefacts, examples of achievements using manual placement of constrained edges and two algorithms suitable for automatic detection and removal of artefacts caused by flat triangle areas. According to our results, problems are not completely removed but the number of problematic areas is decreased substantially.