Utvärdering av olika metoder för framställning av höjdkurvor från laserskannade höjddata
Lantmäteriet (the Swedish mapping, cadastral and land registration authority) has been laser scanning Sweden since 2009. From the laser scanned data a digital elevation model (DEM) in grid format, with a resolution of 2 m, is produced. This DEM is called GSD-Höjddata, grid 2+ and from its data and the laser point cloud itself (in the form of a las-file) contour lines can be extracted. Lantmäteriet has not yet done this, but plans to update the contour lines in their cartographic products exist. If this is to be done in a satisfactory way an evaluation of different methods for it is needed. The aim of this study is therefore to investigate the pros and cons of different methods for generation and generalization of contour lines. The goal is mainly to find a good method for Lantmäteriet?s need, but hopefully other users of the laser data will also be able to benefit from the results of the study. The research was conducted in the form of a literature study of other authors experiences of different methods, a series of own tests were also carried out. The tests were done using the softwares FME, ArcMap and Karttapullautin. The resulting contour lines were evaluated both by ourselves and by cartographers and others with knowledge on the subject working at Lantmäteriet. Detailing, smoothness and the retainment of characteristic shapes and formations in the contour lines were examined. Topological errors and uncertainties in elevation were also observed. The examinations resulted in the tested line smoothing and simplifying algorithms being ruled as unfit for use. All programes generated contour lines with a too high detail level if no steps to generalize were taken. A method where the DEM was smoothed before generating the contour lines was decided to give the best results for use in Lantmäteriet?s cartographic products. We therefore suggest further research on how this method can be implemented.