Using Normal Offsets to Smooth Terrain Models
Patrick Kennelly | Long Island University, NY, USA
Keywords: terrain, smoothing, generalization, digital elevation models, DEMs
Digital elevation models allow for efficient display and analysis of 2.5-dimensional terrain surfaces. They can be smoothed with procedures that typically vary the z-values of grid cells in the elevation model. This presentation proposes an alternative method for generalizing DEMs that varies elevation values in the surface normal direction. These normal offsets can be applied above or below the original surface, and results can be combined for desired effects. Offsets above and below the surface tend to expand major features in the x,y direction that have concave downward (e.g. hills and ridges) and upward (e.g. valleys and drainages) curvature, respectively. Additionally, minor features such as bumps or pits tend
to get smoothed over on the new surfaces. The resulting DEM can be used to create various generalized cartographic products, such as smoothed contour lines or shaded relief maps with widened valleys that provides additional map area for displaying other cartographic features.