The DEM generalization based on the simplification of valley system

The DEM concerns only the elevation of each cell instead of the landform feature such as valley, ridge, saddle, pit and peak. But these features play a significant role in the terrain generalization. Only when cartographers firstly identify and assess these features and their spatial structure correctly could terrain generalization obtain a satisfactory result. This paper proposes an approach to generalize DEM based on the simplification of valley system, which means that the valley systems are extracted and structurized beforehand. Based on the structured valley system, the process of DEM generalization is subdivided into three sub-processes: valley lines generalization, which results from the simplification of the structured channel network; and valley coverages generalization, which consists of a gradual incorporation of the associated valley coverages; and valley surface fitting, which results from the smoothing of the little catchment basins within the extended valley coverage. In this study, the valley system has been taken into consideration and the generalizing decision has been made on the level of hydrological significance. Hence this approach, in contrast to the conventional algorithms which are based on the image processing, can more properly maintain the primary geographical characteristics and discard the fragmental ones.