Computer-assisted terrain sketch mapping that considers the geomorphological features in a loess landform

Abstract

In geography, a terrain sketch map is necessary to understand the features and internal structures of a landscape due to its ability to depict key information in a geographical scene using as few lines as possible. Previous computer-drawn sketch maps have focused on the artistic effect rather than on depicting terrain features and landform structures, and thus, they differ considerably from hand-drawn sketch maps by geographers or geologists. This study develops a DEM-based method for terrain sketch mapping that considers the typical feature descriptions of a loess landform and the visual hierarchy expression in line with the law of visual perspective. The method was tested with experiments on two landforms of Chinese Loess Plateau, based on digital elevation models (DEM) with a horizontal resolution of 5 m. In the developed method, first, typical terrain features, including the visual outline, shoulder line, gully and flow lines, are extracted from the DEM. Second, the map is divided into three visual levels in accordance with the data extension and viewing point. Then, terrain feature lines are assigned to different visual levels. Finally, the visual outlines in the distant view are generalized following the law of visual perspective. Results are assessed through a questionnaire with specialists (experts) and students (non-experts). The sketch map was able to characterise loess landforms, and is somewhat similar to traditional hand-drawn maps. The generalisation method realises the near and distant view characteristics of a sketch map, which are detailed and simplified, respectively. The results of the questionnaire also showed that our method presents terrain morphology and geographical scene more accurately and reliably than a hand-drawn sketch map.