TABLE OF CONTENTS Most of the DTMs currently available have been interpolated from contours by sampling designs and computer algorithms that add artifacts and other distortions inherent in the processing (Shortridge, 2001). This analog data may be digitized through manual digitization, semiautomated line following, or by means of automatic raster scanning and vectorization. The latter method is predominant for large data collection projects. In principle, automated raster to vector conversion performs a similar task to manual digitizing using a digitizing tablet. However, there are many factors that can affect the accuracy of the digitizing process, such as resolution, consistency, stability, and others. With high-resolution scanned contour maps, raster to vector (R2V) methods track contour lines to the resolution of the scanned map. Scanning in fact deletes much of the human intervention and usually produces more accurate digital contours after editing (which is an unavoidable step in both manual digitizing and scanning) than manual digitizing.
The process of converting a paper contour map into vector format includes the following steps:
Scanning the map;
Removing noise;
Detection, binarization, and skeletonization of the contours;
Vectorization of the contours (contour following).
The scanning process converts the analog (paper) map into raster (digital) format. Scanning is an effective means of automating DTM data generation from contour maps. Recent developments in scanning hardware and R2V conversion software have made map scanning a viable tool for automated DTM generation from these maps. Automatic R2V technology encompasses a range of capabilities, from simple line...
