DTM extraction from topographic maps

This paper deals with the automatic quotation of the contour lines extracted from a scanned paper map, in the way to create a DTM (digital terrain model). The great number of contour line interruptions, the connections between two (or more) contour lines and the low density of the elevation information contained on the map, make the quotation task very difficult. Our technique is based on the computation of an intermediate DTM from the global analysis of the main contour lines and the elevation dots. By using this intermediate DTM, we are able to estimate the contour line orientation (i.e. the slopeway), and then to quote the contour lines. By analyzing the trust on the orientation and the coherence of the quotation transitions, we select all the unsuspicious elevations and use them to create a new DTM. We assume that this new DTM is more precise than the intermediate DTM. So we can use, if necessary, this new DTM as a new intermediate DTM to repeat the process (orientation estimation and quotation).