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Figure 4: Testing results. (A) Top left: Original contour map. (B) Top right: Original DTM obtained from the original 
contour map. (C) Middle left: Contour map derived from the improved DTM. (D) Middle right: The improved DTM. (E) 
Bottom left: Contour map derived from the original DTM. (F) Bottom right: The improved DTM superimposed with the 
introduced “skeleton” Lines. 
653 
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B4. Vienna 1996