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. "Interpolation method". 
  
igure 4: Combined hill shading 
x "AME RR 
  
    
  
  
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Figure 5: Oblique hill shading. Reduced illumination angle. Light only in NW, shadow in N, E, S, W. 
2.2 Elevation Contours and Elevation Layers 
Also elevation contours and elevation layers can be generated without any problem. The latter ones can easily be pro- 
duced by a transformation of the original DM data by a stair function, whereas contour lines result out of high-pass fil- 
tering. A simple method is a sort of adapted Laplace Operator (Bóhm, 1998). Despite their accuracy the yielded eleva- 
tion contours do not correspond with the traditionally geaerated ones in all details. It is, however, fact that the elevation 
contours are in total accordance with the DEM. In so far the filter-generated lines clearly showed the limit of the tradi- 
tional isohypse drawing. Shortcomings of filter-generated contours are: 
- Description/definition gaps in flat spaces and too high density of lines in steep spaces due to the too small dynamic 
range. 
— "Shaky" and shifted contour line courses subject to random intersection in flat spaces. 
- Uncertain and wrongly represented saddles, also generated by random surface intersection. 
— Acute intersections of gentle valleys, hollows and ridges subject to the minimum horizontal bending of the relief in 
these locations. 
— Pseudo-depressions and pseudo-passes in narrow valleys due to inadequate spatial resolution and after low-pass 
filterings respectively. 
630 International Archives of Photogrammetry and Remote Sensing. Vol. XXXII, Part 7, Budapest, 1998 
  
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