3 
Ee * #4 
5 
» 
% 
$ “| Proxy 
pen 
A 
E 
à 
* b d 
  
  
be pro- 
ass fil- 
| eleva- 
evation 
e tradi- 
ynamic 
relief in 
w-pass 
  
As already mentioned above, these shortcomings can, however, not be attributed to the method but to the fact that the 
generation procedure is totally different from the classical manual isoline drawing, because frequently during the design 
the cartographer makes corrections: 
- Steeps slopes are represented flatter than they really are. 
- The biases by random surface intersection are reduced by subtle corrections. 
- Contour lines in narrow valleys are constructed in accordance with the drainage. 
- Acute horizontal intersections in valley bottoms are rounded. 
On the other hand, filter-generated elevation contours show hitherto unavailable possibilities: 
- The dynamic range of the elevation contour lines can be significantly extended through the use of more than one (3 
to 5) systems with different height intervals (Fig. 6). 
| Q £$ v. | Sono 
= Loria Q MAS, or 
  
          
  
  
  
Figure 6: Only elevation contours in 5 systems from black to light grey (200 m, 100 m, 50 m, 25 m and 12.5 m). Not a 
vertical hill shading! 
- In steep spaces filter generated isohypses can generate a hitherto unusual 3D effect. They display a gentle transi- 
tion to vertical hill shading. 
- The general appearance of the filter-generated elevation contours looks more natural and more realistic than vector- 
graphic contour lines. These elevation contours tend to show a more distinct pseudo 3D effect. The individual lines, 
however, are not so easily identifiable. 
2.3 Relief Representations of Higher Complexity - New Designed Possibilities of Cartographic Details 
The relief representations of higher complexity comprehend i.a. elevation contours with shadow enhancement, Tanaka- 
Kitiro Lines, and representations generated by manipulations in the image domain. The latter ones can be performed by 
filters with finite pulse response. Low-pass, band-pass, directional, and "coarse" filters have been applied. 
Raster image operators offer a multitude of design possibilities by means of which the traditional design methods can be 
varied and combined, and thus lead to new computer-generated relief representations. One can for instance generate 
- hill shadings consisting of a texture of elevation contour lines with a low height interval, 
- elevation contours with three or more height intervals, e.g. 10 min light grey, 50 m in grey, and 200 m in black, 
- shaded elevation contours with black shadow and grey light lines, 
- hill shading with modified illumination, e.g. 90 degrees light and 270 degrees shadow, 
- colour shadings of various types, 
- aerial perspectives. 
Basically two trends can be recognised in the application of the above mentioned approaches: first, the integration of 
more than one representation method (which are easily combinable), of different representation effects like black-and- 
white shading, colour shading, line shading, of presently less-used graphic means in relief representation like colour or 
acuity/fuzziness, of geomorphological aspects (see below) and of different scales generated through filtering. 
Furthermore, trends of distinction can be identified. This concerns the distinction of the representation type (which is 
easily achievable due to the parameter selectivity), the distinction or differentiation of the representation contents: geo- 
morphological details like ridge lines, drain lines, edge lines and relief entities with defined slopes and aspects etc. can 
be elaborated. This all shows that for a particular purposes a multitude of special relief representations can be gener- 
ated. 
International Archives of Photogrammetry and Remote Sensing. Vol. XXXII, Part 7, Budapest, 1998 631