‘pe. 
an be 
j the 
rity 
similar 
1991). 
  
nge 
tours. 
ero- 
y. À 
W 
risk 
rators 
is- 
an be 
es can 
be updated by means of a mathematical for- 
mular. This means, that object-oriented 
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
b d 
Figure 8 Creation of a soil erosivity map 
a slope map with 3 classes 
b map for soil type with 4 
classes 
c map created by overlapping 
a and b, the classes are de- 
rived by multiplying the 
class-indexes(t=slope x soil) 
d .soil erosivity map with 2 risk 
factors (A and B), they are 
derived from the relation 
L:1-594, t5: 6-113 8 
and topologically structured data allow 
query and analysis, they also enable the 
creation of new objects. They are the pre- 
requisites for a true Geographic Informa- 
tion System (Herring, 1990). 
4. CONCLUSION 
The concept of objects which are topologi- 
cally structured and attributed makes the 
height model more "intelligent". It re- 
sults in more accurate modelling and 
allows manipulation and analyzing.of the 
height data. The height models can then be 
used in Geographic Information Systems 
which makes GIS much more valuable. 
New applications and products can be crea- 
ted, such as 
- slope maps 
- shaded contours 
- generalisation of contours 
- flood plane modelling 
- dam placement studies 
- intervisibility analysis for the tele- 
communication industry 
- landslide and erosivity studies 
- creation of surface water drain areas, 
etc, 
The problems with the higher sophistica- 
tion in using and trouble shooting the 
software packages have to be overcome by 
better training and improvement of the 
user interface. 
ACKNOWLEDGEMENTS: 
The author likes to thank Thomas Jul Jen- 
sen for his help in programming, and Aal- 
borg University for its financial support 
of this investigation. 
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