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üng 
nifi- 
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lata 
een 
n fi- 
  
e IS 
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hich 
data 
3mo- 
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zone 
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(4) 
The 
ne is 
rres- 
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ther, 
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
Figure 8. 
A buffer zone is established as the transition between 
the old data base and the updated area. 
but there are still break points at the borders of the 
buffer zone. A smoother transition is obtained by the 
weight function 
z = zı- cos2(*X) + zo- sin4(** 5 
buffer 1 C) 2 C) ( ) 
which is illustrated in figure 5. 
  
  
  
  
  
  
o 
01 
02+ 
$9 «——— b —» o 
ud 3 "UG 
cr Im 
5p S Buffer Zone des 
EG & 
eG Da 
Figure 4. 
The transition curve of the standard deviation as a 
result of the weights of equation 4. 
529 
  
  
  
  
  
  
o 
01 
O2] 
9 4—— b ——» © 
N N 
us "Ug 
Es Buffer Z ie 
er Zone qd 
ES BR 
OR PQ 
Figure 5. 
A smooth transition curve is obtained by applying the 
weigths of equation 5. 
USE OF THE UPDATED ELEVATION DATA BASE 
The result of an updating procedure is in most cases 
a data base with varying grid spacing and accuracy. 
This will complicate the use of the data base and in- 
crease the risk of misuse. Therefore, it is necessary to 
communicate the non-homogeneity of the data base 
to the user. Special maps or illustrations attached to 
the data base can show these variations together 
with precise table information stored in the data ba- 
se. In particular, transition zones between different 
grid sizes and accuracies are potential areas for mis- 
use of the data base. 
An automatic warning system could be created for fu- 
ture data bases. An example is the construction of 
contours where conventional rules for the relation 
between contour interval and point accuracy could be 
included in the data extraction module. An alarm 
should warn the user, if the contour interval required 
is less than that permitted by the quality of the elev- 
ation data. À more drastic solution would be to pre- 
vent the construction of contours until the require- 
ments on the contour interval is in accordance with 
the data quality. It might be helpful for the skilled 
user and necessary for the unexperienced. 
CONCLUSION 
The updated elevation data base is almost always a 
data base with a more complex structure than the 
original data base. Point density, accuracy and even 
data structure may vary within the data base. This 
accentuates the need for additional information com- 
prising historical data for any step in the creation of 
the data base. Such information is essential in future 
updating as well as to the regular user of the data ba- 
se to prevent misinterpretation of data. The data ba- 
se software should comprise warning systems or per-