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The second part of the rule for road identification is based on 
the shape of roads. Different directional filters were used to 
enhance linear features in the SPOT image. The filters were 
constructed to enhance vertical, horizontal and diagonal lines. 
Four new raster layers, one for each direction, were created by 
filtering. The information in these four layers was combined and 
a raster layer showing linear features in four different directions 
was created. 
  
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Figure 4. Membership values for fuzzy statement "line shaped 
and thin". Roads have membership values close to 1, and appear 
dark in the image. 
A second membership function was defined for the class 
line shaped. and. thin , based on the pixel values in the layer 
with linear features. The membership function was defined in 
the same way as for high. spectral reflectance, using median 
and standard deviation. However, the minimum and maximum 
values for this map layer were set according to: 
min = (median + 3 * standard deviation) 
max = (median + 6 * standard deviation). 
The two resulting layers are fuzzy sets. The logical AND 
operator defines an intersection between these two fuzzy sets 
(high_spectral_reflectance and line shaped and thin) In 
fuzzy logic, the AND operation corresponds to the minimum 
value in the fuzzy sets. Thus, in the combination of the layers, 
each corresponding pixel in the two layers was compared and 
the one with the lowest value was chosen to obtain a map layer 
Showing membership in the class road (e.g. Eastman 1993, 
Altman 1994). As a final step, a mask based on the topographic 
map was used to exclude previously mapped roads. 
Example clear-cuts 
The rule for identification of clear-cuts was constructed in the 
Same way as the rule for roads: 
IF high, spectral reflectance 
ANDIFNOT road 
ANDIFNOT existing clearcut 
THEN new. clearcut 
537 
Here, the combination of map layers is based both on the logical 
AND operator and the NOT operator; corresponding to the 
complement of the fuzzy set for roads, and the minimum value 
of this complement and the membership value for high spectral 
reflectance. Finally, previously mapped clear-cuts were masked 
out to limit the confusion between old and new clear-cuts. 
4. PRELIMINARY RESULTS AND DISCUSSION 
The preliminary results are promising. Five known new roads 
were clearly detected, with practically no confusion with other 
objects of similar spectral characteristics (figure 5). The new 
roads are detected with membership values close to 1. Most of 
the old roads are also detected, but their membership values are 
lower. Since a mask was applied the fact that older roads are 
also detected is not a problem, but implies some robustness in 
the method. In the final map layer the new roads are clearly 
identified and the confusion with other objects is negligible; 
few pixels were incorrectly identified as roads. 
In this dataset, the statement "line shaped and thin" has more 
influence on the result than the statement "high, spectral 
reflectance". Almost exactly the same result was obtained from 
the single statement as from the two statements combined. The 
importance of different parts of the rules would, however, 
change from area to area. If, for example, there was a river 
present in this area, that too would be "line, shaped, and. thin" 
but it would have "low. spectral, reflectance". 
  
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A 
  
  
  
Figure 5. Result from the rule for extraction of new roads. 5 
new roads have been detected. The road pixels have 
membership values close to 1, and appear dark in the image. 
Three new clear-cuts were successfully identified and the 
confusion with older clear-cuts was avoided by application of 
the mask (figure 6). The membership values differ between the 
three clear-cuts The two northern ones mainly have 
membership values between 0.8 and 1, while the clear-cut in the 
south-east has significantly lower values, mostly between 0.3 
and 0.5. However, even without mask they are clearly separated 
from older clear-cuts, for which the membership values range 
between 0.1 and 0.3, with a few exceptions. There is more 
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B4. Vienna 1996