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To dissect the façade elements, we use the knowledge that
facing is always surrounded by oak beams which are much
darker spectrally. This is reflected by an important mean
difference to darker neighbours.
Figure 5. Rule established for the discrimination of
the class “facing” (yellow).
Nevertheless, the rule is not sufficient (Fig.5). So another
feature is introduced according to the mean difference to
general neighbours. The reasoning continues with the beams :
beams, but not only beams, are characterised by dark colours.
Thus we introduce a second criterion according to the
distance separating them from previously classified objects.
Indeed, one beam is always in direct contact to facing, so that
distance is placed to zero.
Each class of interest is analysed in this way. Tiled roof and
freestones (composing the foundations of that house) are
elements of the same parent class and, in addition to their
own feature, inherit the area criterion from their parent class.
After rule development, a classification based on fuzzy logic
is performed over the entire image, without any training
sample. Fig.6 illustrates the resulting classification.
Figure 6. First result of the rule based classification
Fig.3 sums up all experiments and results. Obviously,
although the last classification provides the best results, it
needs to be improved by refining the membership rules.
Considering the last set of rules, other photographs are used
for testing the reliability of the formalisation. Fig 7 shows a
lot of correspondences, but also raises new problems which
will help us to refine the initial set of rules by further
investigations.
Figure 7. Same set of rules directly applied on other
datasets.
4. CONCLUSION AND OUTLOOK
Conventional classification techniques are not anymore
accurate for high resolution imagery. Trying to extract
information automatically from these images, one is
confronted to the difficulty to formalise human knowledge.
Nevertheless, interpretation of this knowledge allows to
sustain a set of rules describing different elements of interest.
Thereby, once the rules are established, they might enable
further automatic classifications of other half-timbered
Alsatian façades and help supplying architectural information
systems.
References
Baatz M.& A. Schäpe (2000): Multiresolution Segmentation:
an optimisation approach for high quality multi-scale image
segmentation. In: Strobl, J.&T. Blaschke (Hrsg) :
Angewandte Geographische Informationsverarbeitung XII.
Beiträge zum AGIT-Symposium Salzburg 2000.
Bianchin, A. & Barvin, L. (2003) : Land use in urban context
from IKONOS image : a case study. The International
Archives of the Photogrammetry, Remote Sensing and
Spatial Information Sciences, Vol.XXXIV-7, Regensburg,
Germany, 27-29 June 2003.
Buck, A., De Kok R., Schneider, T., Ammer, U, (2000) :
Integration von Fernerkundung und GIS zur Beobachtung
und Inventur von Schutzwäldern in de Bayerischen Alpen,
In: Strobl, J.&T. Blaschke (Hrsg) : Angewandte
Geographische Informationsverarbeitung XII. Beiträge zum
AGIT-Symposium Salzburg 2000.
Kauffmann, M. (2002): Facade Interpretation for Damage
Detection, In: PCV02 Photogrammetric Computer Vision -
ISPRS Comission III - Symposium Graz 2002.
Lang, S., Schöpfer, E., Blaschke, T. (2003): Object-specific
change based on assisted feature extraction : a case study of
an expanding suburban area. The International Archives of
the Photogrammetry, Remote Sensing and Spatial
Information Sciences, Vol.XXXIV-7, Regensburg, Germany,
27-29 June 2003.
