Figure 5b Figure 5c
Figure 4: Classification results (5b, 5c) of Area3 (5a)
4. CONCLUSIONS AND FUTURE WORK
In this paper, we introduce Sparse Representation framework to
classify the high resolution airborne images and use DSM
derived from LiDAR data to improve the classification. It's a
pixel-oriented classification method and under the framework of
Supervised Classification. The problem of ground object
recognition is formulated as a Basis Pursuit problem and solved
using convex programming methods
in MATLAB. The key idea of this method is to represent the
spectral vector (vector of IR-R-G value) of a pixel using
observation matrix. The observation matrix consists of spectral
vectors of pixels of typical ground objects (that is buildings,
trees, vegetation and road) which are interactively selected on
the images of test areas. A test procedure is carried out to
examine the distinctiveness of the selected pixels and pixels
which lead to misclassifications are replaced. In the recognition
process, each pixel of images from test areas is classified using
given observation matrix. Misclassifications often result from
both steps of the classification procedure. Misclassifications of
buildings and road in coarse classification procedure are mostly
due to shadows and spectral similarity. Some low bushes in the
shadow at left-bottom of Figure 2b are classified as buildings.
All the buildings with similar color like road are misclassified
as road (Figure 4b). In the procedure of refinement,
misclassifications result from enforcement of only single
elevation threshold on classification of ground objects.
Adaptive methods that take account of local properties of
ground objects and methods based on semantic knowledge may
help improve the result. In our future work generality and
effectiveness of our method will be further investigated and
adaptive methods will be examined.
Acknowledgement
This research is supported by the National Natural Science
Foundation of China (No. 40871211). The Vaihingen data set
was provided by the German Society for Photogrammetry,
Remote Sensing and Geoinformation (DGPF) [Cramer, 2010]:
http://www.ifp.uni-stuttgart.de/dgpf/DKEP-Allg. html
557
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