Using the pre- and post-seismic IKONOS stereo pairs and improved 3D coordinates of the ground points, an individual collapsed building can be detected by calculating the height difference of the corner points of the building. In addition, three statuses of the building being assessed, totally collapsed, partially collapsed or not collapsed, can be determined, and the number of collapsed storeys can be estimated.
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The region of the collapsed buildings can be determined by differencing the pre- and post-seismic DEMs created from both the pre- and post-seismic IKONOS stereo pairs. Accuracies of about 3.1 m and 2.5 m for DEM generation can be achieved using the pre- and post-seismic IKONOS stereo pairs, respectively. An overall accuracy of better than 94% can be achieved for the detection of the collapsed buildings based on the difference DEM using the pixel- and object-based assessment methods. At the same time, the latter method has the advantage of providing more realistic results over the former in that the percentage of the difference DEM pixels that fall inside a building polygon determines if the building being assessed has collapsed. However, the accuracy of detecting the collapsed buildings using the object-based assessment method is sensitive to the percentage threshold for the change in pixel value.