Detection of the Earthquake Damaged Buildings from Post-event Aerial Photographs Using Perceptual Grouping

The collapsed buildings due to Izmit, Turkey earthquake that occurred on 17 August 1999 were detected from post-event aerial photographs using the shadow analysis and the perceptual grouping procedure. The selected area of study is a part of the city of Golcuk, which is one of the urban areas most strongly hit by the earthquake. The area contains a total of 282 buildings, of which 79 are collapsed and 203 are un-collapsed. First, the Canny edge detector was applied to detect the edges between the cast shadows and the surroundings. Second, the output edge image was converted into vector line segments through a raster-to-vector conversion process. These line segments were then grouped together using a two-level hierarchical perceptual grouping procedure. The boundaries of the buildings were available and stored in a GIS as vector polygons. Therefore, after the perceptual grouping procedure, the damage conditions of the buildings were assessed on a building-by-building basis by measuring the aggreement between the detected line segments and the vector building boundaries. The results obtained is satisfactory. The overall accuracy was found to be 72.6%. Of the total 79 collapsed buildings, 63 were detected correctly by the proposed approach, giving 79.7% producer’s accuracy.