Assessment of the state of conservation of buildings through roof mapping using very high spatial resolution images

The assessment of the state of conservation of buildings is extremely important in urban rehabilitation. In the case of historical towns or city centres, the pathological characterization using traditional methods is a laborious and time consuming procedure. This study aims to show that Very High Spatial Resolution (VHSR) multispectral images can be used to obtain information regarding the state of conservation of roofs where, usually, building degradation starts. The study was performed with multispectral aerial images with a spatial resolution of 0.5 m. To extract the required information, a hybrid classification method was developed, that integrates pixel and object based classification methods, as well as information regarding the classification uncertainty. The proposed method was tested on the classification of the historical city centre of Coimbra, in Portugal, that includes over than 800 buildings. The results were then validated with the data obtained from a study conducted during 2 years by a nine element team from the University of Coimbra, using traditional methods. The study performed achieved a global classification accuracy of 78%, which proves that the state of conservation of roofs can be obtained from VHSR multispectral images using the described methodology with a fairly good accuracy.