Towards a strategy for suburban informal building control through automatic change detection

The problem of informal settlements is of significant importance worldwide and has similar causes whether in regions of Europe, Africa, Central and Latin America, or Asia. The type and quality of constructions vary, however. In Greece the majority of informal buildings are good constructions and do not resemble dense slums. Their number is estimated to be almost 1,000,000 all over the country. It can be said that it is actually a social and economic issue, that must be faced by a combination of measures. In this paper, a proposal to face this problem is developed, at technical and administrative level, taking into consideration the criteria of least possible cost and maximum benefit from usage of modern technology. Its basic idea is the development of a system for periodic automatic monitoring and detection of new buildings in large areas. With field control on specific locations, the immediate detection of informal construction becomes possible even before their completion, when measures against their development can be taken more easily. The suggested procedure is based technically on the use of high resolution image stereopairs and the application of automatic change detection, by computation and comparison of Digital Surface Models (DSMs), and building extraction techniques. Over the last twenty years research has been done in the field of automatically detecting and monitoring man made objects, mainly roads and buildings, with promising results and accuracies of 1 pixel or better. The proposed procedure is accompanied by a cost estimate for its application on eastern Attica, which is one of the Hellenic prefectures with a great number of existing but also emerging informal constructions.