On the Use of Historical Flights for the Urban Growth Analysis of Cities Through Time: The Case Study of Avila (Spain)

Historical aerial images are a unique and relatively unexplored means of deriving spatio-temporal information for scenes and landscapes. Such historical imagery can be combined with photointerpretation and image-based 3D modelling techniques, providing the fourth dimension of time to 3D geometrical representations. This allows urban planners, historians, and other specialists to identify, describe, and analyse changes in scenes and landscapes. Urban growth has an important impact on the sustainable development of cities. An important step for the analysis of urban growth is the identification of different urban sectors. To this end, this paper proposes a methodology for the 4D urban growth analysis of cities through time using a free and open source software developed by the authors. This approach uses the latest advances in photogrammetry, including the so-called incremental Structure from Motion, to evaluate the urbanistic changes of a city by means of confronting two-point clouds from different eras. The objectives of this paper are twofold: (i) first, the processing of historical aerial images using modern photogrammetric techniques; (ii) second, deriving spatio-temporal information for urban cities, offering a method for researchers to identify changes over time. In order to validate this method, the urban growth of the city of Avila between 1956 and 2017 was assessed taking the historical American flight of 1956 and the digital aerial flight of 2017. The results were statistically assessed according to georeferencing quality, confirming that the approach developed can be used to support urban growth analysis through time and providing relevant data in 2D and 3D.