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231 José Balsa Barreiro, Dieter Fritsch 3D Modelling of historic urban centres and… per pixel. This point cloud allows us to obtain a very accurate representation of the scanned object, which is perfectly valid for 3D modelling tasks. http://revista.ieee.es Close-up photogrammetry Photographs that are taken from a distance of less than 300 metres are generally considered under this technique. This photogrammetric technique is mainly used to obtain 3D renderings of small objects. Close-up photogrammetry allows for the reconstruction of small pieces in archaeology and architecture, the modelling and manufacture of industrial parts, and can even be used for the evaluation and quantification of material damages in vehicles that have been involved in accidents40. Close-up photogrammetry can be employed to complement the data collection process of laser systems. Thus, within the framework of this same project, Li41 used close-up photogrammetry techniques to obtain information on certain facades or specific areas, given the physical limitations encountered when parking the scanner laser equipment in certain parts of the Nagold riverbed in Calw. Drawing from this particular experience and others of a similar nature, it was decided to take a complete picture of most of the historic buildings of the city. This imaging covers the complete extension of the facades of the buildings concerned from a large number of positions and covering a wide range of perspectives. Between the successive images there must be high levels of overlap that allow them to be linked up through a series of points, thus ensuring a three-dimensional reconstruction of the objects with photogrammetric techniques. Distance or aerial photogrammetry The use of terrestrial laser scanner equipment from ground points permits the acquisition of data from the facades of the buildings, although these systems have certain limitations in terms of acquiring information from the upper parts and/or roofs of these buildings (Figure 4). Aerial photogrammetry complements the terrestrial laser scanner, allowing for the collection of three-dimensional information in areas where it could not be initially obtained. The point clouds obtained by aerial photogrammetry enable a full reconstruction of the urban landscape including, in addition to the roofs, the interior areas of the urban fabric where terrestrial access is usually restricted. 40  LUHMANN, Thomas; ROBSON, Stuart and KYLE, Stephen. «Close range photogrammetry: principles, techniques and applications». Whittles: Dunbeath (United Kingdom), 2007, pp. 528 41  LI, Jing (supervised by, Dieter and KHOSVARANI, Ali M. «High definition modeling of Calw, Badstrasse and its Google Earth’ integration», Master Thesis, Germany, Universidad de Stuttgart, 2014.

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