Abstract
Abstract. The combined use of high-resolution digital images taken from ground as well as from RPAS (Remotely Piloted Aircraft Systems) have significantly increased the potential of close range digital photogrammetry applications in Cultural Heritage surveying and modeling. It is in fact possible, thanks to SfM (Structure from Motion), to simultaneously process great numbers of aerial and terrestrial images for the production of a dense point cloud of an object. In order to analyze the accuracy of results, we started numerous tests based on the comparison between 3D digital models of a monumental complex realized by the integration of aerial and terrestrial photogrammetry and an accurate TLS (Terrestrial Laser Scanner) reference model of the same object. A lot of digital images of a renaissance castle, assumed as test site, have been taken both by ground level and by RPAS at different distances and flight altitudes and with different flight patterns. As first step of the experimentation, the images were previously processed with Agisoft PhotoScan, one of the most popular photogrammetric software. The comparison between the photogrammetric DSM of the monument and a TLS reference one was carried out by evaluating the average deviation between the points belonging to the two entities, both globally and locally, on individual façades and architectural elements (sections and particular). In this paper the results of the first test are presented. A good agreement between photogrammetric and TLS digital models of the castle is pointed out.
Highlights
Digital Photogrammetry has made many advances in recent years
With regard to close range photogrammetry and its application to cultural heritage survey, a significant progress is mainly due to the development of image processing codes (SfM) which automatically realize object point cloud by a simultaneous elaboration of large number of images, taken at any scale and orientation, with even not calibrated cameras (Fonstad et al, 2013; Green et al, 2014)
Given the large number of digital images to be used for data processing, it was decided to reduce the number of at least aerial images, so as to optimize the computational time for the same accuracy of the geometrical model
Summary
Digital Photogrammetry has made many advances in recent years. The combined use of high-resolution digital images, Computer Vision codes and new image acquisition systems, like RPAS (Remotely Piloted Aircraft Systems), have significantly increased the potential of the technique. In the meantime RPAS systems have undergone a rapid evolution with particular regard to micro-RPAS (Nex and Remondino, 2014; Turner et al, 2012; Mancini et al, 2013), opening the way to the integration of aerial and terrestrial close range images. In this way, it is possible to create accurate digital models of entire buildings, including the roof and the parts inaccessible to the scanner (Hashim et al, 2012). The question arises spontaneously, how far a photogrammetric survey based on such integrated approach (Koutsoudis et al, 2014) is reliable and accurate? And again, is it possible to define a procedure that yields the best results in terms of accuracy, optimizing the duration of acquisition and processing images? The solution of the problem is complicated, since the accuracy of the results depends on many factors as, for example, the optical and digital performances of the camera, the spatial distribution, scale, overlapping and orientation of the images, the photogrammetric processing code and the setting of its parameters, etc
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