Quality Assessment of Uav Photogrammetric Archaeological Survey

Abstract

<p><strong>Abstract.</strong> The paper reports the results of a photogrammetric survey made using an Unmanned Aerial Vehicle (UAV) in the archaeological site of the Roman Amphitheatre in Avella (Avellino, Italy). The aim of the study is to verify which modality of image acquisition (if only nadiral images or nadiral plus Oblique images), together with the method of Global Positioning Satellite System (GNSS) survey of the Ground Control Points (GCP) is able to produce the better 3D model, in terms of accuracy, in order to extract traditional graphic drawings (plan, elevation and section), suited to the required representation scales (1<span class="thinspace"></span>:<span class="thinspace"></span>100 and 1<span class="thinspace"></span>:<span class="thinspace"></span>50). The accuracy in georeferencing was evaluated analysing the residues on the GCPs; subsequently, a more detailed analysis of the accuracy of the final 3D model was performed analysing the residuals on the image coordinates, also called re-projection error. The method developed is based on the statistical analysis of the different models, built changing the GCPs survey method and the photogrammetric shots acquired. The results of our analysis show that the photogrammetric survey is more ‘stable’ using only nadiral images and that the nRTK technique allows results comparable to those obtained with static measurements, both in precision and in reliability. Moreover, if the GCPs are measured in nRTK mode, taking into consideration the graphical error, the maximum representation scale is 1<span class="thinspace"></span>:<span class="thinspace"></span>100, whereas the use of static technique makes it possible to describe major details, at a scale of 1<span class="thinspace"></span>:<span class="thinspace"></span>50.</p>

Accuracy Assessment of 3D Photogrammetric Models from an Unmanned Aerial Vehicle

“…Finally, a correlation analysis between the computed quality features will be carried out, to analyse the relationships that exist between them. Figure 4 shows a flow chart of the data processing, including those analysed in the reference work [43]. After the analysis of both the residuals on GCPs and the error projection, only the configuration that optimizes these two parameters will be further analysed with the evaluation of angles and image count.…”

“…Finally, a correlation analysis between the computed quality features will be carried out, to analyse the relationships that exist between them. Figure 4 shows a flow chart of the data processing, including those analysed in the reference work [43].…”

“…This work is the continuation of a previous research, published in [43], which had as its main purpose to verify which method of image acquisition and which modality of Global Positioning Satellite System (GNSS) survey of the GCPs allowed to produce the best 3D model, from which to derive traditional graphic designs, at the scales of representation commonly used.…”

“…The frequency distribution that best fits the data (the reprojection errors) is the Weibull distribution ( Figure 6). Also for these errors the chosen configuration (data set consisting of nadir and oblique images, georeferenced with GCPs surveyed in fast-static) is the one that gave the best results (lowest errors) [43]. Figure 7 shows the classified map of the reprojection errors on the amphitheatre.…”

Advanced Techniques for Fast and Accurate Heritage Digitisation in Multiple Case Studies

“…Bearing in mind the need for accurate documentation of the vertical structural supports and masonry walls that support the wooden frameworks on which salt is produced, and considering that the exclusive use of nadir shots offers less precise results, particularly in geometric description of the vertical planes [30], the use of nadir shots (Gimbal angle of -90°) and oblique shots (Gimbal angle of -45°) was combined. One nadir shot and four oblique shots were thus done per sector, with the latter aligned to the four trajectories that join the vertices of each sector with its centre (Figure 2b Due to the extremely difficult access, and the narrowness and the low clearance of many of the spaces situated under the salt evaporation beds, data collection using photogrammetric techniques or TLS that require tripod stationing is practically undoable.…”