Three-Dimensional Survey of Guattari Cave With Traditional and Mobile Phone Cameras

Abstract

<p><strong>Abstract.</strong> Sometimes, the georeferencing of a cave in the global reference system can be challenging. Some difficulties may arise when narrow passages do not allow the use of classical topographic equipment or a terrestrial laser scanner. In these specific cases, the surveyor can employ a visual-based approach to produce both the followed path and the 3D model of the hypogeum. The report we are presenting is the result of a survey in the Guattari cave carried out using images taken by a Huawei P9 mobile phone and a Nikon D800E camera with a 16 mm fisheye lens. Several targets were measured in order to contain the deformation of the models. Three GCPs located just outside the cave have been used to georeference the models. The data have been acquired by a double frequency GNSS receiver in static session mode. The comparison between the two models shows a substantial concordance only in the area outside the cave where the GCPs were measured. In the innermost areas, the two models differ by as much as two meters.</p>

Solutions and limitations of the geomatic survey of an archaeological site in hard to access areas with a latest generation smartphone: the example of the Intihuatana stone in Machu Picchu (Peru)

“…In these and other works in the literature on the use of smartphones for photogrammetry, quite variable precision and accuracy have been observed, ranging from tens of centimetres [10] to a few centimetres [11], the causes of this variability are still being studied by the scientific community. A very important factor is the use of Ground Control Points (GCPs) without which there are poor and uncontrolled results [12], [13].…”

“…Liquid lens technology is also soon to be released, which will make the optical sensors of smartphones much more versatile but, on the other hand, calibration or self-calibration of the optics will be more complex. In any case, smartphone images have provided interesting results, especially considering their easy transportation [10], [11].…”

“…A very important factor is the use of Ground Control Points (GCPs) without which there are poor and uncontrolled results [12], [13]. Other factors that influence the final results can be: the size and shape of the object to be detected, the acquisition distance and, obviously, the quality of the camera optics; it is precisely because of this last factor that it seems that the most recent smartphones are getting closer and closer to the classic professional cameras, which in any case almost always give more accurate results [10].…”

“…The geometry and sequence of the images to be acquired for correct photogrammetric reconstruction using smartphones is the subject of lively debate in the scientific community, which has also developed useful guidelines [19]. For this experiment, the authors have decided to proceed according to their experience gained in previous experiments [1], [2], [10] and therefore to use mainly the intermediate focal length with a single horizontal strip, maintaining an overlap between one frame and the next never minor than 60 % in the longitudinal direction.…”

The Fusion of External and Internal 3d Photogrammetric Models as a Tool to Investigate the Ancient Human/Cave Interaction: The La Sassa Case Study

“…Some targets could be placed inside and outside the cave to help the orientation of the images. They can be used to constrain the model deformations using their distances, other than strengthen the camera network (Alessandri et al 2019b). The software processes the tie points to build the sparse point cloud.…”