In this paper, we focus on the construction of a full 3D model of a canal tunnel by combining terrestrial laser (for its above-water part) and sonar (for its underwater part) scans collected from static acquisitions. The modeling of such a structure is challenging because the sonar device is used in a narrow environment that induces many artifacts. Moreover, the location and the orientation of the sonar device are unknown. In our approach, sonar data are first simultaneously denoised and meshed. Then, above- and under-water point clouds are co-registered to generate directly the full 3D model of the canal tunnel. Faced with the lack of overlap between both models, we introduce a robust algorithm that relies on geometrical entities and partially-immersed targets, which are visible in both the laser and sonar point clouds. A full 3D model, visually promising, of the entrance of a canal tunnel is obtained. The analysis of the method raises several improvement directions that will help with obtaining more accurate models, in a more automated way, in the limits of the involved technology.

Abstract. The archaeological cave « Les Fraux » (Saint-Martin-de-Fressengeas, Dordogne) forms a great network of galleries, characterized by the exceptional richness of its archaeological Bronze Age remains such as domestic fireplaces, ceramic and metal deposits, fingerings incised in the clayey-walls. The cave has been closed according to the collapse of its entrance, at the end of the Bronze Age. The study in progress takes place in a new kind of tool founded by the Institute of Ecology and Environment (INEE): sites dedicated to the study of global ecology. In that framework, we develop new methods of data acquiring based on 3D contact-free measurement techniques, according to an interdisciplinary way. A partnership among archaeologists and surveyors from INSA allow the 3D recording and modeling of the global volume cave. In the same time, we implement the high resolution recording of parietal representations (engravings and fingerings). The aim of this paper is focusing on the complementarity of data which are produced by the different scales of 3D recording used in the cave. Another purpose is to issue a statement of the different 3D technologies tested in "Les Fraux". Finally, we propose to start a discussion about the way we try to produce an accurate 3D documentation and adapted to the researchers needs.

Mechanical Sonar Scanning (MSS) is a recent technology that allows sonar to be used for static measurements in the same way as Terrestrial Laser Scanners (TLS), which makes it an attractive tool for underwater infrastructure surveys. Nevertheless, the metrological capabilities of this type of device have been little explored in the literature, particularly in narrow and shallow environments. In this paper, we report on the experimental assessment of a recent MSS, the BlueView BV5000, in a lock. The 3D sonar scans performed with the system suspended from the surface are registered using an innovative algorithm that exploits external measurements from a total station and the symmetry of the structure. We review the different errors that impair sonar data, and compare the resulting point cloud to a TLS model that was acquired the day before, while the lock was completely emptied for maintenance. After correcting a tilt angle calibration error, the maximum difference is less than 10 cm, and the standard deviation is about 3 cm. Visual inspection shows that coarse defects of the masonry, such as stone lacks or cavities, can be detected in the MSS point cloud, while details smaller than 4 cm, e.g., damaged joints, are harder to notice.