Computer Vision Photogrammetry for Underwater Archaeological Site Recording in a Low-Visibility Environment

Abstract

ABSTRACT:Computer Vision Photogrammetry allows archaeologists to accurately record underwater sites in three dimensions using simple twodimensional picture or video sequences, automatically processed in dedicated software. In this article, I share my experience in working with one such software package, namely PhotoScan, to record a Dutch shipwreck site. In order to demonstrate the method's reliability and flexibility, the site in question is reconstructed from simple GoPro footage, captured in low-visibility conditions. Based on the results of this case study, Computer Vision Photogrammetry compares very favourably to manual recording methods both in recording efficiency, and in the quality of the final results. In a final section, the significance of Computer Vision Photogrammetry is then assessed from a historical perspective, by placing the current research in the wider context of about half a century of successful use of Analytical and later Digital photogrammetry in the field of underwater archaeology. I conclude that while photogrammetry has been used in our discipline for several decades now, for various reasons the method was only ever used by a relatively small percentage of projects. This is likely to change in the near future since, compared to the 'traditional' photogrammetry approaches employed in the past, today Computer Vision Photogrammetry is easier to use, more reliable and more affordable than ever before, while at the same time producing more accurate and more detailed three-dimensional results.

Camera Calibration Techniques for Accurate Measurement Underwater

“…Rather than highly constrained patterns of stereo photographs and traditional, manual photogrammetric solutions, many photographs from a single camera and the principle of Structure from Motion (SfM) (Pollefeys et al 2000) can be used to automatically generate a detailed 3D model of the site, shipwreck or artefacts. SfM has been used effectively to map archaeological sites (McCarthy 2014;McCarthy and Benjamin 2014;Skarlatos et al 2012;Van Damme 2015), compare sites before and after the removal of encrustations (Bruno et al 2013) and create models for the artefacts from a shipwreck (Balletti et al 2015;Fulton et al 2016;Green et al 2002;McCarthy and Benjamin 2014). Whilst there are some practical considerations that must be respected to obtain an effective and complete 3D virtual model (McCarthy and Benjamin 2014), the locations of the photographs are relatively unconstrained, which is a significant advantage in the underwater environment.…”

Assessing the Accuracy of High Resolution Digital Surface Models Computed by PhotoScan® and MicMac® in Sub-Optimal Survey Conditions

“…This software is commonly used for archeological purposes [18,19], but also for topography and mapping [20]. The procedure for deriving orthophotographs and the DSM consists of four main stages.…”

Underwater Photogrammetric Recording at the Site of Anfeh, Lebanon

“…However, multiimage photogrammetry and its related applications are much wider in scope as they breach the spatial and temporal limitations encountered when working under water, and also constitute a dissemination tool that fosters accessibility and hermeneutic discussions about the archaeological material. The nature, range, and development of photogrammetry go beyond the scope of this chapter and have been argued elsewhere (Balletti et al 2016;Costa et al 2015;Gawlik 2014;Green et al 2002;Drap 2012;Polzer and Casaban 2012;McCarthy 2014;McCarthy and Benjamin 2014;Van Damme 2015;Yamafune et al 2016; and the various chapters in this volume). Notably, McCarthy (2014, 176) stressed the potential of this technique as 'a practical and cost-effective method for accurate survey and as a tool for community engagement with heritage.'…”