Measuring Change Using Quantitative Differencing of Repeat Structure-From-Motion Photogrammetry: The Effect of Storms on Coastal Boulder Deposits

Abstract

Repeat photogrammetry is increasingly the go-too tool for long-term geomorphic monitoring, but quantifying the differences between structure-from-motion (SfM) models is a developing field. Volumetric differencing software (such as the open-source package CloudCompare) provides an efficient mechanism for quantifying change in landscapes. In this case study, we apply this methodology to coastal boulder deposits on Inishmore, Ireland. Storm waves are known to move these rocks, but boulder transportation and evolution of the deposits are not well documented. We used two disparate SfM data sets for this analysis. The first model was built from imagery captured in 2015 using a GoPro Hero 3+ camera (fisheye lens) and the second used 2017 imagery from a DJI FC300X camera (standard digital single-lens reflex (DSLR) camera); and we used CloudCompare to measure the differences between them. This study produced two noteworthy findings: First, volumetric differencing reveals that short-term changes in boulder deposits can be larger than expected, and that frequent monitoring can reveal not only the scale but the complexities of boulder transport in this setting. This is a valuable addition to our growing understanding of coastal boulder deposits. Second, SfM models generated by different imaging hardware can be successfully compared at sub-decimeter resolution, even when one of the camera systems has substantial lens distortion. This means that older image sets, which might not otherwise be considered of appropriate quality for co-analysis with more recent data, should not be ignored as data sources in long-term monitoring studies.Despite these improvements in protocols for data collection and analysis, quantifying change via repeat photogrammetry remains a challenge, generally requiring manipulation of digital terrain models (DTMs) using Geographic Information Systems (GIS) [45,46]. But recent innovations in 3D differencing software, as implemented in the open-source package CloudCompare (www.danielgm.net/cc/) enable rapid, objective, and replicable quantitative differencing [47]. CloudCompare is a cross-platform 3D point cloud and mesh processing package, which provides a suite of features for direct comparison of dense point clouds (>10 million points) and meshes on standard consumer computer hardware [48,49]. Accessibility and ease of use make CloudCompare an attractive tool, and it is applied increasingly in a variety of fields, including mapping [50,51], archaeology [52,53], and geomorphology [54][55][56][57].Another issue relevant to long term monitoring studies is how to deal with repeat imagery captured using different kinds of hardware, with different resolutions and/or distortion levels. The ultra-wide-angle (fisheye) lenses mounted on the popular consumer camera brand GoPro capture a~120 • field of view, but have barrel distortion due to their short focal length. Despite their limitations, GoPro cameras are popular tools for acquiring UAV imagery [24,31,[58][59][60], they are relatively inexpensive, are light enou...

Quantification of contemporary storm‐induced boulder transport on an intertidal shore platform using radio frequency identification technology

“…Thus, storm activity at Bembridge initiates geomorphic change on a larger scale than had previously been realized. This reinforces the findings of Pérez-Alberti and Trenhaile (2015), Gómez-Pazo et al (2019) and Nagle-McNaughton and Cox (2020), who documented widespread, collective mass movement of detached clasts using unmanned aerial vehicles (UAVs).…”

“…This reinforces the findings of Pérez‐Alberti and Trenhaile (), Gómez‐Pazo et al . () and Nagle‐McNaughton and Cox (), who documented widespread, collective mass movement of detached clasts using unmanned aerial vehicles (UAVs).…”

Large-Scale Reality Modeling of a University Campus Using Combined UAV and Terrestrial Photogrammetry for Historical Preservation and Practical Use

“…Agisoft Metashape © (see https://www.agisoft.com accessed 6 November 2021) and Bentley™ ContextCapture frequently receive the photos and metadata as inputs, and outputs fully functional SfM 3D models; the models are processed by readymade standard analyses as well as additional capabilities to manipulate and understand the data/models [35,42,47,58,[73][74][75][76][77]. CloudCompare also streamlines analysis of models and point clouds [42,47,57,58,[78][79][80]. CloudCompare permits cloud to cloud comparisons, iterative point cloud alignment, point density and resolution analyses, cloning of point clouds for additional processing, and more.…”

The complexity of studying coasts: From forms and processes to management

“…This method can be used for analysing the response of beaches and dunes to different storm-induced processes, like swash, collision, boulder movement, overwash, beach surface downwearing, dune front retreat, etc. (Pérez-Alberti and Trenhaile, 2015;Talavera et al, 2018;Nagle-McNaughton and Cox, 2020).…”