Three‐dimensional modeling of coastal boulders using multi‐view image measurements

Abstract

Coarse clastic sediments (boulders) on coastlines have seen a groundswell in geomorphic research interest over recent years, associated in part with the potential of boulder evidence for interpreting characteristics of high-energy wave processes. Yet, the fundamental property of boulder volume is normally difficult to measure accurately owing to complex clast morphology and irregular surface texture. To tackle this problem, this paper concentrates on creating precise, measurable and textured threedimensional (3D) models of coastal boulders without physical contact with the object, based on multi-view image measurement techniques. This method has several advantages over traditional measurements that are inaccurate or alternative solutions using costly techniques such as terrestrial laser scanning. Our methods propose the use of low-cost equipment (digital cameras) that can be used in various coastal environments to easily acquire numerous images of the object of interest. Initial results can be rapidly assessed in the field for immediate quality control. Resulting 3D models, built from overlapping multi-view digital photographs, allow the reconstruction of realistic-looking and textured boulder surfaces. A particular interest in this task is the family of algorithms known as structure from motion (SFM). The work presents analysis of SFM techniques by examining 3D models of boulders observed at a coastal field site on Lu Dao Island in south-eastern Taiwan.

Image-based surface reconstruction in geomorphometry – merits, limits and developments

“…Well-illuminated surfaces result in a high number of detected image features, which is demonstrated for coastal boulders under varying light conditions by Gienko and Terry (2014). Furthermore, Gómez-Gutiérrez et al (2014a) highlight the unfavourable influence of shadows because highest errors are measured in these regions; interestingly, these authors calculate the optimal time for image acquisition from the first DEM for multitemporal data acquisition.…”

“…Applications on 3-D point cloud treatment dating back to the last decade will soon be integrated into SfM photogrammetry post-processing; examples include geomorphological investigations in high-mountain areas (Milan et al, 2007), geological mapping (Buckley et al, 2008;Franceschi et al, 2009), soil erosion studies , investigation of fluvial systems Cavalli et al, 2008;, and mass wasting phenomena (Lim et al, 2005;Oppikofer et al, 2009;Abellán et al, 2010). Some other data treatment techniques that have been developed during the last decade and that will be adapted and enriched by the growing SfM photogrammetry community include automatic lithological segmentation according to the intensity signature (Humair et al, 2015), integration of ground-based lidar with thermal/hyperspectral imaging for lithological discrimination (Kääb, 2008;Hartzell et al, 2014), extraction of the structural settings on a given outcrop (Jaboyedoff et al, 2007;Sturzenegger and Stead, 2009;Gigli and Casagli, 2011;Riquelme et al, 2014) and the automatic extraction of geological patterns such as surface roughness (Poropat, 2009) and discontinuity spacing/persistence/waviness (Fekete et al, 2010;Khoshelham et al, 2011;Pollyea and Fairley, 2011). Concerning 4-D data treatment for investigating changes on natural slope, some lessons learned may be adapted from the two-and threedimensional tracking of mass movements (Teza et al, 2007;Monserrat and Crosetto, 2008), investigation of progressive failures (Royan et al, 2015;Kromer et al, 2015), and from 376 A.…”

Block and boulder transport in Eastern Samar (Philippines) during Supertyphoon Haiyan

“…Discrepancies between the two methods are shown in column V DGPS /V abc and represent the correction factor for V abc values. V DGPS and other emerging approaches such as terrestrial laser scanning (Hoffmann et al, 2013;Hoffmeister et al, 2014) or multi-view image measurement techniques (Khan et al, 2010;Terry et al, 2013;Gienko and Terry, 2014) are assumed to provide the best approximates of the real volume of the clasts. The clasts' bulk density (ρ b ) was calculated from five samples representative of the lithological composition of ESA 7 using the Archimedean principle (buoyancy in sea water) (Hughes, 1987).…”

Synthesis Study of an Erosion Hot Spot, Ocean Beach, California

“…An additional benefit of SfM from oblique photos is the dense topographic point clouds derived on vertical-to-overhanging landscapes (Figure 14), which are locations that airborne LIDAR generally do not image well (Gienko and Terry, 2014;Ružić et al, 2014). Furthermore, investigations using oblique photographs will benefit from the information-such as vegetation patterns and cliff conditions-that can be interpreted from the raw photos and the inherited RGB-color values in the point clouds (e.g., Figures 12 and 13).…”

“…The amount of photographic overlap in these surveys can vary from greater than 50%, and thus are potentially usable for SfM, to less than 50%, and are generally unusable for SfM (Figure 1). Oblique photographs may be ideal for mapping cliffs owing to the potential to generate topographic data on vertical-to-overhanging sections of cliffs that are traditionally poorly resolved with near-vertical aerial photographs and airborne LIDAR data (Gienko and Terry, 2014;Ružić et al, 2014).…”