Potential of Smartphone SfM Photogrammetry to Measure Coastal Morphodynamics

Abstract

With recent advances in photogrammetric processing methods and sensor technologies, smartphones represent a new opportunity of mainstream, low-cost sensor, with a great potential for Structure-from-Motion (SfM) photogrammetry, and in particular for participatory science programs or citizen observatories. Keeping in mind the application in citizen observatories, three smartphone models (Galaxy S7®, Lumia 930® and iPhone 8®) and a bridge camera were compared (separately and in combination) for coastal applications: A coastal cliff and a sandy beach. Various acquisition protocols, at different distances from a cliff face and using “linear” or “fan-shaped” capture mode, were also assessed in their efficiency. A simultaneous Terrestrial Laser Scanner (TLS) survey provided a reference dataset to assess the quality of the SfM reconstructions. Satisfactory reconstructions (mean error < 5 cm) of the cliff face were obtained using all smartphone models tested. To measure the cliff face, fan-shaped capturing mode allowed a quicker image acquisition on site and better results (mean error of 1.3 cm with a standard deviation of 0.1 cm at 20 m from the cliff face) than linear capturing mode (mean error of 2.5 cm with a standard deviation of 21.8 cm), provided that the distance to the cliff face is sufficient to ensure a good image overlap. To obtain satisfactory results over beaches, we show that it is preferable to have high-angle shots of the study area, which may limit the applicability of the method for certain sites.

RTK GNSS-Assisted Terrestrial SfM Photogrammetry without GCP: Application to Coastal Morphodynamics Monitoring

“…For measuring the entire cliff face, the setup was moved to different camera stations. For each station, approximately five to ten photographs are collected according to a "fan-shaped capture" (i.e., spinning the camera around the vertical axis [9]) and the station position is measured by RTK GNSS For measuring the entire cliff face, the setup was moved to different camera stations. For each station, approximately five to ten photographs are collected according to a "fan-shaped capture" (i.e., spinning the camera around the vertical axis [9]) and the station position is measured by RTK GNSS using a 30-s average.…”

“…Aerial surveys are generally performed by Unmanned Aerial Vehicles (UAVs) and mainly used for beach surveys [1][2][3], whereas data collected from a terrestrial point of view are more suited to cliff surveys, allowing for better capturing the cliff face. These terrestrial data are typically obtained using a Terrestrial Laser Scanner (TLS) [4,5], a Mobile Laser Scanner (MLS) [6,7], or terrestrial photogrammetry [8,9]. This article focuses more particularly on these terrestrial methods.…”

Comparison of UAS-Based Structure-from-Motion and LiDAR for Structural Characterization of Short Broadacre Crops

“…Four point cloud comparison methods are commonly used to compare 3D point clouds: DEM of difference (DoD) [53][54][55][56], cloud-to-cloud (C2C) distance [57][58][59][60], C2M distance [47,[61][62][63], and M3C2 distance [64][65][66][67][68][69]. The DoD approach subtracts two DEMs or DSMs using a top view and is fast/easy to implement and interpret.…”

Measurement of Rock Joint Surfaces by Using Smartphone Structure from Motion (SfM) Photogrammetry

“…The results showed that properly calibrated smartphone cameras can be used for photogrammetric tasks with a required accuracy of 1:10,000. The smartphone SfM photogrammetric method has been tested in many fields including flexible structural monitoring [ 18 ], coastal monitoring [ 19 , 20 , 21 ], auxiliary medical examinations [ 22 , 23 ], alpine alluvial fan surveys [ 24 ], and soil water erosion [ 25 ]. Although the smartphone SfM photogrammetric method has been successfully used in these applications and has produced high-resolution results, to the best of the authors’ knowledge, this approach has rarely been used for mapping the topography of rock joint surfaces in geotechnical laboratories.…”