How Reliable Is Structure from Motion (SfM) over Time and between Observers? A Case Study Using Coral Reef Bommies

Raoult, Vincent; Reid-Anderson, Sarah; Ferri, Andreas; Williamson, Jane E.

doi:10.3390/rs9070740

Cited by 38 publications

(43 citation statements)

References 62 publications

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“…Approximately 3,000 images per site were used as source data for photogrammetric reconstruction, resulting in detailed and accurate three‐dimensional digital models (cf. Casella et al, ; Ferrari et al, ; Raoult, Reid‐Anderson, Ferri, & Williamson, ; Storlazzi, Dartnell, Hatcher, & Gibbs, ). We created photomosaic maps and 3D digital elevation models (DEM) for each of our five study sites (Figure a, c).…”

Section: Methodsmentioning

confidence: 99%

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Patchy delivery of functions undermines functional redundancy in a high diversity system

2019

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Globally, many ecosystems are being challenged and transformed by anthropogenic climate change. Future ecosystem configurations will be heavily influenced by the critical ecological functions that affect resilience. Robust measures of these functions will thus be essential for understanding and responding to ecological change. Coral reefs are experiencing unprecedented ecological change due to global mass coral bleaching. After bleaching events and other disturbances, herbivorous fishes provide functions that are critical for reef resilience by controlling harmful proliferation of algae. Identifying functional diversity amongst herbivorous fishes has been a mainstay of reef fish research, but it has remained unclear how, and to what extent, functional diversity translates to functional impacts on reefs. Rather than assessing the functional potential of the herbivorous fish community, we explicitly considered the delivery of herbivory to the reef by quantifying, in unprecedented detail, the spatial extent and overlap of feeding areas across different functional groups. Core feeding areas were highly concentrated and consistently covered just 14% of available reef space. Overlap across functional groups was limited, showing high spatial complementarity as functional groups tended to feed next to one another. Thus, the delivery of critical ecosystem processes was patchy, effectively reducing functional redundancy, even in the presence of a diverse fish assemblage. Our findings caution against assumptions of spatial homogeneity in the delivery of critical ecosystem functions. The functional impact of local herbivorous fish assemblages in current approaches may be overestimated, potentially leading to skewed assessments of reef resilience. Our results highlight the need to incorporate collective animal behaviour and spatio‐temporal scales into future assessments of ecosystem functions and ultimately ecological resilience. A http://onlinelibrary.wiley.com/doi/10.1111/1365-2435.13322/suppinfo is available for this article.

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Section: Methodsmentioning

confidence: 99%

“…Subsequently, every fifth video-frame was extracted. Approximately 3,000 images per site were used as source data for photogrammetric reconstruction, resulting in detailed and accurate three-dimensional digital models (cf Casella et al, 2017;Ferrari et al, 2018;Raoult, Reid-Anderson, Ferri, & Williamson, 2017;Storlazzi, Dartnell, Hatcher, & Gibbs, 2016)…”

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confidence: 99%

Patchy delivery of functions undermines functional redundancy in a high diversity system

2019

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“…Three-dimensional reconstructions can also be used for volumetric analyses to track temporal changes in the habitat structure and/or for obtaining data on the distribution of benthic species after exporting them as orthophotomosaics [14,18,19]. While the use of photogrammetric techniques requires more time for post-survey data processing than in situ observations, it potentially generates high-resolution data [14] with relatively high precision and accuracy [20], and it is less prone to observer bias [21]. Image acquisition for 3D reconstruction is also less time consuming in the field than in situ (i.e., underwater) methods that are commonly used to characterize either the habitat structure (e.g., chain-and-tape rugosity and Habitat Assessment Scores [5]) or benthic cover [22].…”

Section: Introductionmentioning

confidence: 99%

Integrating Three-Dimensional Benthic Habitat Characterization Techniques into Ecological Monitoring of Coral Reefs

Fukunaga

Burns

Craig

et al. 2019

JMSE

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Long-term ecological monitoring of reef fish populations often requires the simultaneous collection of data on benthic habitats in order to account for the effects of these variables on fish assemblage structure. Here, we described an approach to benthic surveys that uses photogrammetric techniques to facilitate the extraction of quantitative metrics for characterization of benthic habitats from the resulting three-dimensional (3D) reconstruction of coral reefs. Out of 92 sites surveyed in the Northwestern Hawaiian Islands, photographs from 85 sites achieved complete alignment and successfully produced 3D reconstructions and digital elevation models (DEMs). Habitat metrics extracted from the DEMs were generally correlated with one another, with the exception of curvature measures, indicating that complexity and curvature measures should be treated separately when quantifying the habitat structure. Fractal dimension D 64 , calculated by changing resolutions of the DEMs from 1 cm to 64 cm, had the best correlations with other habitat metrics. Fractal dimension was also less affected by changes in orientations of the models compared to surface complexity or slope. These results showed that fractal dimension can be used as a single measure of complexity for the characterization of coral reef habitats. Further investigations into metrics for 3D characterization of habitats should consider relevant spatial scales and focus on obtaining variables that can complement fractal dimension in the characterization of reef habitats.

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“…Knowing the best possible results in underwater conditions remains a research gap. Recently, an effort has been made to assess the influence of photo density (the number of photos per m 2 ) on volume-area (Raoult et al, 2017) and rugosity measurements (Bryson et al, 2017). Although most software manuals recommend a minimum overlap between photos to ensure correct bundle adjustments and accurate models [80% overlap + 60% side-overlap (Agisoft, 2018)], it proved difficult to quantify the influential factors.…”

Section: Introductionmentioning

confidence: 99%

Monitoring Marine Habitats With Photogrammetry: A Cost-Effective, Accurate, Precise and High-Resolution Reconstruction Method

Marre

Holon²,

Luque

et al. 2019

Front. Mar. Sci.

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Underwater photogrammetry has been increasingly used to study and monitor the three-dimensional characteristics of marine habitats, despite a lack of knowledge on the quality and reliability of the reconstructions. More particularly, little attention has been paid to exploring and estimating the relative contribution of multiple acquisition parameters on the model resolution (distance between neighbor vertices), accuracy (closeness to true positions/measures) and precision (variability of positions/measures). On the other hand, some studies used expensive or cumbersome camera systems that can restrict the number of users of this technology for the monitoring of marine habitats. This study aimed at developing a simple and cost-effective protocol able to produce accurate and reproducible high-resolution models. Precisely, the effect of the camera system, flying elevation, camera orientation and number of images on the resolution and accuracy of marine habitat reconstructions was tested through two experiments. A first experiment allowed for testing all combinations of acquisition parameters through the building of 192 models of the same 36 m 2 study site. The flying elevation and camera system strongly affected the model resolution, while the photo density mostly affected bundle adjustment accuracy and total processing time. The camera orientation, in turn, mostly affected the reprojection error. The best combination of parameters was used in a second experiment to assess the accuracy and precision of the resulting reconstructions. The average model resolution was 3.4 mm, and despite a decreasing precision in the positioning of markers with distance to the model center (0.33, 0.27, and 1.2 mm/m Standard Deviation (SD) in X, Y, Z, respectively), the measures were very accurate and precise: 0.08% error ± 0.06 SD for bar lengths, 0.36% ± 0.51 SD for a rock model area and 0.92% ± 0.54 SD for its volume. The 3D geometry of the rock only differed by 1.2 mm ± 0.8 SD from the ultra-high resolution in-air reference. These results suggest that this simple and cost-effective protocol produces accurate and reproducible models that are suitable for the study and monitoring of marine habitats at a small reef scale.

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How Reliable Is Structure from Motion (SfM) over Time and between Observers? A Case Study Using Coral Reef Bommies

Cited by 38 publications

References 62 publications

Patchy delivery of functions undermines functional redundancy in a high diversity system

Patchy delivery of functions undermines functional redundancy in a high diversity system

Integrating Three-Dimensional Benthic Habitat Characterization Techniques into Ecological Monitoring of Coral Reefs

Monitoring Marine Habitats With Photogrammetry: A Cost-Effective, Accurate, Precise and High-Resolution Reconstruction Method

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