https://pure.aber.ac.uk/portal/files/4916016/Westoby_et_al._GEOMORPH_2012_Accepted.pdf

‘Structure-from-Motion’ photogrammetry: A low-cost, effective tool for geoscience applications

Topographic measurements for detailed studies of processes such as erosion or mass movement are usually acquired by expensive laser scanners or rigorous photogrammetry. Here, we test and use an alternative technique based on freely available computer vision software which allows general geoscientists to easily create accurate 3D models from field photographs taken with a consumer-grade camera. The approach integrates structure-from-motion (SfM) and multi-view-stereo (MVS) algorithms and, in contrast to traditional photogrammetry techniques, it requires little expertise and few control measurements, and processing is automated. To assess the precision of the results, we compare SfM-MVS models spanning spatial scales of centimeters (a hand sample) to kilometers (the summit craters of Piton de la Fournaise volcano) with data acquired from laser scanning and formal close-range photogrammetry. The relative precision ratio achieved by SfM-MVS (measurement precision : observation distance) is limited by the straightforward camera calibration model used in the software, but generally exceeds 1:1000 (i.e. centimeter-level precision over measurement distances of 10s of meters). We apply SfM-MVS at an intermediate scale, to determine erosion rates along a ~50-m-long coastal cliff. Seven surveys carried out over a year indicate an average retreat rate of 0.70±0.05 m a-1. Sequential erosion maps (at ~0.05 m grid resolution) highlight the spatio-temporal variability in the retreat, with semivariogram analysis indicating a correlation between volume loss and length scale. Compared with a laser scanner survey of the same site, SfM-MVS produced comparable data and reduced data collection time by ~80%.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2011JF002289

Straightforward reconstruction of 3D surfaces and topography with a camera: Accuracy and geoscience application

Accurate, precise and rapid acquisition of topographic data is fundamental to many sub-disciplines of physical geography. Technological developments over the past few decades have made fully distributed data sets of centimetric resolution and accuracy commonplace, yet the emergence of Structure from Motion (SfM) with Multi-View Stereo (MVS) in recent years has revolutionised three-dimensional topographic surveys in physical geography by democratising data collection and processing. SfM-MVS originates from the fields of computer vision and photogrammetry, requires minimal expensive equipment or specialist expertise and, under certain conditions, can produce point clouds of comparable quality to existing survey methods (e.g. Terrestrial Laser Scanning). Consequently, applications of SfM-MVS in physical geography have multiplied rapidly. There are many practical options available to physical geographers when planning a SfM-MVS survey (e.g. platforms, cameras, software), yet, many SfM-MVS end-users are uncert...

/pdf/structure-from-motion-photogrammetry-in-physical-geography-1yja1579z5.pdf

Structure from Motion Photogrammetry in Physical Geography

https://meetingorganizer.copernicus.org/EGU2011/EGU2011-8188.pdf

Geomorphometric assessment of spatial sediment connectivity in small Alpine catchments

. Photogrammetry and geosciences have been closely linked since the late 19th century due to the acquisition of high-quality 3-D data sets of the environment, but it has so far been restricted to a limited range of remote sensing specialists because of the considerable cost of metric systems for the acquisition and treatment of airborne imagery. Today, a wide range of commercial and open-source software tools enable the generation of 3-D and 4-D models of complex geomorphological features by geoscientists and other non-experts users. In addition, very recent rapid developments in unmanned aerial vehicle (UAV) technology allow for the flexible generation of high-quality aerial surveying and ortho-photography at a relatively low cost. The increasing computing capabilities during the last decade, together with the development of high-performance digital sensors and the important software innovations developed by computer-based vision and visual perception research fields, have extended the rigorous processing of stereoscopic image data to a 3-D point cloud generation from a series of non-calibrated images. Structure-from-motion (SfM) workflows are based upon algorithms for efficient and automatic orientation of large image sets without further data acquisition information, examples including robust feature detectors like the scale-invariant feature transform for 2-D imagery. Nevertheless, the importance of carrying out well-established fieldwork strategies, using proper camera settings, ground control points and ground truth for understanding the different sources of errors, still needs to be adapted in the common scientific practice. This review intends not only to summarise the current state of the art on using SfM workflows in geomorphometry but also to give an overview of terms and fields of application. Furthermore, this article aims to quantify already achieved accuracies and used scales, using different strategies in order to evaluate possible stagnations of current developments and to identify key future challenges. It is our belief that some lessons learned from former articles, scientific reports and book chapters concerning the identification of common errors or "bad practices" and some other valuable information may help in guiding the future use of SfM photogrammetry in geosciences.

/pdf/image-based-surface-reconstruction-in-geomorphometry-merits-g68ovc3a9x.pdf

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

A total of 15 rainfall simulation experiments were conducted in a 1 m by 2 m box varying slope (10, 20, 30%) and rainfall intensity (60, 90, 120 mm h−1) The experiments were performed to study how rill networks initiate and evolve over time under controlled conditions with regard to the treatment variables considered, and to allow for input in a computer simulation model Runoff and sediment yield samples were collected Digital elevation models were calculated by means of photogrammetry for several time steps of most experiments The soil used in the experiments was a basal till derived Cambisol typical for the Swiss Plateau While significant differences were found for sediment yield, runoff did not vary significantly with treatment combinations Increasing rainfall intensity had a larger effect on sediment yield than increasing slope Rill density and energy expenditure decreased with time, suggesting that energy expenditure was a useful parameter to describe the emergence of rill network at the laboratory scale Copyright © 2010 John Wiley & Sons, Ltd

Rill development and soil erosion: a laboratory study of slope and rainfall intensity

Many of the processes involved in soil erosion have dimensions on the millimetre scale. Modelling and quantification of such processes require information on soil surface topography with adequate resolution. The purpose of this study was to generate digital elevation models (DEMs) from soil surfaces with high spatial and temporal resolution. Digital photogrammetry was applied for measuring erosion rates on complex-shaped soil surfaces under laboratory rainfall conditions. A total of 60 DEMs were generated, covering a planimetric area of 16 m 2 . The DEMs had a grid resolution of 3 mm. A vertical precision of approximately 1 mm was desired for DEM analysis. A consumer-grade digital camera was used for image acquisition. The camera was calibrated using BLUH software. Homologous points in overlapping images were identified with least squares matching software. Irregularly spaced object coordinates were interpolated to a regular grid in a geographic information system. The resulting DEMs represented the soil surface well. A precision of 1AE26 mm in the vertical was attained. The precision of DEM production was limited to camera calibration. Improvements of the setup presented could include the use of better control points and more advanced image matching strategies for identification of homologous points. The DEMs allowed for detailed analysis of soil surface evolution.

/pdf/digital-close-range-photogrammetry-for-measurement-of-soil-2wpofmlt73.pdf

Digital close range photogrammetry for measurement of soil erosion

The ability to understand gully erosion development is closely related to our ability to quantify the morphology of gullies At present, various technologies are at hand to collect data at increasing levels of detail However, many of the developed technologies are time-consuming, difficult to apply or expensive As an alternative, image-based modelling offers a cost-efficient, flexible and rapid method to quantify gully morphology from photographs taken in the field In this study, the use of image-based modelling was tested and fine-tuned to quantify the morphology of four gully heads in contrasting biophysical environments prone to gully erosion: two bank gullies in Central Belgium and two permanent gullies in Northern Ethiopia Ground photographs (n = 88–235) were taken with a reflex Canon EOS 450D camera having a 20 mm wide-angle lens with a fixed focal length The data collection occurred during days of 30–100% cloud cover and after removing excessive vegetation in the gullies Processing of the photographs occurred in PhotoScan 102 software using the semi-automated Structure from Motion–Multi View Stereo (SfM–MVS) workflow, and allowed to produce 3D Digital Elevation Models with accuracies that range from millimetres to centimetres In addition, for the same surface, 25D models were created in ArcGIS Gully morphological properties were derived and included cross-sections, total volume and volume of undercut walls and soil pipe inlets For the volume calculation, OPTOCAT software was used Cross-sections were also quantified by tape meter measurements When compared to 3D models, cross-sections quantified from tape meter measurements and from 25D models underestimate the cross-sectional area by

https://biblio.ugent.be/publication/5808131/file/5808133.pdf

Dirk Rieke-Zapp

Papers

Rill development and soil erosion: a laboratory study of slope and rainfall intensity

Digital close range photogrammetry for measurement of soil erosion

Detailed recording of gully morphology in 3D through image-based modelling

Limits of sediment transfer in an alpine debris-flow catchment, Illgraben, Switzerland

Slope Shape Effects on Erosion