Soil deformation measurement using particle image velocimetry (PIV) and photogrammetry
TL;DR: A deformation measurement system based on particle image velocimetry (PIV) and close-range photogrammetry has been developed for use in geotechnical testing as mentioned in this paper.
Abstract: A deformation measurement system based on particle image velocimetry (PIV) and close-range photogrammetry has been developed for use in geotechnical testing. In this paper, the theory underlying this system is described, and the performance is validated. Digital photography is used to capture images of planar soil deformation. Using PIV, the movement of a fine mesh of soil patches is measured to a high precision. Since PIV operates on the image texture, intrusive target markers need not be installed in the observed soil. The resulting displacement vectors are converted from image space to object space using a photogrammetric transformation. A series of validation experiments are reported. These demonstrate that the precision, accuracy and resolution of the system are an order of magnitude higher than previous image-based deformation methods, and are comparable to local instrumentation used in element testing. This performance is achieved concurrent with an order of magnitude increase in the number of meas...
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TL;DR: In this article, a review of the 2D digital image correlation (2D DIC) technique for displacement field measurement and strain field estimation is presented, and detailed analyses of the measurement accuracy considering the influences of both experimental conditions and algorithm details are provided.
Abstract: As a practical and effective tool for quantitative in-plane deformation measurement of a planar object surface, two-dimensional digital image correlation (2D DIC) is now widely accepted and commonly used in the field of experimental mechanics. It directly provides full-field displacements to sub-pixel accuracy and full-field strains by comparing the digital images of a test object surface acquired before and after deformation. In this review, methodologies of the 2D DIC technique for displacement field measurement and strain field estimation are systematically reviewed and discussed. Detailed analyses of the measurement accuracy considering the influences of both experimental conditions and algorithm details are provided. Measures for achieving high accuracy deformation measurement using the 2D DIC technique are also recommended. Since microscale and nanoscale deformation measurement can easily be realized by combining the 2D DIC technique with high-spatial-resolution microscopes, the 2D DIC technique should find more applications in broad areas.
2,530 citations
TL;DR: A survey of 19 soils, with textures ranging from loamy sand to silty clay loam, found that mechanical impedance is often a major limitation to root elongation in these soils even under moderately wet conditions, and is important to consider in breeding programmes for drought-resistant crops.
Abstract: Root elongation in drying soil is generally limited by a combination of mechanical impedance and water stress. Relationships between root elongation rate, water stress (matric potential), and mechanical impedance (penetration resistance) are reviewed, detailing the interactions between these closely related stresses. Root elongation is typically halved in repacked soils with penetrometer resistances >0.8‐2 MPa, in the absence of water stress. Root elongation is halved by matric potentials drier than about ‐0.5 MPa in the absence of mechanical impedance. The likelihood of each stress limiting root elongation is discussed in relation to the soil strength characteristics of arable soils. A survey of 19 soils, with textures ranging from loamy sand to silty clay loam, found that ;10% of penetration resistances were >2 MPa at a matric potential of ‐10 kPa, rising to nearly 50% >2 MPa at ‐ 200 kPa. This suggests that mechanical impedance is often a major limitation to root elongation in these soils even under moderately wet conditions, and is important to consider in breeding programmes for drought-resistant crops. Root tip traits that may improve root penetration are considered with respect to overcoming the external (soil) and internal (cell wall) pressures resisting elongation. The potential role of root hairs in mechanically anchoring root tips is considered theoretically, and is judged particularly relevant to roots growing in biopores or from a loose seed bed into a compacted layer of soil.
787 citations
Cites background from "Soil deformation measurement using ..."
...For example, particle image velocimetry (White et al., 2003) of maize roots growing in sand showed that displacements (resolved down to 0....
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...For example, particle image velocimetry (White et al., 2003) of maize roots growing in sand showed that displacements (resolved down to 0.5 lm) extended up to eight times the root diameter into the sand, and resulted in localized compression of sand in front of the tip of decapped mutants that did…...
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TL;DR: Optical flow techniques enable tracking of root surfaces with time to yield estimates of two-dimensional velocity fields, and it is demonstrated that these techniques can be applied successfully to time-lapse sequences of confocal microscope images of living roots, in order to determine velocity fields and strain rates of groups of cells.
Abstract: Root growth in the field is often slowed by a combination of soil physical stresses, including mechanical impedance, water stress, and oxygen deficiency. The stresses operating may vary continually, depending on the location of the root in the soil profile, the prevailing soil water conditions, and the degree to which the soil has been compacted. The dynamics of root growth responses are considered in this paper, together with the cellular responses that underlie them. Certain root responses facilitate elongation in hard soil, for example, increased sloughing of border cells and exudation from the root cap decreases friction; and thickening of the root relieves stress in front of the root apex and decreases buckling. Whole root systems may also grow preferentially in loose versus dense soil, but this response depends on genotype and the spatial arrangement of loose and compact soil with respect to the main root axes. Decreased root elongation is often accompanied by a decrease in both cell flux and axial cell extension, and recent computer-based models are increasing our understanding of these processes. In the case of mechanical impedance, large changes in cell shape occur, giving rise to shorter fatter cells. There is still uncertainty about many aspects of this response, including the changes in cell walls that control axial versus radial extension, and the degree to which the epidermis, cortex, and stele control root elongation. Optical flow techniques enable tracking of root surfaces with time to yield estimates of two-dimensional velocity fields. It is demonstrated that these techniques can be applied successfully to time-lapse sequences of confocal microscope images of living roots, in order to determine velocity fields and strain rates of groups of cells. In combination with new molecular approaches this provides a promising way of investigating and modelling the mechanisms controlling growth perturbations in response to environmental stresses.
445 citations
Cites background or methods from "Soil deformation measurement using ..."
...(a) Image of 35S ER-GFP Arabidopsis root with overlaid patches used for correlation-based optical flow analysis (method of White et al., 2003) and (b) resulting longitudinal velocities for two individual 14-d-old roots (hollow and filled circles)....
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...(a) Image of 35S ER-GFP Arabidopsis root with overlaid patches used for correlation-based optical flow analysis (method of White et al., 2003 ) and (b) resulting longitudinal velocities for two individual 14-d-old roots (hollow and filled circles)....
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TL;DR: In this paper, a 2D discrete model for granular materials with rolling resistance is presented, which consists of a geometrically derived kinematical model, physically based mechanical contact models and locally equilibrated equations governing the motion of the rigid particles; only one additional parameter δ needs to be introduced in the model when compared with the standard discrete element method.
399 citations
TL;DR: The updated approach combines a range of advances in image analysis algorithms and techniques best suited to geotechnical applications and achieves an improvement by at least a factor of 10 in measurement precision relative to the most commonly used particle image velocimetry (PIV) approach.
Abstract: This paper describes and benchmarks a new implementation of image-based deformation measurement for geotechnical applications. The updated approach combines a range of advances in image analysis al...
274 citations
References
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TL;DR: A review of these methods can be found in articles by Lauterborn & Vogel (1984), Adrian (1986a), Hesselink (1988), and Dudderar et al..
Abstract: An important achievement of modern experimental fluid mechanics is the invention and development of techniques for the measurement of whole, instantaneous fields of scalars and vectors. These techniques include tomographic interferometry (Hesselink 1988) and planar laser-induced fluorescence for scalars (Hassa et al 1987), and nuclear-magnetic-resonance imaging (Lee et al 1987), planar laser-induced fluorescence, laser-speckle velocimetry, particle-tracking velocimetry, molecular-tracking velocimetry (Miles et al 1989), and particle-image velocimetry for velocity fields. Reviews of these methods can be found in articles by Lauterborn & Vogel (1984), Adrian (1986a), Hesselink (1988), and Dudderar et al (1988), in books written by Merzkirch (1987) and edited by Chiang & Reid (1988) and Gad-el-Hak (1989).
3,413 citations
17 Jun 1997
TL;DR: This paper presents a four-step calibration procedure that is an extension to the two-step method, and a linear method for solving the parameters of the inverse model is presented.
Abstract: In geometrical camera calibration the objective is to determine a set of camera parameters that describe the mapping between 3-D reference coordinates and 2-D image coordinates. Various methods for camera calibration can be found from the literature. However surprisingly little attention has been paid to the whole calibration procedure, i.e., control point extraction from images, model fitting, image correction, and errors originating in these stages. The main interest has been in model fitting, although the other stages are also important. In this paper we present a four-step calibration procedure that is an extension to the two-step method. There is an additional step to compensate for distortion caused by circular features, and a step for correcting the distorted image coordinates. The image correction is performed with an empirical inverse model that accurately compensates for radial and tangential distortions. Finally, a linear method for solving the parameters of the inverse model is presented.
2,283 citations
25 Aug 1996
TL;DR: A camera calibration procedure intended for a 3D measurement application is presented, paying attention to the various error sources, and notices that a more complete camera model is needed to explain all the error components.
Abstract: A camera calibration procedure intended for a 3D measurement application is presented, paying attention to the various error sources. The error may be measurement noise that is random by nature, but it may also be systematic originating from the calibration target used, geometrical distortions and illumination. In order to obtain good calibration results, the systematic error sources should be eliminated or their effects compensated for. Then, the camera parameters can be determined by fitting the corrected measurements to the camera model which in our case is a combination of a pinhole camera and lens distortion models. We also notice that a more complete camera model is needed to explain all the error components.
155 citations
TL;DR: In this article, the authors present a survey of small-strain measuring devices and their modes of operation, benefits, capabilities, and limitations, as well as a classification of internal and external measuring devices.
Abstract: Conventional procedures for determining deformations during triaxial tests are based on measurements made externally to the cell. This practice is inadequate, particularly if the small strain stiffness of the soil is being investigated, because errors are introduced which limit the accuracy and resolution of the measurements. The errors can only be eliminated if axial strains are determined internally, within the cell, and locally over the central one third of the specimen. Likewise, the radial dimensions should be monitored at specimen midheight. The last ten years has seen the introduction of a diverse range of small-strain measuring devices. This has been largely in response to recognition of the importance of achieving strain measurement accuracy of at least 10−3% for small-strain stiffness evaluation. This paper summarizes the types of instrumentation currently available and their modes of operation, benefits, capabilities, and limitations. Typical results comparing external and internal strain measurements are presented. A system for classifying internal-strain measuring devices is presented. It is anticipated that test results based on small strain determinations will be a more frequent requirement in the future. Accordingly, the paper is intended to assist prospective users in becoming familiar with the various techniques that have been used and presents information that should enable selection of appropriate equipment for particular applications. Given that improvements in existing systems are warranted, it is hoped that the paper will also provide stimulus for further research and development.
106 citations