158 research outputs found
Polymer-based treatments to control runoff, leachate and erosion from engineered slopes at Simfer Mine, Guinea, Africa
No full textIt is necessary to understand the erodibility and hydrological response of mine-site slope forming materials (SFMs), because of increasing awareness of the environmental impacts of mining. Steep engineered slopes in high intensity rainfall environments present a serious erosion risk. Temporary surface stabilisers, such as polyacrylamides (PAMs) and polyvinylacrylic latex (PVALs) are potentially cost effective erosion control solutions. In this study PAM and PVAL efficacy to reduce runoff, leachate and erosion was assessed at two application rates, with and without gypsum on SFMs from an iron ore mine in Guinea (West Africa). NSPASS (near-surface photogrammetry assessment of slope forming materials’ surface roughness) is a novel method that integrates digital image capture and GIS. It is shown to detect and quantify surface micro-relief changes of 2-3 mm, not visible to the naked eye.
As expected, soil and non-soil SFMs were significantly different in terms of their physical and chemical properties. Phase I of the study investigated the erodibility of ten SFMs, including soil, ore and waste-rock. The results indicate that the hydrological response to rainfall of most SFMs is to generate leachate. Weathered phyllite (PHY-WEA) is the most erodible SFM by both runoff and leachate. Multiple regression analysis demonstrated that magnetic susceptibility, mineralogy and dry aggregate distribution; parameters not commonly assessed in erosion studies, are important in explaining SFM erodibility and hydrological response.
Phase II evaluated critically the effectiveness of three commercially available polymer solutions (two PAMs and one PVAL) at reducing runoff, leachate and erosion from four of the most erodible SFMs identified in Phase I. The results indicate that some PAM and PVAL treatments significantly reduce runoff, leachate and erosion. Polymer efficacy is highly dependent on the physical and chemical properties of the SFM, as well as the mechanism of polymer to SFM adsorption. Increasing the application rate of select treatments lowered leachate volumes, runoff and leachate total sediment loads. Contrary to previous studies, gypsum amendments did not significantly improve polymer efficiency.
This research has added to our understanding of the erodibility and hydrological response of soil and non-soil SFMs. This is the first study to evaluate critically the efficacy of PVALs in controlling erosion from mine-site SFMs. Future studies should continue to optimise NSPASS performance in monitoring changes in surface micro-relief
Impact of Alternative Land Management Options on Soil Fertility and Erosion in Uganda
No full textUsing a data set collected in eight districts of Uganda, this study investigates how investment in soil fertility management (SFM) and conservation practices may affect natural resource outcomes, particularly the extent and level of soil erosion and soil nutrient loss. The study used ordered probit models and the results suggest that investment in SFM and conservation practices greatly improves soil fertility and reduces soil erosion. From a policy perspective, public investment to encourage use of SFM and conservation technologies would help the country achieve sustainable agricultural production.Land Management, Soil Fertility, Ordered Probit, Erosion, Land Economics/Use,
Merging Top-View Lidar Data With Street-View SFM Data To Enhance Urban Flood Simulation
No full textTop-view data obtainedfrom LiDAR systemshas long been used as topographic-input data for urban flood modelling applications. This high-resolution input data has considerable potential to improve urban flood modelling predictions with more detail. However, the difficulty of employing top-view data is that it may create some missing urban features because this type ofdata cannot represent anyurban features,which are hiddenunderneath other objects. These hidden featuresmay play a substantial part in diverting floodwater flowing through,especially in complex urban areas. The recent advances in Photogrammetry and Computer Vision techniques offer an opportunity to create high-resolution topographic data. By using a consumer digital camera, 2D digital photoscan betaken from different viewpoints. The so-called Structure from Motion (SfM) techniquecan usethese overlappingphotos and reconstruct theminto3D pointcloud data with a high level of accuracy and resolution,usinga cost effective approach. In this work, we create street-view SfM point-cloud data obtained from street viewpoints. We also introduce a new multi-view approach by merging top-view LiDAR data withstreet-view SfM data. This new multi-view data can be used as topographic input data for a coupled 1D-2D model. When applyingsuch newdata, the flood simulation results can highlight some flood propagations much better than using the traditional top-view LiDAR data. Therefore, it has the potential toenhance the multi-view approach into practicable flood-modelling applications for the present and future urbanizing areas.Environmental Fluid Mechanic
Correspondence-Guided SfM-Free 3D Gaussian Splatting for NVS
No full textNovel View Synthesis (NVS) without Structure-from-Motion (SfM) pre-processed camera poses--referred to as SfM-free methods--is crucial for promoting rapid response capabilities and enhancing robustness against variable operating conditions. Recent SfM-free methods have integrated pose optimization, designing end-to-end frameworks for joint camera pose estimation and NVS. However, most existing works rely on per-pixel image loss functions, such as L2 loss. In SfM-free methods, inaccurate initial poses lead to misalignment issue, which, under the constraints of per-pixel image loss functions, results in excessive gradients, causing unstable optimization and poor convergence for NVS. In this study, we propose a correspondence-guided SfM-free 3D Gaussian splatting for NVS. We use correspondences between the target and the rendered result to achieve better pixel alignment, facilitating the optimization of relative poses between frames. We then apply the learned poses to optimize the entire scene. Each 2D screen-space pixel is associated with its corresponding 3D Gaussians through approximated surface rendering to facilitate gradient back propagation. Experimental results underline the superior performance and time efficiency of the proposed approach compared to the state-of-the-art baselines.arXiv admin note: text overlap with arXiv:2312.07504 by other author
Efficient tree-structured SfM by RANSAC generalized Procrustes analysis
No full textThis paper proposes a tree-structured structure-from-motion (SfM) method that recovers 3D scene structures and estimates camera poses from unordered image sets. Starting from atomic structures spanning the scene, we build well-connected structure groups, and propose RANSAC generalized Procrustes analysis (RGPA) to glue structures in the same group. The grouping-aligning operations hierarchically proceed until the full scene is reconstructed. Our work is the first attempt of using GPA for modern 3D reconstruction tasks. RGPA is able to merge multiple structures at a time and automatically identify outliers. The reconstruction tree is much more compact and balanced than previous hierarchical SfM methods and has a very shallow depth. These advantages, along with the resulting removal of intermediate bundlCadjustments, lead to significantly improved computational efficiency over state-of-the-art SfM methods. The cameras and 3D scene can be robustly recovered in the presence of moderate noise. We verify the efficacy of our method on a variety of datasets, and demonstrate that our method is able to produce metric reconstructions efficiently and robustly. (C) 2017 Elsevier Inc. All rights reserved.National Natural Science Foundation (NSF) of China [61232014, 61421062, 61472010]; National Basic Research Program of China (973 Program) [2015CB351806]; National Key Technology R&D Program of China [2015BAKO1B06]; 973 Program [2015CB352502]; NSF of China [61625301, 61231002]; QualcommSCI(E)ARTICLE,SI179-18915
Topographical dynamics based on global and UAV-SfM derived DEM products: a case study of transboundary Teesta River, Bangladesh
No full textTopographical changes in riverine floodplains need to be measured for assessing geomorphological dynamics and protecting floodplain areas, although topographic evaluation in disaster-prone floodplain in South Asia has been limited due to the lack of multitemporal, high-definition digital elevation models (DEMs) derived from modern techniques including airborne laser scanning, structure-from-motion (SfM) photogrammetry accompanied with Unmanned Aerial Vehicle (UAV, often referred as drone), and field-based mapping approaches. Here we conducted a preliminary study at two locations of Teesta River (Brahmaputra's tributary) in Bangladesh using the UAV-SfM techniques and generated high-resolution DEMs. The selected locations represent dynamic changes of sediment and water on the floodplain over the years, and the UAV-SfM approach can be an effective method for monitoring those changes, but an archive of the past data has been unavailable. Here we evaluated the topographic changes by comparing the UAV-SfM-derived DEMs of 2022 with global DEM products (NASADEM of 1999), which are often the only available choice of DEMs in this river floodplain. The elevation differences of these two sets of DEMs were in the range of -5.23 to -84.66 m, and volumetric changes of -4.11 +/- 0.15 to -86.25 +/- 0.20 million m3, likely dominated by erosional processes towards the left side bank where the elevation errors are supposed to be several meters for UAV-DEM and ca. 5-12 m for NASADEM. Although it is not easy to accurately evaluate the absolute values of the changes, these changes may be associated with the upper basin's morphodynamics
Bank erosion processes measured with UAV-SfM along complex banklines of a straight mid-sized river reach
No full textWe apply structure from motion (SfM) photogrammetry with imagery from an unmanned aerial vehicle (UAV) to measure bank erosion processes along a mid-sized river reach. This technique offers a unique set of characteristics compared to previously used methods to monitor banks, such as high resolution and relatively fast deployment in the field. We analyse the retreat of a 1.2 km restored bank of the Meuse River which has complex vertical scarps laying on a straight reach, features that present specific challenges to the UAV-SfM application. We surveyed eight times within a year with a simple approach, combining different photograph perspectives and overlaps to identify an effective UAV flight. The accuracy of the digital surface models (DSMs) was evaluated with real-time kinematic (RTK) GPS points and airborne laser scanning of the whole reach. An oblique perspective with eight photo overlaps and 20 m of cross-sectional ground-control point distribution was sufficient to achieve the relative precision to observation distance of ∼ 1 : 1400 and 3 cm root mean square error (RMSE), complying with the required accuracy. A complementary nadiral view increased coverage behind bank toe vegetation. Sequential DSMs captured signatures of the erosion cycle such as mass failures, slump-block deposition, and bank undermining. Although UAV-SfM requires low water levels and banks without dense vegetation as many other techniques, it is a fast-in-the-field alternative to survey reach-scale riverbanks in sufficient resolution and accuracy to quantify bank retreat and identify morphological features of the bank failure and erosion processes. Improvements to the adopted approach are recommended to achieve higher accuracies.Rivers, Ports, Waterways and Dredging EngineeringEnvironmental Fluid Mechanic
The effect of mono- versus multi-segment musculoskeletal models of the foot on simulated triceps surae lengths in pathological and healthy gait
No full textBackground: Estimating muscle-tendon complex (MTC) lengths is important for planning of soft tissue surgery and evaluating outcomes, e.g. in children with cerebral palsy (CP). Conventional musculoskeletal models often represent the foot as one rigid segment, called a mono-segment foot model (mono-SFM). However, a multi-segment foot model (multi-SFM) might provide better estimates of triceps surae MTC lengths, especially in patients with foot deformities. Research question: What is the effect of a mono- versus a multi-SFM on simulated ankle angles and triceps surae MTC lengths during gait in typically developing subjects and in children with CP with equinus, cavovarus or planovalgus foot deformities? Methods: 50 subjects were included, 10 non-affected adults, 10 typically developing children, and 30 children with spastic CP and foot deformities. During walking trials, marker trajectories were collected for two marker models, including a mono- and multi-segment foot; respectively Newington gait model and Oxford foot model. Two musculoskeletal lower body models were constructed in OpenSim with either a mono- or multi-SFM based on the corresponding marker models. Normalized triceps surae MTC lengths (soleus, gastrocnemius medialis and lateralis) and ankle angles were calculated and compared between models using statistical parametric mapping RM-ANOVAs. Root mean square error values between simulated MTC lengths were compared using Wilcoxon signed-rank and rank-sum tests. Results: Mono-SFM simulated significantly more ankle dorsiflexion (7.5 ± 1.2°) and longer triceps surae lengths (difference; soleus:2.6 ± 0.29 %, gastrocnemius medialis:1.7 ± 0.2 %, gastrocnemius lateralis:1.8 ± 0.2%) than a multi-SFM. Differences between models were larger in children with CP compared to typically developing children and larger in the stance compared to the swing phase of gait. Largest differences were found in children with CP presenting with planovalgus (4.8 %) or cavovarus (3.8 %) foot deformities. Significance: It is advisable to use a multi-SFM in musculoskeletal models when simulating triceps surae MTC lengths, especially in individuals with planovalgus or cavovarus foot deformities.Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Biomechatronics & Human-Machine Contro
- …
