Shape Estimation Research Articles

Two-Dimensional Shape and Distal Force Estimation for the Continuum Robot Based on Learning From the Proximal Sensors

Accurate shape sensing and distal contact force estimation of the flexible continuum robots remains challenging due to critical hysteresis profiles for modeling and the difficulties on sensor integration at their distal ends. This paper proposes a learning-based approach to predict distal-tip interaction information by solely utilizing the sensory measurements from the proximal end. A workflow including multilayer perception (MLP) and long short-term memory (LSTM) was investigated to simultaneously estimate and predict the whole shape and distal contact force. Experiments were carried out on a typical single-section continuum robot to verify the effectiveness of the proposed method. The proposed method could achieve high accuracy of root mean square error (RMSE) =0.26 N for force prediction and a relative error of less than 1.2% for shape estimation. Notably, the LSTM-based method could precisely identify the force hysteresis profile. In summary, the proposed framework could be applied to the cable-drive continuum robotic systems for precise contact force and shape feedback without requiring sensors at the distal tip.

Efficient Spatial Resampling Using the PDF Similarity

In real-time rendering, spatiotemporal reservoir resampling (ReSTIR) is a powerful technique to increase the number of candidate samples for resampled importance sampling. However, reusing spatiotemporal samples is not always efficient when target PDFs for the reused samples are dissimilar to the integrand. Target PDFs are often spatially different for highly detailed scenes due to geometry edges, normal maps, spatially varying materials, and shadow edges. This paper introduces a new method of rejecting spatial reuse based on the similarity of PDF shapes for single-bounce path connections (e.g., direct illumination). While existing rejection methods for ReSTIR do not support arbitrary materials and shadow edges, our PDF similarity takes them into account because target PDFs include BSDFs and shadows. In this paper, we present a rough estimation of PDF shapes using von Mises--Fisher distributions and temporal resampling. We also present a stable combination of our rejection method and the existing rejection method, considering estimation errors due to temporal disocclusions and moving light sources. This combination efficiently reduces the error around shadow edges with temporal continuities. By using our method for a ReSTIR variant that reuses shadow ray visibility for the integrand, we can reduce the number of shadow rays while preserving shadow edges.

Part-to-Surface Mesh Segmentation for Mechanical Models Based on Multi-Stage Clustering

In this paper, we propose a part-to-surface mesh segmentation method for engineering models characterized by a multi-stage clustering of surface patches generated by the Variational Shape Approximation (VSA) method. Initially, border types between topologically adjacent surface patches are estimated and surface patches bonded by certain border types are grouped into clusters. Secondly, clusters of surface patches are iteratively aggregated into volumetric part-level sub-meshes according to the convexity variations of intermediate sub-meshes. At last, surface patches within their respective part-level sub-meshes are merged into surface-level sub-meshes that are well-fitted by basic primitive shapes based on an improved surface-aware similarity metric. Experimental results demonstrate that the proposed method can achieve better results on mechanical models both quantitatively and perceptually, especially for objects with non-zero genus topology and rich in tiny features.

Social media, youth (im)mobilities, and the risks of connectivity in urban Somaliland

Young people in cities in the Horn of Africa engage with diasporic mobility through social media on a daily basis. Apparent opportunities on these platforms both reflect and shape ideas about life in the diaspora, potential migration, and social mobility. These connections also bring risks of scamming, extortion and misinformation that contribute to the involuntary immobility of those who wish to move for economic or educational opportunities. Drawing from ‘screen-shot elicitation’ group interviews with young men in Hargeisa (Somaliland) and digital ethnographic investigation of social media content gathered before, during and after these sessions, this article argues that transnational flows of mobility-related information need to be studied from the perspective of people within contexts commonly understood as ‘sources’ of south-north migration, but beyond policy-orientated questions about the impact of ICTs on rates of migration. Emphasising the highly ambivalent role played by social media in shaping aspirations and experiences of youth (im)mobility, this approach brings into view a wider range of socially significant online practices. These include the transnational assemblage of elaborate digital scamming techniques, as well as multiple other types of mobility-focused user-generated content that circulate in transnational Somali social (media) networks.

The Era of Bengali Rennaissance – A Legacy of the Hallowed Sons of Bengal

The Bengal Renaissance (Bengali: বাংলার নবজাগরণ — Banglar Navajagaran), also known as the Bengali Renaissance, was a cultural, social, intellectual, and artistic movement that took place in the Bengal region of the British Raj, from the late 18th century to the early 20th century.Historians have traced the beginnings of the movement to the victory of the British East India Company at the 1757 Battle of Plassey, as well as the works of reformer Raja Rammohan Roy, considered the "Father of the Bengal Renaissance," born in 1772.[2] Nitish Sengupta stated that the movement "can be said to have … ended with Rabindranath Tagore," Asia's first Nobel laureate. Print language and literature played a vital role in shaping ideas and identities in colonial Bengal from the 18th century onwards. With its adoption by the ruling class and the indigenous population, Bengali marked a site that also oversaw contests for domination across a broad social spectrum. For the latter moreover, the language also defined their cultural identity, as part of the attempt to create a new literary prose Bengali to distinguish it from earlier colloquial forms. The new Bengali became an essential tool for the urban, educated upper middle classes to establish their power over lesser privileged groups - women, the lowly classes and poor Muslims. However, commercial print cultures that emanated from numerous cheap presses in Calcutta and its suburbs disseminated wide-ranging literary preferences that afforded a space to different sections of the Bengali middle classes to voice their own distinctive concerns.

3D human pose and shape estimation via de-occlusion multi-task learning

Three-dimensional human pose and shape estimation is to compute a full human 3D mesh given a single image. The contamination of features caused by occlusion usually degrades its performance significantly. Recent progress in this field typically addressed the occlusion problem implicitly. By contrast, in this paper, we address it explicitly using a simple yet effective de-occlusion multi-task learning network. Our key insight is that feature for mesh parameter regression should be noiseless. Thus, in the feature space, our method disentangles the occludee that represents the noiseless human feature from the occluder. Specifically, a spatial regularization and an attention mechanism are imposed in the backbone of our network to disentangle the features into different channels. Furthermore, two segmentation tasks are proposed to supervise the de-occlusion process. The final mesh model is regressed by the disentangled occlusion-aware features. Experiments on both occlusion and non-occlusion datasets are conducted, and the results prove that our method is superior to the state-of-the-art methods on two occlusion datasets, while achieving competitive performance on a non-occlusion dataset. We also demonstrate that the proposed de-occlusion strategy is the main factor to improve the robustness against occlusion. The code is available athttps://github.com/qihangran/De-occlusion_MTL_HMR.

Bidirectional temporal feature for 3D human pose and shape estimation from a video

Abstract3D human pose and shape estimation is the foundation of analyzing human motion. However, estimating accurate and temporally consistent 3D human motion from a video remains a challenge. By now, most of the video‐based methods for estimating 3D human pose and shape rely on unidirectional temporal features and lack more comprehensive information. To solve this problem, we propose a novel model “bidirectional temporal feature for human motion recovery” (BTMR), which consists of a human motion generator and a discriminator. The transformer‐based generator effectively captures the forward and reverse temporal features to enhance the temporal correlation between frames and reduces the loss of spatial information. The motion discriminator based on Bi‐LSTM can distinguish whether the generated pose sequences are consistent with the realistic sequences of the AMASS dataset. In the process of continuous generation and discrimination, the model can learn more realistic and accurate poses. We evaluate our BTMR on 3DPW and MPI‐INF‐3DHP datasets. Without the training set of 3DPW, BTMR outperforms VIBE by 2.4 mm and 14.9 mm/s2 in PA‐MPJPE and Accel metrics and outperforms TCMR by 1.7 mm in PA‐MPJPE metric on 3DPW. The results demonstrate that our BTMR produces better accurate and temporal consistent 3D human motion.

Development of active noise control simulation with virtual controller based on computational aeroacoustics

Noise reduction and control research are actively conducted as increasing noise problems compel the stringent noise requirement. Active noise control (ANC) is constructively used in various applications to reduce low-frequency noise. In previous studies, ANC systems were designed based on experiments, requiring extensive effort for effective implementation. In this paper, a real-time ANC simulation in a computational aeroacoustics framework based on the virtual-controller method is presented. The aims are to investigate sound field changes following ANC system operation and gain more insight into ANC system design through a computational approach. Using a virtual-controller ANC simulation, the approximate shape of the acoustic path filter and changes in the sound field when ANC is either "on" or "off" at the target domain can be obtained, enabling practical and detailed analyses. Then, the computational results of the duct and open space cases are predicted and compared with the experimental results to validate the prediction capability of the proposed method. In addition, the ANC system design parameters and their effects on sound fields with unintended phenomena can be predicted. Through case studies, the ability to design, optimize, and predict the performance of the ANC system using the computational method is also demonstrated.

One-way collinear wave mixing in solids with cubic nonlinearity based on Murnaghan’s potential

Ultrasonic wave mixing is a powerful new nondestructive evaluation technique for accessing hidden subtle imperfections in materials. First, this paper derives the resonance conditions of one-way collinear mixing with cubic nonlinearity. The results show that the mixing of two collinear longitudinal waves can generate a resonant longitudinal wave, the mixing of two transverse waves can generate a resonant transverse wave, and the resonant longitudinal wave and transverse wave can be generated, respectively, when two primary longitudinal and transverse waves satisfy different resonance conditions. This is different from the case with quadratic nonlinearity. Furthermore, we obtain the analytical solutions of resonant waves generated by the mixing of harmonic longitudinal and transverse pulses. The waveforms are approximate hexagonal shapes according to the analysis of the envelopes. Finally, the numerical simulation results conducted on material aluminum prove the correctness of the analytical solution. Compared with quadratic nonlinearity, the resonant wave is more sensitive to material constants for some materials when considering one-way collinear mixing of primary longitudinal and transverse pulses based on cubic nonlinearity. The results provide new opportunities on mixing wave applications in nondestructive evaluation.

The influence of fossils in macroevolutionary analyses of 3D geometric morphometric data: A case study of galloanseran quadrates.

In birds and other reptiles, the quadrate acts as a hinge between the lower jaw and the skull and plays an important role in avian cranial kinesis. Though previous studies have qualitatively described substantial variation in quadrate morphology among birds, none have attempted to quantify evolutionary changes in quadrate shape. Here, we investigate geometric evolution of the quadrate in Galloanserae, a major clade of extant birds uniting chicken-like (Galliformes) and duck-like (Anseriformes) fowl. We quantified morphological variation in the quadrate across 50 extant galloanseran species covering all major extant subclades using three-dimensional geometric morphometrics, and performed ancestral shape reconstructions in the context of an up-to-date neornithine phylogeny. We find that our results based only on extant quadrates may overlook plesiomorphic features captured by fossil taxa, resulting in an ancestral state reconstruction for Galloanserae that is seemingly an approximation of the average shape of the extant data set. By contrast, analyses incorporating early fossil galloanseran quadrates (from taxa such as Asteriornis, Presbyornis, and Conflicto) result in ancestral geometric reconstructions more similar to the morphology of extant galliforms, indicating that the quadrate of the last common ancestor of galloanserans may have been more morphologically and functionally similar to those of extant galliforms than to extant anseriforms. These results generally corroborate previous inferences of galloanseran quadrate plesiomorphies and identify several additional plesiomorphic features of the galloanseran quadrate for the first time. Our results illustrate the importance of incorporating fossil taxa into ancestral shape reconstructions and help elucidate important aspects of the morphology and function of the avian feeding apparatus early in crown bird evolutionary history.

Inversion of potential fields by interactive optimization of 3D subsurface models using a spring-based space warping and evolution strategy

The rapid development of dynamic data-integrative modeling of geologic processes and subsurface structures is an important factor for the sustainable utilization of natural resources. One of the current gaps in data-integrative modeling is the interactive construction of realistic 3D models of the earth’s underground. We have developed here a methodology of 3D interactive processing of potential fields — gravity and magnetics — as well as their potentials and derivatives, combining forward and inverse modeling. Forward computations are based on the approximation of geologic subsurface structures by polyhedra with triangulated surfaces. Inverse computations for the model geometry are performed by means of the covariance matrix adaptation evolution strategy (CMA-ES), which is proved to be efficient in the case of a strongly nonlinear problem and high-dimensional parameter space, as in potential field models. The main disadvantage is related to triangulation, as certain algorithmic constraints must be applied during the approximation of geologic body shapes. To avoid topology distortions, we use a concept of warping the space containing the model, rather than the model itself. However, the optimized lengths of grid sides are dependent on each other, which degrades the self-adaptation of the CMA-ES. The elegant solution is to introduce a system of virtual elastic springs connecting the grid nodes. We develop a numerical formulation of this system and provide a proof of the concept rather than an overview of the theoretical concepts of the inversion schemes. The new workflow is tested on the 3D SEG Advanced Modeling Program model and applied to a real case study of salt dome modeling in the Northwest German Basin. In the context of the inversion procedure described here, we determine how an interpreter can visually control and influence the quality of the inversion on a timeline.

Searching for sliding surfaces in multi-level loess slopes based on the brachistochrone

As a key problem in slope-stability analysis, searching for potential sliding surfaces has attracted the attention of experts and scholars for a long time. However, the commonly used sliding surface curves are only considered in terms of shape approximation and lack physical significance. The search process involved in stability analysis of multi-level slopes is complex and a large amount of calculation is required. In order to solve this problem, this paper proposes a new sliding surface form based on physical interpretation of the brachistochrone, and establishes a search model for the brachistochrone sliding surface of a multi-level loess slope. At the same time, in order to further expand the search range and find a more ideal potential sliding surface curve shape and position with a lower safety factor, we recommend continuing the sliding-surface search after the brachistochrone is improved. We compared the calculation results for the position of the potential sliding surface and the stability safety factor with the corresponding results for an arc sliding surface (in combination with a calculation example) to verify its rationality. The approach offered here not only provides a new choice of sliding surface curve form for slope-stability analysis, but also significantly improves search efficiency for potential sliding surfaces of multi-level loess slopes.

Thermoluminescence of rose quartz from Minas Gerais, Brazil

This article reports the thermoluminescence (TL) properties of rose quartz from Minas Gerais (Brazil), a translucent pink variety of quartz. Firstly, the sample shows a pure α-quartz phase, based on X-ray diffraction results. Also, the mineral shows a wide optical absorption band at about 500 nm, typical of rose quartz. In addition, X-ray fluorescence showed a high percentage of purity (99.1% of the SiO2), and the inductively coupled plasma optical emission spectrometry (ICP OES) recorded the presence of elements such as Al, Ca, Fe and Ti. The TL measurements were carried out using a commercial Risø TL/OSL reader, model DA-20, equipped with a built in 90Sr/90Y beta source, used to irradiate the sample to different radiation doses (0.01 – 1Gy). The glow curve, measured at a heating rate of 1 K/s, consists of a prominent peak at 355 K followed by other low intensity peaks at higher temperatures. Measurements of the main peak are reproducibility with a coefficient of variation (C.V.) of ∼1.3% and a repeatability of ∼1.8%. Kinetic analysis of the main peak was carried out using experimental methods comprising Tm-Tstop technique, the initial rise method, peak shape estimation and various computational methods (TGCD, TLanal, TLDecoxcel and GlowFit). The peak obeys first order kinetics, with activation energy of 0.86 eV, and a frequency factor of the order of 1011 s−1. Finally, in the dose range studied, the peak shows a sublinear dose response after which supralinearity sets in.

Blind spots and spotlights in bureaucratic politics: An analysis of policy co‐production in environmental governance dynamics in Indonesia

SummaryMotivationThere has been growing interest in recent years in a better understanding of knowledge/science and policy co‐production in environmental governance.PurposeWe aim to shed more light on the politics among the numerous actors shaping ideas that drive environmental policy in Indonesia. We focus our theoretical engagement on a framing of bureaucratic politics, which is a research tradition that has made various strides in explaining the formal and non‐formal processes that influence environmental governance outcomes.Methods and approachBuilding from a wide range of case studies drawn from deep engagement of participatory research in policy‐making in Indonesia, we established a simple typology that helps explain eight categories that emerge when bureaucracies, knowledge institutions, and publics come together to shape environmental governance outcomes.FindingsThe bureaucratic politics specifically clarified the features of cases that have clear fragmentation of bureaucracy but clear explanation variables from the formal and informal interest of bureaucracy. Potential uncovered by bureaucratic politics framing means that, if the metapolitical works alter, the bureaucracy works smoothly or makes it impossible for bureaucracy to operationalize their formal and informal interest in capturing the dynamics of macro and micro politics. In terms of form of knowledge, knowledge produced “from below” can also be used in policy co‐production. It can be produced by non‐expert actors, or from dialogue among them and sympathetic experts that occur below the bureaucracy's radar (people‐driven).Policy implicationsOur ideal policy co‐production implication is where the three actors have a strong foundation of “common consciousness” and interact equally to address a particular environmental policy agenda, with enough working space to jointly commit to creating the knowledge base to shape policy.

Object-Occluded Human Shape and Pose Estimation With Probabilistic Latent Consistency.

Occlusions between human and objects, especially for the activities of human-object interactions, are very common in practical applications. However, most of the existing approaches for 3D human shape and pose estimation require that human bodies are well captured without occlusions or with minor self-occlusions. In this paper, we focus on the problem of directly estimating the object-occluded human shape and pose from single color images. Our key idea is to utilize a partial UV map to represent an object-occluded human body, and the full 3D human shape estimation is ultimately converted as an image inpainting problem. We propose a novel two-branch network architecture to train an end-to-end regressor via a latent distribution consistency, which also includes a novel visible feature sub-net to extract the human information from object-occluded color images. To supervise the network training, we further build a novel dataset named as 3DOH50K. Several experiments are conducted to reveal the effectiveness of the proposed method. Experimental results demonstrate that the proposed method achieves state-of-the-art compared with previous methods. The dataset and codes are publicly available at https://www.yangangwang.com/papers/ZHANG-OOH-2020-03.html.

A Hybrid Approach to 3D Shape Estimation of Catheters Using Ultrasound Images

Catheter-based cardiac interventions have substantially improved the efficacy of the treatment. However, catheter navigation still poses several challenges including its poor visualization and localisation. Therefore, various imaging methods have been used to localize the catheter and estimate its shape. The use of ultrasound imaging is superior to other modalities in many aspects, but suffers from poor spatial resolution. Hence, we present a hybrid approach involving deep learning and classical approach to 3D shape estimation of catheters. Our novel approach uses two stages. First, a UNet-3D model is proposed to estimate the catheter centroid in the ultrasound image. Then, an adaptive Kalman Filter (AKF) is used to fuse the points into the 3D world coordinate frame. Simulation studies, phantom and ex-vivo experimentation results demonstrate the robustness of the method to ultrasound noise and extreme configurations (sharp curves).

Reliability Assessment of a Vision-Based Dynamic Displacement Measurement System Using an Unmanned Aerial Vehicle.

In recent years, many studies have been conducted on the vision-based displacement measurement system using an unmanned aerial vehicle, which has been used in actual structure measurements. In this study, the dynamic measurement reliability of a vision-based displacement measurement system using an unmanned aerial vehicle was examined by measuring various vibrations with a frequency of 0 to 3 Hz and a displacement of 0 to 100 mm. Furthermore, free vibration was applied to model structures with one and two stories, and the response was measured to examine the accuracy of identifying structural dynamic characteristics. The vibration measurement results demonstrated that the vision-based displacement measurement system using an unmanned aerial vehicle has an average root mean square percentage error of 0.662% compared with the laser distance sensor in all experiments. However, the errors were relatively large in the displacement measurement of 10 mm or less regardless of the frequency. In the structure measurements, all sensors demonstrated the same mode frequency based on the accelerometer, and the damping ratios were extremely similar, except for the laser distance sensor measurement value of the two-story structure. Mode shape estimation was obtained and compared using the modal assurance criterion value compared with the accelerometer, and the values for the vision-based displacement measurement system using an unmanned aerial vehicle were close to 1. According to these results, the vision-based displacement measurement system using an unmanned aerial vehicle demonstrated results similar to those of conventional displacement sensors and can thus replace conventional displacement sensors.

The stress-free state of human erythrocytes: Data-driven inference of a transferable RBC model

The stress-free state (SFS) of red blood cells (RBCs) is a fundamental reference configuration for the calibration of computational models, yet it remains unknown. Current experimental methods cannot measure the SFS of cells without affecting their mechanical properties, whereas computational postulates are the subject of controversial discussions. Here, we introduce data-driven estimates of the SFS shape and the visco-elastic properties of RBCs. We employ data from single-cell experiments that include measurements of the equilibrium shape of stretched cells and relaxation times of initially stretched RBCs. A hierarchical Bayesian model accounts for these experimental and data heterogeneities. We quantify, for the first time, the SFS of RBCs and use it to introduce a transferable RBC (t-RBC) model. The effectiveness of the proposed model is shown on predictions of unseen experimental conditions during the inference, including the critical stress of transitions between tumbling and tank-treading cells in shear flow. Our findings demonstrate that the proposed t-RBC model provides predictions of blood flows with unprecedented accuracy and quantified uncertainties.

Relationships between Dental Topography, Gross Wear, and Bang and Ramm/Liversidge and Molleson Age Estimates for a Sample of Human Premolar Teeth.

Molar crown wear is often used in bioarchaeological research as a proxy for age at death. However, a small number of researchers have used premolars or compared the application of different methods of relative age estimation. Using a sample of 197 previously extracted maxillary first premolars from US dental patients, we considered three protocols for estimating age: the Bang and Ramm/Liversidge and Molleson (BRLM) age estimate method, occlusal topographic analysis, and the Smith system of macrowear scoring. A previous study utilizing the Bang and Ramm method yielded an age estimate range of 9.4 to 10.8 years for the sample. Our analyses showed no associations between occlusal topography parameters (occlusal slope, relief, or faceting) and BRLM age estimates, but some concordance was found between Smith scoring and BRLM ages estimates and between Smith scoring and occlusal topography parameters. The results of the present study suggest that relationships between gross tooth wear, tooth shape, and dental age estimates are complex, and available methods should be considered together to gain a more comprehensive understanding of how teeth change their shape with wear throughout the lifecourse.

Estimation of the Cartilage Volume Loss Due to Knee Osteoarthritis - Case Study

Osteoarthritis (OA) is a degenerative disease of the knee joint caused by the formation of cracks within the collagen fibers of the articular cartilage. Current research is directed towards less invasive procedures for treating this degenerative disease using tissue engineering and 3D bioprinting. Therefore, it is crucial to obtain the exact shape of the damaged tissue, reconstruct the original shape of the tissue, and estimate the volume and area resulting from the wear of the contact surfaces. The study used the tibial plateau of a patient with OA that was removed during total knee arthroplasty, and the data was collected using a 3D scanner. After the reconstruction of the tibial plateau, an assessment of the area and volume of wear on the medial condyle of the tibia was performed, along with a FEM analysis of the real and approximate shape of the cartilage tissue. In this way, it is possible to simulate and create a patient-specific 3D model with a reconstructed wear volume, which can be highly attractive for future treatment strategies for cartilage damage or early stages of OA.