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Virtual Rephotography: Novel View Prediction Error for 3D Reconstruction

ACM TRANSACTIONS ON GRAPHICS 2017年第1期36卷 1-1页

作者： Waechter, Michael Beljan, Mate Fuhrmann, Simon Moehrle, Nils Kopf, Johannes Goesele, Michael Tech Univ Darmstadt Graph Capture & Massively Parallel Comp Grp Rundeturmstr 12 D-64283 Darmstadt Germany 1101 Dexter Ave N Seattle WA 98109 USA

The ultimate goal of many image-based modeling systems is to render photorealistic novel views of a scene without visible artifacts. Existing evaluation metrics and benchmarks focus mainly on the geometric accuracy of the reconstructed model, which is, however, a poor predictor of visual accuracy. Furthermore, using only geometric accuracy by itself does not allow evaluating systems that either lack a geometric scene representation or utilize coarse proxy geometry. Examples include a light field and most image-based rendering systems. We propose a unified evaluation approach based on novel view prediction error that is able to analyze the visual quality of any method that can render novel views from input images. One key advantage of this approach is that it does not require ground truth geometry. This dramatically simplifies the creation of test datasets and benchmarks. It also allows us to evaluate the quality of an unknown scene during the acquisition and reconstruction process, which is useful for acquisition planning. We evaluate our approach on a range of methods, including standard geometry-plus-texture pipelines as well as image-based rendering techniques, compare it to existing geometry-based benchmarks, demonstrate its utility for a range of use cases, and present a new virtual rephotography-based benchmark for image-based modeling and rendering systems.

关键词： image-based rendering image-based modeling 3D reconstruction multi-view stereo novel view prediction error

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Numerical and experimental analysis of the Young's modulus of cold compacted powder materials

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MECHANICS OF MATERIALS 2017年第Sep.期112卷 56-70页

作者： Salvadori, A. Lee, S. Gillman, A. Matous, K. Shuck, C. Mukasyan, A. Beason, M. T. Gunduz, I. E. Son, S. F. Univ Notre Dame Ctr Shock Wave Proc Adv React Mat Notre Dame IN 46556 USA Univ Notre Dame Dept Aerosp & Mech Engn Notre Dame IN 46556 USA Univ Notre Dame Dept Chem & Biomol Engn Notre Dame IN 46556 USA Purdue Univ Sch Mech Engn W Lafayette IN 47907 USA

We present co-designed experimental, theoretical, and numerical investigations aiming at estimating the value of the Young's modulus for cold compacted powder materials. The concept of image-based modeling is used to reconstruct the morphology of the powder structure with high fidelity. Analyses on aluminum powder pellets provide significant understanding of the microstructural mechanisms that preside the increase of the elastic properties with compaction. The role of the stress percolation path and its evolution during material densification is highlighted. (C) 2017 Elsevier Ltd. All rights reserved.

关键词： Young's modulus Cold compacted metal powders image-based modeling Co-designed experiments and simulations

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Wall shear stress at the initiation site of cerebral aneurysms

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BIOMECHANICS AND modeling IN MECHANOBIOLOGY 2017年第1期16卷 97-115页

作者： Geers, A. J. Morales, H. G. Larrabide, I. Butakoff, C. Bijlenga, P. Frangi, A. F. Univ Pompeu Fabra CISTIB Barcelona Spain Medisys Philips Res Paris Paris France UNICEN PLADEMA CONICET Tandil Argentina Univ Pompeu Fabra PhySense Barcelona Spain Hop Univ Geneve Geneva Switzerland Fac Med Geneva Geneva Switzerland Univ Sheffield CISTIB Sheffield S Yorkshire England

Hemodynamics are believed to play an important role in the initiation of cerebral aneurysms. In particular, studies have focused on wall shear stress (WSS), which is a key regulator of vascular biology and pathology. In line with the observation that aneurysms predominantly occur at regions of high WSS, such as bifurcation apices or outer walls of vascular bends, correlations have been found between the aneurysm initiation site and high WSS. The aim of our study was to analyze the WSS field at an aneurysm initiation site that was neither a bifurcation apex nor the outer wall of a vascular bend. Ten cases with aneurysms on the A1 segment of the anterior cerebral artery were analyzed and compared with ten controls. Aneurysms were virtually removed from the vascular models of the cases to mimic the pre-aneurysm geometry. Computational fluid dynamics (CFD) simulations were created to assess the magnitude, gradient, multidirectionality, and pulsatility of the WSS. To aid the inter-subject comparison of hemodynamic variables, we mapped the branch surfaces onto a two-dimensional parametric space. This approach made it possible to view the whole branch at once for qualitative evaluation. It also allowed us to empirically define a patch for quantitative analysis, which was consistent among subjects and encapsulated the aneurysm initiation sites in our dataset. To test the sensitivity of our results, CFD simulations were repeated with a second independent observer virtually removing the aneurysms and with a 20 % higher flow rate at the inlet. We found that branches harboring aneurysms were characterized by high WSS and high WSS gradients. Among all assessed variables, the aneurysm initiation site most consistently coincided with peaks of temporal variation in the WSS magnitude.

关键词： Aneurysm initiation Cerebral aneurysms Computational fluid dynamics Hemodynamics image-based modeling Flow pulsatility Wall shear stress

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Pervasive Agriculture: Measuring and Predicting Plant Growth Using Statistics and 2D/3D Imaging

Pervasive Agriculture: Measuring and Predicting Plant Growth...

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IEEE International Instrumentation and Measurement Technology Conference (I2MTC) - Discovering New Horizons in Instrumentation and Measurement

作者： Shadrin, Dmitrii Somov, Andrey Podladchikova, Tatiana Gerzer, Rupert Skolkovo Inst Sci & Technol Moscow Russia

ISBN: (纸本)9781538622223

The growing of Earth population and the need of food provisioning to remote areas make pervasive agriculture the research problem of high priority. In this work, we present a 2D/3D scanning system with the intelligent data processing mechanism which can be easily deployed in a greenhouse. The proposed solution enables finding of correlations between the leaf area and biomass and thereby helps predict the plant metrics including the growth rate and leaf area. This knowledge is of particular significance for actuating the plant growth parameters depending on the context and feedback. Our experimental results conducted on two sorts of tomatoes and salad demonstrate high potential of this approach.

关键词： 3D imaging growth rate plant modeling image-based modeling pervasive agriculture

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Changes in articular cartilage mechanics with meniscectomy: A novel image-based modeling approach and comparison to patterns of OA

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JOURNAL OF BIOMECHANICS 2011年第12期44卷 2307-2312页

作者： Haemer, Joseph M. Song, Yongnam Carter, Dennis R. Giori, Nicholas J. Stanford Univ Dept Mech Engn San Jose CA 95172 USA VA Palo Alto Hlth Care Syst Ctr Bone & Joint Palo Alto CA USA Korea Univ Dept Mech Engn Seoul South Korea Stanford Univ Dept Orthoped Surg San Jose CA 95172 USA

Meniscectomy is a significant risk factor for osteoarthritis, involving altered cell synthesis, central fibrillation, and peripheral osteophyte formation. Though changes in articular cartilage contact pressure are known, changes in tissue-level mechanical parameters within articular cartilage are not well understood. Recent imaging research has revealed the effects of meniscectomy on the time-dependent deformation of physiologically loaded articular cartilage. To determine tissue-level cartilage mechanics that underlie observed deformation, a novel finite element modeling approach using imaging data and a contacting indenter boundary condition was developed. The indenter method reproduces observed articular surface deformation and avoids assumptions about tangential stretching. Comparison of results from an indenter model with a traditional femur-tibia model verified the method, giving errors in displacement, solid and fluid stress, and strain below 1% (RMS) and 7% (max.) of the absolute maximum of the parameters of interest. Indenter finite element models using real joint image data showed increased fluid pressure, fluid exudation, loss of fluid load support, and increased tensile strains centrally on the tibial condyle after meniscectomy patterns corresponding to clinical observations of cartilage matrix damage and fibrillation. Peripherally there was decreased consolidation, which corresponds to reduced contact and fluid pressure in this analysis. Clinically, these areas have exhibited advance of the subchondral growth front, biological destruction of the cartilage matrix, cartilage thinning, and eventual replacement of the cartilage via endochondral ossification. Characterizing the changes in cartilage mechanics with meniscectomy and correspondence with observed tissue-level effects may help elucidate the etiology of joint-level degradation seen in osteoarthritis. (C) 2011 Elsevier Ltd. All rights reserved.

关键词： Osteoarthritis Meniscectomy Articular cartilage Finite element analysis Magnetic resonance imaging image-based modeling

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Visual simulation of clouds

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Visual Informatics 2017年第1期1卷 1-8页

作者： Yoshinori Dobashi Kei Iwasaki Yonghao Yue Tomoyuki Nishita Hokkaido University/UEI Research Japan Wakayama University/UEI Research Japan The University of Tokyo Japan UEI Research/Hiroshima Shudo University Japan

Clouds play an important role when synthesizing realistic images of outdoor *** realistic display of clouds is therefore one of the important research topics in computer *** order to display realistic clouds,we need methods for modeling,rendering,and animating clouds *** is also important to control the shapes and appearances of clouds to create certain visual *** this paper,we explain our efforts and research results to meet such requirements,together with related researches on the visual simulation of clouds.

关键词： Clouds Procedural modeling image-based modeling Fluid simulation Feedback control Genetic algorithms

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Multi-view Wire Art

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ACM TRANSACTIONS ON GRAPHICS 2018年第6期37卷 242-242页

作者： Hsiao, Kai-Wen Huang, Jia-Bin Chu, Hung-Kuo Natl Tsing Hua Univ Hsinchu Taiwan Virginia Tech Blacksburg VA USA

Wire art is the creation of three-dimensional sculptural art using wire strands. As the 2D projection of a 3D wire sculpture forms line drawing patterns, it is possible to craft multi-view wire sculpture art - a static sculpture with multiple (potentially very different) interpretations when perceived at different viewpoints. Artists can effectively leverage this characteristic and produce compelling artistic effects. However, the creation of such multi-view wire sculpture is extremely time-consuming even by highly skilled artists. In this paper, we present a computational framework for automatic creation of multi-view 3D wire sculpture. Our system takes two or three user-specified line drawings and the associated viewpoints as inputs. We start with producing a sparse set of voxels via greedy selection approach such that their projections on the virtual cameras cover all the contour pixels of the input line drawings. The sparse set of voxels, however, do not necessary form one single connected component. We introduce a constrained 3D pathfinding algorithm to link isolated groups of voxels into a connected component while maintaining the similarity between the projected voxels and the line drawings. Using the reconstructed visual hull, we extract a curve skeleton and produce a collection of smooth 3D curves by fitting cubic splines and optimizing the curve deformation to best approximate the provided line drawings. We demonstrate the effectiveness of our system for creating compelling multi-view wire sculptures in both simulation and 3D physical printouts.

关键词： image-based modeling wire art skeleton extraction shape deformation

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Evaluation of image-based modeling and laser scanning accuracy for emerging automated performance monitoring techniques

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AUTOMATION IN CONSTRUCTION 2011年第8期20卷 1143-1155页

作者： Golparvar-Fard, Mani Bohn, Jeffrey Teizer, Jochen Savarese, Silvio Pena-Mora, Feniosky Virginia Tech Charles E Via Dept Civil & Environm Engn Blacksburg VA 24061 USA Virginia Tech Myers Lawson Sch Construct Blacksburg VA 24061 USA Georgia Inst Technol Sch Civil & Environm Engn Atlanta GA 30332 USA Univ Michigan Ann Arbor MI 48109 USA Columbia Univ Fu Fdn Sch Engn & Appl Sci New York NY 10027 USA

Accurate and rapid assessment of the as-built status on any construction site provides the opportunity to understand the current performance of a project easily and quickly. Rapid project assessment further identifies discrepancies between the as-built and as-planned progress, and facilitates decision making on the necessary remedial actions. Currently, manual visual observations and surveying are the most dominant data capturing techniques but they are time-consuming, error-prone, and infrequent, making quick and reliable decision-making difficult. Therefore, research on new approaches that allow automatic recognition of as-built performance and visualization of construction progress is essential. This paper presents and compares two methods for obtaining point cloud models for detection and visualization of as-built status for construction projects: (1) A new method of automated image-based reconstruction and modeling of the as-built project status using unordered daily construction photo collections through analysis of Structure from Motion (SfM);(2) 3D laser scanning and analysis of the as-built dense point cloud models. These approaches provide robust means for recognition of progress, productivity, and quality on a construction site. In this paper, an overview of the newly developed automated image-based reconstruction approach and exclusive features which distinct it from other image-based or conventional photogrammetric techniques is presented. Subsequently the terrestrial laser scanning approach carried out for reconstruction and comparison of as-built scenes is presented. Finally the accuracy and usability of both of these techniques for metric reconstruction, automated production of point cloud models, 3D CAD shape modeling, and as-built visualizations is evaluated and compared on eight different case studies. It is shown that for precise defect detection or alignment tasks, image-based point cloud models may not be as accurate and dense as laser scanners

关键词： Progress monitoring image-based modeling Structure from motion Laser scanning Computer aided design Construction field imagery Range point clouds As-built modeling

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Compliance boundary conditions for patient-specific deformation simulation using the finite element method

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BIOMEDICAL PHYSICS & ENGINEERING EXPRESS 2018年第2期4卷

作者： Ozkan, Ece Goksel, Orcun Swiss Fed Inst Technol Comp Assisted Applicat Med Grp Zurich Switzerland

Tissue deformation simulations for pre-operative planning or intra-operative guidance of medical procedures require accurate patient-specific models and are commonly performed using the Finite Element Method (FEM). Since only a small part of the entire body is typically observed with medical imaging, the deformation models are often limited to a relatively small region-of-interest (ROI). Surrounding this ROI, one then needs to define suitable boundary conditions for an accurate simulation. Conventionally, boundary conditions are set arbitrarily or heuristically at chosen model locations;typically as either zero-displacement or -force constraint, which obviously are suboptimal where ROI borders are neither fixed (e.g. on bone) or free (e.g. skin facing the air). In this work, we present a novel boundary-condition formulation, called compliance boundary conditions (CBC), which approximate the effect of anatomy outside this ROI and augment this onto the ROI border nodes. CBC can be parametrized from observed tissue displacements, e.g. tracked in ultrasound (US) or magnetic-resonance imaging. It is inherently embedded in the FEM deformation model to be used for computing any interaction response. CBC is a generalization of conventional boundary constraints, where the typical zero-displacement and -force constraints are obtained at the two extremes of the given CBC parameter. We demonstrate CBC for linear-and quadratic-strain FEM models in 2D and 3D numerical phantoms, for which different element/integration formulations and the effect of noise are studied. CBC is shown to reduce displacement errors for both 2D and 3D numerical phantoms by more than 50% compared to conventional boundary conditions. We also present CBC on tissue-mimicking gelatin phantom experiments from displacements observed in US images. In an application scenario of simulating needle insertion for prostate brachytherapy, CBC is shown to reduce seed placement errors by more than 70% compared to convent

关键词： FEM image-based modeling boundary conditions

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Example-based Synthesis of Three-dimensional Clouds from Photographs 17

Example-based Synthesis of Three-dimensional Clouds from Pho...

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34th International Conference on Computer Graphics (CGI)

作者： Iwasaki, Kei Dobashi, Yoshinori Okabe, Makoto Wakayama Univ UEI Res Wakayama Japan Hokkaido Univ UEI Res Sapporo Hokkaido Japan Shizuoka Univ Shizuoka Japan

ISBN: (纸本)9781450352284

In this paper, we propose a modeling method of clouds from a single photograph. To synthesize realistic images of outdoor scenes, modeling of 3D clouds is necessary. However, synthesizing realistic clouds is still a difficult task. To address this problem, we propose an example-based volume texture synthesis to model non-homogeneous density volumes. Our method prepares an example cloud volume data using a physically-based fluid simulator. Then the output cloud volume is automatically synthesized from the example cloud volume data so that its rendered image becomes similar to the clouds in the input photograph. In contrast to the previous texture synthesis methods, our method synthesizes density volumes taking into account scattering and transmittance of light. We show several cloud volumes whose rendered images are similar to the input photograph.

关键词： image-based modeling natural phenomena texture synthesis

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