Sequence Of Meshes Research Articles

Adaptive representation of dynamic 3D meshes for low-latency applications

Recently, 3D visual representations of highly deformable 3D models, such as dynamic 3D meshes, are becoming popular due to their capability to represent realistically the motion of real-world objects/humans, paving the road for new and more advanced immersive virtual, augmented and mixed reality experiences. However, the real-time streaming of such models introduces increasing challenges related to low cost, low-latency and scalable coding of the acquired information. In view of this, this article proposes an efficient scalable coding mechanism, that decomposes a mesh sequence into spatial and temporal layers that remove a single vertex at each layer. The removed vertices are predicted by performing Laplacian interpolation of the motion vectors. The artifacts that are introduced in low-resolution representations are mitigated using a subspace based normal-vector denoising procedure, that is optimized to support low-latency streaming scenarios using incremental SVD. A novel initialization strategy offers robustness to outliers generated due to local deformations. An extensive evaluation study using several synthetic and scanned dynamic 3D meshes highlights the benefits of the proposed approach in terms of both execution time and reconstruction quality even in very low throughput scenarios of bit-per-vertex-per-frame (bpvf).

Applications of a High-Order Harmonic Basis for Solving Some Magnetostatic Problems

The aim of this work is to investigate the possibilities of using a high-order harmonic basis for solving some magnetostatic problems. We consider known methods with our basis and the approach earlier elaborated by the authors. We present numerical results of their comparison when solving a linear problem on sequences of meshes with various parameters h and p. For a nonlinear problem with respect to two scalar potentials, it is shown that this model, in the suggested new weak formulation, keeps the property of monotonicity. From the results of this work it may be concluded that the harmonic basis gives more exact approximations on adaptive meshes for the considered magnetostatic problems in comparison with the usual approach.

Effective Descriptors for Human Action Retrieval from 3D Mesh Sequences

Two novel methods for fully unsupervised human action retrieval using 3D mesh sequences are presented. The first achieves high accuracy but is suitable for sequences consisting of clean meshes, such as artificial sequences or highly post-processed real sequences, while the second one is robust and suitable for noisy meshes, such as those that often result from unprocessed scanning or 3D surface reconstruction errors. The first method uses a spatio-temporal descriptor based on the trajectories of 6 salient points of the human body (i.e. the centroid, the top of the head and the ends of the two upper and two lower limbs) from which a set of kinematic features are extracted. The resulting features are transformed using the wavelet transformation in different scales and a set of statistics are used to obtain the descriptor. An important characteristic of this descriptor is that its length is constant independent of the number of frames in the sequence. The second descriptor consists of two complementary sub-descriptors, one based on the trajectory of the centroid of the human body across frames and the other based on the Hybrid static shape descriptor adapted for mesh sequences. The robustness of the second descriptor derives from the robustness involved in extracting the centroid and the Hybrid sub-descriptors. Performance figures on publicly available real and artificial datasets demonstrate our accuracy and robustness claims and in most cases the results outperform the state-of-the-art.

Advanced Volumetric Capture and Processing

Volumetric video is regarded worldwide as the next important development in media production, especially in the context of rapidly evolving virtual and augmented reality markets where volumetric video is becoming a key technology. Fraunhofer Heinrich Hertz Institute (HHI) has developed a novel technology for volumetric video. The 3D Human Body Reconstruction (3DHBR) technology captures real persons with our novel volumetric capture system and creates naturally moving dynamic 3D models, which can then be observed from arbitrary viewpoints in a virtual or augmented reality scene. The capture system consists of an integrated multicamera and lighting system for a full 360° acquisition. A cylindrical studio has been developed with a diameter of 6 m and consists of 32 20-MPixel cameras and 120 light-emitting-diode (LED) panels that allow for an arbitrary lit background. Hence, diffuse lighting and automatic keying are supported. The avoidance of green screen and provision of diffuse lighting offers the best possible conditions for relighting of the dynamic 3D models afterward at the design stage of the virtual reality (VR) experience. In contrast to classical character animation, facial expressions and moving clothes are reconstructed at high geometrical detail and texture quality. The complete workflow is fully automatic, requires about 12 hr/min of mesh sequence, and provides a high level of quality for immediate integration in virtual scenes. Meanwhile, a second, professional studio has been built up on the film campus of Potsdam Babelsberg. This studio is operated by VoluCap GmbH, a joint venture between Studio Babelsberg, ARRI, UFA, Interlake, and Fraunhofer Heinrich Hertz Institute (HHI).

Tooth Root Crack Detection of Planet and Sun Gears Based on Resonance Demodulation and Vibration Separation

Due to the epicyclic motion of planet gears, the vibration picked up from planetary gearboxes is different from that observed from the fixed-axis gearboxes. In particular, the vibration transfer path is time-varying, which makes the time synchronous averaging (TSA) not directly usable to reduce the nonsynchronous interferences for improving the signal-noise ratio (SNR) of vibration. Hence, it is difficult to detect teeth faults of planet and sun gears. In order to address this issue, a novel scheme is proposed in this paper, which combines the vibration separation, equi-angle resampling, and resonance demodulation approaches. In the proposed scheme, the complex envelope of the vibration is extracted by the fast kurtogram algorithm at first. Then, the envelope is equi-angle resampled to eliminate the inevitable speed fluctuations. Subsequently, a window function is used to grab the envelope data series at a fixed angular position related to the ring gear, such that the problems caused by time-varying vibration transfer paths are solved. Then, synthetic envelopes can be constructed by connecting the data in the data blocks according to the teeth mesh sequences of the interesting gear, where a data mapping scheme and a synthetic envelope determining strategy based on maximum kurtosis are introduced. Furthermore, the TSA is applied to the synthetic gear envelope to improve the SNR. Finally, spectral analysis is utilized to expose the characteristic frequencies. The effectiveness of the proposed method is validated by comparative experiments with the normal and faulty planet and sun gears in a planetary gearbox test rig.

NLME: a nonlinear motion estimation-based compression method for animated mesh sequence

This paper proposes an efficient compression algorithm for animated three-dimensional meshes by introducing nonlinear transformations to model the motion field of deforming patches. First, a segmentation process is applied to separate the 3D model into different patches which have similar motion patterns through the sequence. Next, the motion of the resulting patches is accurately described by a nonlinear motion estimation model. The main idea is to exploit the temporal coherence of the geometry component by using a nonlinear predictor in order to get better approximation of vertex locations. Nonlinear motion transforms are computed at previous frame to match the subsequent ones. Moreover, an adaptive bit allocation algorithm is employed to determine the near-optimal number of bits for quantizing the prediction errors. The number of quantization bits for each segmented patch is determined by analyzing the geometry complexity of the patch and the statistical properties of the prediction errors. Finally, an extensive experimental study has been conducted to evaluate the coding efficiency of the proposed compression scheme. Simulation results demonstrate that the proposed method is very efficient in terms of rate-distortion performance, particularly for the animated models with non-rigid deformations, and outperforms the state-of-the-art methods.

Affordable Explicitly Filtered Large-Eddy Simulation for Reacting Flows

This paper focuses on improving the grid convergence properties of large-eddy simulations. To isolate the impact of numerical filtering and the associated errors inherently present in implicitly filtered large-eddy simulation approaches, the authors have developed a novel explicit filtering approach suitable for any mesh topology and filter kernel. Simulations of a bluff-body stabilized, premixed flame configuration on a sequence of meshes are used to demonstrate this methodology. Grid convergence assessment is also performed for another approach, wherein the filter width at each computational cell is explicitly set. Comparisons show that solutions from prescribed-width implicitly filtered large-eddy simulation and explicitly filtered large-eddy simulation approaches exhibit good convergence for the mean quantities. The explicitly filtered large-eddy simulation results show clear convergence trends in the rms quantities, unlike the prescribed-width implicitly filtered large-eddy simulation approach and previously reported implicitly filtered large-eddy simulation results. While discrepancies exist in the level of agreement between the grid converged rms solutions with measured data, this could now be attributed to the errors in the physical models and boundary conditions. Importantly, the proposed explicitly filtered large-eddy simulation approach only reduces the computational efficiency by approximately 30% on the fine grid simulation, relative to the implicitly filtered large-eddy simulation approach.

Comparing Anisotropic Adaptive Strategies on the Second AIAA Sonic Boom Workshop Geometry

The recent release of the second AIAA sonic boom geometry offers the opportunity to review the classical anisotropic adaptive strategies for complex geometries. The design of Mach-aligned tailored grids is also a great challenge to see how adaptivity can compete with user-defined tailored grids. Two classical adaptive strategies, multiscale and goal-oriented, are compared with the results obtained on tailored grids. For the flow solver, several low-dissipation numerical schemes of order 4 and 6 are discussed with respect to regular second-order scheme both on inviscid and Reynolds-averaged Navier–Stokes flow models. Finally, a nonlinear error analysis is performed to assess the convergence of the sequence of adaptive meshes with respect to tailored grids. All results and discussions are based on the C25D baseline geometry provided for the Second AIAA Sonic Boom Prediction Workshop.

Compressed dynamic mesh sequence for progressive streaming

AbstractDynamic mesh sequence (DMS) is a simple and accurate representation for precisely recording a 3D animation sequence. Despite its simplicity, this representation is typically large in data size, making storage and transmission expensive. This paper presents a novel framework that allows effective DMS compression and progressive streaming by eliminating spatial and temporal redundancy. To explore temporal redundancy, we propose a temporal frame‐clustering algorithm to organize DMS frames by their motion trajectory changes, eliminating intracluster redundancy by principal component analysis dimensionality reduction. To eliminate spatial redundancy, we propose an algorithm to transform the coordinates of mesh vertex trajectory into a decorrelated trajectory space, generating a new spatially nonredundant trajectory representation. We finally apply a spectral graph wavelet transform with color set partitioning embedded block encoding to turn the resultant DMS into a multiresolution representation to support progressive streaming. Experiment results show that our method outperforms several existing methods in terms of storage requirement and reconstruction quality.

Robust and effective mesh denoising using [formula omitted] sparse regularization

Mesh denoising is of great practical importance in geometric analysis and processing. In this paper we develop a novel L0 sparse regularization method to robustly and reliably eliminate noises while preserving features with theoretic guarantee, and our assumption is that, local regions of a noise-free shape should be smooth unless they contain geometric features. Both vertex positions and facet normals are integrated into the L0 norm to measure the sparsity of geometric features, and are then optimized in a sparsity-controllable fashion. We design an improved alternating optimization strategy to solve the L0 minimization problem, which is proved to be both convergent and stable. As a result, our sparse regularization exhibits its advantage to distinguish features from noises. To further improve the computational performance, we propose a multi-layer approach based on joint bilateral upsampling to handle large and complicated meshes. Moreover, the aforementioned framework is naturally accommodating the need of denoising time-varying mesh sequences. Both theoretical analysis and various experimental results on synthetic and natural noises have demonstrated that, our method can robustly recover multifarious features and smooth regions of 3D shapes even with severe noise corruption, and outperform the state-of-the-art methods.

Unsupervised human action retrieval using salient points in 3D mesh sequences

The problem of human action retrieval based on the representation of the human body as a 3D mesh is addressed. The proposed 3D mesh sequence descriptor is based on a set of trajectories of salient points of the human body: its centroid and its five protrusion ends. The extracted descriptor of the corresponding trajectories incorporates a set of significant features of human motion, such as velocity, total displacement from the initial position and direction. As distance measure, a variation of the Dynamic Time Warping (DTW) algorithm, combined with a k ? means based method for multiple distance matrix fusion, is applied. The proposed method is fully unsupervised. Experimental evaluation has been performed on two artificial datasets, one of which is being made publicly available by the authors. The experimentation on these datasets shows that the proposed scheme achieves retrieval performance beyond the state of the art.

Fast deformable model-based human performance capture and FVV using consumer-grade RGB-D sensors

In this paper, a novel end-to-end system for the fast reconstruction of human actor performances into 3D mesh sequences is proposed, using the input from a small set of consumer-grade RGB-Depth sensors. The proposed framework, by offline pre-reconstructing and employing a deformable actor’s 3D model to constrain the on-line reconstruction process, implicitly tracks the human motion. Handling non-rigid deformation of the 3D surface and applying appropriate texture mapping, it finally produces a dynamic sequence of temporally-coherent textured meshes, enabling realistic Free Viewpoint Video (FVV). Given the noisy input from a small set of low-cost sensors, the focus is on the fast (“quick-post”), robust and fully-automatic performance reconstruction. Apart from integrating existing ideas into a complete end-to-end system, which is itself a challenging task, several novel technical advances contribute to the speed, robustness and fidelity of the system, including a layered approach for model-based pose tracking, the definition and use of sophisticated energy functions, parallelizable on the GPU, as well as a new texture mapping scheme. The experimental results on a large number of challenging sequences, and comparisons with model-based and model-free approaches, demonstrate the efficiency of the proposed approach.

Anisotropic Meshes and Stabilization Parameter Design of Linear SUPG Method for 2D Convection-Dominated Convection–Diffusion Equations

We propose a numerical strategy to generate a sequence of anisotropic meshes and select appropriate stabilization parameters simultaneously for linear SUPG method solving two dimensional convection-dominated convection–diffusion equations. Since the discretization error in a suitable norm can be bounded by the sum of interpolation error and its variants in different norms, we replace them by some terms which contain the Hessian matrix of the true solution, convective field, and the geometric properties such as directed edges and the area of triangles. Based on this observation, the shape, size and equidistribution requirements are used to derive corresponding metric tensor and stabilization parameters. Numerical results are provided to validate the stability and efficiency of the proposed numerical strategy.

Eigenspace compression: dynamic 3D mesh compression by restoring fine geometry to deformed coarse models

Dynamic 3D mesh compression is of great practical important issues in computer graphics and multimedia applications. In this paper, an efficient compression algorithm is proposed to represent animated mesh sequences in a compact way, so that the storage and transmission of dynamic 3D meshes can be accomplished efficiently. The focus of this paper is on the animated mesh sequences with shared connectivity. The proposed method first computes coarse models (low frequency modes) of the animated sequence using the graph Laplacian matrix. Obtained coordinate weights are used at the decoder to reconstruct the coarse models of the sequence. Then, a novel approach is proposed to extract fixed details (high frequency modes or finer features) of the animated mesh. Finally, a details restoration process is applied at the decoder to add details back to the coarse models of the reconstructed sequence. The superiority of the proposed method to the current state of the arts is demonstrated in terms of low data rates for a given degree of perceived distortion.

Exponential convergence of the hp virtual element method in presence of corner singularities

In the present work, we analyze the hp version of virtual element methods for the 2D Poisson problem. We prove exponential convergence of the energy error employing sequences of polygonal meshes geometrically refined, thus extending the classical choices for the decomposition in the hp finite element framework to very general decomposition of the domain. A new stabilization for the discrete bilinear form with explicit bounds in h and p is introduced. Numerical experiments validate the theoretical results. We also exhibit a numerical comparison between hp virtual elements and hp finite elements.

Algorithm-based fault recovery of adaptively refined parallel multilevel grids

On future extreme scale computers, it is expected that faults will become an increasingly serious problem as the number of individual components grows and failures become more frequent. This is driving the interest in designing algorithms with built-in fault tolerance that can continue to operate and that can replace data even if part of the computation is lost in a failure. For fault-free computations, the use of adaptive refinement techniques in combination with finite element methods is well established. Furthermore, iterative solution techniques that incorporate information about the grid structure, such as the parallel geometric multigrid method, have been shown to be an efficient approach to solving various types of partial different equations. In this article, we present an advanced parallel adaptive multigrid method that uses dynamic data structures to store a nested sequence of meshes and the iteratively evolving solution. After a fail-stop fault, the data residing on the faulty processor will be lost. However, with suitably designed data structures, the neighbouring processors contain enough information so that a consistent mesh can be reconstructed in the faulty domain with the goal of resuming the computation without having to restart from scratch. This recovery is based on a set of carefully designed distributed algorithms that build on the existing parallel adaptive refinement routines, but which must be carefully augmented and extended.

Spatiotemporal atlas parameterization for evolving meshes

We convert a sequence of unstructured textured meshes into a mesh with incrementally changing connectivity and atlas parameterization. Like prior work on surface tracking, we seek temporally coherent mesh connectivity to enable efficient representation of surface geometry and texture. Like recent work on evolving meshes, we pursue local remeshing to permit tracking over long sequences containing significant deformations or topological changes. Our main contribution is to show that both goals are realizable within a common framework that simultaneously evolves both the set of mesh triangles and the parametric map. Sparsifying the remeshing operations allows the formation of large spatiotemporal texture charts. These charts are packed as prisms into a 3D atlas for a texture video. Reducing tracking drift using mesh-based optical flow helps improve compression of the resulting video stream.

H-multigrid agglomeration based solution strategies for discontinuous Galerkin discretizations of incompressible flow problems

In this work we exploit agglomeration based h-multigrid preconditioners to speed-up the iterative solution of discontinuous Galerkin discretizations of the Stokes and Navier–Stokes equations. As a distinctive feature h-coarsened mesh sequences are generated by recursive agglomeration of a fine grid, admitting arbitrarily unstructured grids of complex domains, and agglomeration based discontinuous Galerkin discretizations are employed to deal with agglomerated elements of coarse levels. Both the expense of building coarse grid operators and the performance of the resulting multigrid iteration are investigated. For the sake of efficiency coarse grid operators are inherited through element-by-element L2 projections, avoiding the cost of numerical integration over agglomerated elements. Specific care is devoted to the projection of viscous terms discretized by means of the BR2 dG method. We demonstrate that enforcing the correct amount of stabilization on coarse grids levels is mandatory for achieving uniform convergence with respect to the number of levels. The numerical solution of steady and unsteady, linear and non-linear problems is considered tackling challenging 2D test cases and 3D real life computations on parallel architectures. Significant execution time gains are documented.

A multilevel decoupling method for the Navier–Stokes/Darcy model

This paper considers a multilevel decoupling method for the coupled Navier–Stokes/Darcy model describing a free flowing fluid over a porous medium. The method utilizes a sequence of meshes on which a low dimensional fully coupled nonlinear problem is solved only on a very coarse initial mesh. On subsequent finer meshes, the approximate solution in each flow region is obtained by solving a linear decoupled problem and performing a correction step. The correction step in each domain is achieved by solving a linear system that differs from the original decoupled system only in the right hand side. We prove optimal error estimates and demonstrate that for a sequence of meshes with spacing hj=hj−12, the decoupling method is computationally efficient and achieves the same order of approximation as the fully coupled method.

Quadrangulations of Animation Sequence

This paper presents a novel approach to quadrangulate a sequence of meshes with global optimization method, generating consistent quad meshes expressing global topological and geometric characteristics during animation. The key contribution is that our method first proposes a grouping strategy to extract the geometric and topological features of the sequence in animation quadrangulation. Animation sequence is firstly divided into groups through picked key frames. Then analyze the local deformation of each group and detect the surface feature for each reference frame, inducing a set of hard and soft constraints for each key frame of every subgroup, next smooth the cross field of each reference frame and combine them through singularities for the whole sequence, finally compute a field guided global parametrization and quad meshes extraction with an off-the-shelf method. It is effective and easy to implement, and experiment results and comparisons show that our method achieves better quality.