Shape exploration of 3D heterogeneous models based on cages

Shape exploration of 3D heterogeneous models is essential for special effects in 3D animation and games. As heterogeneous models have different numbers of vertices and different topological structures,the mapping between source and target model may be ambiguous for deformation transfer. We propose a new framework for heterogeneous model shape exploration based on cages, which provides a feasible and fast solution to this open problem. Using a public cage as an intermediate medium, the deformation of the source models can be denoted as the position changing of the cage. When applying the cage change to the target model, rough deformation transfer can be achieved. After an optimization and interpolation to generate the explored shape of the heterogeneous target model, animation can be acquired. Our method is not only suitable for triangle meshes, but also for quadrilateral meshes or any other type of meshes. We demonstrate the validity of our scheme by a series of shape exploration experiments with different models.     

Customizing 3D garments based on volumetric deformation

Improving the reusability of design results is very important for garment design industry, since designing an elegant garment is usually labor-intensive and time-consuming. In this paper, we present a new approach for customizing 3D garment models. Our approach can transfer garment models initially dressed on a reference human model onto a target human model. To achieve this goal, firstly a spatial mapping between the two human models is established with the shape constraints of cross-sections. Secondly, the space around the clothed reference human model is tetrahedralized into five tetrahedral meshes each of which either can be worked dependently with its adjacent ones or can be worked independently. The clothed reference human model is parametrically encoded in the tetrahedral meshes. Thirdly, these tetrahedral meshes are deformed by fitting the reference human model onto the target human model by using constrained volumetric graph Laplacian deformation. The updated garment models are finally decoded from the deformed tetrahedral meshes. As a result, the updated garment models are fitted onto the target human model. Experiments show that our approach performs very well and has the potential to be used in the garment design industry.     

Deformation Transfer to Multi‐Component Objects

We present a simple and effective algorithm to transfer deformation between surface meshes with multiple components. The algorithm automatically computes spatial relationships between components of the target object, builds correspondences between source and target, and finally transfers deformation of the source onto the target while preserving cohesion between the target's components. We demonstrate the versatility of our approach on various complex models.     

Segmenting a deforming mesh into near-rigid components

Given a deforming mesh in an animation, we propose a new method to segment this mesh into several near-rigid sub-meshes. From this deforming mesh over all frames of an animation, we can analyze the degree of deformation between two nearby faces on the mesh. Then, our algorithm partitions the given deforming mesh into near-rigid components where the segmentation boundaries always pass at regions of large deformation. As a result, the mesh segmentation is invariant to all frames of the given animation and the motion of faces in each near-rigid-component can be represented by the same approximate affine transformation. To demonstrate the usefulness of the algorithm, we solve the restriction of deformation transfer for triangle meshes [31] which requires similar reference poses between source mesh and target mesh.     

基于变形图的谱姿态迁移

为减低谱姿态迁移结果受几何代理 Cage 的影响程度,提出基于变形图的谱姿态迁 移方法。首先,利用优化二次误差度量方法简化源网格得到变形图,将源网格顶点以测地距离 为权重用变形图顶点表示,强制源网格顶点与基于耦合准调和基的姿态迁移结果尽可能相同, 同时保持变形图的拉普拉斯坐标,获得低频姿态迁移结果,并利用嵌入变形算法对此结果进行 优化;然后,通过观察找到次级姿态学习不充分的局部网格,分割出局部子网格,对这些子网 格使用低频姿态迁移方法,可以学习到次级姿态。实验结果表明,在一定程度上降低了几何代 理的影响,有效地提高了谱姿态迁移结果。     

Landmark transfer with minimal graph

We present an efficient and robust algorithm for the landmark transfer on 3D meshes that are approximately isometric. Given one or more custom landmarks placed by the user on a source mesh, our method efficiently computes corresponding landmarks on a family of target meshes. The technique is useful when a user is interested in characterization and reuse of application-specific landmarks on meshes of similar shape (for example, meshes coming from the same class of objects). Consequently, across a set of multiple meshes consistency is assured among landmarks, regardless of landmark geometric distinctiveness. The main advantage of our method over existing approaches is its low computation time. Differently from existing non-rigid registration techniques, our method detects and uses a minimum number of geometric features that are necessary to accurately locate the user-defined landmarks and avoids performing unnecessary full registration. In addition, unlike previous techniques that assume strict consistency with respect to geodesic distances, we adopt histograms of geodesic distance to define feature point coordinates, in order to handle the deviation of isometric deformation. This allows us to accurately locate the landmarks with only a small number of feature points in proximity, from which we build what we call a minimal graph. We demonstrate and evaluate the quality of transfer by our algorithm on a number of Tosca data sets.     

基于顶点变形梯度的点云曲面变形传输

为了重用现有模型的变形结果,给出一种点云曲面的变形传输方法.利用顶点变形梯度来编码源点云的变形信息,通过一个全局的二次能量优化,实现了点云曲面的变形传输.顶点的变形梯度由顶点的k邻近点决定,并从能量优化的角度得出了顶点变形梯度的一个闭合解.该方法可直接在点云上进行,无需类似网格的拓扑结构,也不要求源点云与目标点云具有相同的采样点数和一致的对应关系.实验结果表明,该方法能有效地实现源点云与目标点云之间的变形传输.     

Interactive 3D caricature from harmonic exaggeration

A common variant of caricature relies on exaggerating characteristics of a shape that differs from a reference template, usually the distinctive traits of a human portrait. This work introduces a caricature tool that interactively emphasizes the differences between two three-dimensional meshes. They are represented in the manifold harmonic basis of the shape to be caricatured, providing intrinsic controls on the deformation and its scales. It further provides a smooth localization scheme for the deformation. This lets the user edit the caricature part by part, combining different settings and models of exaggeration, all expressed in terms of harmonic filter. This formulation also allows for interactivity, rendering the resulting 3d shape in real time.     

3D conforming power diagrams for radial LGR in CPG reservoir grids

Mesh generation becomes a crucial step in reservoir flow simulation of new generation. The mesh must faithfully represent the architecture of the reservoir and its heterogeneity. In (Flandrin et al. in IJNME 65(10):1639–1672, 2006) a three-dimensional hybrid mesh model was proposed to capture the radial characteristics of the flow around the wells. In this hybrid mesh, the reservoir is described by a non-uniform Cartesian structured mesh and the drainage areas around the wells are represented by structured radial circular meshes. Unstructured polyhedral meshes are used to connect these two kinds of structured grids. The construction of these transition meshes is based on 3D power diagrams (Aurenhammer in SIAM J Comput 16(1):78–96, 1987) to ensure finite volume properties such as mesh conformity, dual orthogonality and cell convexity. In this paper, we propose an extension of this hybrid model to the case where the reservoir is described by a corner point geometry (CPG) grid. At first, the CPG grid is mapped, in a reference space, into a non-uniform Cartesian grid by minimizing the mapping deformation. Then, a hybrid mesh is generated in this reference space using the previous method. Finally, this mesh is mapped back into the real space. Some quality criterions are introduced to measure and improve the quality of the polyhedral transition mesh.     

Identification of spring parameters for deformable object simulation

Mass spring models are frequently used to simulate deformable objects because of their conceptual simplicity and computational speed. Unfortunately, the model parameters are not related to elastic material constitutive laws in an obvious way. Several methods to set optimal parameters have been proposed but, so far, only with limited success. We analyze the parameter identification problem and show the difficulties, which have prevented previous work from reaching wide usage. Our main contribution is a new method to derive analytical expressions for the spring parameters from an isotropic linear elastic reference model. The method is described and expressions for several mesh topologies are derived. These include triangle, rectangle, and tetrahedron meshes. The formulas are validated by comparing the static deformation of the MSM with reference deformations simulated with the finite element method.     

Elastic Correspondence between Triangle Meshes

We propose a novel approach for shape matching between triangular meshes that, in contrast to existing methods, can match crease features. Our approach is based on a hybrid optimization scheme, that solves simultaneously for an elastic deformation of the source and its projection on the target. The elastic energy we minimize is invariant to rigid body motions, and its non‐linear membrane energy component favors locally injective maps. Symmetrizing this model enables feature aligned correspondences even for non‐isometric meshes. We demonstrate the advantage of our approach over state of the art methods on isometric and non‐isometric datasets, where we improve the geodesic distance from the ground truth, the conformal and area distortions, and the mismatch of the mean curvature functions. Finally, we show that our computed maps are applicable for surface interpolation, consistent cross‐field computation, and consistent quadrangular remeshing of a set of shapes.     

人脸妆容迁移研究综述

人脸妆容迁移的目标是在保持源图像面部特征的同时,将人脸妆容从参考图像迁移到源图像,具有重要的理论研究价值和巨大的市场应用价值。目前,生成对抗网络已成为解决人脸妆容迁移问题的主流技术。阐述了人脸妆容迁移面临的主要挑战,按照重点解决问题的不同系统地梳理了已有的人脸妆容迁移方法并分析了其优点和局限性,总结了人脸妆容迁移网络常用的损失函数,介绍了常用的人脸妆容迁移数据集以及模型评价方法,讨论了人脸妆容迁移领域未来的发展趋势。     

Selective refinement queries for volume visualization of unstructured tetrahedral meshes

We address the problem of the efficient visualization of large irregular volume data sets by exploiting a multiresolution model based on tetrahedral meshes. Multiresolution models, also called Level-Of-Detail (LOD) models, allow encoding the whole data set at a virtually continuous range of different resolutions. We have identified a set of queries for extracting meshes at variable resolution from a multiresolution model, based on field values, domain location, or opacity of the transfer function. Such queries allow trading off between resolution and speed in visualization. We define a new compact data structure for encoding a multiresolution tetrahedral mesh built through edge collapses to support selective refinement efficiently and show that such a structure has a storage cost from 3 to 5.5 times lower than standard data structures used for tetrahedral meshes. The data structures and variable resolution queries have been implemented together with state-of-the art visualization techniques in a system for the interactive visualization of three-dimensional scalar fields defined on tetrahedral meshes. Experimental results show that selective refinement queries can support interactive visualization of large data sets.     

Constrained Modelling of 3‐Valent Meshes Using a Hyperbolic Deformation Metric

Polygon meshes with 3‐valent vertices often occur as the frame of free‐form surfaces in architecture, in which rigid beams are connected in rigid joints. For modelling such meshes, it is desirable to measure the deformation of the joints' shapes. We show that it is natural to represent joint shapes as points in hyperbolic 3‐space. This endows the space of joint shapes with a geometric structure that facilitates computation. We use this structure to optimize meshes towards different constraints, and we believe that it will be useful for other applications as well.     

Large steps in GPU-based deformable bodies simulation

The interactive deformation and visualization of volumetric objects is still a challenging problem for many application areas. We present a novel integrated system which implements physically-based deformation and volume visualization of tetrahedral meshes on modern graphics hardware by exploiting the last features of vertex and fragment shaders.We achieve fast and stable deformation of tetrahedral meshes by means of a GPU-based implicit solver and present a hardware-based single-pass raycaster for deformed tetrahedral meshes. Thus, direct visualization of the inner structures of the deformed mesh is possible, while keeping the data on the graphics hardware throughout the entire simulation.     

Performance characteristics of the multi-zone NAS parallel benchmarks

We describe a new suite of computational benchmarks that models applications featuring multiple levels of parallelism. Such parallelism is often available in realistic flow computations on systems of meshes, but had not previously been captured in benchmarks. The new suite, named NPB (NAS parallel benchmarks) multi-zone, is derived from the NPB suite, and involves solving the application benchmarks LU, BT and SP on collections of loosely coupled discretization meshes. The solutions on the meshes are updated independently, but after each time step they exchange boundary value information. This strategy provides relatively easily exploitable coarse-grain parallelism between meshes. Three reference implementations are available: one serial, one hybrid using the message passing interface (MPI) and OpenMP, and another hybrid using a shared memory multi-level programming model (SMP+OpenMP). We examine the effectiveness of hybrid parallelization paradigms in these implementations on four different parallel computers. We also use an empirical formula to investigate the performance characteristics of the hybrid parallel codes.     

基于网格形变的立体图像内容重组

目的 近年来,随着数字摄影技术的飞速发展,图像增强技术越来越受到重视。图像构图作为图像增强中影响美学的重要因素,一直都是研究的热点。为此,从立体图像布局调整出发,提出一种基于Delaunay网格形变的立体图像内容重组方法。方法 首先将待重组的一对立体图像记为源图像,将用于重组规则确定的一幅图像记为参考图像;然后对源图像需要调整的目标、特征线和其他区域进行取点操作,建立Delaunay网格。将源图像的左图与参考图像进行模板匹配操作,得到源图像与参考图像在结构布局上的对应关系;最后利用网格形变的特性,移动和缩放目标对象,并对立体图像的深度进行自适应调整。结果 针对目标对象的移动、缩放和特征线调整几方面进行优化。当只涉及目标对象的移动或特征线调整时,立体图像视差保持不变;当目标对象缩放时,立体图像中目标对象的视差按照缩放比例变化而背景视差保持不变。实验结果表明,重组后的立体图像构图与参考图像一致且深度能自适应调整。与最新方法比较,本文方法在目标对象分割精度和图像语义保持方面具有优势。结论 根据网格形变相关理论,构建图像质量、布局匹配和视差适应3种能量项,实现了立体图像的内容重组。与现有需要提取和粘贴目标对象的重组方法不同,本文方法对目标对象的分割精度要求不高,不需要图像修复和混合技术,重组后的立体图像没有伪影和语义错误出现。用户可以通过参考图像来引导立体图像的布局调整,达到期望的图像增强效果。     

基于样例的交互式三维动画的生成

在基于草图的三维动画复制的基础上,提出了基于样例的交互式三维动画生成方法.在保留源动画基本风格的前提下,用户可以加入自己的创作思想.该方法不需要源网格和目标网格有相同的顶点数和三角面片数,也不需要有类似的拓扑信息.该方法由以下几个步骤组成:1)使用线型草图在源网格和目标网格间建立对应关系;2)在目标对象上设置控制点;3)交互地调整控制点,通过优化算法,计算出对应于各个样例姿势的权重,合成适合各个控制点的目标对象的关键帧.该方法直观易用,可以生成逼真的三维动画.通过一系列不同的样例姿势,在不同数量控制点的情况下测试了计算结果,验证了其可行性.     

Solutions of 3D Navier-Stokes benchmark problems with adaptive finite elements

This paper presents a numerical study of 3D Navier-Stokes benchmark problems defined within the DFG high-priority research program in 1996. Specifically, we investigate the accuracy of an equal-order finite element method based on piecewise quadratic shape functions with local projections stabilization on locally refined meshes for stationary laminar flows around an obstacle with circular and square cross-section. It turns out that on globally refined meshes the new stabilization method is comparable to element which was the best one in recent investigations of John [Int J Numer Math Fluids 2002;40:775-98]. Furthermore, on locally refined meshes we are able to produce reference values for the geometry with singularities (square cross-section) which were still unknown up to now.