基于骨架的网格模型变形

现有骨架驱动变形算法多以单一骨架驱动变形,且骨架预设十分复杂。为此,提出一种基于骨架的网格模型变形算法。结合多分辨率Reeb图方法提取模型的骨架结构,确定各骨架点对应的局部区域,将骨架点插值构造二次Bézier曲线,通过交互式拖动任意骨架点,计算与其相连多骨架点的动态变化情况,实现模型局部区域的自然形变。实验结果表明,该算法能获得较为自然平滑的变形结果。     

基于骨架关节点约束的交互式局部变形

利用广义元球变形技术,提出一种基于骨架关节点约束的交互式局部变形方法。该方法提取多边形网格模型的骨架关节点并结合模型骨架图结构确定骨架关节点对应的局部区域,计算三维网格点到骨架节点的欧式距离,将约束区域的最大欧氏距离作为约束半径,得到各骨架节点对应的势函数值,通过控制骨架节点的空间位置给出三角形面片点的新坐标位置。实验结果表明,该方法有效保持多边形网络模型的局部特征,并确保了模型变形的直观性和高效性。     

高斯曲率约束的MRG骨架提取优化算法

三维模型的骨架保持了模型的拓扑特性,并被广泛应用于模型相似性比较、计算机动画及压缩等领域.根据多分辨率Reeb图的原理,提出了一种基于离散高斯曲率约束的骨架提取优化算法.通过计算网格顶点的离散高斯曲牢判断曲面局部凸凹特性,以获取模型表面的双曲极值点作为约束点;并依据约束点及其邻域的μ函数值产生的分裂线进行区域细分,获得子连通区域、确定关节点、形成优化的骨架结构.实验结果表明,该算法有效地突出了模型的拓扑分支特征以及模型表面的细节,提高了骨架提取的精度和效率.     

基于细分的网格模型骨架驱动变形技术

针对传统骨架驱动变形方法中模型细节特征不能得到有效保持的问题,提出一种基于细分的骨架驱动网格模型变形方法。首先,对网格模型待变形区域基于截交线进行局部骨架提取和控制网格构建,分别建立骨架与控制网格以及控制网格所对应细分曲面与待变形模型区域之间的关联关系;然后,将基本函数作用下的自由变形方法应用于骨架变形,通过骨架变形驱动控制网格变形,将变形前后控制网格所对应细分曲面的变化信息转为网格模型泊松梯度场的改变;最后,根据改变后梯度场重建网格模型。实例表明,该变形方法针对不同网格模型均可以得到较好的编辑效果,且细节信息在变形后都得到了有效保持。与传统骨架驱动变形方法相比,该方法除具备交互操作简单直观的优势外,同时能够更好保持变形模型几何细节特征,更为适合具有丰富几何细节的复杂模型的变形编辑。     

三维人体模型的自动驱动方法

传统的由运动数据驱动三维模型需要手工标定骨架,匹配关节点和设定皮肤权重,工作量大而复杂.提出了三维人体模型自动驱动的方法,使用横向切分匹配来自动提取骨架和匹配相应的关节点,然后用改进后的线性混合皮肤变形技术进行模型皮肤权值的自动分配,绑定皮肤,最终实现了三维人体模型的自动驱动.整个提取绑定时间短,需求简单,速度快,最后给出的实验结果验证了算法的有效性.     

从单幅图像构建三维叶雕模型

针对传统镂空叶雕具有手工制作烦琐且不便传承的缺点,提出一种由单幅叶雕图像生成叶雕三维模型的辅助设计方法.首先将叶雕图像划分为镂空区域、无用区域和有用区域,根据用户选择遍历像素提取细长叶柄;然后通过距离图像生成初始三维模型并用S型函数进行高度调整;再利用灰度形态学处理方法获取叶脉图像叠加在模型上进行叶脉构建,采用保留特征的光滑算法光滑整个模型;最后以扩散流形式提取狭长区域骨架点,并进行接续,延伸,三角结构重构处理避免凹陷现象,利用模型上约束关系获取边缘点,重置边缘点、狭长区域骨架点以及叶柄骨架点高度调整模型,通过新点插入法处理缺断得到最终模型.实验结果表明,该方法能得到效果良好的叶雕三维模型.     

基于轮廓线的三维网格曲面绘制

在融合了交互式轮廓绘制与网格造型技术的基础上,提出了一种快速三维网格曲面建模方法.根据绘制轮廓线的特征点分布,进行约束化三角网格剖分,提取二维轮廓线的骨架;选取骨架点和采样点投影到三维空间椭球曲面,并引入二面角原则,优化了空间离散数据点的三角化算法;最后缝合骨架点,获得三维网格曲面表示.实验结果表明了该算法的直观性、高效性.     

单位化建模衰减变形新方法

针对软组织自由变形中调整控制顶点难以准确控制物体变形的问题,提出了一种基于单位化建模的衰减变形算法。该算法利用三角网格进行单位化建模,将变形软组织碰撞点的三维世界坐标转换为三角网格二维顶点坐标,通过确定以碰撞点所在顶点为中心的自适应变形区域,控制区域内顶点偏移量发生衰减变化,从而直接作用于物体顶点进行形变,同时通过设计合适的衰减函数使偏移量呈抛物线衰减。通过实验证明该算法所建模型具有通用性,变形在局部区域内可取得准确的抛物线衰减效果。     

三维模型近刚性保体变形

为保持三维模型表面细节和模型体积,提高模型变形的真实感效果,提出一种基于能量最小化的近刚性保体变形方法.首先对模型进行Laplacian变形,在此基础上,通过极分解求解曲面局部区域三角形的旋转变形,构建模型刚性变形能;然后通过模型体积积分离散化将模型体积变形约束转化为模型曲面变形约束,构建体积变形能;再通过衡量约束点的位置变形误差构建约束变形能.在最小二乘意义下最小化上述加权变形能,获得模型变形结果.实例结果表明,文中方法能够在线性的算法效率下获得近刚性保体变形效果,为模型的真实感变形提供了一条有效的途径.     

快速非刚体人体运动三维重建

为了实现基于单目深度传感器的快速非刚体人体运动三维重建,提出一种基于骨架的非刚体人体运动点云融合算法.首先利用分割的人体局部点云配准,对深度传感器提取的人体骨架进行修正,提高了骨架提取的准确性;当相邻2帧之间存在较大人体运动时,利用骨架驱动人体表面点云进行点云粗配准;在粗配准的基础上,利用非刚体点云融合算法进行点云的精细配准,得到精确的表面重建.实验结果表明,该算法能够鲁棒地重建快速非刚体三维人体运动.     

Finite element mesh deformation with the skeleton-section template

To develop fast finite element (FE) adaptation methods for simulation-driven design optimization, we propose a radial basis functions (RBF) method with a skeleton-section template to globally and locally deform FE meshes of thin-walled beam structures.The skeleton-section template is automatically formulated from the input mesh and serves as a hierarchical parameterization for the FE meshes. With this hierarchical parameterization, both the global and the local geometries of a thin-walled beam can be processed in the same framework, which is of importance for designing engineering components. The curve skeleton of the mesh is constructed with Voronoi decomposition, while the cross-sections are extracted from the mesh based on the curve skeleton.The RBF method is employed to locally and globally deform the mesh model with the cross-sections and the skeleton, respectively. The RBF method solves the spatial deformation field given prescribed deformations at the cross-sections. At the local scale, the user modifies the cross-sections to deform a region of the surface mesh. At the global level, the skeleton is manipulated and its deformation is transferred to all cross-sections to induce the mesh deformation.In order to handle curved mesh models and attain flexible local deformations, the input mesh is embedded into its skeleton frame field using an anisotropic distance metric. In this way, even strip-like features along arbitrary directions can be created on the mesh model using only a few cross-sections as the deformation handles. In addition, form features can be rigidly preserved at both deformation levels.Numerical examples demonstrate that intuitive and qualified FE mesh deformations can be obtained with manipulation of the skeleton-section template.     

Eigen deformation of 3D models

Recent advances in mesh deformations have been dominated by two techniques: one uses an intermediate structure like a cage which transfers the user intended moves to the mesh, the other lets the user to impart the moves to the mesh directly. The former one lets the user deform the model in real-time and also preserve the shape with sophisticated techniques like Green Coordinates. The direct techniques on the other hand free the user from the burden of creating an appropriate cage though they take more computing time to solve larger non-linear optimizations. It would be ideal to develop a cage-free technique that provides real-time deformation while respecting the local geometry. Using a simple eigen-framework, we devise such a technique. Our framework creates an implicit skeleton automatically. The user only specifies the motion in a simple and intuitive manner, and our algorithm computes a deformation whose quality is similar to that of the cage-based scheme with Green Coordinates.     

骨架驱动的作物叶片变形模拟

针对作物器官的变形问题,将骨架驱动物体变形的方法应用于作物器官的局部变形,提出了一种骨架驱动的叶片变形方法：生成叶片骨架模型,驱动骨架模型发生变形,并根据变形后的叶片骨架将变形操作应用到叶片曲面上,进而实现叶片曲面变形。应用该方法,分别对小麦叶片曲面进行弯曲和扭曲变形模拟。实验结果表明,基于骨架驱动的作物叶片形变方法能灵活控制叶片弯曲和扭曲程度,从而获得自然的叶片曲面变形效果。     

勾画式泊松网格编辑

结合勾画式自由变形方法简单直观易用的优点和基于微分方程的网格变形方法能够保持形变物体几何细节的性质,提出一种勾画式的泊松网格编辑方法.通过允许目标勾画线和参照勾画线不必位于相同的相机平面,把原有的二维勾画变形推广至三维,并提出了一组完整的变形操作.这些变形操作根据参照勾画线与目标勾画线决定了一系列的局部变换,并由这些局部变换产生出用户希望的梯度场,最终根据用户需要的梯度场重建出变形后的三维模型.丰富的编辑实例表明了该方法具有直观便捷的交互特点.     

Automatic hexahedral mesh generation for multi-domain composite models using a hybrid projective grid-based method

This paper presents an algorithm to generate an all-hexahedral mesh of a multi-domain solid model using a hybrid grid-based approach. This is based on a projective concept during the boundary adaptation of the initial mesh. In general, the algorithm involves the generation of a grid structure, which is superimposed on the solid model. This grid structure forms an initial mesh consisting of hexahedral elements, which intersect fully or partially with the solid model. This initial mesh is then shrunk in an outside-in manner to the faces of the model through a node projection process using the closest position approach. To match the resulting mesh to the edges of the model, a minimal deformation angle method is used. Finally, to match the vertices with the nodes on the mesh, a minimal warp angle method is employed. To create the mesh of a multi-domain solid model, an outside-in and inside-in hybrid of the grid-based method is used. This hybrid method ensures that the meshes of the different domains are conforming at their common boundary. This paper also describes two methods for resolving cases of degenerate elements: a splitting technique and a wedge insertion technique.     

An improved contraction-based method for mesh skeleton extraction

Contraction-based skeleton extraction methods have the feature that during skeleton extraction process, the correspondence between skeleton and mesh regions can be obtained, which makes this class of algorithm attractive. Besides, among all mesh skeleton extraction methods, contraction-based methods possesses the merits of robustness to noise, rotation invariant and no requirement on additional boundary conditions. However, contraction-based methods still suffer some flaws such as not promising homotopy or centeredness, or not capable of processing non-closed meshes, etc. In this paper, an improved contraction-based skeleton extraction method is proposed which covers the failure of existing methods at non-closed part of a model and increases the rationality of the centeredness correction of the skeleton: First, non-closed models are virtually closed by a preprocessing stage such that models with boundaries can be contracted in the same way as the closed ones. Second, to improve the centeredness of the skeleton, we present a simpler and more effective one-ring area sequence weighting scheme by which the displacements measuring the shift of skeleton nodes can be calculated. Experimental results show the effectiveness of our work.     

On the Algebraic Construction of Multilevel Transfer Operators

The basic idea of our new approach is to determine in a first step for each node those pairs of nodes which allow a good interpolation of the unknowns located at this node. These pairs of neighbor nodes (in some cases only one node) are called parent nodes. This is done by solving a local minimization problem which, in addition, yields the interpolation and restriction coefficients. The construction scheme has been generalized to systems of convection-diffusion-reaction equations using a point-block approach. After these suitable pairs of parent nodes have been determined, the nodes are labeled as C- and F-nodes such that each F-node can be interpolated using one of these suitable pairs of parent nodes and the already computed coefficients. Additionally, a simple heuristic algorithm tries to minimize the number of C-nodes and the number of non-zero entries in the coarse grid matrix. The algorithm has been parallelized and shows mesh size independent convergence for standard model problems. Realistic numerical experiments confirm the efficiency of the presented algorithm.