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。     

基于测地距离的多边形网格模型约束变形

提出了一种基于测地线的多边形网格模型的约束变形方法.首先给定一系列的变形约束源(可以是点、线或者面)以及约束源的有效半径及变形目标(偏移量、缩放比例、旋转轴和旋转角度),然后通过计算三角形网格的各顶点到约束源的测地距离来确定各顶点的场值,这个场值将作为变形的权值.在基于欧氏距离的传统约束变形中,对某一约束区域的变形往往导致对约束源附近区域不需要的变形结果,而利用测地距离来计算各点的变形权值,可以很好地避免这种现象的出现.实验结果表明,这种变形方法是直观而且有效的.     

智能配镜三维特征参数提取方法研究

摘 要：针对智能配镜中三维面部特征点提取算法复杂度较高的问题,提出一种将三维点 云转换为映射图像定位特征点的方法。采用 Voronoi 方法计算面部三角网格各顶点处的高斯曲 率、平均曲率。选取鼻尖、眼角等曲率特征明显的区域估计面部点云姿态。根据曲率旋转不变 性,使用初选的点云方向向量简化旋转矩阵的计算,使面部点云正面朝向视点。将点云映射转 换为图像,三维网格模型中三角面片一对一映射到图像中的三角形。搭建卷积神经网络,使用 Texas 3DFRD 数据集进行模型训练。进行人脸对齐,预测所得各面部特征点分别限制在图像某 三角形中。根据图像中三角形映射查找三维网格模型中对应三角面片,通过三角面片顶点坐标 计算配镜所需的面部特征点位置坐标,实现配镜特征参数的提取。     

基于面法向量谱变换的网格光顺算法

微分坐标是刻画网格模型几何细节特征的有力工具,面法向量作为网格模型的一阶微分量,计算简单、不易受噪声影响,能真实反映网格模型的细节特征。基于此,提出一种改进的网格光顺去噪算法,使用信号处理技术中的谱网格处理方法,通过分解面法向量的拉普拉斯矩阵,将网格模型的面法向量变换到频谱域中,利用低频滤波器去除高频噪声得到连续的面法向量信号,基于三角面片重心约束条件重建网格顶点坐标,得到光顺的网格模型。实验结果表明,该算法使用的面法向量不易受到噪声影响,比顶点法向量更鲁棒,大幅提高了谱分解的效率,并且能克服光顺过程中产生的体积收缩、变形和过光滑等现象。     

三维模型面片链码表示方法

将三维模型的三角面片表示与基于体素的链码技术相结合,提出一种基于体素的三维模型面片链码表示方法.首先对三维模型进行基于体素空间的切分,将获得的面片顶点归一化在体素顶点上,构造基于体素三角面片的模型表示;然后依据构造的体素三角面片间连接边与第3顶点的位置关系定义面片链码的数据结构;再根据连接边的类型和方向计算层次三角面片法向量的大小和方向;最后通过逐层遍历体素内归一化的三角面片,获得三维模型的面片链码表示.相应地,给出了面片链码的解码方法.文中比较了面片链码与其他三维模型压缩算法的压缩效率和时间开销,计算了不同体素粒度切分的三维模型与被切分的原始模型之间以及与体素切分模型具有同级别面片数量的原始模型之间的误差,结果表明,该方法能够有效地表达三维模型.     

一种基于面片的三维重建算法

传统基于面片的多视角立体视觉算法在扩展面片时缺少空间几何约束,导致Poisson表面重建时生成错误顶点。为此,提出一种基于面片的三维重建算法。利用相邻面片初始化扩展面片,根据顶点k近邻的距离检测并去除离群顶点,从而得到物体表面的三维模型。实验结果证明了该算法的有效性和准确性。     

基于视觉曲率估算的文物线图绘制方法

针对表面富含噪声的文物三维模型特征线的有效提取问题,分析了预处理阶段导致纹理细节丢失的原因,提出了一种基于视觉曲率估算的文物线图自动绘制方法。首先,对三角网格模型顶点的高度函数空间进行均匀采样,通过统计高度函数中极值点的个数,实现对模型顶点的视觉曲率估算;然后,根据多尺度约束下模型顶点的视觉曲率分布,将模型划分为平坦区域和特征区域;接着,依据考古领域均值对特征区域的顶点进行锐化滤波,计算出新的三角网格模型的顶点坐标;最后,对三角网格模型提取特征轮廓线,实现对文物线图的自动绘制。实验结果表明,基于视觉曲率的特征轮廓线在保留文物模型表面纹理细节的同时,有效避免了简单脊线/谷线法绘制线图呈现的尖锐现象。     

基于手绘线条的三维模型雕刻

为了生成复杂模型表面的几何纹理,提出一种三维模型的高效雕刻方法.首先根据用户交互方式生成手绘线条,通过曲线细化操作确定手绘曲线经过的三维模型表面边点,并去除手绘曲线经过的模型三角面片,将去除部分经三角剖分成小三角面片之后再插入到原始模型中;然后计算三维模型上的顶点到手绘线条集的距离,确定三维模型上与手绘曲线集的距离小于等于特定纹理宽度的顶点,并根据用户选取的轮廓函数计算顶点平移距离以及平移方向;最后对三维模型上手绘线条附近的顶点进行平移,得到模型的雕刻效果.实验结果表明,该方法能够方便、高效地实现三维模型表面的线条雕刻效果.     

基于三维网格模型的双重数字盲水印算法

为提高一重三维模型数字水印的安全性,提出一种基于三维网格模型的双重数字盲水印算法。通过改变三角网格顶点在其一环相邻顶点所确定的局部几何空间中的位置和三角面片顶点排列顺序,嵌入双重水印,使模型能抵抗严重的剪切攻击及一定程度的噪声攻击。算法在提取水印时无需原始模型。仿真结果表明,该算法能够有效抵抗平移、旋转、均匀缩放、顶点乱序、多边形乱序及剪切等攻击,具有嵌入可读水印的不可见性。     

计算空间曲面顶点法向量的方法

在处理三维物体表面光照时,通常都需要计算空间曲面各顶点的法向量。本文针对三角形网格表示的空间曲面,设计了一种计算空间曲面顶点法向量的算法。并且根据上述空间曲面顶点法向量的算法,利用高程场的特性,推导出一种计算高程场顶点法向量的快速算法。     

一种3维动画中间帧非线性插值算法

关键帧动画是3维动画制作的常用模式，中间帧插值又是关键帧动画中最为繁琐的环节。提出了一种针对无骨架3维网格模型的非线性插值算法，用于对网格模型的关键帧姿态进行插补，自动生成中间帧动画序列。该算法首先计算动画角色的网格模型各三角片在相邻关键帧中的仿射变换，并据此生成变形梯度向量，作为3维网格模型的形变信息，这种表示形式体现了变形过程中网格顶点之间的局部互相关关系。随后将各仿射变换分解为旋转成分与拉伸缩放成分，对拉伸缩放成分进行线性插值，而对旋转成分采用四元数插值算法进行非线性插值，合成中间帧姿态的变形梯度向量，并据此计算出中间帧网格模型。当相邻关键帧姿态存在较大差异时，该算法也能快速生成平稳而生动的中间帧动画，可有效减少关键帧的数量，提高动画制作效率。     

Geometry-aware bases for shape approximation

We introduce a new class of shape approximation techniques for irregular triangular meshes. Our method approximates the geometry of the mesh using a linear combination of a small number of basis vectors. The basis vectors are functions of the mesh connectivity and of the mesh indices of a number of anchor vertices. There is a fundamental difference between the bases generated by our method and those generated by geometry-oblivious methods, such as Laplacian-based spectral methods. In the latter methods, the basis vectors are functions of the connectivity alone. The basis vectors of our method, in contrast, are geometry-aware since they depend on both the connectivity and on a binary tagging of vertices that are "geometrically important" in the given mesh (e.g., extrema). We show that, by defining the basis vectors to be the solutions of certain least-squares problems, the reconstruction problem reduces to solving a single sparse linear least-squares problem. We also show that this problem can be solved quickly using a state-of-the-art sparse-matrix factorization algorithm. We show how to select the anchor vertices to define a compact effective basis from which an approximated shape can be reconstructed. Furthermore, we develop an incremental update of the factorization of the least-squares system. This allows a progressive scheme where an initial approximation is incrementally refined by a stream of anchor points. We show that the incremental update and solving the factored system are fast enough to allow an online refinement of the mesh geometry     

Gradient Domain Mesh Deformation - A Survey

This survey reviews the recent development of gradient domain mesh deformation method. Different to other deformation methods, the gradient domain deformation method is a surface-based, variational optimization method. It directly encodes the geometric details in differential coordinates, which are also called Laplacian coordinates in literature. By preserving the Laplacian coordinates, the mesh details can be well preserved during deformation. Due to the locality of the Laplacian coordinates, the variat...     

Rigidity Constraints for Large Mesh Deformation

It is a challenging problem of surface-based deformation to avoid apparent volumetric distortions around largely deformed areas. In this paper, we propose a new rigidity constraint for gradient domain mesh deformation to address this problem. Intuitively the proposed constraint can be regarded as several small cubes defined by the mesh vertices through mean value coordinates. The user interactively specifies the cubes in the regions which are prone to volumetric distortions, and the rigidity constraints ...     

基于顶点法向量约束的Catmull-Clark细分插值方法

提出一种基于顶点法向量约束实现插值的两步Catmull-Clark细分方法.第一步,通过改造型Catmull-Clark细分生成新网格.第二步,通过顶点法向量约束对新网格进行调整.两步细分分别运用渐进迭代方法和拉格朗日乘子法,使得极限曲面插值于初始控制顶点和法向量.实验结果证明了该方法可同时实现插值初始控制顶点和法向量,极限曲面具有较好的造型效果.     

基于局部相似变换的网格变形复制

使用标记点在源和目标间建立关联;然后根据源标记点移动目标标记点,非标记点在标记点的基础上进行变换;最后采用改进的约束方程对结果进行后处理,得到光滑变形结果.该方法不仅适合动画制作初学者,而且可以很容易扩展到非结构化表示的三维模型中,具有良好的通用性.     

Quasi-angle-preserving mesh deformation using the least-squares approach

We propose an angle-based mesh representation, which is invariant under translation, rotation, and uniform scaling, to encode the geometric details of a triangular mesh. Angle-based mesh representation consists of angle quantities defined on the mesh, from which the mesh can be reconstructed uniquely up to translation, rotation, and uniform scaling. The reconstruction process requires solving three sparse linear systems： the first system encodes the length of edges between vertices on the mesh, the second system encodes the relationship of local frames between two adjacent vertices on the mesh, and the third system defines the position of the vertices via the edge length and the local frames. From this angle-based mesh representation, we propose a quasi-angle-preserving mesh deformation system with the least-squares approach via detail-preserving mesh editing examples are presented to handle translation, rotation, and uniform scaling. Several demonstrate the effectiveness of the proposed method.     

Normal vector compression of 3D mesh model based on clustering and relative indexing

As the transmission of 3D shape models through Internet becomes more important, the compression issue of shape models gets more critical. While the compressions of topology and geometry have been explored significantly, the same issue for normal vectors has not yet been studied as much as it deserves.

Presented in this paper is an approach to compress the normal vectors of a 3D mesh model using the concept of clustering and relative indexing. The model is assumed to be manifold triangular mesh model with normal vectors associated with vertices. The proposed scheme clusters the normal vectors of given model and the representative normal vector of each cluster is referred to via a mixed use of relative as well as absolute indexing concepts. It turns out that the proposed approach achieves a significant compression ratio (less than 10% of the original VRML model files) without a serious sacrifice of the visual quality.