一种基于多区域并行的网格模型简化的两步法

针对三角形网格模型简化中保持细节特征的要求,引入了图像的区域分割原理,提出了一种基于区域生长的网格模型区域分割方法．在此基础之上,提出了一种基于多区域并行的自适应三角网格模型简化的两步法,对于不同的区域采取按照比例进行简化的并行机制．此方法的特点是保持模型细节的基础上,大大地加快了模型的简化速度．另外,还提出了一种基于多区域并行的累进网格模型的实现方法,有效地实现了保持细节特征的多分辨率模型,并实现了具有细节特征的多分辨模型间的层次过渡．经实验证明,该方法能够快速有效地对三角形网格模型进行简化,并具有保持模型的三角形网格密度分布的特点．     

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.     

Boundary-trimmed 3D triangular mesh segmentation based on iterative merging strategy

This paper presents a segmentation algorithm for 3D triangular mesh data. The proposed algorithm uses iterative merging of adjacent triangle pairs based on their orientations. The oversegmented regions are merged again in an iterative region merging process. Finally, the noisy boundaries of each region are refined. The boundaries of each region contain perceptually important geometric information of the entire mesh model. According to the purpose of the segmentation, the proposed mesh-segmentation algorithm supports various types of segmentation by controlling parameters.     

基于区域生长的网格模型分割技术

针对三角形网格模型简化中保持细节特征的要求,提出了以顶点和三角形作为种子的区域生长策略,并采用可变阈值的生长方法.首先将与顶点相关的三角形面积的均值作为顶点的属性值,在区域生长过程中重复选择具有极大属性值的图元作为种子;在预分割后,区域要进行合并和平滑处理.实验表明,该方法快速有效,能够满足网格模型简化中保持局部区域特征的需要.     

ROI Scissor: Interactive Segmentation of Feature Region of Interest in a Triangular Mesh

We present a simple and effective method for the interactive segmentation of feature regions in a triangular mesh. From the user-specified radius and click position, the candidate region that contains the desired feature region is defined as geodesic disc on a triangle mesh. A concavity-aware harmonic field is then computed on the candidate region using the appropriate boundary constraints. An initial isoline is chosen by evaluating the uniformly sampled ones on the harmonic field based on the gradient magnitude. A set of feature points on the initial isoline is selected and the anisotropic geodesics passing through them are then determined as the final segmentation boundary, which is smooth and locally shortest. The experimental results show several segmentation results for various 3D models, revealing the effectiveness of the proposed method.     

A novel 3D mesh compression using mesh segmentation with multiple principal plane analysis

This paper proposes a novel scheme for 3D model compression based on mesh segmentation using multiple principal plane analysis. This algorithm first performs a mesh segmentation scheme, based on fusion of the well-known k-means clustering and the proposed principal plane analysis to separate the input 3D mesh into a set of disjointed polygonal regions. The boundary indexing scheme for the whole object is created by assembling local regions. Finally, the current work proposes a triangle traversal scheme to encode the connectivity and geometry information simultaneously for every patch under the guidance of the boundary indexing scheme. Simulation results demonstrate that the proposed algorithm obtains good performance in terms of compression rate and reconstruction quality.     

一种基于拓扑连接图的三维模型检索方法

提出了一种基于分割技术的拓扑连接图构造方法。并用于三维模型检索．首先构造多层邻域计算用于度量每个三角片平坦度的信号值。根据这些信号值采用一种改进的分水岭方法把模型分割成不同的曲面片．然后利用这些曲面片之间的连接关系构造拓扑连接图．最后通过比较不同模型的拓扑连接图相似性来得到它们的匹配度。根据匹配度进行三维模型检索．     

Consistent segmentation of 3D models

This paper proposes a method to segment a set of models consistently. The method simultaneously segments models and creates correspondences between segments. First, a graph is constructed whose nodes represent the faces of every mesh, and whose edges connect adjacent faces within a mesh and corresponding faces in different meshes. Second, a consistent segmentation is created by clustering this graph, allowing for outlier segments that are not present in every mesh. The method is demonstrated for several classes of objects and used for two applications: symmetric segmentation and segmentation transfer.     

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。     

CAD模型表面区域分割方法

三维模型表面区域分割技术在形状分析,尤其是局部形状分析中具有重要作用,传统的表面分割方法主要针对网格模型,而机械工程中的CAD模型通常用B-rep表达.提出一种B-rep形式的CAD模型表面区域分割方法,将模型表面划分为局部凸区域、凹区域和平区域的组合,并使得分割后的区域数量最少.为提高计算效率,提出一种二步法:首先在模型面的局部凸凹性分析的基础上,快速地将模型表面分割成初始的凸区域、凹区域和平区域;然后通过区域合并的方法对分割后的区域进行组合优化,得到一个最优的分割结果.实验结果证明,该方法能有效地分割模型的表面区域.     

Feature suppression based CAD mesh model simplification

Dynamic simulation and high quality FEA mesh generation need the CAD mesh model to be simplified, that is, suppressing the detailed features on the mesh without any changes to the rest. However, the traditional mesh simplification methods for graphical models can not satisfy the requirements of CAD mesh simplification. In this paper, we develop a feature suppression based CAD mesh model simplification framework. First, the CAD mesh model is segmented by an improved watershed segmentation algorithm, constructing the region-level representation required by feature recognition. Second, the form features needing to be suppressed are extracted using a feature recognition method with user defined feature facility based on the region-level representation, establishing the feature-level representation. Third, every recognized feature is suppressed using the most suitable one of the three methods, i.e. planar Delaunay triangulation, Poisson equation based method, and the method for blend features, thus simplifying the CAD mesh model. Our method provides an effective way to make CAD mesh model simplification meet the requirements of engineering applications. Several experimental results are presented to show the superiority and effectivity of our approach.     

A framework for quad/triangle subdivision surface fitting: Application to mechanical objects

In this paper we present a new framework for subdivision surface approximation of three‐dimensional models represented by polygonal meshes. Our approach, particularly suited for mechanical or Computer Aided Design (CAD) parts, produces a mixed quadrangle‐triangle control mesh, optimized in terms of face and vertex numbers while remaining independent of the connectivity of the input mesh. Our algorithm begins with a decomposition of the object into surface patches. The main idea is to approximate the region boundaries first and then the interior data. Thus, for each patch, a first step approximates the boundaries with subdivision curves (associated with control polygons) and creates an initial subdivision surface by linking the boundary control points with respect to the lines of curvature of the target surface. Then, a second step optimizes the initial subdivision surface by iteratively moving control points and enriching regions according to the error distribution. The final control mesh defining the whole model is then created assembling every local subdivision control meshes. This control polyhedron is much more compact than the original mesh and visually represents the same shape after several subdivision steps, hence it is particularly suitable for compression and visualization tasks. Experiments conducted on several mechanical models have proven the coherency and the efficiency of our algorithm, compared with existing methods.     

A hybrid approach to feature segmentation of triangle meshes

Segmentation of a polygonal mesh is a method of breaking the mesh down into ‘meaningful’ connected subsets of meshes called regions or features. Several methods have been proposed in the past and they are either vertex based or edge based. The vertex method used here is based on the watershed segmentation scheme which appears prominently in the image segmentation literature and was later applied to the 3D segmentation problem [9] and [10]. Its main drawback is that it is a vertex based method and no hard boundaries (edges) are created for the features or regions. Edge based methods rely on the dihedral angle between polygon faces to determine if the common edge should be classified as a Feature Edge. However, this method results in many disconnected edges and thereby incomplete feature loops.We propose a hybrid method which takes advantage of both methods mentioned earlier and create regions with complete feature loops. Satisfactory results have been achieved for both CAD parts as well as other laser scanned objects such as bones and ceramic vessels.     

一种三角形折叠网格模型简化的改进算法

目前提出的网格简化算法中,三角形折叠简化方法是一种主要的简化方法,在网格压缩、多细节层次模型生成、递进网格构造中得到了广泛地应用。提出一种基于三角形折叠的网格模型简化改进算法,在基于三角形折叠的基础上,在计算三角形折叠误差代价时引入局部区域面积度量参数,有效控制简化模型的三角形折叠顺序。实验表明,采用该文算法简化后的模型更逼近原始模型。     

综合曲率约束的在线网格模型分割方法研究

针对现有三角网格模型块分割方法普遍存在计算复杂度高,无法体现工程意义,综合效果不理想,不满足Web环境下高效快速分割等问题,提出一种面向Web环境的简单高效的三角网格模型分割方法。根据高斯曲率和平均曲率特性划分出网格模型的凹区域,在凹区域中依据最小负曲率阈值提取凹特征区域,结合区域中心特征线提取方法以及边界线闭合和优化算法构造出闭合分割线,通过分割线将三角网格模型分割成有意义的分块。依托开源数字几何处理软件MeshLabJS,运用WebGL的几何处理及图形渲染功能,在普林斯顿标准数据集和COSEG形状数据集上进行算法测试,验证所提方法能够在Web环境下快速、高效、有意义地分割三维模型。     

保特征的联合滤波网格去噪算法

目的 在去噪的过程中保持网格模型的特征结构是网格去噪领域研究的热点问题。为了能够在去噪中保持模型特征,本文提出一种基于变分形状近似（VSA）分割算法的保特征网格去噪算法。方法 引入变分形状近似分割算法分析并提取噪声网格模型的几何特征,分3步进行去噪。第1步使用变分形状近似算法对网格进行分割,对模型进行分块降噪预处理。第2步通过分析变分形状近似算法提取分割边界中的特征信息,将网格划分为特征区域与非特征区域。对两个区域用不同的滤波器联合滤波面法向量。第3步根据滤波后的面法向量,使用非迭代的网格顶点更新方法更新顶点位置。结果 相较于现有全局去噪方法,本文方法可以很好地保持网格模型的特征,引入的降噪预处理对于非均匀网格的拓扑结构保持有着很好的效果。通过对含有不同程度高斯噪声的网格模型进行实验表明,本文算法无论在直观上还是定量分析的结果都相较于对比的方法有着更好的去噪效果,实验中与对比算法相比去噪效果提升15%。结论 与现有的网格去噪算法对比,实验结果表明本文算法在中等高斯噪声下更加鲁棒,对常见模型有着比较好的去噪效果,能更好地处理不均匀采样的网格模型,恢复模型原有的特征信息和拓扑结构。     

基于逆 Loop 细分的半正则网格简化算法

摘 要：三维网格简化是在保留目标物体几何形状信息的前提下尽量减小精细化三维模型 中的点数和面数的一种操作,对提高三维网格数据的存取和网络传输速度、编辑和渲染效率具 有十分重要的作用。针对大多网格简化算法在简化过程中未考虑网格拓扑结构与视觉质量的问 题,提出了一种基于逆 Loop 细分的半正则网格简化算法。首先根据邻域质心偏移量进行特征 点检测,随后随机选取种子三角形,以边扩展方式获取正则区域并执行逆 Loop 细分进行简化。 最后,以向内分割方式进行边缘拼接,获取最终的简化模型。与经典算法在公开数据集上进行 实验对比,结果表明,该算法能够在简化的同时有效地保持网格特征,尽可能保留与原始网格 一致的规则的拓扑结构,并且在视觉质量上优于边折叠以及聚类简化算法。     

A direct approach for subdivision surface fitting from a dense triangle mesh

This article presents a new and direct approach for fitting a subdivision surface from an irregular and dense triangle mesh of arbitrary topological type. All feature edges and feature vertices of the original mesh model are first identified. A topology- and feature-preserving mesh simplification algorithm is developed to further simplify the dense triangle mesh into a coarse mesh. A subdivision surface with exactly the same topological structure and sharp features as that of the simplified mesh is finally fitted from a subset of vertices of the original dense mesh. During the fitting process, both the position masks and subdivision rules are used for setting up the fitting equation. Some examples are provided to demonstrate the proposed approach.     

Ordering Points for Incremental TIN Construction from DEMs

The standard method of building compact triangulated surface approximations to terrain surfaces (TINs) from dense digital elevation models (DEMs) adds points to an initial sparse triangulation or removes points from a dense initial mesh. Typically, in each triangle in the current TIN, the worst fitting point, in terms of vertical distance, is selected. The order of insertion of the points is determined by the magnitude of the maximum vertical difference. This measure produces triangulations that minimize the maximum vertical distance between the TIN and the source DEM. Other approximation criteria are often used, however, including the root-mean-squared error or the mean absolute error, both for the vertical difference and normal difference, i.e., the distance in the direction of the normal to the triangular approximation. For these approximation criteria, we still select the worst fit point, but determine the insertion order by various sums of errors over the triangle. Experiments show that using these better evaluation measures significantly reduces the size of the TIN for a given approximation error.