蒙太奇网格融合

三维物体融合是一种新的几何造型方法,它利用三维模型之间的剪贴操作从两个或多个现有的几何模型中光滑融合出新的几何模型.提出了一种基于局部调和映射的三维网格蒙太奇融合新方法.首先利用网格上的近似等距线算法来抽取出待融合区域,然后对两个待融合区域进行带内孔的调和映射参数化,最后通过拓扑合并和融合控制来实现网格的光滑融合.与原有的基于全局调和映射的融合方法相比,新方法的算法效率大幅度提升,求解时间不再随融合模型顶点数的增加而呈指数增长;减少了二维网格拓扑合并中奇异情况出现的概率,提高了算法的稳定性;被剪切网格的细节得到完整保留;消除了原算法对融合区域拓扑的限制.实验结果表明,此方法可以用来生成许多三维动画中的特殊夸张造型效果,在影视动画中具有应用价值.     

一种网格融合算法

快速建模是三维游戏动画领域的重要技术,从已有模型经过修改、编辑、融合构建出新的模型是一种高效的建模方法.本文提出了一种网格模型融合算法,该算法首先将需要的部分网格从源模型上交互剪切下来,并将其配准对齐;然后将两网格模型转化成点模型表示,并将点模型转化成RBF隐函数表示;再对两隐函数进行布尔运算;最后将布尔运算生的隐函数曲面在两网格接合区域进行三角形化,得到最终的网格模型.算法定义了隐函数曲面的影响区域,有效控制融合过渡.采用边界扩展的三角形化方法,保留了融合区域以外源模型的特征.实验结果表明,本文算法具有很好的网格融合结果,可用于游戏动画中快速造型.     

真实感人脸模型的细分曲面重建

提出一种利用2张正交照片和细分曲面进行真实感三维人脸建模的方法,并实现了不同模型间的三维变形.为了构造个性化的人脸几何模型,将网格简化、自由曲面变形和细分结合起来,得到多个层次细节下的人脸模型;再经过纹理融合和映射,完成个性化的真实感三维人脸建模;同时利用线性插值实现了同拓扑真实感模型间的光滑变形.实验结果表明：该方法不仅可以进行有效的真实感三维人脸建模,而且变形简单流畅,具有广阔的应用前景.     

基于谷脊线特征的三维网格模型简化方法

已有的网格简化算法容易丢失大量褶皱、边界等明显几何特征,导致简化后的模型在视觉上失真,为此提出一种基于谷脊线特征的三维网格模型简化方法.首先基于隐式曲面提取网格模型的谷脊线,得到体现重要性几何信息的模型特征点;然后利用层次化的紧支撑径向基函数(CS-RBFs)将上述模型特征点恢复成隐式曲面,得到简化后的三维网格模型.与N-Garland方法对比的实验结果表明,文中方法能显著地减少网格模型顶点数,生成的模型精确度高,生成过程高效.     

边界保持的隐式曲面三角化方法

隐式曲面三角化是隐式曲面绘制的常用算法.对于开区域上散乱点数据重建的隐式曲面,常用的隐式曲面三角化方法得到网格模型不能很好地保持散乱点数据的边界.针对该问题,提出了一种边界保持的隐式曲面三角化方法.根据散乱点数据的空间分布,控制等值面的抽取范围,实现了边界保持.实验结果表明,该算法能够产生和散乱点数据边界一致的三角网格.     

基于“几何-拓扑”迭代优化的三维网格模型修复算法

针对三维网格模型孔洞保特征修复问题,提出一种基于"几何-拓扑"迭代优化的三维数据修复算法.给定残缺的三角网格模型,首先识别孔洞区域,利用动态规划方法对孔洞区域进行初始的三角剖分,赋予孔洞区域拓扑连接关系;然后识别孔洞边界一对特征点,基于特征点及其法向粗略拟合特征曲线,在特征曲线的指导下调整孔洞局部的拓扑结构,即孔洞区域拓扑连接关系优化;最后基于孔洞及其N环邻域构建保特征的局部总变分能量函数,迭代求解孔洞及其邻域的顶点几何位置,即局部顶点几何位置的优化,重复局部拓扑连接关系优化和顶点几何位置优化,直到拓扑结构优化处理中不再发生连接关系调整,即完成了三维网格模型的修复.在现有的完整三维网格模型上人为去除部分构造带孔洞的残缺模型,以此作为数据,与其他修复算法进行对比实验的结果表明,所提算法可以有效地恢复孔洞区域的显著特征,并且在修复时间和误差统计上占有明显优势.     

三维地质结构模型中闭合地质块体的构建

三维地质建模中现有地质闭合区块搜索算法基于网格单元间的拓扑进行拓扑搜索,面临着拓扑信息冗余、计算量大、计算复杂度高等缺点.针对这一问题,以搜索拓扑封闭三维地质区块作为研究目标,提出一种适合表达地质界面复杂拓扑关系的拓扑模型,并在该模型上实现快速地质闭合块体搜索.由于地质闭合区块的搜索本质上应该在拓扑空间进行,因此分别定义了拓扑分界点、拓扑分界线、拓扑分界面片、拓扑分界面、闭合区块来表达复杂的地质模型在拓扑空间中的结构,将几何空间与拓扑空间分开表达存储,并在构建过程利用地质曲面的边界信息,遵从点、线、面、体的顺序逐级进行构建:依据拓扑分界点定义在三维曲面边界信息中构建拓扑分界点;在2个拓扑分界点间构建拓扑分界线并填充其拓扑信息;在拓扑分界面上追踪由拓扑分界线组成的封闭拓扑分界面片;对全局拓扑分界面片进行拓扑分析得到闭合区块.实例测试表明,由于拓扑模型的构建过程只利用了地质曲面的边界信息,因此构建过程快速,大大简化了识别的复杂度,可以满足任意复杂曲面间的接触关系的处理,也就从理论上解决了任意复杂的三维地质闭合区块的快速识别问题.     

一种精度可控的CAD网格模型及轻量化算法的研究

针对现有三维CAD系统中,CAD网格模型显示精度固定,难以动态调整以及细分后网格数量过多等瓶颈问题,在原始模型基础上,结合CAD模型中边、面等几何与拓扑信息,提出了一种精度可控的三维CAD网格模型.根据该模型的结构特点,采用曲面内部插值与边界曲线插值相结合的轻量化分类细分算法来实现模型精度调整,并有效控制细分后的网格数量,可满足三维CAD系统对模型精度可控、减少网格数量的需要.     

基于任意骨架的隐式曲面造型技术

给出了一个新的基于任意多面体网格骨架的构造性自由曲面造型算法.算法首先由每个给定骨架构造出一个距离场,然后利用隐函数光滑过渡技术和CSG(constructive solid geometry)表示技术将所构造的隐式曲面自由地两两粘合成一张光滑曲面.隐式曲面的多边形化算法则用来生成最终曲面网格.以任意骨架作为基本体素,突破了传统隐式曲面以点为基本骨架的限制.而且,距离曲面很好地逼近了原骨架形状,使用户可直观地对复杂曲面进行交互设计.而形变函数的引入,则极大地丰富了此方法的造型能力.实验结果表明,基于该算法的原型系统能够方便、直观地构造复杂的自由曲面.     

曲率约束的隐式曲面三角网格化

提出一种有效的隐式曲面三角网格化算法。从隐式曲面上的一个种子点开始,生成网格的边界作为扩张多边形,且该多边形最小角对应的顶点为扩张点,计算从扩张点处欲生成的三角网格,为了防止新生成的三角网格和已经存在的三角网格重叠,要进行冲突检测。在隐式曲面三角网格化的过程中,扩张多边形是不断变化的,需要重复上述步骤,直至没有扩张多边形时结束。该算法分别应用于解析隐式曲面和变分隐式曲面的三角网格化。实验结果表明,该算法不需要重新网格化的步骤,生成的三角网格具有较高的质量,且三角网格随曲率适应性变化,因此说明了该算法的有效性。     

基于Hermite插值的网格拼接和融合

网格模型的拼接和融合是3维形状编辑和造型中的一个重要方面。基于Hermite插值技术,提出一种适用于具有一般边界点空间分布的三角网格模型之间无缝光滑拼接和融合方法。首先查找网格模型待拼接区域的边缘点集,并利用二次B样条曲线插值边缘点集分别得到边缘曲线;然后对边缘曲线进行Hermite插值得到拼接区域连续曲面;最后对拼接曲面分别进行三角网格化和Laplacian光顺平滑处理以实现网格模型的光滑拼接和融合。由于利用B样条曲线插值待拼接模型边界,本文方法适用于具有各种不同边界情形的网格模型拼接和融合,它不仅仅可以处理平面边界曲线情形也可以处理空间边界曲线情形。结合Hermite曲面插值拼接过渡区域,使得产生的拼接网格能光滑地衔接待拼接模型。实验结果表明,本文方法能够有效地实现三角网格模型的光滑拼接、模型修复和模型融合。     

基于Hermite插值的网格拼接和融合-CIDE2013

网格模型的拼接和融合是3维形状编辑和造型中的一个重要方面。基于Hermite插值技术,提出了一种适用于具有一般边界点空间分布的三角网格模型之间无缝光滑拼接和融合方法。首先查找网格模型待拼接区域的边缘点集,并利用二次B样条曲线插值边缘点集分别得到边缘曲线;然后对边缘曲线进行Hermite插值得到拼接区域连续曲面;最后对拼接曲面分别进行三角网格化和Laplacian光顺平滑处理以实现网格模型的光滑拼接和融合。由于利用B样条曲线插值待拼接模型边界,本文方法适用于具有各种不同边界情形的网格模型拼接和融合,它不仅仅可以处理平面边界曲线情形也可以处理空间边界曲线情形。结合Hermite曲面插值拼接过渡区域,使得产生的拼接网格能光滑地衔接待拼接模型。实验结果表明,本文方法能够有效地实现三角网格模型的光滑拼接、模型修复和模型融合。     

Mesh fusion using functional blending on topologically incompatible sections

Three-dimensional mesh fusion provides an easy and fast way to create new mesh models from existing ones. We introduce a novel approach of mesh fusion in this paper based on functional blending. Our method has no restriction of disk-like topology or one-ring opening on the meshes to be merged. First of all, sections with boundaries of the under-fusing meshes are converted into implicit representations. An implicit transition surface, which joins the sections together while keeping smoothness at the boundaries, is then created based on cubic Hermite functional blending. Finally, the implicit surface is tessellated to form the resultant mesh. Our scheme is both efficient and simple, and with it users can easily construct interesting, complex 3D models.     

Embedded Implicit Stand-Ins for Animated Meshes: A Case of Hybrid Modelling

In this paper, we address shape modelling problems, encountered in computer animation and computer games development that are difficult to solve just using polygonal meshes. Our approach is based on a hybrid-modelling concept that combines polygonal meshes with implicit surfaces. A hybrid model consists of an animated polygonal mesh and an approximation of this mesh by a convolution surface stand-in that is embedded within it or is attached to it. The motions of both objects are synchronised using a rigging skeleton. We model the interaction between an animated mesh object and a viscoelastic substance, which is normally represented in an implicit form. Our approach is aimed at achieving verisimilitude rather than physically based simulation. The adhesive behaviour of the viscous object is modelled using geometric blending operations on the corresponding implicit surfaces. Another application of this approach is the creation of metamorphosing implicit surface parts that are attached to an animated mesh. A prototype implementation of the proposed approach and several examples of modelling and animation with near real-time preview times are presented.     

Free-form geometric modeling by integrating parametric and implicit PDEs

Parametric PDE techniques, which use partial differential equations (PDEs) defined over a 2D or 3D parametric domain to model graphical objects and processes, can unify geometric attributes and functional constraints of the models. PDEs can also model implicit shapes defined by level sets of scalar intensity fields. In this paper, we present an approach that integrates parametric and implicit trivariate PDEs to define geometric solid models containing both geometric information and intensity distribution subject to flexible boundary conditions. The integrated formulation of second-order or fourth-order elliptic PDEs permits designers to manipulate PDE objects of complex geometry and/or arbitrary topology through direct sculpting and free-form modeling. We developed a PDE-based geometric modeling system for shape design and manipulation of PDE objects. The integration of implicit PDEs with parametric geometry offers more general and arbitrary shape blending and free-form modeling for objects with intensity attributes than pure geometric models     

带纹理的三维模型简化算法

三维物体的几何造型中,物体通常用三角形网格来描述.随着计算机建模、仿真,虚拟现实与可视化技术的发展,经常会遇到带有纹理的三角形网格模型的简化问题.为此,提出一种带纹理的三角形网格模型简化算法.该算法中综合考虑了模型几何信息以及纹理信息的全局误差,并通过记录每步边折叠操作来消除累计误差,最终生成在形状和纹理上与原始模型最相似的简化模型.     

Geometric fusion for a hand-held 3D sensor

Abstract. This article presents a geometric fusion algorithm developed for the reconstruction of 3D surface models from hand-held sensor data. Hand-held systems allow full 3D movement of the sensor to capture the shape of complex objects. Techniques previously developed for reconstruction from conventional 2.5D range image data cannot be applied to hand-held sensor data. A geometric fusion algorithm is introduced to integrate the measured 3D points from a hand-held sensor into a single continuous surface. The new geometric fusion algorithm is based on the normal-volume representation of a triangle, which enables incremental transformation of an arbitrary mesh into an implicit volumetric field function. This system is demonstrated for reconstruction of surface models from both hand-held sensor data and conventional 2.5D range images. Received: 30 August 1999 / Accepted: 21 January 2000     

Implicit Surface-Based Geometric Fusion

This paper introduces a general purpose algorithm for reliable integration of sets of surface measurements into a single 3D model. The new algorithm constructs a single continuous implicit surface representation which is the zero-set of a scalar field function. An explicit object model is obtained using any implicit surface polygonization algorithm. Object models are reconstructed from both multiple view conventional 2.5D range images and hand-held sensor range data. To our knowledge this is the first geometric fusion algorithm capable of reconstructing 3D object models from noisy hand-held sensor range data.This approach has several important advantages over existing techniques. The implicit surface representation allows reconstruction of unknown objects of arbitrary topology and geometry. A continuous implicit surface representation enables reliable reconstruction of complex geometry. Correct integration of overlapping surface measurements in the presence of noise is achieved using geometric constraints based on measurement uncertainty. The use of measurement uncertainty ensures that the algorithm is robust to significant levels of measurement noise. Previous implicit surface-based approaches use discrete representations resulting in unreliable reconstruction for regions of high curvature or thin surface sections. Direct representation of the implicit surface boundary ensures correct reconstruction of arbitrary topology object surfaces. Fusion of overlapping measurements is performed using operations in 3D space only. This avoids the local 2D projection required for many previous methods which results in limitations on the object surface geometry that is reliably reconstructed. All previous geometric fusion algorithms developed for conventional range sensor data are based on the 2.5D image structure preventing their use for hand-held sensor data. Performance evaluation of the new integration algorithm against existing techniques demonstrates improved reconstruction of complex geometry.