基于Delaunay三角剖分和高斯小波函数插值的三维表面重建算法

在稀疏数据的三维表面重建中,通过插值的方法得到更为稠密的数据点是一个很重要的环节。该文在比较其它插值算法的基础上,提出了一种三维表面重建算法。该算法在对原始数据进行Delaunay三角剖分的基础上采用二维高斯小波函数插值,它不仅能有效地处理非均匀采样的三维稀疏数据,而且能克服其它插值算法中需要定义权重或估计参数的缺点。最终的实验结果验证了该算法的有效性和实用性。     

基于平行截面的三维散乱点物体表面重构

三维物体的散乱点构型技术是近几年计算机视觉领域中的热点问题,它在众多行业有着广泛的应用前景。该文提出了一种新的能够适用于大多数物体的构型方法,并且计算量也相应地得到了控制。     

基于地层轮廓的三维重构的设计和实现

在进行海底地质地层调查勘探时,通常根据测量仪器采集的数据生成地层断面轮廓线,按照这些连续的轮廓线的分布特征及其灰底不同来粗略地分辨地层的性质.然而这些单一的剖面轮廓还不足以直观地反映该地域整体地层的三维形状分布信息.根据地质地层分布的特性,通过对相邻断层轮廓线点集的匹配和三角剖分算法来进行地层分布的三维重构,并利用基于三角域的Bernstein-Bezier曲面构造三次光滑曲面,从而模拟三维的地层分布效果图.     

A Theory of Refractive and Specular 3D Shape by Light-Path Triangulation

We investigate the feasibility of reconstructing an arbitrarily-shaped specular scene (refractive or mirror-like) from one or more viewpoints. By reducing shape recovery to the problem of reconstructing individual 3D light paths that cross the image plane, we obtain three key results. First, we show how to compute the depth map of a specular scene from a single viewpoint, when the scene redirects incoming light just once. Second, for scenes where incoming light undergoes two refractions or reflections, we show that three viewpoints are sufficient to enable reconstruction in the general case. Third, we show that it is impossible to reconstruct individual light paths when light is redirected more than twice. Our analysis assumes that, for every point on the image plane, we know at least one 3D point on its light path. This leads to reconstruction algorithms that rely on an “environment matting” procedure to establish pixel-to-point correspondences along a light path. Preliminary results for a variety of scenes (mirror, glass, etc.) are also presented. Part of this research was conducted while K. Kutulakos was serving as a Visiting Scholar at Microsoft Research Asia.     

基于Delaunay四面体剖分的网格分割算法

为了构建有意义曲面分片,提出一种基于Delaunay四面体剖分的网格分割算法.首先根据Delaunay四面体剖分得到多边形网格内部的四面体,求出每个面上反映网格内部信息的Delaunay体距离;然后对Delaunay体距离进行平滑处理,再对网格上面的Delaunay体距离进行聚类,用高斯混合模型对Delaunay体距离作柱状图的拟合,利用期望最大化算法来快速求得拟合结果;最后结合图切分技术,同时考虑聚类的结果、分割区域的边界平滑和视觉认知中的最小规则,得到最终的网格分割结果.实验结果表明,采用文中算法可以有效地实现有意义的网格分割.     

Internet环境三维流式传输算法研究

nternet/Intranet环境的网络带宽和传输速率成为实现协同CAD的瓶颈,针对协同CAD的实时数据传输问题,本文提出了三维流式传输技术,这种新的实时数据传输方法是与视点相关的,将三维几何数据分段、连续地进行传输,可以有效地缩短启动延时,本文具体地研究了相关的实现算法,并通过实验结果证明三维流式传输可以明显地缩短启动延时,能够较好地满足协同CAD的应用需要。     

Generation of anisotropic mesh by ellipse packing over an unbounded domain

With the advance of the finite element method, general fluid dynamic and traffic flow problems with arbitrary boundary definition over an unbounded domain are tackled. This paper describes an algorithm for the generation of anisotropic mesh of variable element size over an unbounded 2D domain by using the advancing front ellipse packing technique. Unlike the conventional frontal method, the procedure does not start from the object boundary but starts from a convenient point within an open domain. The sequence of construction of the packing ellipses is determined by the shortest distance from the fictitious centre in such a way that the generation front is more or less a circular loop with occasional minor concave parts due to element size variation. As soon as an ellipse is added to the generation front, finite elements are directly generated by properly connecting frontal segments with the centre of the new ellipse. Ellipses are packed closely and in contact with the existing ellipses by an iterative procedure according to the specified anisotropic metric tensor. The anisotropic meshes generated by ellipse packing can also be used through a mapping process to produce parametric surface meshes of various characteristics. The size and the orientation of the ellipses in the pack are controlled by the metric tensor as derived from the principal surface curvatures. In contrast to other mesh generation schemes, the domain boundary is not considered in the process of ellipse packing, this reduces a lot of geometrical checks for intersection between frontal segments. Five examples are given to show the effectiveness and robustness of anisotropic mesh generation and the application of ellipse packing to mesh generation over various curved surfaces.     

CAD-based reconstruction of 3D polycrystalline alloy microstructures from FIB generated serial sections

This paper develops a robust CAD-based methodology for simulating 3D microstructures of polycrystalline metals using crystallographic input data on sections created by a focused ion beam (FIB)-scanning electron microscopy (SEM) system. The method is able to construct consistent polycrystalline microstructures with control on the resolution necessary for meaningful computational analysis in microstructure-property estimation. The microstructure simulation methodology is based on a hierarchical geometrical representation using primitives used in CAD modeling. It involves steps of data cleanup, interface point identification, polynomial and NURBS function-based parametric surface segments construction, generalized cell decomposition, geometric defeaturing, and gap and overlap removal. The implementation of the entire procedure described above is performed with the aid of user-programming facilities of a commercial CAD package Unigraphics NX3. The microstructure simulation algorithm is validated using various error criteria and measures for an extracted microstructure of a nickel superalloy.     

一种多张裁减曲面的快速三角化算法

针对多张裁减曲面的三角化问题,提出一种多张裁减曲面三角化边界的算法。该算法在进行多张裁减曲面的三角化时,采用点对应的方法离散曲面的公共边界,因而能有效地防止曲面相交处出现裂缝、孔洞和覆盖等现象,提高了多张裁减曲面三角化算法的正确性。同时采用了目前比较先进的基于局部优先的平面任意区域三角剖分算法,因而提高了三角化的效率。     

地下空间三维数据模型分析与设计

三维空间数据模型是地下空间三维建模的基础。讨论了地下空间三维数据模型设计的实体依赖性、数据依赖性、需求依赖性和实现依赖性等特性,并分析了当前地下空间建模的三维数据模型存在的不足,提出了一种新的面向对象的地下空间三维矢量拓扑数据模型。初步实验结果表明,该模型在地下空间对象的存储管理、查询分析以及模型动态编辑等方面都表现出较好的性能。     

一种快速三维散乱点云的三角剖分算法

改进了一种三维散乱点云三角剖分算法。三角剖分是点云数据曲面重构的主要算法之一,但针对三维散乱点云的三角剖分存在剖分效率不高,剖分得到的三角曲面形状无法控制,细节特征表现不足的问题。提出了基于空间栅格划分的三角剖分算法,并提出了一个新的评价函数,以控制三角网格曲面的生长。实验证明,改进后的算法极大的提高了剖分效率,而且能保证最终生成的三角网格曲面平滑而保有丰富的细节特征,适用于在虚拟现实、曲面重构等领域推广使用。     

高速铁路桥梁三维参数化建模方法研究

针对高速铁路桥梁大规模三维建模的需求,提出一种面向组件的桥梁半自动建模方法。首先对高速铁路桥梁进行组件拆分与子类划分,形成建模的最小构件,采用参数化方法描述构件的几何、定位、材质特征,通过输入参数值获得形态迥异的构件实例;然后根据组件的相互作用规则与定位参数,将组件自动组合为桥梁;最后采用VC 2008语言开发3ds Max插件,在3ds Max平台下实现模型绘制、参数编辑和数据导出。该插件已成功应用于长昆线271座桥建模,取得了良好的应用效果。     

Triangulation of molecular surfaces

Given a molecule, which consists of a set of atoms, a molecular surface is defined for a spherical probe approximating a solvent molecule. Molecular surface is used for both the visualization of the molecule and the computation of various molecular properties such as the area and volume of a protein, which are important for studying problems such as protein docking and folding.In this paper, we present an O(n) time algorithm, in the worst case, for triangulating molecular surface based on the combinatorial information provided by the β-shape of the molecule with n atoms. The proposed algorithm takes advantage of the concise representation of topology among atoms stored in the β-shape.A molecular surface consists of two parts: a blending surface consisting of blending patches and a (solvent) contact surface consisting of (solvent) contact patches. For each blending patch, the algorithm uses compact masks for the construction of a triangular mesh in O(c^′) time in the worst case, where c^′ is the number of point evaluations on the blending patch. For each contact patch, the algorithm uses a template, for each atom type, for the triangulation of the boundary of the atom. Then, the triangular mesh is trimmed off by hyperplanes where each hyperplane corresponds to an arc of the boundary of the contact patch. The triangulation of a contact patch takes O(c^″) time in the worst case, where c^″ is the number of point evaluations on the boundary of an atom. Since there are at most O(n) patches, the worst case time complexity is O(n).The proposed algorithm also handles internal voids and guarantees the watertightness of the produced triangular mesh of a molecular surface. In addition, the level-of-detail is easily achieved as a by-product of the proposed scheme. The proposed algorithm is fully implemented and statistics from experiments are also collected.     

二维、三维空间信息系统的结合和应用

详细介绍了如何结合二维的GIS技术和三维GIS技术,制作一个既能逼真的显示地理信息又具有完整的信息分析功能的地理信息系统的方法。分析了二维的GIS技术和三维GIS技术各自的优缺点,并简略的介绍了2．5维GIS技术和纯三维GIS技术研究现状。     

Triangulation of Points,Lines and Conics

The problem of reconstructing 3D scene features from multiple views with known camera motion and given image correspondences is considered. This is a classical and one of the most basic geometric problems in computer vision and photogrammetry. Yet, previous methods fail to guarantee optimal reconstructions—they are either plagued by local minima or rely on a non-optimal cost-function. A common framework for the triangulation problem of points, lines and conics is presented. We define what is meant by an optimal triangulation based on statistical principles and then derive an algorithm for computing the globally optimal solution. The method for achieving the global minimum is based on convex and concave relaxations for both fractionals and monomials. The performance of the method is evaluated on real image data.

有限元网格的三角划分

三角形网格划分在有限元和计算机图形学中有着广泛的应用,本文主要讨论平面有限元三角形划分的两种算法,后一种是前一种改进了的快速算法。这两种算法可以使得用计算机实现三角网格的划分变得更加容易。     

三维重建中的点云配准方法研究

对序列点云拼接实现三维场景重建的方法进行研究,在重建方法中引入体积空间映射方法,有效地去除了拼接结果中的重复点、并填补了空洞.提出了改进的ICP算法和体积空间融合算法相结合的三维重建方法.实验证明该方法能有效地提高拼接结果的精度.     

基于一维插值的人头像三维表面重建

描述了一种基于一维插值的人头像三维表面的重建方法。该方法从几个不同侧面的人体头部条形图获得人头像的三维条形图．经过型值点的提取,一维三次样条插值,三维重建,进而得到任意分辨率的人体头部三维曲而的数字表示及三角形、四边形网格图等表示形式,一维插值与传统的三维曲面重建的二维插值方法相比较,算法简单,三维曲面重建所需的时间也较少。该方法已在PIII 800PC机上进行了验证,获得了较好的效果。     

复杂断层轮廓集分段分面三角化表面重构

针对多嵌套、多分支任意复杂断层轮廓集的三角化表面重建,提出一种基于轮廓拓扑分类编码和结构识别的分段分面表面重构方法(DS-P).通过设计一种拓扑编码方案,提出确定轮廓匹配关系、分支及分支类型的准则;讨论了多轮廓合并、单轮廓分裂及嵌套分支、连通分支处理方法;设计了任意复杂断层轮廓集表面重建的软件系统架构和工作流程.实验结果表明,该方法应用简单、运算效率高、可靠性强.与经典方法和BPLI方法相比,文中方法不仅能更好地处理轮廓匹配中的二义性及分支问题,还能有效地解决导致BPLI方法失效的投影面内边重叠和多重交叉、轮廓嵌套、轮廓严重偏置、轮廓线释放等情况下的表面重构问题.