一种应用平面展开完成任意曲面纹理映射的新方法

本文提出一种新的纹理映射方法。该方法在任意曲面和它的平面展开之间定义映射,并用映射特征来评价映射精度,能有效地减少任意曲面纹理映射中的映射变形误差。     

Direct Manipulation and Interactive Sculpting of PDE Surfaces

This paper presents an integrated approach and a unified algorithm that combine the benefits of PDE surfaces and powerful physics-based modeling techniques within one single modeling framework, in order to realize the full potential of PDE surfaces. We have developed a novel system that allows direct manipulation and interactive sculpting of PDE surfaces at arbitrary location, hence supporting various interactive techniques beyond the conventional boundary control. Our prototype software affords users to interactively modify point, normal, curvature, and arbitrary region of PDE surfaces in a predictable way. We employ several simple, yet effective numerical techniques including the finite-difference discretization of the PDE surface, the multigrid-like subdivision on the PDE surface, the mass-spring approximation of the elastic PDE surface, etc. to achieve real-time performance. In addition, our dynamic PDE surfaces can also be approximated using standard bivariate B-spline finite elements, which can subsequently be sculpted and deformed directly in real-time subject to intrinsic PDE constraints. Our experiments demonstrate many attractive advantages of our dynamic PDE formulation such as intuitive control, real-time feedback, and usability to the general public.     

辐射度算法在动态虚拟环境中的应用研究

本文研究了在静态曲面环境辐射度算法基础上的动态环境辐射度算法，并提出了判断景物阴影相交的中心点法和锥体相交法，最后讨论了如何用面向对象的方法实现本算法。     

IRIS: illustrative rendering for integral surfaces

Integral surfaces are ideal tools to illustrate vector fields and fluid flow structures. However, these surfaces can be visually complex and exhibit difficult geometric properties, owing to strong stretching, shearing and folding of the flow from which they are derived. Many techniques for non-photorealistic rendering have been presented previously. It is, however, unclear how these techniques can be applied to integral surfaces. In this paper, we examine how transparency and texturing techniques can be used with integral surfaces to convey both shape and directional information. We present a rendering pipeline that combines these techniques aimed at faithfully and accurately representing integral surfaces while improving visualization insight. The presented pipeline is implemented directly on the GPU, providing real-time interaction for all rendering modes, and does not require expensive preprocessing of integral surfaces after computation.     

Generalised Epipolar Constraints

In this paper we will discuss structure and motion problems for curved surfaces. These will be studied using the silhouettes or apparent contours in the images. The problem of determining camera motion from the apparent contours of curved three-dimensional surfaces, is studied. It will be shown how special points, called epipolar tangency points or frontier points, can be used to solve this problem. A generalised epipolar constraint is introduced, which applies to points, curves, as well as to apparent contours of surfaces. The theory is developed for both continuous and discrete motion, known and unknown orientation, calibrated and uncalibrated, perspective, weak perspective and orthographic cameras. Results of an iterative scheme to recover the epipolar line structure from real image sequences using only the outlines of curved surfaces, is presented. A statistical evaluation is performed to estimate the stability of the solution. It is also shown how the motion of the camera from a sequence of images can be obtained from the relative motion between image pairs.     

裁剪自由曲面的隐藏线消除

以十字链表作为基础的网状数据结构为依据，提出了一种裁剪自由曲面的隐藏线消除算法，该方法省去了对图象空间或物体空间的划分及曲面片的分类、排序处理，直接采用一种邻域搜索法来确定网格点的可见性。     

任意摆放的二次曲面体的三维重建

本文采用特征点匹配的方法,先由二维视力获取三维空间的点和曲线,然后经过一系列线性运算得出三维曲面。本算法可对任意二次曲面进行三维重建,不仅对曲面的空间摆放沿有限制,而且对曲面自身的对称性也无要求。因此,可将重建对象扩展为圆柱、椭圆柱、球、椭球、双曲面、抛物面等。本文给出的算例表明了算法的有效性。     

基于沟底形状的大脑皮层褶皱模式表达

提出一种基于大脑皮层表面脑沟基底形状的模式表达方法。该方法从大脑皮层表面半自动提取左右2个脑半球上14个主要的脑沟基底,采用仿射传播(AP)聚类算法,对每个脑沟基底进行形状的模式分类,作为大脑皮层表面褶皱模式的初级表达,每个样本的 14个沟底被看作一个整体,进行AP方法聚类,获得大脑皮层褶皱模式的全局表达。该方法已被应用在281个正常人大脑皮层表面上,获得了有意义的结果。     

曲面的展开与折叠方法综述

作为曲面变形领域的重要课题,展开与折叠已经成为近年来的研究热点.为了满足三维物体在美学、力学等方面的约束,通常需要为其设计展开与折叠结构.利用计算机相关技术模拟物体的展开与折叠,可设计出满足约束条件的几何结构.目前,展开与折叠广泛应用于工业设计、生物医疗、智能机器人、家具设计等领域.主要介绍近年来计算机展开与折叠物体的...     

Affine reconstruction of curved surfaces from uncalibrated views ofapparent contours

In this paper, we consider uncalibrated reconstruction of curved surfaces from apparent contours. Since apparent contours are not fixed features (viewpoint independent), we cannot directly apply the recent results of the uncalibrated reconstruction from fixed features. We show that, nonetheless, curved surfaces can be reconstructed up to an affine ambiguity from their apparent contours viewed from uncalibrated cameras with unknown linear translations. Furthermore, we show that, even if the reconstruction is nonmetric (non-Euclidean), we can still extract useful information for many computer vision applications just from the apparent contours. We first show that if the camera motion is linear translation (but arbitrary direction and magnitude), the epipolar geometry can be recovered from the apparent contours without using any optimization process. The extracted epipolar geometry is next used for reconstructing curved surfaces from the deformations of the apparent contours viewed from uncalibrated cameras. The result is applied to distinguishing curved surfaces from fixed features in images. It is also shown that the time-to-contact to the curved surfaces can be computed from simple measurements of the apparent contours     

d:x reflectance measurement for curved surface with integrating sphere

Ambient contrast ratio (ACR) is a useful parameter to evaluate the quality of displays when used under diffuse lighting conditions. The methodology recommended by most documentary standards calculates the ACR of the display from d:x reflectance. Reflectance measurement of flat surfaces typically employs an integrating sphere and a flat white reference plate. However, the shape difference between the flat white standard and test curved sample causes changes to the amount of light illuminating their surfaces and thus gives measurement errors. Especially for concave test surfaces, the error is significant when the sample has small radius of curvature. To increase the measurement accuracy, this paper derives the correction factor to compensate the effect caused by shape difference between the reference plate and test curved sample. The associated uncertainty analysis is also discussed in this paper.     

Image‐based modeling of 3D objects with curved surfaces

This paper addresses an image‐based method for modeling 3D objects with curved surfaces based on the non‐uniform rational B‐splines (NURBS) representation. The user fits the feature curves on a few calibrated images with 2D NURBS curves using the interactive user interface. Then, 3D NURBS curves are constructed by stereo reconstruction of the corresponding feature curves. Using these as building blocks, NURBS surfaces are reconstructed by the known surface building methods including bilinear surfaces, ruled surfaces, generalized cylinders, and surfaces of revolution. In addition to them, we also employ various advanced techniques, including skinned surfaces, swept surfaces, and boundary patches. Based on these surface modeling techniques, it is possible to build various types of 3D shape models with textured curved surfaces without much effort. Copyright © 2007 John Wiley & Sons, Ltd.     

Advanced Geometric Modeler with Hybrid Representation

An advanced geometric modeler GEMS4.0 has been developed,in which feature representation is used at the highest level abstraction of a product model.Boundary representation is used at the bottom level,while CSG model is adopted at the median level.A BRep data structure capable of modeling non-manifold is adopted.UNRBS representation is used for all curved surfaces,Quadric surfaces have dual representations consisting of their geometric data such as radius,center point,and center axis.Boundary representation of free form surfaces is easily built by sweeping and skinning method with NURBS geometry.Set operations on curved solids with boundary representation are performed by an evaluation process consisting of four steps.A file exchange facility is provided for the conversion between product data described by STEP and product information generated by GEMS4.0.     

计算机数控加工仿真中误差检测技术的研究与实现

为了在数控加工仿真系统中对对数控加工代码的正确性进行分析和评定，本文提出一种简单快速的误差检测算法，该算法的基本思想是，在对零件模型进行Z空间离散的基础上，通过对离散模型分别与零件曲面的STL集合及刀位切削段的拉掠面进行求交运算，从而获得零件设计曲面和加工结果曲面的几何表示，法向投影误差计算法精确，简单地计算出零件加工误差的分布。     

Java处理器中指令合并技术的研究与实现

文中在分析Ｊａｖａ虚拟机及字节码特性基础上,研究了Ｊａｖａ处理器中的指令合并技术。对３种合并策略：２条指令的合并,３条指令的合并及４条指令的合并进行了分析比较,并分别实现了这３种合并策略。研究表明４条指令合并策略具有较高的性能／开销比。     

A Radiosity Solution for Curved Surface Environments

Radiosity has been a popular method for photorealistic image generation.But the determination of form factors between curved patches is the most difficult and time consuming procedure,and also the errors caused by approximating source patch‘s radiosity with average values are obvious.In this paper,a radiosity algorithm for rendering curved surfaces represented by parameters is described.The contributed radiosity from differential areas on four vertices of the source patch to a receiving point is calculated firstly,then the contribution from the inner area of the source patch is evaluated by interpolating the values on four corners.Both the difficult problem of determining form-factors between curved surfaces and errors mentioned above have been avoided.Comparison of the experimental results using the new algorithm has been made with the ones obtained by traditional method.Some associated techniques such as the visibility test and the adaptive subdivision are also described.     

曲面体线图的标记与匹配

三维曲面体的标记与匹配,是计算机视觉研究领域中一项相当有用但又是非常困难的技术。本文讨论了一种曲面体标记的新方法。通过引入线段的一些新的标记类型,圆满地解决了利用 Huffman 标记技术描述曲面体时,可能出现的不一致性。根据以上的标记结果,本文还给出了一匹配曲面体线图的新方法。在匹配过程中,我们注重的不是图象的二维特征,而是其对应的物体的三维特征,因而对物体的旋转、遮挡、尺度变化及远视失真等极不敏感。实验结果表明本算法是相当令人满意的。     

MESSAGE——具有自由曲面造型功能的立体造型系统

MESSAGE是一具有自由曲面造型功能的立体造型系统,它能够处理二次曲面、旋转曲面、 广义sweeping曲面、自由曲面以及由平面和上述曲面围成的三维物体,系统以平面及双三次 有理B样条曲面为基本曲面模型,提供了布尔运算、glue运算及多种局部修改运算.系统还 具有一个独立的几何数据库,可以支持一些重要的工程应用.     

A subdivision algorithm for axisymmetric sections

In the generation of curved surfaces through a subdivision process, Sabin and Doo applied and extended Chaikin's algorithm to three dimensions by using linear combinations of the vertices of a polyhedron. A similar smoothing subdivision algorithm was brought out by Catmull and Clark. This paper describes an alternative algorithm which uses a similar approach but applies to sections of axisymmetric objects. It shows that axisymmetric free-formed surfaces can be generated easily and effeciently.     

A comparison of local parametric C Bézier interpolants for triangular meshes

Parametric curved shape surface schemes interpolating vertices and normals of a given triangular mesh with arbitrary topology are widely used in computer graphics for gaming and real-time rendering due to their ability to effectively represent any surface of arbitrary genus. In this context, continuous curved shape surface schemes using only the information related to the triangle corresponding to the patch under construction, emerged as attractive solutions responding to the requirements of resource-limited hardware environments. In this paper we provide a unifying comparison of the local parametric C⁰ curved shape schemes we are aware of, based on a reformulation of their original constructions in terms of polynomial Bézier triangles. With this reformulation we find a geometric interpretation of all the schemes that allows us to analyse their strengths and shortcomings from a geometrical point of view. Further, we compare the four schemes with respect to their computational costs, their reproduction capabilities of analytic surfaces and their response to different surface interrogation methods on arbitrary triangle meshes with a low triangle count that actually occur in their real-world use.