Shape reconstruction of parallelogram flaw

To reconstruct the shape of the scatterer in elastic media, the authors deduce the Born approximation solution of the two-dimensional scattering problem, which includes the shape factor that embodies all information about the shape of the scatterer. Accordingly, the change in the shape of the scatterer only necessitates the number of the corresponding new shape factors. For a parallelogram void in a long Al rod, its shape factor can be obtained. In view of the definition of a characteristic function, the shape factor has a corresponding integral representation. Obviously, the shape factor can be considered as a Fourier transform of the characteristic function, which is reconstructed from the inverse Fourier transform. The integral equation is considered as the basic equation to reconstruct the shape of the scatterer. The identification of the geometrical character of a flaw is then given by the two dimensional inverse Born approximation in a low-frequency range. For the parallelogram void, a theoretical calculating identification is performed. At the same time, the numerical results are obtained by the finite element method.     

Shape reconstruction of mixed type void flaws using Born inversion method

We study an approximate technique for determining the shapes of mixed type void flaws in elastic media from knowledge of the ultrasonic scattering amplitudes. It is well known that the technique is highly effective under weak scattering conditions. In the paper, two cement paste cylindrical specimens with mixed type void flaws are prepared and ultrasonic measurements are carried out by experimental means. The measurement area is restricted in the plane perpendicular to the axis of cylindrical specimen. The measured wave data are fed into the approximate technique formula—the Born inversion method and cross-sectional image is obtained. We find that good results have been obtained for strong scattering void flaws such as mixed type void flaws in cement paste cylindrical specimens.     

Shape reconstruction of parallelogram flaw

To reconstruct the shape of the scatterer in elastic media, the authors deduce the Born approximation solution of the two-dimensional scattering problem, which includes the shape factor that embodies all information about the shape of the scatterer. Accordingly, the change in the shape of the scatterer only necessitates the number of the corresponding new shape factors. For a parallelogram void in a long Al rod, its shape factor can be obtained. In view of the definition of a characteristic function, the shape factor has a corresponding integral representation. Obviously, the shape factor can be considered as a Fourier transform of the characteristic function, which is reconstructed from the inverse Fourier transform. The integral equation is considered as the basic equation to reconstruct the shape of the scatterer. The identification of the geometrical character of a flaw is then given by the two dimensional inverse Born approximation in a low-frequency range. For the parallelogram void, a theoretical calculating identification is performed. At the same time, the numerical results are obtained by the finite element method.     

Shape reconstruction, shape manipulation, and direct generation of input data from point clouds for rapid prototyping

Shape reconstruction from point clouds has received considerable attention in recent years on account of its ability to directly integrate reverse engineering with rapid prototyping. The primary objective of this study is to develop an integrated system that enables one to generate input data for rapid prototyping by constructing complete shape models from point clouds obtained with various measuring devices, including laser scanners, digitizers, and coordinate-measuring machines. We first present a novel approach to reconstructing a shape from point clouds based on implicit surface interpolation combined with domain decomposition. We then propose various related algorithms for generating input data for rapid prototyping, ranging from shape manipulation to complete solid generation. The validity of this new technique is demonstrated for a variety of point clouds with differing degrees of complexity.     

Shape Reconstruction from Unorganized Points Using Voronoi Diagrams

Given only a set of points, without any geometric information such as the adjacency among the points, the scanning order or the scanning direction, it is a difficult problem to reconstruct a surface model corresponding to the original shape. For the reconstruction of open shapes, many effective approaches have been proposed. It is, however, hard to find a robust and effective method for the reconstruction of closed shapes. In this paper, an algorithm is proposed to reconstruct a three-dimensional closed shape from a set of good sample points using the properties of Delaunay triangulation and Voronoi diagrams. The proposed method consists of three steps; (1) constructing a convex hull consisting of mutually exclusive tetrahedra by 3D Delaunay triangulation of input points, (2) generating a Voronoi diagram of input points by utilising the properties of Delaunay triangulation, and (3) extracting the triangles on the shape boundary, defined by input points, after selecting the tetrahedra which are contained inside the shape using the properties of Voronoi diagrams. The proposed method in this paper has some advantages compared to the previous approaches. First, the distance parameter, such as α in the α-shape approach, is not required in the proposed approach. The determination of a proper parameter by trial and error is not appropriate, especially in the automation of shape reconstruction. Secondly, the time complexity of the proposed approach is O(n) since, in a single pass, this algorithm determines whether each tetrahedron is located inside or outside the shape boundary. ID="A1"Correspondance and offprint requests to: Dr K. S. Kim, Department of Industrial Engineering, Pohang University of Science and Technology, San 31, Hyojadong, Pohang, 790–784, Korea. E-mail: kskim@postech.ac.kr     

用二维逆Born近似法对杆中混合型缺陷的重构

为了重构弹性介质中缺陷的形状,本文在三维弹性波散射问题的Born近似解基础上,进一步分析了在纵波入射条件下二维散射问题的Born近似解,对铝质长杆中的混合型空穴缺陷的散射场情况进行了对比分析;最后,提出了在低频下识别缺陷几何特征的二维逆Born近似法,并用此法对铝质长杆中的混合型空穴缺陷作了计算机模拟.     

三维误差的分解与重建

在分析小波变换理论的基础上 ,提出采用小波变换方法对三维误差进行去噪处理和三维误差的重建 ,获得剔除随机误差和高频误差的周期性三维误差 ,实现有用信息的提取 ,从而为误差的分离和可补偿研究提供补偿依据。     

镗削内孔形状误差的诊断

在具备精密镗削的工艺条件下，工件仍出现精度超差现象，本文给出了这类问题探源方法和实例。     

逆向工程中扫描数据点的曲面重构

针对三维扫描数据点的曲面重构技术在实际系统中的应用,提出了一种以B样条曲面为基础的曲面构造算法。已知数据点按简明行方式排列,算法产生一个连续的B样条曲面,该曲面的参数化过程不受每行数据点分布的影响。根据所传递的候选节点矢量,采用柔性间距选择,有效地减少了控制顶点数,同时应用三维图形标准以及图形函数库,在VC 6．0平台上完成了该软件的编制。通过实际系统应用验证,该算法改进了传统曲面重构方法在处理非均匀扫描数据点时曲线曲面形状的失真和运算的不稳定现象,计算简单,易于编程实现。     

基于关系图的无人机影像三维重建

针对增量式运动恢复结构算法在无人机影像三维重建中运行效率低的问题,提出了一种基于关系图的无人机影像批处理重建方法。利用无人机低精度的位置姿态测量系统数据概略估算影像间的重叠关系,在关联影像之间进行尺度不变特征变换匹配,使用随机抽取一致性算法和三视图约束进一步剔除弱关联的影像连接关系,再通过深度优先搜索得到最终参加重建的影像集连通分量,构建出强关联的稳健影像关系图。然后,根据影像相对位姿参数,由最小二乘法解算全局一致性旋转参数,利用三视几何约束和线性规划求解全局一致位置参数,最后进行一次光束法平差优化。实验结果表明:与经典的增量式重建Bundler算法相比,该方法运行速度至少提高了2.6倍,且生成的三维点数量增加了76.5%,更真实地恢复出场景的几何形态。该算法在改善重建效果的同时提高了处理效率,能够满足无人机快速响应应用的需求。     

Morphometrical study of plant vacuolar dynamics in single cells using three-dimensional reconstruction from optical sections

In higher plants, vacuoles increase their volumes in accordance with cell enlargement and occupy most of the cell volume. However, quantitative analyses of vacuolar contributions during changes in cell morphology have been hampered by the inadequacies and frequent artifacts associated with current three-dimensional (3-D) reconstruction methods of images derived from light microscopy. To overcome the limitations of quantifying 3-D structures, we have introduced 3-D morphometrics into light microscopy, adopting a contour-based approach for which we have developed an interpolation method. Using this software, named REANT, the morphological and morphometrical changes in protoplasts and vacuoles during plasmolysis could be investigated. We employed the tobacco (Nicotiana tabacum) BY-2 cell line No.7, expressing a GFP-AtVam3p fusion protein, BY-GV7, using GFP as a marker of vacuolar membranes (VMs). By vital staining of the plasma membrane (PM) of cells, we simultaneously obtained optical sections of both the PM and VM. We, therefore, reconstructed the 3-D structures of protoplasts and vacuoles before and after plasmolysis. We were able to identify the appearance of elliptical structures of VMs in the vacuolar lumen, and to determine that they were derived from cytoplasmic strands. From the 3-D structures, the volumes and surface areas were measured at the single cell level. The shrinkage of vacuoles accounted for most of the decrease in protoplast volume, while the surface area of the vacuoles remained mostly unchanged. These morphometrical analyses suggest that the elliptical structures are reservoirs for excess VMs that result from the response to rapid decreases in vacuolar and protoplast volumes.     

形状记忆合金的应用

形状记忆合金是一种新型的功能材料，目前在许多领域都得到了应用。本文首先讨论了SMA材料的形状记忆原理，针对现行损伤模拟方法无法模拟结构损伤形成积累过程的不足之处，提出了将形状记忆合金SMA材料应用于损伤可控构件制作的方法，并介绍了形状记忆合金在机械、工程、电子以及医学领域的应用，并对前景作了分析。     

板形标准曲线的理论计算方法

联立板形预报模型和板形判别模型,提出板带轧机板形标准曲线的理论计算方法。该理论计算方法的思路和原则是最大限度地消除板凸度并同时兼顾板形良好,最终使板形趋于最好,这种计算方法的目标是实现板形和板凸度的综合最优控制。以1 220 mm五机架带钢冷连轧机和900 mm单机架带钢冷轧机5道次轧制为例,分别对轧制中凸板和中凹板的情况进行计算,计算结果证实了理论分析计算的正确性。这种板形标准曲线的理论计算方法为进一步从理论上定量研究板形标准曲线模型奠定了良好的理论基础。     

Computer reconstruction of nucleolar architecture by interactive three-dimensional color display

The first complete three dimensional ultrastructural reconstruction of pancreatic cell nucleoli, was done using EM and computer 3D-assisted reconstruction of serial sections with interactive 3D back-to-front and color display methods based on voxel representation. The purpose of the study was to depict the architecture of the nucleolar components. We obtained information about the location of the nucleolus within the nuclear volume and about the shape and polarity of the 3 main nucleolar territories.     

基于明暗恢复形状的目标物体深度信息提取算法设计

明暗恢复形状的方法（shape from shading简称SFS）分为全局最小化法、全局演化法、局部分析法、局部线性化法,但这4种方法都有一定的局限性,故在参考局部分析法的基础上,提出了基于明暗恢复形状的目标物体深度信息提取的简单算法。’     

徒手设计效果图的三维重建技术研究

将徒手设计效果图,根据透视图的基本原理、应用数据融合算法进行透视反求,分析计算确定透视条件,实现二维信息到三维信息的转化,从而进行三维重建.     

Controlled serial grinding for high-resolution three-dimensional reconstruction

This work reports an improved preparation procedure for acquiring SEM images for three‐dimensional (3D) reconstruction. The images are acquired consecutively after serial grinding and polishing. Ugelstad beads are used as landmarks for registration purposes and for determining the thickness of the abraded sections. An estimation of the bead sizes necessary for suitable thickness quantification at the corresponding spatial resolution and uncertainty is given. Shape‐based interpolation is used for filling the gaps between the cross‐sections. An indication of the distance between cross‐sections necessary for good interpolation is also given. An example of a 3D reconstructed paper volume is presented. The method is suitable for preparation of fibre and paper as well as other materials.     

Cryo-electron microscopy and three-dimensional reconstruction of actin filaments

Actin filaments have been examined by electron microscopy whilst in a frozen-hydrated state. Filaments embedded in a vitreous water layer are basically similar to those prepared by negative staining and show characteristic helical substructure, where the pitches of the helices are about 70 nm and 6 nm. Variability in spacing between long pitch helix cross-over points has been observed, which is consistent with intrinsic angular disorder between successive filament subunits. Fourier transforms of the most ordered filaments show four strong layer lines that index as the first, fifth, sixth and seventh orders of a 35 nm repeat. A three-dimensional helical reconstruction, calculated to a resolution of about 4 nm, shows the individual subunits to be orientated with their long axes roughly perpendicular to the filament axis. Each subunit is somewhat curved and is resolved into two domains. Most connections between successive subunits appear to be made close to the filament axis. We also report on the performance of the specimen holder (Philips PW 5699) used in this work.     

移动高光对三维场景重建的影响与消除

针对制造车间光滑地面在阳光或灯光照射下的扫描图像往往存在反射光斑,且随相机位置变化而变化,会严重干扰图像处理和利用的问题,提出了一种识别和去除高光的方法,用于改善图像处理效果和三维重建精度。基于扫描序列图像的三维场景重建流程和SURF特征原理,分析移动的高亮反光斑对图像特征点提取和匹配的影响;对于缺乏表面纹理的灰度图像,提出一种基于逐行多级阈值和动态模板高光识别与去除方法,保留非高光点的特征信息,识别与修复同步完成。实验结果表明,无高反光的前后两帧图像的匹配特征点对比有高光情况下至少高出8%,优化后的余留匹配特征点更多;扫描一段30m长的车间场景序列图像,用提出的方法修复高光后进行三维重建,点云拼接误差减小了10cm。表明移动高光对图像序列三维重建有不可忽视的影响,本文提出的方法能有效地去除高光。     

Principles of Shape from Specular Reflection

The reconstruction of (partially) specular object by means of deflectometric methods is a challenging task. It has a long and fairly branched history within the metrology and machine vision communities. We are not aware of any scientific publication surveying the state of the art in a unifying manner and thus stimulating further research. This contribution is intended to close this gap, bringing together prominent ideas from both fields. In avoidance of unnecessary technicality, we lay out the basic theory, including all known forward models of the reflection process. The corresponding inverse problem is ill-posed, so that special emphasis is put on the question of regularization. We embed some novel results on the uniqueness problem and the effectiveness of regularization approaches. Also an overview of numerical methods related to Shape from Specular Reflection is given. For the sake of completeness, we share some thoughts on the construction of an actual measurement system and discuss a practical example.