基于工业计算机断层成像技术的三维CAD模型重构方法

为解决复杂形状产品的三维计算机辅助设计模型的重构难题,提出了一种基于工业计算机断层成像技术的三维计算机辅助设计模型的重构方法.首先用工业计算机断层成像技术对产品进行扫描,得到产品切片图像,然后通过切片图像获取体数据;在采用高斯滤波对体数据进行预处理后,使用移动立方体算法重建三维表面,并用顶点删除法和二次误差测度算法简化三维表面;在采用Laplacian算法平滑三维表面后,将三维表面模型保存为STL格式的文件;最后,将STL格式的文件导入到UG中,重构出产品的三维计算机辅助设计模型.实际应用验证了该方法的有效性和正确性.     

一种逐层切削CCD成像模型重构的试验研究

提出一种基于逐层切削CCD成像的复杂零件轮廓表面及内腔的三维重构技术。此技术通过将被测物体用高分子材料包裹后进行逐层切削,再由CCD拍摄并传送至计算机,通过对图像的分析处理及边缘检测,得到被测物体的三维模型数据信息。根据检测得到的三维点云数据的特点,再用IMAGEWARE进行曲线及曲面拟合,得到三维模型。实验结果表明基于逐层切削CCD成像的复杂零件轮廓表面及内腔的三维重构技术具有检测准确、快捷等特点,且能对复杂零件内腔进行有效检测与三维重构。     

基于工业CT切片数据的反求建模技术研究

针对目前的反求技术研究都是对无分叉不带型腔的简单情况的零件,研究了复杂零件的工业CT(Industrial computed Tomography)切片数据建模技术,主要包括分割工业CT图像的方法、断层图像间的插值方法和反求重构等.采用基于边缘特征的二值化算法对图像进行分割,在此基础上提出了一种基于距离变换的目标图像插值方法,最后采用体绘制的方法对断层图像进行反求建模.对摩托车气缸头复杂零件工业CT断层数据进行了实验研究,实验结果表明,反求模型的合理性和平滑过渡都比较令人满意.     

应用于医学三维影像的血管结构自动提取

针对从计算机断层扫描血管造影术(CTA)的三维体数据中提取血管结构信息通常需要大量的人为介入操作的问题,提出了一种全自动血管分割方法。首先,采用多尺度增强滤波器对数据中的管状结构进行增强,剔除非管状结构,并过滤噪声。然后,利用Sigmoid函数作用于梯度图像产生水平集的速度图像,并通过测地活动轮廓模型迭代逼近真实的三维血管轮廓。最后,通过拉普拉斯算法对提取的血管表面网格进行平滑处理,获得光滑的血管曲面。实验采用胸部和颈部的CTA体数据对算法进行测试,结果表明:该方法无需人工干预即可从CTA体数据中准确地提取出血管的三维信息;血管中心线提取的平均误差为0.26mm,直径测量平均误差为0.16mm,分割精度满足临床血管疾病辅助诊疗的要求。     

基于单目视觉的叶轮零件三维重构方法研究

针对高像素图像合成模型运算量大、图像标定过程复杂等问题,对图像预处理、图像信息提取和匹配等方面进行了研究,提出了一定角度的序列图像重构模型方法。基于单目视觉重建原理,利用SIFT算法提取、匹配图像的特征点集,对基本矩阵进行了奇异值分解,得到了摄像机矩阵;引入了绝对对偶二次曲面的自标定算法,用于自动建立物体坐标系,依据反向投影原理恢复了模型;搭建了叶轮零件的三维重构实验平台,进行了网格模型重构实验。研究结果表明:所提出的方法能将零件的三维模型准确重构,实现高精度、高效率的自动化三维逆向建模;提供了一种可靠的模型获取方式,可为3D打印加工提供上游技术支持。     

采用切片数据的多孔复杂模型三维实体重建

为了实现基于切片数据的多孔复杂模型的三维文体重建,提出将基丁轮廓线的局部优化方法与移动立方体(Marc-hing Cubes,MC)算法相结合,通过采用辅助轮廓法精确提取等值线,制定模型复杂程度的分类原则,合理选择配置方法,克服了多分支轮廓拓扑重构的困难,重建出由三角面片组成的三维形体表面模型.利用ANSYS参数化设计语言(AP-DL)在ANSYS中实现面模型向实体模型的转化,使重建后的模型不仅三维显示,还可直接用于有限元分析,使提出的三维重建方法具有更好的实用性.     

基于单幅图像数据的三维重构方法研究

针对传统的基于阴影恢复形状方法（SFS）的三维重构方法的局限性,综合运用计算机视觉、图像处理和计算机辅助几何设计理论与技术,提出了一种实用的三维重构方法。采用SFS方法获取三维形貌信息,利用图像分割技术提取物体的二维轮廓信息,通过三维形貌信息与二维轮廓信息的融合建立物体的数字化模型,通过B样条方法实现数字化模型的重构。实例表明,该方法能够有效地去除图像的背景信息,改善重构模型的分辨力,为基于图像的三维重构技术的广泛应用提供了条件。     

基于地貌学的零件表面三维形貌评定

Motif方法作为轮廓法的一种,用7个参数可以完成2维粗糙度和波纹度的评定.近年来,国际上加大了对零件三维形貌评定方法的研究,基于地貌学的理论和Motif方法,对零件三维表面结构要素进行了定义,采用变化树和图形分割等方法,用特殊的点和线表述零件表面山峰和谷地的特性,用谷地的概念描述3维Motif.为了避免过分割现象,需要将无意义的谷地合并为有意义的较大的谷地.峰顶密度、封闭的谷周面积、封闭的谷体体积等评定参数可用于零件三维表面形貌的评定.     

全局最优混合活动轮廓模型肺组织三维重构

医学图像三维重构是一种重要的计算机辅助可视化技术,对医学诊断和辅助治疗具有重要影响。在胸腔CT图像中,肺部组织密度远小于胸腔壁、骨骼等外围组织。因此,在对肺组织进行三维建模的过程中,肺部易被外围组织遮挡,严重影响其三维观测和定量分析。提出了一种针对胸腔CT序列肺部组织的非遮挡三维重构方法。首先提出一种全局最优的混合活动轮廓模型准确分割连续胸腔CT图像中的肺部组织,然后采用基于错切变形的最大密度投影体绘制实现肺部三维模型重构。通过对30例患者CT数据进行实验,结果表明所提出的混合活动轮廓模型可实现准确的肺部组织分割。平均Dice相似性系数为0.983,平均双向Hausdorff距离为6.1 mm,每个病例的平均分割效率为4.5 min。采用错切变形体绘制重构后可获得无遮挡的肺部三维模型。     

三维CAD模型模块划分的蚁群聚类图分割方法

为了使三维CAD模型模块划分的结果保持较好的结构完整性,提出一种面向图分割的蚁群聚类算法.用属性连接图表示复杂的CAD模型并进行简化;通过对模型连接方式和零件属性的分析,获得零件的结构、功能和材料相关性并建立综合相关度矩阵;根据零件的连接层次关系重构了蚁群聚类的局部范围界定和密度函数计算方法,实现了面向图分割的的蚁群聚类.采用上述方法对某型飞机襟翼模型进行模块划分,验证了所提方法的正确性和有效性.     

基于轮廓线法的三维重建技术研究

提出基于轮廓线法的改进算法,使其更加适用人体组织的三维重建。先根据医学图像的特点将轮廓数据进行分类,然后分别在各类中进行对应处理和分支处理确定轮廓间的拓扑关系,最后以最小对角线为优化目标进行三角面片的拼接,进而得到三维模型。由于较好地确定了拓扑关系,使得组织器官的三维模型表达更精确,建模效率更高。     

Feature extraction from slice data for reverse engineering

A new approach to feature extraction for slice data points is presented. The reconstruction of objects is performed as follows. First, all contours in each slice are extracted by contour tracing algorithms. Then the data points on the contours are analyzed, and the curve segments of the contours are divided into three categories: straight lines, conic curves and B-spline curves. The curve fitting methods are applied for each curve segment to remove the unwanted points with pre-determined tolerance. Finally, the features, which consist of the object and connection relations among them, are founded by matching the corresponding contours in adjacent slices, and 3D models are reconstructed based on the features. The proposed approach has been implemented in OpenGL, and the feasibility of the proposed method has been verified by several cases.     

3D打印制件外轮廓线的自适应分层算法研究

针对3D打印三维模型直接转换成STL文件进行切片分层处理过程中,存在模型表面信息缺失、打印精度不高等问题,提出了面向3D打印制件外轮廓线的自适应分层算法。该算法利用Z轴方向特征曲线的方法得到打印制件外轮廓曲线,采用微元思想对模型分段处理,确定打印方向与外轮廓切线夹角的关系,运用概率统计、叠加求和等数学理论求出每一层切片的自适应分层方法。通过实例打印表明,该算法减少了转换成STL文件时的信息缺失,提高了3D打印的精度与效率。     

基于贝叶斯自适应估计的光子计数集成成像

针对光子数极少环境下三维目标的重构问题,基于光子计数集成成像系统提出了一种贝叶斯自适应估计方法,来提高三维目标深度切片的重构质量。首先,通过光子计数集成成像系统获得一系列光子计数元素图像。接着,从光子计数过程的泊松分布出发,利用集成成像系统中对于同一个目标像素的多次采样特性,引入了局部自适应均值因子,从而建立起元素图像像素光子数估计的单参数后验概率模型。最后,通过后验概率模型的均值计算获得更新后的光子计数元素图像,并基于光束可逆原理重构出深度切片图像。实验结果表明:采用该方法在场景的两个深度处重构的切片图像相比传统贝叶斯重构图像的峰值信噪比提高了7.4dB和8.5dB,极大地提升了微弱光三维目标的重构质量。     

Three-dimensional reconstruction of cells from serial sections and whole-cell mounts using multilevel contouring of stereo micrographs

A comprehensive computer-graphics-based system (STERECON) is described for tracing and digitizing contours from individual or stereopair electron micrographs. The contours are drawn in parallel planes within the micrographs. Provision is also made for tracing and digitizing in full three-dimensional (3-D) coordinates in any direction along linear structures such as cytoskeletal elements. The stereopair micrographs are viewed in combination with the contours being traced on a graphics terminal monitor. This is done either by projecting original electron micrograph (EM) negatives onto a screen and optically combining these images with contour lines being drawn on the monitor, or by first digitizing the images and displaying them directly on the monitor along with the contour lines. Prior image digitization allows computer enhancement of the structures to be contoured. Correction and alignment routines are included to deal with variable section thickness, section distortion and mass loss, variations in photography in the electron microscope, and terminal screen curvature when combining projected images with contour lines on the monitor. The STERECON system organizes and displays the digitized data from successive sections as a 3-D reconstruction. Reconstructions can be viewed in any orientation as contour stacks with hidden lines removed; as wire-frame models; or as shaded, solid models with variable lighting, transparency, and reflectivity. Volumes and surface areas of the reconstructed objects can be determined. Particular attention was paid to making the system convenient for the biological user. Users are given a choice of three different stereo-viewing methods.     

Topological hierarchy-contour tracing algorithm for nests of interconnected contours

As a simple meaningful external illustration, a group of boundary contours is commonly used for representing the physical appearance of an object of interest on a 2D plane (e.g., a part drawing, CT scan image, a sliced layer, tile pattern). The illustration is understood from the composition of the contours and their attributes that include their shapes, sizes, locations and relationships. Therefore, not only is geometrical information important for contours to be useful in subsequent operations but their topological hierarchy relationships also are essential. Presented in this paper is a topological hierarchy-contour tracing algorithm that is capable of tracing nests of interconnected contours often found in practice and of identifying their topological hierarchy relationships automatically during contour tracing. The algorithm organizes contours by family rather than by group or as individual. However, contours are traced across families generation by generation instead of going deep with one family branch at a time. The outputs of the algorithm are ordered sequences of boundary pixels representing all closed contours and their topological hierarchy relationships. The algorithm has been implemented on LabVIEW, and tested with several samples to illustrate its applications.     

An automatic segmentation algorithm for 3D cell cluster splitting using volumetric confocal images

With the rapid advance of three-dimensional (3D) confocal imaging technology, more and more 3D cellular images will be available. Segmentation of intact cells is a critical task in automated image analysis and quantification of cellular microscopic images. One of the major complications in the automatic segmentation of cellular images arises due to the fact that cells are often closely clustered. Several algorithms are proposed for segmenting cell clusters but most of them are 2D based. In other words, these algorithms are designed to segment 2D cell clusters from a single image. Given 2D segmentation methods developed, they can certainly be applied to each image slice with the 3D cellular volume to obtain the segmented cell clusters. Apparently, in such case, the 3D depth information with the volumetric images is not really used. Often, 3D reconstruction is conducted after the individualized segmentation to build the 3D cellular models from segmented 2D cellular contours. Such 2D native process is not appropriate as stacking of individually segmented 2D cells or nuclei do not necessarily form the correct and complete 3D cells or nuclei in 3D. This paper proposes a novel and efficient 3D cluster splitting algorithm based on concavity analysis and interslice spatial coherence. We have taken the advantage of using the 3D boundary points detected using higher order statistics as an input contour for performing the 3D cluster splitting algorithm. The idea is to separate the touching or overlapping cells or nuclei in a 3D native way. Experimental results show the efficiency of our algorithm for 3D microscopic cellular images.     

Contour-based algorithms for generating 3D CAD models from medical images

This paper concerns contour-based algorithms for generating a 3D CAD model from medical images. The 3D model generated by contour-based algorithms can be used to generate CAM data for fabrication where the accuracy is of most concern. The overall procedure includes: (1) contour data extraction from medical images, (2) smoothing of the extracted contours, and (3) creation of a surface model from contours. For this, various methods should be applied to generate a high-quality surface model. The main contribution of this paper is to propose a new contour smoothing method, called bi-directional smoothing. The basic idea behind the proposed bi-directional smoothing method is to refine contours along both (u, v) parametric directions. Compared to conventional smoothing methods, the recontouring that comprises the first part of the method can prevent the shape of a contour from shrinking with a large number of iterations. Along with recontouring, a vertical connectivity estimation and a vertical smoothing method are also proposed. The overall procedure for this approach is demonstrated with an application example using CT images of a femur.     

Direct slicing and G-code contour for rapid prototyping machine of UV resin spray using PowerSOLUTION macro commands

Rapid prototyping processes produce parts layer by layer directly from 3D CAD models. An important technique is required to slice the geometric model of a part into layers and to generate a motion code of the cross-sectional contour. Several slicing methods are available, such as slicing from sterolithgraphy (STL) files, tolerate-error slicing, adaptive slicing, direct slicing, and, adaptive and direct slicing. This paper proposes direct slicing from 3D CAD models and generating a G-code contour of each layer using PowerSOLUTION software (Delcam International, Birmingham, UK). PowerSOLUTION includes two main modules: PowerSHAPE is used to build 3D CAD models and PowerMILL is used to produce G-Code tool paths. It provides macro language, picture files and cutting paths for secondary development work.The authors used macro commands to write an interface generating direct slicing from 3D CAD models and G-code contours for all layers. Most well-known controllers in the market accept the G-Code. Therefore, it is easier to apply this scheme in a CNC-machining center to produce rapid prototyping such as laminated object manufacturing (LOM) for complex geometries. The interface was successfully applied the interface to the UV resin spray rapid prototyping (UVRS-RP) machine that was developed to produce RP.