一种基于八邻域深度差的点云边缘提取算法

提出了一种基于八邻域深度差(8N-DD)的点云边缘提取算法。算法根据目标特征的点云,对每个特征点沿深度方向进行垂直投影并对投影点进行栅格划分,计算出每个栅格内投影点所对应深度的平均值作为该栅格的深度值;然后比较每个栅格与其八邻域栅格的深度差,根据深度差判断该栅格内是否存在边缘点,并采用排序法从栅格内筛选出目标的点云边缘点。针对含有非孔洞和孔洞的两种典型点云数据,利用八邻域深度差算法进行点云边缘提取,验证了算法的有效性。     

基于线段扫描的碎纸片边界检测算法研究

提出了基于短线段扫描的碎纸片图像边缘检测算法,该算法用一系列短线段拟合碎纸片的边缘,这些短线段首尾相连,组成碎片边缘拟合曲线;在碎片边界拟合过程中,使用直线插补方法获得线段离散点,通过点的属性来判断线段与碎片边缘的拟合程度,同时使用圆插补方法旋转扫描线段,以保证线段扫描方向连续而没有间断;还分析了碎片图像噪声分布特点,提出了噪声点去除方法;同时提出了多碎片图像边缘检测方法.根据所提出的算法,研制了碎纸片边缘检测程序,并利用这些程序对两实际例子进行了分析,分析结果表明所提出的碎片边缘检测方法是可靠和有效的.     

The development of a technique for 3D complex surface reconstruction from unorganized point cloud

In this paper, we propose a new neural network based on our two-level adaptive hierarchical clustering algorithm. The algorithm is to manage unorganized points, so that the triangular mesh models can be correctly obtained by applying the triangular mesh creation algorithm. We also develop adaptive self-flipping triangle edges to improve triangular mesh structure. Only one parameter, the maximal edge length of triangle, is needed in the neural network. The proposed two-level consists of the first level for clustering the cloud of points that has same order of the maximal edge length into a same cluster and the second level for generating triangular surface model or drape surfaces over the points of the same cluster. The normal vector for the generated triangular 3D surface model can be obtained from the second level. This helps to generate the STL file or stereolithography format. From the experimental results it can be shown that the proposed method is very effective for clustering unorganized point clouds for generating a triangular mesh of complex surfaces.     

A robust approach to edge detection of scanned point data

In reverse engineering, segmentation is used to divide a point data set into subsequent regions according to its shape. It is vital for interpretation of discrete scanned data since surface reconstruction can be accomplished one-by-one on a given region. Edge detection is crucial to the segmentation process. The level of edge detection depends on the complexity of the part, and it determines the eventual success or failure of the reverse engineering (RE) process. This paper proposes a novel approach to the edge detection of 3D points based on a region growing technique. The proposed algorithm consists of two parts. First, polygonal meshes are generated to the scanned point data using the Delaunay triangulation algorithm. Second, the normal vector and the area of a polygonal mesh are checked to find boundary meshes using cost criteria (angle criterion and area criterion) based upon a region growing technique. The region growing technique aggregates meshes into a region until the area of aggregated meshes reaches an area threshold from a series of seed meshes. The proposed edge detection method is found to be effective when compared with other methods.     

逆向工程中的参数化建模技术及应用

逆向参数化建模方法是在逆向工程的基础上,加入参数化技术形成的一种新的建模方法,该方法不仅有利于提取原始设计信息,重建更为精确的CAD模型;而且易于实现模型的参数化修改,推动产品的创新设计。简要介绍了逆向工程的概念和逆向参数化建模方法,以汽车后视镜为例,利用Geomagic Studio软件对扫描点云进行处理,拟合出特征识别后的初始曲面。通过参数转换功能把初始曲面导入Solidworks中进行编辑,最后得到汽车后视镜的参数化模型。实践表明这为反求模型的参数化建模提供了一种切实可行的方法。     

利用邻域方向分布的机载激光雷达点云建筑物外轮廓提取

机载激光雷达点云密度分布不均、建筑物形状不规则且复杂多样等多种因素,导致现有建筑物轮廓提取方法存在参数难以设置、适应性较差等问题,为此本文提出一种利用邻域方向分布的机载激光雷达点云建筑物外轮廓提取方法.首先采用固定邻域点数分析各点的邻域方向分布,以获取不同邻域方向间的夹角,根据建筑物外轮廓点的特点,定义潜在轮廓点并将其...     

基于三坐标测量的模具反求设计

论述了从三坐标测量机得到的数据重建模具CAD模型的工作过程,包括点云的预处理如点云对齐、误差点剔除;曲面重构:包括点云的网格化、孔洞填充、边界处理、曲面拟合及曲面评估.利用Geomagic软件完成了对某梁的逆向设计,证明了反求工程理论的可行性.     

基于线结构光的水下旋转扫描高精度测量方法研究

随着海洋工程领域的不断发展，如何高精度地获取水下物体的三维点云具有重要学术和应用价值。由于光在不同介质中传播会引起光路的变化，导致水下线结构光视觉测量获得的点云受折射畸变影响，精度降低。针对上述问题，设计了一种基于线结构光的水下旋转扫描测量系统。提出了一种轴眼标定算法，能够将多视角水下点云配准到统一坐标系中。提出了一种引人折射补偿的水下相机成像模型，该模型可准确的描述激光在不同介质间传播过程中的光路，基于水下激光平面方程的约束，对水下点云进行折射校正，提高了水下点云的重建精度。水下测量实验结果表明，提出的高精度测量方法能够获得水下物体的三维点云信息，可测量水下目标的尺寸信息，距离目标30~80cm 时测量精度达到0.2mm，满足了水下目标三维高精度测量要求，     

基于逆向工程的空调遥控器三维模型设计研究

针对市场对家电产品开发周期日益苛刻的需求,为满足家电产品快速开发,快速更新的需要,以空调遥控器外形三维模型重建与再设计为例,从遥控器外形点云数据的快速测量、点云数据的处理、点云几何拓扑结构分析、主辅曲面重建以及结合新产品开发需求再设计遥控器三维模型结构等方面对家电产品的快速设计进行了研究。对基于逆向工程的家电产品三维模型快速设计方法进行了归纳,提出一种正、逆向设计相结合的产品三维模型快速设计方法。研究结果表明,基于逆向工程技术的再设计方法,有利于提高家电产品设计效率,为家电类产品的开发提供了一种方便、快捷的手段。     

逆向工程中孔洞的分段填充方法研究

由于物体曲面形状复杂和扫描设备的原因,扫描得到的点云中难免有孔洞出现。为产生封闭的实体曲面,需要对孔洞进行填充。国内外许多学者提出了许多关于孔洞填充的算法,不过这些算法主要针对曲率较小区域的孔洞。这里提出了一种新的改进算法,解决了高曲率区域的复杂孔洞填充问题。通过将复杂孔洞分割成许多简单子孔洞,再将各子孔洞分别填充,完成复杂孔洞填充。最后对孔洞填充区域进行光顺和细化处理,并更新其拓扑信息。     

B-spline surface reconstruction and direct slicing from point clouds

The issue of surface reconstruction and slicing from point clouds has been receiving extensive attention recently. When using the B-spline surface fitting technique, the difficulty of parameterization exists. At the same time, for interfacing between reverse engineering and rapid prototyping, the point clouds are usually converted to an stereolithography (STL) model. This leads to a huge file size and requires expert modeling skills. The objective of this work is to establish a base surface parameterization and direct slicing strategy for scattered data based on a cross-sectional design technique. We first present a new method of directly extracting sectional contours from point clouds. Then, we create a base surface by skinning the primary boundary curves and interior sectional curves. Based on a good parameterization, the final surface is achieved with tight tolerance. Several practical examples have demonstrated the feasibility of the proposed method. It can be widely used in Number Control (NC) machining and rapid prototyping.     

汽车覆盖件逆向工程设计研究与应用

逆向工程在汽车覆盖件设计过程中得到了越来越广泛的应用.以某车型翼子板的逆向设计为例,采用数码摄影和光学扫描相结合的非接触式基于光学原理的ATOS & TriTop系统得到数据点,针对汽车覆盖件的特点,结合逆向工程软件Imageware,详细阐述了由大量数据点进行曲线、曲面反求的汽车覆盖件逆向工程设计方法.     

基于边缘预测和稀疏约束的湍流图像盲复原

大气湍流严重影响天文观测图像的成像效果,必须对退化图像进行处理才能获得清晰的图像。经典的湍流退化图像盲复原算法(IBD、NAS-RIF等)使用的先验知识过于简单,导致很多场合不能获得较优的复原效果。近几年提出的稀疏表达理论,使用自然图像边缘的稀疏先验信息指导图像复原,能复原出较多的细节,但它直接使用模糊图像的梯度图像指导点扩散函数复原,而模糊的梯度图像包含很多噪声和伪边缘,无效的梯度会误导点扩散函数的估计,从而使复原图像中出现较多伪迹。针对上述问题,提出了一种基于边缘预测和稀疏比值正则约束的湍流退化图像盲复原算法,该算法首先从当前的复原图像中预测出有效的边缘,然后将边缘预测信息与自然图像边缘的稀疏先验信息相结合指导点扩散函数复原,得到点扩散函数后,再通过一种非盲复原算法恢复出当前的目标图像,并将此复原图像作为下一次边缘预测的输入图像,如此迭代循环直到求出最终清晰的目标图像。所提算法结合了图像的先验信息与退化图像自身包含的有效信息,能有效抑制图像复原过程中产生的伪迹,获得令人满意的结果。针对多幅模拟的湍流退化图像进行仿真测试,验证了算法的有效性。     

基于孔洞分割的点云孔洞填充算法

逆向设计过程中,由于物体曲面形状复杂和扫描设备的原因,扫描得到的点云中难免有孔洞出现。为了产生封闭的实体曲面,需要对孔洞进行填充。国内外许多学者提出了许多关于孔洞填充的算法,不过这些算法主要针对曲率较小区域的孔洞。基于此,提出了一种新的改进算法,解决了高曲率区域的复杂孔洞填充问题。通过孔洞在投影面上的投影,判断是否存在交叉点,将孔洞分为简单的孔洞和复杂的孔洞。当遇到复杂孔洞时,采用分割的方法把复杂的孔洞分割成简单的孔洞,再对其进行修补。     

Point cloud comparison under uncertainty. Application to beam bridge measurement with terrestrial laser scanning

In this paper a methodology to compare two point clouds of an object, obtained with different equipment or in different conditions, is proposed. First, the point clouds are registered to the same reference system using an iterative algorithm that performs a rigid body transformation. Then, the standard deviation of the measurements is estimated, in order to evaluate the uncertainty in the measurements. Afterwards, two surfaces are adjusted to each of the point clouds by means of a kernel smoothing technique and compared. Finally, the effect of uncertainty in the point coordinates is considered by means of a bootstrap analysis.The methodology was used to compare two point clouds of a beam bridge measured using two different types of terrestrial laser scanner (time-of-flight and phase-shift based systems). According to the results obtained, some statistically significant differences exist between both point clouds.     

Reverse engineering of turbine blades based on design intent

The purpose of this paper is to describe a new approach to process the data points measured from turbine blade airfoils in order to make a valid shape via reverse engineering method. Currently, preliminary B-rep models can be created by fitting surfaces to point clouds using a 3D laser scanner. In case of a turbine blade, due to high shape complexity, the resulting model is often unsuitable in practice. A small change in blade geometry can lead to a large change in turbine performance. Therefore, control of the blade shape is critical to the design process. Authors believe that the only way to capture the valid shape of a blade airfoil out of the many manufacturing deviations is to incorporate design key-points during reverse engineering. Implementation of the new method using segmentation and constrained fitting algorithm (SCFA) on a heavy-duty industrial gas turbine blade has been reported and discussed.     

In-field performance of an optical digitizer for the reverse engineering of free-form surfaces

The use of OPL-3D, a robust, flexible and easy-to-use optical digitizer, in conjunction with reverse engineering procedures is presented. The optical digitizer is used as a stand-alone (i.e., not in tandem with popular CMM’s) system, whose output point clouds can be manipulated, by means of both specifically-designed software and high-performance commercial software, to produce mesh surfaces and NURBS of the acquired shape. The digitizer-process combination yields accurate digital replicas of the target object, the accuracy of the whole combination being on the order of 1/1500 of the measurement range. The speed of acquisition, combined with the above high accuracy, the ease of use and the fact that recalibration is seldom required makes the digitizer ideal for reverse engineering in an enormous number of applications ranging from automotive to biomedical.     

基于法线方向的点包容检测

过待定点作一射线,此射线可能与多边形的某几条边有交点,从待定点向这条边的两端点作两个向量,求这两向量的法线方向,对法线方向进行计数。若法线方向为正向,将计数器加1;若法线方向为反向,将计数器减1。求待定点与每条相交边的两向量的法线方向并计数,当法线方向的正反次数相同时,待定点在多边形外,否则在多边形内。此算法避免了某些其他算法的错误,计算量很小,简单易行。通过编写程序计算验证表明,算法简单有效、稳定可靠,对简单多边形、自相交多边形及带孔多边形等多类情况同样适用。     

基于局部样本增益优化的α-shape曲面拓扑重建

在曲面重建中,提高棱边特征重建精度是逆向工程和计算机辅助设计制造等领域的难点问题。采用样点的近似拓扑近邻点集作为曲面局部样本,对α-shape算法进行优化,使α-shape尺度阈值能更为准确地反映样点分布密度,从而提高α-shape曲面拓扑重建结果的正确性。样点的近似拓扑近邻点集的获取本质上是欧氏近邻点集的增益优化,使后者向邻近的稀疏区域适度延伸,从而弥补因数据分布不均匀而导致的拓扑邻域信息缺失。基于增益优化后的样点近邻点集并结合曲面重建先验知识可确定α-shape尺度阈值,使α-shape曲面拓扑重建过程中尺度阈值可自适应调整。试验表明:该算法使所得网格曲面基本不含孔洞和棱边凹痕,能更好保持棱边特征的形位精度,可减少初次过滤结果中的非流形面片,同时具有与主流Delaunay网格过滤算法相近的重建效率。     

具有复杂形状内腔的斗齿零件的曲面重构技术研究

为获取外形不规则且具有复杂形状内腔的挖掘机斗齿形状、尺寸等数字信息,基于实物反求工程技术路线,对其进行逆向设计曲面重构技术研究.对曲面反求过程中的数据采集、对齐点云、数据分割及曲面重构等环节有系统的分析总结,对型面数量多的斗齿点云进行了有效的数据分割,提出了基于零件结构特征的直接交互式点云分割法,且反求得到的斗齿曲面精度满足要求,该方法对复杂内型面零件的反求有一定的借鉴作用.