三角形网格的分块DCT压缩

在现有的代表性三角形网格压缩方法中,先采用一定的网格遍历方法来压缩连接信息,同时用遍历路径上的相邻顶点来对每个顶点的几何坐标进行预测,以压缩几何信息.其主要缺点是只利用了遍历路径上的相邻顶点来进行预测,并没有充分去掉顶点间的相关性.其实在空间中一定局部范围内,所有顶点的坐标间都存在着一定的相关性,这些顶点虽然在空间上相邻,但并不一定在遍历路径上相邻.和图像压缩标准JPEG的思路类似,本文提出一种新的基于分块DCT的网格几何信息压缩方法.先将网格划分成很多基本同样大小的块,利用每个块内的所有顶点按遍历次序排列成一维序列后,坐标呈周期性分布的事实,采用一维DCT变换来去除块内顶点间的相关性.实验表明,分块DCT方法取得了较好的几何信息压缩性能.     

一种基于量化方法的3D模型盲水印算法

相对非盲算法而言,盲算法因在水印检测时不需要传输原始载体而使其应用更为广泛。虽然盲水印算法的鲁棒性稍弱,但仍有提高的空间。该文提出一种3D网格盲水印算法,利用伪随机数产生经过模型质心的直线,选取以直线与模型交点为球心的球形邻域作为嵌入对象,水印信息是通过抖动调制邻域内顶点的重心来嵌入的。因为重心依赖于球形邻域所有顶点坐标,所以需解决由调整后的重心逆向估计邻域内顶点坐标问题,文中给出相应的算法。水印算法除了具有抵御顶点重排的免疫力外,也把每比特水印关联到直线与模型的多个交点和多个交点的球形邻域内的成组顶点上,能较好地抵抗剪切攻击和随机噪声。实验数据说明了算法的鲁棒性能。     

基于面元模型的FDTD网格及涂敷层网格生成技术

提出了一种基于面元模型的FDTD网格剖分技术和涂敷层网格的生成技术。这种网格剖分技术可以方便地剖分封闭的面元模型和实体模型。针对均匀涂敷复杂模型难以直接产生的问题,提出在FDTD网格模型基础上,生成涂敷网格模型的方法。这种方法很容易得到任意复杂FDTD网格模型的涂敷层网格模型,克服了复杂表面模型和实体模型直接产生涂敷模型的困难。     

基于顶点删除的三角网格模型简化新方法

为进一步提高海量三角网格模型的简化速度,在经典顶点删除算法的基础上,从顶点法向量的保持、平均平面的近似获取、顶点删除后所留空洞的直接三角化3方面进行了改进.实验结果表明,改进后的顶点删除算法对三角网格模型的简化速度显著加快,简化后的模型与原模型相比在视觉上保持了良好的一致性,证明了该算法的有效性和可靠性.     

一种改进的FDTD网格剖分算法

分析了时域有限差分(FDTD)网格的生成原理,提出了一种新型非均匀FDTD网格生成算法.该算法通过读取模型获得轴线上的不连续分界点,将整个空间沿x轴、y轴和z轴方向各自分成多个区间;然后通过各区间的长度及其在模型中所处的位置,来确定该不同区间剖分时所采用的具体网格生成算法,由此得到一种新型的分区递变非均匀网格.此算法能够完全由程序实现,避免了普通网格剖分算法所带来的人为误差.在最大限度降低网格数量的同时,克服了剖分算法中由于最大网格过大而导致的高频数值色散问题,使得最后的FDTD程序具有计算时间短、收敛速度快的优点.     

基于数码照片的虚拟现实建模技术

本文首先简单介绍了虚拟现实建模技术及利用照片建模的流程,着重阐述了基于特征点的三维网格模型重建算法,然后分析了3种算法的误差,通过试验选出最佳的重建算法。文中的实例重建了某汽车覆盖件的3D网格模型,验证了该算法的可行性,达到了较为理想的效果。     

MPEG-4中基于DT网格编码算法的实现

本文按照MPEG-4标准对DT网格对象编码的要求,设计了一套完整的基于DT网格的编码算法.首先提出了网格对象编码的系统框架.在此基础上,着重研究了网格运动编码,提出了一种新的三角形运动连续预测方法及相应的残差图像处理方法.最后,对整个数据结构进行转换,使之完全按照标准规定的顺序进行编码.本文算法同H.263进行了全面的比较.结果表明,DT作为MPEG-4标准中的一种编码方法,有一定的实用价值.     

基于最优均方误差意义下的非对称3D数字水印算法

提出一种基于最优均方误差意义下的非对称3D几何模型数字水印算法.算法基本思想是,使嵌入水印受到3D几何模型几何变换和拓扑变换所带来的误差能量影响最小,即首先通过顶点的选择和排序,使嵌入的水印受到三维网格拓扑变换影响最小,然后计算排序后顶点的特征空间,将水印嵌入到最不受三维模型影响的子空间,使嵌入水印受到三维网格的几何变换影响最小.仿真得到结果,证明算法的鲁棒性.     

基于三角形网格的立体视差估计和遮挡点检测混合算法

本文提出一种新的用于立体图像编码的视差估计和遮挡点检测混合算法.其中的视差估计方法利用极线约束条件,在缩小搜索范围的同时提高了视差估计的准确性.遮挡点检测方法仅使用了匹配点唯一性约束和视差梯度限制这两个基本条件,降低了算法的复杂度.整个算法利用DT(Dalaunay triangulation)网格这一数学工具把散乱的点结合起来进行处理,使算法在实现方面更加简单化.本文算法首先对立体图像对中的左图像进行DT网格剖分,把各三角形的顶点作为"特征点"在右图像中寻找它们的匹配点.然后利用匹配点唯一性条件提取出其中一些顶点进行遮挡检测.实验结果表明,本文算法对"特征点"的视差估计比较准确,也能较为准确地检测出其中的遮挡点.借助DT 网格在图像编码方面的优势,本文算法可以方便地用于立体图像编码.     

一种基于P2P的网格资源发现算法

为了解决网格技术中节点随机加入及资源动态共享的问题,采用了P2P与网格技术有机融合的方式,改进了网格的动态性和可扩展性,建立了基于P2P的网格资源体系结构模型,并提出了一种融合DHT和蚁群算法的资源发现算法.该算法能有效地提高P2P网格环境下的资源发现性能,可以准确可靠的进行信誉值高、综合费用低的分布式资源发现.     

基于最小能量准则的参数估计圆周SAR三维成像方法

针对圆周合成孔径雷达成像模式下应用参数化估计的三维成像算法效率低、精度差的问题,提出一种基于最小能量准则的参数估计圆周SAR三维成像算法。该算法首先对成像场景进行粗略网格划分,利用参数估计的方法得到目标的粗略位置,其次利用最小能量准则和精细化网格的方法得到目标精确三维位置和散射强度系数,最后通过CLEAN技术消除已估计点带来的影响,实现场景的三维成像。仿真实验结果表明:所提成像方法能有效对圆周观测下目标进行三维成像,同时与传统算法相比,解决了传统算法效率低、对目标估计不准确的问题,验证了所提算法的有效性。     

Reconstruction of 3-D objects from cone beam projections

A true three-dimensional reconstruction (TTR) algorithm which is applicable to a cone beam with 4π detection geometry is introduced. The TTR differs from conventional slice by slice 3-D reconstruction methods. Promising areas of application for the TTR algorithm are position and X-ray computerized tomographic image reconstruction.     

SNR and temporal scalable coding of 3-D mesh sequences using singular value decomposition

A signal-to-noise ratio (SNR) and temporal scalable coding algorithm for 3-D mesh sequences using singular value decomposition (SVD) is proposed in this work. The proposed algorithm employs SVD to represent a mesh sequence with a small number of basis vectors, and encodes those basis vectors with a bit plane coder. We analytically derive the contribution of each bit plane to the reconstructed mesh quality, and transmit the bit planes in the decreasing order of their amounts of contribution. As the decoder receives more bit planes, it reconstructs higher quality mesh sequences progressively. Moreover, we develop a temporal prediction mode to improve the rate–distortion (R–D) performance further, which also supports temporal scalability. Simulation results demonstrate that the proposed algorithm yields significantly better R–D performance than conventional SVD-based coders.     

Guide wire reconstruction and visualization in 3DRA using monoplane fluoroscopic imaging

A method has been developed that, based on the guide wire position in monoplane fluoroscopic images, visualizes the approximate guide wire position in the three-dimensional (3-D) vasculature, that is obtained prior to the intervention with 3-D rotational X-ray angiography (3DRA). The method assumes the position of the guide wire in the fluoroscopic images is known. A two-dimensional feature image is determined from the 3DRA data. In this feature image, the guide wire position is determined in a two-step approach: a mincost algorithm is used to determine a suitable position for the guide wire, and subsequently a snake optimization technique is applied to move the guide wire to a better position. The resulting guide wire can then be visualized in 3-D in combination with the 3DRA dataset. The reconstruction accuracy of the method has been evaluated using a 3DRA image of a vascular phantom filled with contrast, and monoplane fluoroscopic images of the same phantom without contrast and with a guide wire inserted. The evaluation has been performed for different projection angles, and with different parameters for the method. The final result does not appear to be very sensitive to the parameters of the method. The average mean error of the estimated 3-D guide wire position is 1.5 mm, and the average tip distance is 2.3 mm. The effect of inaccurate C-arm geometry information is also investigated. Small errors in geometry information (up to 1 degrees) will slightly decrease the 3-D reconstruction accuracies, with an error of at most 1 mm. The feasibility of this approach on clinical data is demonstrated.     

Extension of the 3-D range migration algorithm to cylindrical andspherical scanning geometries

A near field three-dimensional (3-D) synthetic-aperture radar (SAR) algorithm specially tailored for cylindrical and spherical scanning geometries is presented. An imaging system with 3-D capability can be implemented by using a stepped-frequency radar which synthesizes a two-dimensional (2-D) aperture. Typical scanning geometries commonly used are planar, cylindrical, and spherical. The 3-D range migration algorithm (RMA) can be readily used with a planar scanning geometry. This algorithm is extremely accurate, preserves the phase, and corrects for the wavefront curvature. The RMA cannot be directly applied with nonplanar scanning geometries. However, as an alternative solution, we propose to backpropagate the backscattered data onto a planar aperture in the vicinity of the measurement aperture and then apply the 3-D RMA. The proposed imaging algorithm is validated both numerically and experimentally     

Effective quantisation scheme for principal components of 3-D mesh sequences

Three-dimensional (3-D) mesh sequences using the principal component analysis technique are encoded. First, rate and distortion models for principal components are developed and then a rate-distortion optimised quantisation scheme is proposed. Simulation results show that the proposed algorithm provides a much higher coding gain than conventional coders.     

Dead-reckoning sensor system and tracking algorithm for 3-D pipeline mapping

A dead-reckoning sensor system and a tracking algorithm for 3-D pipeline mapping are proposed for a tap water pipeline for which the diameter is small and the inner surface is rough due to pipe scales. The goals of this study are to overcome the performance limitations of small and low-grade sensors by combining various sensors with complementary functions and achieve robustness against a severe environment. A dead-reckoning sensor system consists of a small, low-cost micro electromechanical system inertial measurement unit (MEMS IMU) and an optical navigation sensor (used in laser mice). A tracking algorithm consists of a multi-rate extended Kalman filter (EKF) to fuse redundant and complementary data from the MEMS IMU and the optical navigation sensor and a geometry compensation method to reduce position estimation error using the end point of the pipeline. Two sets of experimental data have been obtained by driving a radio-controlled car equipped with the sensor system in a 3-D pipeline and on asphalt pavement. Our study can be used to estimate the path of a 3-D pipeline or mobile robots.     

VIDEO OBJECT SEGMENTATION BY 2-D MESH-BASED MOTION ANALYSIS

Video object extraction is a key technology in content-based video coding.A novel video object extracting algorithm by two Dimensional (2-D) mesh-based motion analysis is proposed in this paper.Firstly,a 2-D mesh fitting the original frame image is obtained via feature detection algorithm. Then,higher order statistics motion analysis is applied on the 2-D mesh representation to get an initial motion detection mask.After post-processing,the final segmenting mask is quickly obtained.And hence the video object is effectively extracted.Experimental results show that the proposed algorithm combines the merits of mesh-based segmenting algorithms and pixel-based segmenting algorithms,and hereby achieves satisfactory subjective and objective performance while dramatically increasing the segmenting speed.     

Three-Dimensional Microwave Breast Imaging: Dispersive Dielectric Properties Estimation Using Patient-Specific Basis Functions

Breast imaging via microwave tomography involves estimating the distribution of dielectric properties within the patient's breast on a discrete mesh. The number of unknowns in the discrete mesh can be very large for 3-D imaging, and this results in computational challenges. We propose a new approach where the discrete mesh is replaced with a relatively small number of smooth basis functions. The dimension of the tomography problem is reduced by estimating the coefficients of the basis functions instead of the dielectric properties at each element in the discrete mesh. The basis functions are constructed using knowledge of the location of the breast surface. The number of functions used in the basis can be varied to balance resolution and computational complexity. The reduced dimension of the inverse problem enables application of a computationally efficient, multiple-frequency inverse scattering algorithm in 3-D. The efficacy of the proposed approach is verified using two 3-D anatomically realistic numerical breast phantoms. It is shown for the case of single-frequency microwave tomography that the imaging accuracy is comparable to that obtained when the original discrete mesh is used, despite the reduction of the dimension of the inverse problem. Results are also shown for a multiple-frequency algorithm where it is computationally challenging to use the original discrete mesh.      

基于二维网孔互连网络的并行矩阵乘算法

矩阵乘法是数值分析领域中一种十分常用的基本运算，被广泛应用于模式识别、图像和信号处理。由于矩阵运算具有局部性、一致性的特点，特别适合用二维网孔并行计算机来实现。文章讨论了基于二维网孔互连网络的矩阵乘并行算法的实现，首先给出了一种正方网孔处理机阵列的并行算法，然后将其推广到长方网孔处理机阵列中。最后通过在LSMPP计算机的应用，证明算法是可行的、有效的。