体数据的多精度等值面抽取

Marching Cubes（MC）算法是一个被广泛应用的体数据等值面抽取算法H本文提出的Marching Boxes（MB）算法结合显示所需精度，对MC算法作了优化，减少了由MC算法生成的三角面片数，使实时观察体数据成 为可能。在保留图象细节的前提下MB算法输出的三角面片数比MC算法减少了一半以上,从而加快了体数据的 面绘制速度.     

基于标签化医学图像的多阈值三维重建算法

针对传统面绘制重建方法 MC无法一次性提取多个阈值器官的问题,提出一种将MRI图像中靶区及其周边组织进行标签化分割的多阈值三维重建算法。该算法通过将二维图像中的多阈值器官标签化为简单的整数,降低提取等值面时的数据存储量,进而提高等值面的绘制速度。同时,定义了多阈值三维重建时体素顶点索引方式和等值面相交形态,减少了传统MC算法提取多个阈值器官时存在三角面片与顶点复用的情况,且仅需一次性扫描即可重建多个器官等值面。实验结果表明,本文算法较传统MC算法,重建器官数量越多,器官彼此结构越紧密,三角面片与顶点复用情况减少越明显,在保证重建效果的同时,绘制速度可提高30%。     

基于最近邻Marching Cubes的医学图像三维重建

在医学图像三维可视化中,移动立方体算法（Marching Cubes,MC）是面绘制的经典算法。针对MC算法计算插值点导致执行速度慢、效率不高的缺点,提出一种基于最近邻逼近的MC算法,该方法在n次等分点量化序列中寻找等值面最近邻点代替线性或非线性插值,既避免了插值的大量计算又保证了误差精度,还可改善三角面片结构。利用可视化工具开发包VTK对人体脸部和脚部CT数据集进行三维重建,实验表明改进算法明显缩短了绘制时间,提高了重建效率。     

三维模型有向三角面片链码压缩方法

首先提出一种适用于三角面片链码算法的改进MC规格化方法,使用单位为2的体素作为改进MC算法中的单位体素,并使用其中的27个顶点重新构建等值面,最终获取高质量的规格化三角网格模型.在新的规格化模型上提出一种新的面片遍历方式,在三角面片链码算法的基础上,采用优先遍历右连接面片原则,控制面片的遍历方向,该方法能够减少面片遍历...     

基于改进MC算法的医学图像三维重建研究

MC算法是经典的三维重建方法。但它重建时效率低,产生了大量的三角面片,增加了绘制的时间和空间。而且存在拓扑二义性,会使重建后的图像产生空洞的结构,重建的效果也不是很理想。对此,提出相应的改进策略。介绍了如何提高计算效率、减少三角面片数量、消除二义性和平滑图像等方面。通过实验证明了改进算法的可行性。     

海量断层数据三维重建算法优化

采用MC(Marching Cubes)算法进行三维重建时,如果要利用结果数据进行拼接、平滑、简化等进一步处理,就需要取得各三角面片的拓扑关系.提出"双缓存、三层交换"思想,对MC算法的实现流程实施改进,使得算法程序既能满足海量断层数据处理的要求,又能使算法程序性能得到一定的提升.     

一种点面混合的复杂三维模型加速绘制方法

在主流个人计算机硬件条件下,为加速百万以上三角面片构成的复杂稠密几何模型的绘制速度,综合基于几何的建模与绘制方法GBMR和基于点的建模与绘制方法PBMR的优点,提出了一种同时使用三角面片和点作为基本单元进行对象建模与绘制的点面混合方法．在预处理阶段,对模型表面进行网格分割,存储子块三角面片和顶点点云数据,同时对顶点点云按顶点重要度排序并序列化为线性结构．在实时绘制阶段,进行视相关的裁剪和背面剔除,不同子块按视点距离分别由三角形或点进行绘制．以上过程充分利用图形处理单元GPU,实现了基于GPU的点面混合的对象连续多分辨率绘制,有效地提高了复杂模型的绘制效率．     

面向装配的飞行器超大模型实时可视化技术

针对飞行器大数据量CAD模型实时绘制困难的问题,提出一种LOD自动批处理生成以及实时自适应绘制方法.以零部件为处理对象以保留装配树信息,结合模型分割完成超大模型简化,并根据计算机存储能力、实时绘制能力以及CAD模型特点,实现了定量的LOD自动批处理生成;以精确遮罩查询为基础,根据计算机实时绘制负载和CAD模型面片密度,动态地调整LOD精度等级,使得各个模型的精度基本一致,避免了传统算法的弊端,实现了LOD实时自适应绘制,并进行了优化.实验结果表明:采用文中技术处理千万级三角面片的模型约1h完成LOD生成,并可在普通计算机上实现实时的自适应绘制.     

三维表面模型的快速切割算法

讨论了一个三维表面模型的快速切割算法.由改进的MC(marching cubes)方法抽取、构成了连续曲面的分组信息以及构成曲面的三角面片的层次包围盒信息，并利用记录了上述信息的B+树模型,完成了三维表面模型的快速切割算法.讨论的算法通过充分发掘和利用MC算法中所隐含的三角面片的包围盒信息和物体各部分间的三维相关信息，在对三维表面模型进行切割计算时,可以快速定位交点，并且根据交点信息，不必遍历模型的所有三角面片，而直接完成对整个被切割模型的分割.研究背景是髋关节整型手术中平面手术刀及球面手术刀对髋关节的切     

工业CT数据场面绘制和体绘制改进算法研究

工业CT图像的重建速度和精度是工业CT产品的两个重要指标。针对面绘制的MC算法提出了一种基于相似性区域分割的三维工业图像表面重建算法,实现了准确分割,并利用分割结果精确地提取等值面,显著提高了检测效率;针对体绘制的光线投射算法提出了一种基于二维最大熵阈值的分割预处理方法,利用二维直方图熵最大化寻找阈值的最佳组合,能有效减少重建体数据量,实测数据表明体绘制速度明显提高。     

A type-merging algorithm for extracting an isosurface from volumetric data

A new approach for reducing the number of triangles representing an isosurface in volumetric data is presented. The basic idea is to classify the configurations of the marching cubes approach into types. Surface patches traversing neighboring cubes of the same type can be merged into patches, which can be approximated with fewer and larger triangles. Experimental results show that the number of triangles is about 50% of that obtained with the marching cubes algorithm, with comparable image quality. The execution time is somewhat longer than that of the marching cubes algorithm.     

针对脊柱CT图像三维重构MC方法的改进

对原始MC（Marching Cubes）方法存在的问题和局限进行改进,并以此为基础重构脊柱三维模型,使之满足术前分析和远程手术的要求。采用双曲渐近线判别式消除面二义性问题,利用插值函数的空间连续性解决体二义性问题。提出基于对象相关性的cube连通性判断,减少三角面片过多的问题,进一步采用Decimation算法消减面片网格。实验证明了上述改进方法的有效性和正确性,可得到良好的三维重构效果。     

Adaptive marching cubes

The marching cubes algorithm (MC) is a powerful technique for surface rendering that can produce very high-quality images. However, it is not suitable for interactive manipulation of the 3D surfaces constructed from high-resolution volume datasets in terms of both space and time. In this paper, we present an adaptive version of MC called adaptive marching cubes (AMC). It significantly reduces the number of triangles representing the surface by adapting the size of the triangles to the shape of the surface. This improves the performance of the manipulation of the 3D surfaces. A typical example with the volume dataset of size 256×256×113 shows that the number of triangles is reduced by 55%. The quality of images produced by AMC is similar to that of MC. One of the fundamental problems encountered with adaptive algorithms is thecrack problem. Cracks may be created between two neighboring cubes processed with different levels of subdivision. We solve the crack problem by patching the cracks using polygons of the smae shape as those of the cracks. We propose a simple, but complete, method by first abstracting 22 basic configurations of arbitrarily sized cracks and then reducing the handling of these configurations to a simple rule. It requires onlyO(n ²) working memory for an×n×n volume data set.     

A Fast Ambient Occlusion Method for Real-Time Plant Rendering

Global illumination effects are crucial for virtual plant rendering. Whereas real-time global illumination rendering of plants is impractical, ambient occlusion is an efficient alternative approximation. A tree model with millions of triangles is common, and the triangles can be considered as randomly distributed. The existing ambient occlusion methods fail to apply on such a type of object. In this paper, we present a new ambient occlusion method dedicated to real time plant rendering with limited user interaction. This method is a three-step ambient occlusion calculation framework which is suitable for a huge number of geometry objects distributed randomly in space. The complexity of the proposed algorithm is O（n）, compared to the conventional methods with complexities of O（n^2）. Furthermore, parameters in this method can be easily adjusted to achieve flexible ambient occlusion effects. With this ambient occlusion calculation method, we can manipulate plant models with millions of organs, as well as geometry objects with large number of randomly distributed components with affordable time, and with perceptual quality comparable to the previous ambient occlusion methods.     

采用空间分割的平滑曲面重构算法

面绘制是科学计算可视化中一个重要的研究方向，移动立方体是实现面绘制的一个重要算法，八叉树是一种有效的表示三维物体的方法，该文在八叉树生成的基础上，提出一种基于空间分割的表面重构算法，将绘制空间分别按X轴、Y轴和Z轴进行分割，生成的树的节点个数小于等于8个，与八叉树方法相比，减少了所生成叶结点数量，再通过移动立方体算法生成三角面片。三角面片通过平滑处理，提高了图形显示质量。     

Multiresolution Isosurface Extraction with Adaptive Skeleton Climbing

An isosurface extraction algorithm which can directly generate multiresolution isosurfaces from volume data is introduced. It generates low resolution isosurfaces, with 4 to 25 times fewer triangles than that generated by marching cubes algorithm, in comparable running times. By climbing from vertices (0-skeleton) to edges (1-skeleton) to faces (2-skeleton), the algorithm constructs boxes which adapt to the geometry of the true isosurface. Unlike previous adaptive marching cubes algorithms, the algorithm does not suffer from the gap-filling problem. Although the triangles in the meshes may not be optimally reduced, it is much faster than postprocessing triangle reduction algorithms. Hence the coarse meshes it produces can be used as the initial starts for the mesh optimization, if mesh optimality is the main concern.     

一种改进的MC算法

为了对等值面与子等值面进行提取和分组,在MC算法原理的基础上,提出了一种改进的等值面提取与子等值面分组算法。该算法首先将数据场分解为点、棱边、面与体元的拓扑结构;然后在整个数据场范围内求所有棱边与等值面的交点,并在面内连接交点形成面与等值面的交线,交线在体元内连接生成空间多边形;接着通过三角化各个体元内的空间多边形得到由顶点表与三角形表组成的等值面数据;最后根据三角形在顶点处的连接关系,采用种子算法对属于同一子等值面的三角形与顶点进行标记,属于同一子等值面的顶点与三角形将被存放在独立的顶点表与三角形表中。实验结果表明,该算法可以高效地实现等值面提取与子等值面的分组。     

Real-time motion blur using extruded triangles

Several algorithms have been introduced to render motion blur in real time by solving the visibility problem in the spatial-temporal domains. However, some algorithms render at interactive frame rates but have artifacts or noise. Therefore, we propose a new algorithm that renders real-time motion blur using extruded triangles. Our method uses two triangles in the previous frame and the current frame to make an extruded triangle then send it to rasterization. By using the standard rasterization, visibility determination is performed efficiently. To solve the occlusion between extruded triangles for a given pixel, we introduce a combination solution using a sorting in front-to-back order and bitwise operations in the spatial-temporal dimensions. This solution ensures that only non-occluded extruded triangles are shaded. We further improve performance of our algorithm using a coverage map.     

On approximating contours of the piecewise trilinear interpolantusing triangular rational quadratic Bezier patches

Given a three dimensional (3D) array of function values F_i,j,k on a rectilinear grid, the marching cubes (MC) method is the most common technique used for computing a surface triangulation T approximating a contour (isosurface) F(x, y, z)=T. We describe the construction of a C⁰ continuous surface consisting of rational quadratic surface patches interpolating the triangles in T. We determine the Bezier control points of a single rational quadratic surface patch based on the coordinates of the vertices of the underlying triangle and the gradients and Hessians associated with the vertices