基于体元投影的一种非规则数据场体绘制方法

随着科学计算可视化的发展及其在实践中的应用,非规则数据场的可视化已成为当前的研究热点之一。由于非规则场中样点的大小、形状和分布是不一致的,在成像时面临更多的困难。常用的方法有光线投射法,单元投影法,以及单元投影与光线投射相结合等算法。吸取了上述算法的优点,同时利用非规则数据场的一些特性,采用了一些加速措施来加速绘制。通过实验验证,可以达到比较理想的效果。     

交互式动态体绘制及其加速算法

体绘制三维成象法是一门新兴的3D采样数据场可视化技术，在医学成象和科学可视化领域有着极为广泛的应用，但由于3D数据量大，其使用往往受到巨大计算开销的限制，因此很多研究人员致力于静态体绘制加速算法的研究，并解决医学图象三维可视化中三维体数据显示速度与成象质量问题，因而提出了一种交互式动态体绘制算法，即从任意的视点距离和视线方向进行动态编制，并在分析其算法复杂度的基础上，提出一种新的加速算法，同时使得动态体绘制过程几乎达到实时的效果，经验证，这种算法比标准算法快4～5倍。     

非规则数据场体绘制技术的研究

科学计算可视化的核心是三维数据场的可视化．当前三维可视化的研究热点是体绘制技术。文中介绍了三维非规则数据场体绘制技术的研究现状。在此基础上，通过对已有非规则数据场体绘制技术和算法的分析比较．预测非规则数据场体绘制技术今后的发展趋势以及将来应该重视的研究方向。除了改进已有算法、将各种算法结合起来外，还应该在硬件及系统加速技术方面做研究，同时结合漫游技术研究和开发高效的三维空间非规则数据场的可视化技术和并行算法。     

一种非规则数据场的体绘制算法

非规则数据场的体绘制是可视化的一个热点和难点。常用直接体绘制算法有光线投射法、单元投影法、快速体绘制算法。本文吸取了上述三种算法的优点,采用体元面投影的方法来确定光线路径;同时考虑到非规则数据场的一些特性,采取三个有效的措施大大加快了投影和求交速度;在采样中用分段积分法代替等距采样,从而进一步提高了图象质量。     

基于有效裁剪被遮挡单元的非规则数据场体绘制算法

提出了一种被遮挡单元的裁剪算法,以加速非规则数据场的体绘制过程。在基于一组平行切割平面的体绘制方法上,新算法通过对图像不透明度缓冲区中的值进行求平均操作,并将所计算的结果存储在一个与不透明度缓冲区间同样大小的平均不透明度缓冲区中,使得只需根据每一数据单元重心投影点在平均不透明度缓冲区中的值,就可得到此数据单元的可见性,从而有效裁剪掉被遮挡单元,降低需处理的数据量,加速体绘制过程。     

基于空间数据插值算法的空间散乱数据体绘制实现

体绘制技术是一种能够真实地反映空间数据场内部信息的可视化技术。在体绘制研究领域中,非规则的空间散乱数据体绘制目前仍然是一个研究热点。文中采用空间数据插值算法对散乱的原始数据进行网格化插值,然后使用光投影体绘制算法对规则网格数据进行体绘制。最后,通过新方法实现了某油藏区地下流体压力和孔隙度分布结构的体绘制。     

非规则数据场体绘制技术的研究

科学计算可视化的核心是三维数据场的可视化,当前三维可视化的研究热点是体绘制技术.文中介绍了三维非规则数据场体绘制技术的研究现状.在此基础上,通过对已有非规则数据场体绘制技术和算法的分析比较,预测非规则数据场体绘制技术今后的发展趋势以及将来应该重视的研究方向.除了改进已有算法、将各种算法结合起来外,还应该在硬件及系统加速技术方面做研究,同时结合漫游技术研究和开发高效的三维空间非规则数据场的可视化技术和并行算法.     

一种基于矢量场结构的等值面构造方法

为得到非结构矢量场中的等值面图像,给出了一种基于矢量场曲线结构的等值面构造新方法.算法利用矢量可视化映射过程中获得的曲线结构来组织数据并计算等值点,采取自适应聚类划分方法获得各个等值面包含的数据点集合后利用曲面重建算法来构造等值面.在计算等值点时,不但利用了数据场中各个数据点处的空间位置与场值大小,而且充分考虑了数据点处的矢量方向信息.实验表明,该方法能够稳定、有效地构造出非结构矢量数据场中的等值面.与基于体元的传统等值面构造方法相比,可以有效加快计算进程,得到更为准确的计算结果.     

图形硬件辅助的快速数据场体绘制方法

本文以规则数据场的体绘制过程进行了讨论，在此基础上给出一种图形硬件辅助的体绘制方法，该方法通过ＧＯｐｅｎＧＬ提供的函数和接口，利用高性能图形工作站ＳＧＩ的硬件支持快速实现规则数据场的体绘制。本文给出实现方法以及实验结果。     

光线投射算法中重采样的设计和实现

体绘制技术在医学成像和科学可视化领域有着极为广泛的应用，但由于其巨大的计算开销，限制了其实时动态体绘制的应用，因此许多研究人员致力于静态体绘制加速算法的研究，为了提高体绘制速度。分析了三维规则数据场重采样的原理。光线投射算法中对3D数据场重采样的实现方法；根据具体重建对象，提出了在3D数据场重采样中采用球形包围盒的方法，给出了人体头部和眼球的三维可视化结果，实验表明：这种算法能有效地减少重采样的计算量，并使求交计算更加简单。     

Adaptable Splatting for Irregular Volume Rendering

By employment of a footprint table in conducting intensity integration, splatting method has been very successful in rendering regular data volumes. Recently, the method has also been extended to render irregular data volumes. However, since samples in irregular volumes vary greatly in size and shape, the footprint table is unable to be employed in an efficient manner. This hinders the application of splatting approach from being used in the irregular volume case. In this paper, an adaptable splatting method is proposed, which provides an efficient way to integrate color intensity in terms of footprint table for the samples in various sizes. Experiments show that the new method may be used to produce better images without extra expense.     

基于可见性选择体元的投影成像体绘制方法

基于可见性避免了对不可见体元的合成操作,是提高体绘制速度的有效方法.为此提出了一种方法,根据体元基于体元面的相邻性及累积非透明度没有饱和的像素来挑选体元进行处理.这使得投影成像方法能有效地避免处理不可见体元.该方法不仅适用于平行投影和透视投影的成像运算,而且能处理各种规则场和非规则场.     

Interactive point-based isosurface exploration and high-quality rendering

We present an efficient point-based isosurface exploration system with high quality rendering. Our system incorporates two point-based isosurface extraction and visualization methods: edge splatting and the edge kernel method. In a volume, two neighboring voxels define an edge. The intersection points between the active edges and the isosurface are used for exact isosurface representation. The point generation is incorporated in the GPU-based hardware-accelerated rendering, thus avoiding any overhead when changing the isovalue in the exploration. We call this method edge splatting. In order to generate high quality isosurface rendering regardless of the volume resolution and the view, we introduce an edge kernel method. The edge kernel upsamples the isosurface by subdividing every active cell of the volume data. Enough sample points are generated to preserve the exact shape of the isosurface defined by the trilinear interpolation of the volume data. By employing these two methods, we can achieve interactive isosurface exploration with high quality rendering.     

Research issues in volume visualization

Volume visualization is a method of extracting meaningful information from volumetric data sets through the use of interactive graphics and imaging. It addresses the representation, manipulation, and rendering of volumetric data sets, providing mechanisms for peering into structures and understanding their complexity and dynamics. Typically, the data set is represented as a 3D regular grid of volume elements (voxels) and stored in a volume buffer (also called a cubic frame buffer), which is a large 3D array of voxels. However, data is often defined at scattered or irregular locations that require using alternative representations and rendering algorithms. There are eight major research issues in volume visualization: volume graphics, volume rendering, transform coding of volume data, scattered data, enriching volumes with knowledge, segmentation, real-time rendering and parallelism, and special purpose hardware     

一个新的体绘制加速算法

针对目前加速方式与传递函数交互设定需求的矛盾,提出了一个新的基于边缘切除原理的体绘制加速算法。算法针对两个关键难点:如何消除传递函数调整依赖性,如何识别空体素,提出了有效的绝对空体素识别准则,设计了高效的边缘空体素分离机制,构成了不依赖传递函数调整的加速模式。在保持高的图像质量的前提下,边缘切除算法具有显著的绘制速度提升。边缘切除过程在预处理阶段进行,算法参数易于选取和推广,具有广泛的适应性,非常适合需要交互设定传递函数的普及型医学图像分析系统应用。算法采用了规则的边缘切除方式,收缩后的体数据非常方便后续光线投射或溅射算法应用,可以方便地与其他各种加速方式组合使用,使不同角度的加速效果实现叠加,是当前各种主流加速技术的一个很好的互补技术。不同背景的运算实例,测试和验证了算法的有效性。     

Binary volume rendering using Slice-based Binary Shell

This paper presents a new data structure, Slice-based Binary Shell (SBS), for efficient manipulation and rendering of binary volume data. Since SBS stores only surface voxels with selected attributes of the voxels in a slice-based data structure that allows direct access to the voxels, it shows high storage and computational efficiency. This efficiency becomes more prominent when representing multiple binary objects. We also present an efficient rendering algorithm for SBS. The algorithm, based on the shear-warp technique, provides high-speed interactive rendering for binary volumes of many objects on a PC with no specialized hardware.     

Splatting errors and antialiasing

The paper describes three new results for volume rendering algorithms utilizing splatting. First, an antialiasing extension to the basic splatting algorithm is introduced that mitigates the spatial aliasing for high resolution volumes. Aliasing can be severe for high resolution volumes or volumes where a high depth of field leads to converging samples along the perspective axis. Next, an analysis of the common approximation errors in the splatting process for perspective viewing is presented. In this context, we give different implementations, distinguished by efficiency and accuracy, for adding the splat contributions to the image plane. We then present new results in controlling the splatting errors and also show their behavior in the framework of our new antialiasing technique. Finally, current work in progress on extensions to splatting for temporal antialiasing is demonstrated. We present a simple but highly effective scheme for adding motion blur to fast moving volumes     

非规则数据场并行体绘制算法

并行算法是实现体绘制加速的重要途径，然而现有的并行体制绘制算法大部分是针对规则数据场的。     

Photon Differential Splatting for Rendering Caustics

We present a photon splatting technique which reduces noise and blur in the rendering of caustics. Blurring of illumination edges is an inherent problem in photon splatting, as each photon is unaware of its neighbours when being splatted. This means that the splat size is usually based on heuristics rather than knowledge of the local flux density. We use photon differentials to determine the size and shape of the splats such that we achieve adaptive anisotropic flux density estimation in photon splatting. As compared to previous work that uses photon differentials, we present the first method where no photons or beams or differentials need to be stored in a map. We also present improvements in the theory of photon differentials, which give more accurate results and a faster implementation. Our technique has good potential for GPU acceleration, and we limit the number of parameters requiring user adjustment to an overall smoothing parameter and the number of photons to be traced.