A particle system for interactive visualization of 3D flows

We present a particle system for interactive visualization of steady 3D flow fields on uniform grids. For the amount of particles we target, particle integration needs to be accelerated and the transfer of these sets for rendering must be avoided. To fulfill these requirements, we exploit features of recent graphics accelerators to advect particles in the graphics processing unit (GPU), saving particle positions in graphics memory, and then sending these positions through the GPU again to obtain images in the frame buffer. This approach allows for interactive streaming and rendering of millions of particles and it enables virtual exploration of high resolution fields in a way similar to real-world experiments. The ability to display the dynamics of large particle sets using visualization options like shaded points or oriented texture splats provides an effective means for visual flow analysis that is far beyond existing solutions. For each particle, flow quantities like vorticity magnitude and A2 are computed and displayed. Built upon a previously published GPU implementation of a sorting network, visibility sorting of transparent particles is implemented. To provide additional visual cues, the GPU constructs and displays visualization geometry like particle lines and stream ribbons.     

Flow charts: visualization of vector fields on arbitrary surfaces

We introduce a novel flow visualization method called Flow Charts, which uses a texture atlas approach for the visualization of flows defined over curved surfaces. In this scheme the surface and its associated flow are segmented into overlapping patches which are then parameterized and packed in the texture domain. This scheme allows accurate particle advection across multiple charts in the texture domain, providing a flexible framework that supports various flow visualization techniques. The use of surface parameterization enables flow visualization techniques requiring the global view of the surface over long time spans, such as Unsteady Flow LIC (UFLIC), particle-based Unsteady Flow Advection-Convolution (UFAC), or dye advection. It also prevents visual artifacts normally associated with view-dependent methods. Represented as textures, Flow Charts can be naturally integrated into GPU flow visualization techniques for interactive performance.     

Illuminated 3D Scatterplots

In contrast to 2D scatterplots, the existing 3D variants have the advantage of showing one additional data dimension, but suffer from inadequate spatial and shape perception and therefore are not well suited to display structures of the underlying data. We improve shape perception by applying a new illumination technique to the pointcloud representation of 3D scatterplots. Points are classified as locally linear, planar, and volumetric structures—according to the eigenvalues of the inverse distance-weighted covariance matrix at each data element. Based on this classification, different lighting models are applied: codimension-2 illumination, surface illumination, and emissive volumetric illumination. Our technique lends itself to efficient GPU point rendering and can be combined with existing methods like semi-transparent rendering, halos, and depth or attribute based color coding. The user can interactively navigate in the dataset and manipulate the classification and other visualization parameters. We demonstrate our visualization technique by showing examples of multi-dimensional data and of generic pointcloud data.     

Output-sensitive 3D line integral convolution

We propose an output-sensitive visualization method for 3D line integral convolution (LIC) whose rendering speed is largely independent of the data set size and mostly governed by the complexity of the output on the image plane. Our approach of view-dependent visualization tightly links the LIC generation with the volume rendering of the LIC result in order to avoid the computation of unnecessary LIC points: early-ray termination and empty-space leaping techniques are used to skip the computation of the LIC integral in a lazy-evaluation approach; both ray casting and texture slicing can be used as volume-rendering techniques. The input noise is modeled in object space to allow for temporal coherence under object and camera motion. Different noise models are discussed, covering dense representations based on filtered white noise all the way to sparse representations similar to oriented LIC. Aliasing artifacts are avoided by frequency control over the 3D noise and by employing a 3D variant of MIPmapping. A range of illumination models is applied to the LIC streamlines: different codimension-2 lighting models and a novel gradient-based illumination model that relies on precomputed gradients and does not require any direct calculation of gradients after the LIC integral is evaluated. We discuss the issue of proper sampling of the LIC and volume-rendering integrals by employing a frequency-space analysis of the noise model and the precomputed gradients. Finally, we demonstrate that our visualization approach lends itself to a fast graphics processing unit (GPU) implementation that supports both steady and unsteady flow. Therefore, this 3D LIC method allows users to interactively explore 3D flow by means of high-quality, view-dependent, and adaptive LIC volume visualization. Applications to flow visualization in combination with feature extraction and focus-and-context visualization are described, a comparison to previous methods is provided, and a detailed performance analysis is included.     

自适应分块细节水平的多分辨率体绘制方法

采用多分辨率体绘制医学数据时,一般使用相同的阈值或者细节水平生成纹理,很难处理大规模数据,为此提出一种多分辨率纹理生成方法.首先采用基于方差加权香农熵的自适应分块细节水平选择算法建立原始体数据的统一划分多分辨率表示;然后采用分块纹理重组操作,生成具有更高压缩率的体数据多分辨率压缩纹理.文中方法已在GPU上实现,而且实验结果对比表明,该方法既能得到较好的体数据压缩率,又能完成高质量的绘制.     

Particle Level Set Advection for the Interactive Visualization of Unsteady 3D Flow

Typically, flow volumes are visualized by defining their boundary as iso‐surface of a level set function. Grid‐based level sets offer a good global representation but suffer from numerical diffusion of surface detail, whereas particle‐based methods preserve details more accurately but introduce the problem of unequal global representation. The particle level set (PLS) method combines the advantages of both approaches by interchanging the information between the grid and the particles. Our work demonstrates that the PLS technique can be adapted to volumetric dye advection via streak volumes, and to the visualization by time surfaces and path volumes. We achieve this with a modified and extended PLS, including a model for dye injection. A new algorithmic interpretation of PLS is introduced to exploit the efficiency of the GPU, leading to interactive visualization. Finally, we demonstrate the high quality and usefulness of PLS flow visualization by providing quantitative results on volume preservation and by discussing typical applications of 3D flow visualization.     

基于GPU的风暴数据场多维纹理混合绘制

在气象领域,三维风暴数据场可视化是风暴监测及灾害预测的重要技术手段之一。可视化效率及质量直接影响到风暴体分析研究的准确性和时效性。针对传统的二维、三维纹理映射体绘制方法进行了研究,提出了一种基于GPU的风暴数据场多维纹理混合绘制技术。该方法采用了三维纹理存储风暴数据场并结合代理几何体动态生成方法,克服了传统方法中纹理数据冗余的问题,并保证了模型的三维交互流畅性。该方法中提出的纹理映射光滑重采样策略,显著提高了风暴体模型显示效果,并在一定程度上避免了CPU-GPU通信瓶颈。     

Sparse GPU Voxelization of Yarn‐Level Cloth

Most popular methods in cloth rendering rely on volumetric data in order to model complex optical phenomena such as sub‐surface scattering. These approaches are able to produce very realistic illumination results, but their volumetric representations are costly to compute and render, forfeiting any interactive feedback. In this paper, we introduce a method based on the Graphics Processing Unit (GPU) for voxelization and visualization, suitable for both interactive and offline rendering. Recent features in the OpenGL model, like the ability to dynamically address arbitrary buffers and allocate bindless textures, are combined into our pipeline to interactively voxelize millions of polygons into a set of large three‐dimensional (3D) textures (>10⁹ elements), generating a volume with sub‐voxel accuracy, which is suitable even for high‐density woven cloth such as linen.     

3D非均匀直线网格GPU体绘制方法研究

计算机图形硬件技术的快速发展可以用来加速可视化过程,为此针对非均匀直线网格,给出了基于均匀辅助网格的CPU光线投射算法、基于辅助纹理的GPU光线投射算法,以及基于切片的3D纹理体绘制算法,并在Nvidia Geforce 6800GT图形卡上对这些算法进行了测试。结果表明,GPU算法远远快于CPU算法,而基于切片的3D纹理体绘制算法则快于GPU光线投射算法。     

Special relativistic visualization by local ray tracing

Special relativistic visualization offers the possibility of experiencing the optical effects of traveling near the speed of light, including apparent geometric distortions as well as Doppler and searchlight effects. Early high-quality computer graphics images of relativistic scenes were created using offline, computationally expensive CPU-side 4D ray tracing. Alternate approaches such as image-based rendering and polygon-distortion methods are able to achieve interactivity, but exhibit inferior visual quality due to sampling artifacts. In this paper, we introduce a hybrid rendering technique based on polygon distortion and local ray tracing that facilitates interactive high-quality visualization of multiple objects moving at relativistic speeds in arbitrary directions. The method starts by calculating tight image-space footprints for the apparent triangles of the 3D scene objects. The final image is generated using a single image-space ray tracing step incorporating Doppler and searchlight effects. Our implementation uses GPU shader programming and hardware texture filtering to achieve high rendering speed.     

基于PC硬件的大规模数据场快速可视化方法

科学可视化技术在众多领域具有十分广泛的应用,然而直接体绘制技术却有着计算量大、计算时间长的缺点,在普通的PC机上很难实现对大规模数据的实时交互绘制。目前的三维可视化系统通常需要架构在高端的图形工作站或转用计算机上。随着计算机软硬件技术的发展,普通的PC机图形处理器GPU(Graphic Processing Unit)具有了可编程功能。正是借助GPU的可编程功能及其强大的并行处理能力,研究并实现了一种基于普通PC硬件的体会之方法。最后应用该方法对工业、医学等体数据进行可视化,结果证明该方法可以在普通PC上实现较大规模数据的快速可视化。     

图形处理器流水线数据压缩技术研究综述

提高功耗效率是高端GPU的关键设计目标之一,在3D图形渲染流水线的多个阶段使用数据压缩技术能够显著减少GPU片外存储器的访问量,从而达到提高图形绘制性能和降低功耗的效果。为了对图形处理器流水线数据压缩技术的应用现状进行总结和分析,立足于GPU图形渲染流水线和存储系统的结构特征,归纳了各种缓冲区对象、纹理数据专用压缩算法的关键特性;分析了图形流水线数据压缩技术的研究现状、不足与挑战;并基于应用需求指明GPU流水线数据压缩技术进一步的研究内容。     

基于最优化分块的大规模数据体绘制加速方法

GPU加速体绘制已成为体可视化领域的研究热点,然而超出显存的大规模数据无法直接载入,成为GPU应用的瓶颈。分块技术能够在保证图像质量的条件下解决该问题,但分块数据的频繁加载和访问明显降低了绘制速度。针对上述问题,通过建立最优化分块模型得到了大规模数据的最优分块,并通过构造节点编号纹理和改进距离模板设计的方法进一步提高了基于八叉树的分块体绘制算法的绘制速度。实验结果表明,该方法加速效果明显。     

Visualization of fibrous and thread-like data

Thread-like structures are becoming more common in modern volumetric data sets as our ability to image vascular and neural tissue at higher resolutions improves. The thread-like structures of neurons and micro-vessels pose a unique problem in visualization since they tend to be densely packed in small volumes of tissue. This makes it difficult for an observer to interpret useful patterns from the data or trace individual fibers. In this paper we describe several methods for dealing with large amounts of thread-like data, such as data sets collected using Knife-Edge Scanning Microscopy (KESM) and Serial Block-Face Scanning Electron Microscopy (SBF-SEM). These methods allow us to collect volumetric data from embedded samples of whole-brain tissue. The neuronal and microvascular data that we acquire consists of thin, branching structures extending over very large regions. Traditional visualization schemes are not sufficient to make sense of the large, dense, complex structures encountered. In this paper, we address three methods to allow a user to explore a fiber network effectively. We describe interactive techniques for rendering large sets of neurons using self-orienting surfaces implemented on the GPU. We also present techniques for rendering fiber networks in a way that provides useful information about flow and orientation. Third, a global illumination framework is used to create high-quality visualizations that emphasize the underlying fiber structure. Implementation details, performance, and advantages and disadvantages of each approach are discussed.     

飞行器表面矢量场数据动态纹理可视化方法

面向飞行器表面流场数据可视化的应用需求,提出一种基于线性卷积（LIC）及纹理平流（IBFVS）相结合的动态纹理可视化方法。算法通过将IBFVS方法的背景随机噪声替换为LIC纹理方式,结合了LIC纹理结果对比度高及IBFVS方法生成速度快的优势;针对LIC绘制速度慢的不足,利用GPU对曲面矢量场投影并插值,生成规则矢量数据场;用GPU对LIC部分进行并行加速,有效提高了LIC纹理图像产生速度;将LIC结果图像加入到IBFVS进行平流,生成纹理图像,最后加入颜色映射,丰富流场信息。实验结果表明,该方法生成的飞行器表面动态纹理图像对比度高,清晰度强,实时绘制性能好。     

Real-time visualization of large volume datasets on standard PC hardware

In medical area, interactive three-dimensional volume visualization of large volume datasets is a challenging task. One of the major challenges in graphics processing unit (GPU)-based volume rendering algorithms is the limited size of texture memory imposed by current GPU architecture. We attempt to overcome this limitation by rendering only visible parts of large CT datasets. In this paper, we present an efficient, high-quality volume rendering algorithm using GPUs for rendering large CT datasets at interactive frame rates on standard PC hardware. We subdivide the volume dataset into uniform sized blocks and take advantage of combinations of early ray termination, empty-space skipping and visibility culling to accelerate the whole rendering process and render visible parts of volume data. We have implemented our volume rendering algorithm for a large volume data of 512 x 304 x 1878 dimensions (visible female), and achieved real-time performance (i.e., 3-4 frames per second) on a Pentium 4 2.4GHz PC equipped with NVIDIA Geforce 6600 graphics card ( 256 MB video memory). This method can be used as a 3D visualization tool of large CT datasets for doctors or radiologists.     

基于GPU的实时光线投射算法

介绍了一种基于GPU（可编程图形处理单元）的快速实时光线投射算法。为满足大规模体数据集的绘制要求,利用当前GPU的新特性,直接将体数据作为纹理载入显存,采用预积分分类方法在GPU中对体数据进行重采样和分类,避免了计算机主内存与GPU纹理内存之间数据交换的瓶颈问题;利用硬件支持的三维纹理和片元着色器,实时计算每个体素的梯度,实现高质量的光照,保证高质量的图像绘制效果。实验结果表明该方法在医学三维数据场可视化中,能够实时、高效地生成高质量的交互式体可视化图像。     

多重散射的天空光照效果建模与实时绘制

依据大气散射的物理原理,提出了一种考虑多重散射的天空光照效果建 模与实时绘制方法。该方法首先以太阳和天空光作为光源建立了多重散射的天空光照效果模 型,然后综合多种大气粒子密度, 采用合理的分段采样策略,对天空颜色模型的积分进行简 化,以减少积分近似计算所带来的误差;通过对简化后的模型进行分析提出了采用二维纹理 与三维纹理对光学深度预计算的方法,避免了运行时计算光学深度积分的问题;最后该算法 在GPU 的片段处理器上执行,实现了天空光照效果模型的实时绘制,可以满足各种实时应 用需求。     

基于BRDF 和GPU 并行计算的全局光照实时渲染

基于光线追踪,将屏幕图像像素分解为投射光线与场景对象交点面片辐射亮度和 纹理贴图的合成,每个面片的辐射亮度计算基于双向反射分布函数(BRDF)基的线性组合,并通 过图形处理器(GPU)处理核心并行绘制进行加速,最后与并行计算的纹理映射结果进行合成。 提出了一种基于BRDF 和GPU 并行计算的全局光照实时渲染算法,利用GPU 并行加速,在提 高绘制效率的前提下,实现动态交互材质的全局光照实时渲染。重点研究：对象表面对光线的 多次反射用BRDF 基的线性组合来表示,将非线性问题转换为线性问题,从而提高绘制效率; 利用GPU 并行加速,分别计算对象表面光辐射能量和纹理映射及其线性组合,进一步提高计算 效率满足实时绘制需求。