Visualization of vector fields using seed LIC and volume rendering

Line integral convolution (LIC) is a powerful texture-based technique for visualizing vector fields. Due to the high computational expense of generating 3D textures and the difficulties of effectively displaying the result, LIC has most commonly been used to depict vector fields in 2D or over a surface in 3D. We propose new methods for more effective volume visualization of three-dimensional vector fields using LIC: 1) we present a fast method for computing volume LIC textures that exploits the sparsity of the input texture. 2) We propose the use of a shading technique, called limb darkening, to reveal the depth relations among the field lines. The shading effect is obtained simply by using appropriate transfer functions and, therefore, avoids using expensive shading techniques. 3) We demonstrate how two-field visualization techniques can be used to enhance the visual information describing a vector field. The volume LIC textures are rendered using texture-based rendering techniques, which allows interactive exploration of a vector field.     

基于微分的增强型三维矢量场可视化

为提高3D矢量场可视化效果,提出了一种基于微分滤波的流线增强方法。首先对三维纹理进行线性卷积运算,生成具有空间相关性的卷积纹理;其次对卷积纹理进行分数阶微分滤波,增强流线之间强度对比;最后采用纹理映射体绘制技术实现三维矢量场可视化,并通过设计体绘制的传输函数来显示矢量场的内部结构。实验结果表明,该方法有效地增强了流线间的对比,使绘制的流线更加平滑,同时也有效地消除了卷积数据过多引起的紊乱与相互遮挡。     

Interactive exploration of tensor fields in geosciences using volume rendering

Volume rendering methods enable the user to explore interactively scalar data on regularly spaced three-dimensional grids. This article discusses how to use this method to explore and analyse three-dimensional tensor fields. The proposed visualization makes use of the programmability of modern graphics hardware and of “Line Integral Convolution”, a texture-based technique for the visualization of vector fields. While an example from geomechanics is used for presentation purposes, the rendering methods introduced are generic and would suit other application areas that involve volumetric data with several attributes equally well.     

High-quality and interactive animations of 3D time-varying vector fields

In this paper, we present an interactive texture-based method for visualizing three-dimensional unsteady vector fields. The visualization method uses a sparse and global representation of the flow, such that it does not suffer from the same perceptual issues as is the case for visualizing dense representations. The animation is made by injecting a collection of particles evenly distributed throughout the physical domain. These particles are then tracked along their path lines. At each time step, these particles are used as seed points to generate field lines using any vector field such as the velocity field or vorticity field. In this way, the animation shows the advection of particles while each frame in the animation shows the instantaneous vector field. In order to maintain a coherent particle density and to avoid clustering as time passes, we have developed a novel particle advection strategy which produces approximately evenly-spaced field lines at each time step. To improve rendering performance, we decouple the rendering stage from the preceding stages of the visualization method. This allows interactive exploration of multiple fields simultaneously, which sets the stage for a more complete analysis of the flow field. The final display is rendered using texture-based direct volume rendering     

Efficient level of detail for texture‐based flow visualization

In this paper, we present an efficient level of detail algorithm for texture‐based flow visualization. Our goal is to enhance visual perception and performance and generate smooth animation. To achieve our goal, we first model an adaptive input texture taking into account flow patterns to output view‐dependent high‐quality images. Then, we compute field lines only from sparse sampling points of the input noise texture for outputting volume line integral convolution textures and skip empty space utilizing two quantized binary histograms. To improve image quality, we implement anti‐aliasing through adjusting the line integral convolution step size and thickness of trajectory lines with an opacity function. We further extend our solution to unsteady flow. Flow structures and evolution are clearly shown through smooth animation achieved with coherent evolution of particles, handling of discontinuous flow lines, and spatio‐temporal linear constraint of the underlying noise volume. In the result section, we show high‐quality level of detail of three‐dimensional texture‐based flow visualization with high performance. We also demonstrate that our algorithm can achieve smooth evolution for unsteady flow with spatio‐temporal coherence. Copyright © 2015 John Wiley & Sons, Ltd.     

二维和三维矢量场的可视化

矢量场可视化用来帮助人们直观理解二维和三维矢量场。由于目前的矢量场可视化方法只能展示二维矢量场的方向而不能展示强度,并且对于三维矢量场可视化的效果不太令人满意,因此本文提出了用线积分卷积来实现二维平面矢量场可视化,以及三维空间矢量场可视化的方法。对于线积分卷积中的流线跟踪,利用扩展的Bresenham画线算法的思想,实现了二维平面和三维空间流线的跟踪,并且通过建立一个二维表和三维表来分别存储二维平面矢量场和三维空间矢量场中每个点在流线中的上一个点和下一点的位置,来避免传统流线跟踪方法的冗余计算,提高了效率。对于二维平面矢量场,把线积分卷积的结果和矢量的强度进行加权平均,从而利用输出图像的纹理和颜色,共同来表现矢量场的方向和强度。对于三维空间矢量场,利用体线积分卷积（Volume Line Integral Convolution, Volume LIC）的方法来得到输出体纹理,并且用光线投射的体渲染方法来展示三维空间矢量场。结果显示出本文的方法能够清晰直观的看到二维平面矢量场和三维空间矢量场。     

ClearView: An interactive context preserving hotspot visualization technique

Volume rendered imagery often includes a barrage of 3D information like shape, appearance and topology of complex structures, and it thus quickly overwhelms the user. In particular, when focusing on a specific region a user cannot observe the relationship between various structures unless he has a mental picture of the entire data. In this paper we present ClearView, a GPU-based, interactive framework for texture-based volume ray-casting that allows users which do not have the visualization skills for this mental exercise to quickly obtain a picture of the data in a very intuitive and user-friendly way. ClearView is designed to enable the user to focus on particular areas in the data while preserving context information without visual clutter. ClearView does not require additional feature volumes as it derives any features in the data from image information only. A simple point-and-click interface enables the user to interactively highlight structures in the data. ClearView provides an easy to use interface to complex volumetric data as it only uses transparency in combination with a few specific shaders to convey focus and context information.     

基于动态纹理载入的大规模数据场体绘制

为克服图形硬件对传统纹理映射体绘制的限制,提出了一种在普通PC上进行大规模数据场体绘制的有效方法。该方法中,体数据被划分为合适大小的数据块,这些数据块被动态的载入图形硬件,并利用3维纹理映射进行绘制。在整个绘制过程中,仅有一个数据块存储在图形硬件上,有效地提高了对大规模体数据的绘制能力。同时,充分利用目前PC图形硬件成熟的可编程特性,通过对梯度的实时计算来减少在传统纹理映射体绘制中巨大的内存消耗。实验结果表明,该方法在普通PC上可以对超过纹理内存容量的大规模体数据进行交互式体绘制。     

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。     

Material Space Texturing

Many objects have patterns that vary in appearance at different surface locations. We say that these are differences in  materials,  and we present a  material-space  approach for interactively designing such textures. At the heart of our approach is a new method to pre-calculate and use a 3D texture tile that is periodic in the spatial dimensions ( s ,  t ) and that also has a material axis along which the materials change smoothly. Given two textures and their feature masks, our algorithm produces such a tile in two steps. The first step resolves the features morphing by a level set advection approach, improved to ensure convergence. The second step performs the texture synthesis at each slice in material-space, constrained by the morphed feature masks. With such tiles, our system lets a user interactively place and edit textures on a surface, and in particular, allows the user to specify which material appears at given positions on the object. Additional operations include changing the scale and orientation of the texture. We support these operations by using a global surface parameterization that is closely related to quad re-meshing. Re-parameterization is performed on-the-fly whenever the user's constraints are modified.     

A streaming narrow-band algorithm: interactive computation and visualization of level sets

Deformable isosurfaces, implemented with level-set methods, have demonstrated a great potential in visualization and computer graphics for applications such as segmentation, surface processing, and physically-based modeling. Their usefulness has been limited, however, by their high computational cost and reliance on significant parameter tuning. This paper presents a solution to these challenges by describing graphics processor (GPU) based algorithms for solving and visualizing level-set solutions at interactive rates. The proposed solution is based on a new, streaming implementation of the narrow-band algorithm. The new algorithm packs the level-set isosurface data into 2D texture memory via a multidimensional virtual memory system. As the level set moves, this texture-based representation is dynamically updated via a novel GPU-to-CPU message passing scheme. By integrating the level-set solver with a real-time volume renderer, a user can visualize and intuitively steer the level-set surface as it evolves. We demonstrate the capabilities of this technology for interactive volume segmentation and visualization.     

基于多频稀疏噪声的流场运动方向可视化算法

针对现有流场可视化算法存在的矢量场运动指向二义性以及缺乏对矢量场速率区分等问题进行了研究,提出了一种基于多频稀疏噪声纹理的改进线积分卷积算法,用来提高流场可视化后的信息表达效果。该方法首先根据矢量场速率量级的大小划分频率不同的噪声群,并合成适用于该向量场的特定多频噪声纹理;然后使用斜坡卷积核根据向量场流线对噪声纹理进行卷积;最后生成一幅同时具有矢量场运动方向和运动速率信息的彩色图像。实验结果表明,该方法可以增强用户对流场流量大小和矢量场方向的感知效果,在大规模风场数据可视化的验证实验上取得了良好的可视化效果。     

基于纹理合成的向量场可视化

在纹理合成过程中利用向量场作为指导,生成反映向量场大小和方向变化的合成结果.采用块纹理合成的流程,在对向量场合成块均匀划分的基础上,通过进一步的自适应分割,将向量场划分成为不同大小和不同形状的最终合成块,使之与向量场的变化趋势相吻合.对向量变化过于剧烈的区域,则采用点合成的方式进行纹理合成,以保证合成效果的平滑.实验表明,文中的方法可以实现快速而高质量的向量场可视化.     

Mesh-driven vector field clustering and visualization: an image-based approach

Vector field visualization techniques have evolved very rapidly over the last two decades, however, visualizing vector fields on complex boundary surfaces from computational flow dynamics (CFD) still remains a challenging task. In part, this is due to the large, unstructured, adaptive resolution characteristics of the meshes used in the modeling and simulation process. Out of the wide variety of existing flow field visualization techniques, vector field clustering algorithms offer the advantage of capturing a detailed picture of important areas of the domain while presenting a simplified view of areas of less importance. This paper presents a novel, robust, automatic vector field clustering algorithm that produces intuitive and insightful images of vector fields on large, unstructured, adaptive resolution boundary meshes from CFD. Our bottom-up, hierarchical approach is the first to combine the properties of the underlying vector field and mesh into a unified error-driven representation. The motivation behind the approach is the fact that CFD engineers may increase the resolution of model meshes according to importance. The algorithm has several advantages. Clusters are generated automatically, no surface parameterization is required, and large meshes are processed efficiently. The most suggestive and important information contained in the meshes and vector fields is preserved while less important areas are simplified in the visualization. Users can interactively control the level of detail by adjusting a range of clustering distance measure parameters. We describe two data structures to accelerate the clustering process. We also introduce novel visualizations of clusters inspired by statistical methods. We apply our method to a series of synthetic and complex, real-world CFD meshes to demonstrate the clustering algorithm results.     

A new line integral convolution algorithm for visualizingtime-varying flow fields

New challenges on vector field visualization emerge as time dependent numerical simulations become ubiquitous in the field of computational fluid dynamics (CFD). To visualize data generated from these simulations, traditional techniques, such as displaying particle traces, can only reveal flow phenomena in preselected local regions and thus, are unable to track the evolution of global flow features over time. The paper presents an algorithm, called UFLIC (Unsteady Flow LIC), to visualize vector data in unsteady flow fields. Our algorithm extends a texture synthesis technique, called Line Integral Convolution (LIC), by devising a new convolution algorithm that uses a time-accurate value scattering scheme to model the texture advection. In addition, our algorithm maintains the coherence of the flow animation by successively updating the convolution results over time. Furthermore, we propose a parallel UFLIC algorithm that can achieve high load balancing for multiprocessor computers with shared memory architecture. We demonstrate the effectiveness of our new algorithm by presenting image snapshots from several CFD case studies     

基于矢量线强化的增强型2维流场实时绘制

在流场绘制中,合理地结合矢量场的多种属性有助于矢量场的特征分析,据此提出了一种基于矢量线强化的增强型2维流场实时绘制算法。通过对流场的一些标量属性如大小、角度和曲率进行色彩映射,该算法不仅可以清晰显示流场运动方向,而且能显示矢量场的多种属性,有助于了解流场矢量特征分布和主要拓扑结构。该算法采用了一种矢量线强化策略,即通过对卷积纹理在垂直矢量方向上进行1维高通滤波,增加了矢量线间的对比,改善了图像质量。利用现代图形卡的可编程能力,该算法可以在微机上达到实时绘制性能。     

基于流线纹理合成的2D矢量场可视化

针对科学试验数据可视化问题,提出了一种2D矢量场可视化的方法－流线纹理合成方法,即通过将1D纹理映射到流线上,再利用流线纹理来合成可视化图象,因为移动1D纹理很容易形成矢量场动画。该方法是利用局部区域内流线的近似平行性,首先依据临界点来设定流线宽度,然后把流线绘制成多条平行流线,再分别将多条不同的1D纹理映射到流线上,从而能够加快计算。实际结果表明,由于流线纹理合成的纹理图象上清楚地显示了流线,因而反映了矢量场的方向信息,同时,该方法计算速度快,可以达到交互可视化的要求。     

基于纹理的增强型3D流场绘制

提出一种基于纹理的增强型3D矢量场可视化算法,可显著地改善传统纹理法的绘制质量.首先通过对3D纹理的线性卷积运算生成具有空间相关性的卷积纹理;然后对卷积纹理进行高通滤波,以增加流面内流线之间强度的对比;最后通过体绘制方式展示3D卷积纹理.借助权重区域,该算法可以显示用户感兴趣区域或特征区域,避免卷积数据过多引起的紊乱及相互遮挡.     

Multiresolution volume visualization with a texture-based octree

Although 3D texture-based volume rendering guarantees image quality almost interactively, it is difficult to maintain an interactive rate when the technique has to be exploited on large datasets. In this paper, we propose a new texture memory representation and a management policy that substitute the classical one-texel per voxel approach for a hierarchical approach. The hierarchical approach benefits nearly homogeneous regions and regions of lower interest. The proposed algorithm is based on a simple traversal of the octree representation of the volume data. Driven by a user-defined image quality, defined as a combination of data homogeneity and importance, a set of octree nodes (the cut) is selected to be rendered. The degree of accuracy applied for the representation of each one of the nodes of the cut in the texture memory is set independently according to the user-defined parameters. The variable resolution texture model obtained reduces the texture memory size and thus texture swapping, improving rendering speed.