Direct volume rendering of multiple scalar fields

Rendering of volume data without forming geometric objects is often termed direct volume rendering. Most of the previously developed methods for this purpose are restricted to display of one scalar variable. This paper presents methods for direct volume rendering of several scalar variables defined at discrete points in three-dimensional space. Typical requirements for the rendering of such data are proposed and then used as a basis for the derivation of a computational model. The proposed model uses a classification technique to composite specific types of information from different scalar fields. The visual display of the composite information is controlled through a set of rendering parameters.     

基于快速求交的自适应光线投射法

光线投射是一个重要的体绘制算法,但直线上采样点的确定是非常费时的,也是影响体绘制实时性的重要因素。该文利用直线和平面族的交点可以快速求得直线上的采样点及其特征值,该方法充分利用了直线的相关性,避免了大量的三线性插值计算。该文还基于快速求交提出了自适应采用方法,以提高绘制图像的质量。     

Application paper. Applying ray casting to the flow visualization data using linear and B-spline hyperpatch interpolation

Visualizing the flow of air or fluids is especially challenging because of their transparency and possible high velocity. Complex patterns are created when the flow is over or around an object. Our aim is to visualize the flow in three dimensions, eliminating the need for mentally piecing the flow from two-dimensional slices. We have applied the well-known ray casting technique to visualize the flow around an aircraft wing. During ray casting, when the ray does not intercept the lattice points, linear and B-spline hyperpatch interpolations are used to estimate the colour. We describe the shading equation, and compare the linear and the B-spline hyperpatch interpolation schemes during ray casting. Several images are produced to show the difference in the image quality of these two methods, and their image generation time.     

基于GPU与Monte-Carlo的体绘制光线投射算法的研究

体绘制过程中等距离采样在显示效果不理想的情况下,每减少一个采样步长会增加大量采样点,大大增加了体绘制过程中的计算负担。针对这个问题,提出了一种基于Monte-Carlo积分方法的光线投射实现的实时体绘制算法,采用Monte-Carlo积分方法解决了光照明方程中的积分问题。实验结果表明,在显示效果几乎一样的前提下,采用本文的方法绘制效率提高了十多帧。     

基于PC的医学图像体绘制方法研究与仿真

体绘制技术是一种能够准确反映体数据内部信息的可视化技术。本文主要介绍了一种改进的体绘制算法，即首先对三维医学图像施加模糊增强，然后对增强后的图像进行模糊阈值分割，从而可以清晰地对三维数据场进行分类，即边界区与非边界区。对边界区与非边界区分别进行绘制。在PC机上进行仿真的结果表明，此方法既能提高绘制的速度，又能保证绘制质量。     

Using 2- and 2 -dimensional seed filling in view lattice to accelerate volumetric rendering

In this paper we propose new methods for calculating the projection of an opaque 3-dimensional 6-connected volumetric object into a two-dimensional view using 2- and 2 -dimensional seed-filling in the view space. When a 3-dimensional volumetric data set is sampled by parallel rays at a resolution exceeding the Nyquist ratio, the 6-connectivity of objects is maintained from volume lattice to view lattice. Given a seed point for each 6-connected object in the volumetric data set, a seed-filling algorithm may access all sample points in view lattice, while simultaneously composing the rendered view. The algorithms presented in this paper minimize the number of voxels that need to be processed. We implemented these methods on a general purpose computer architecture and tested them with several artificial and real-life medical volumetric data sets. It is shown that the algorithms may be used to speed up the parallel ray casting of opaque medical objects. The actual frame rate achieved by the combined method allows interactive (10 frames/sec) rotation of the object on a common single-processor personal computer without specialized hardware.     

大规模数据快速体绘制方法的设计与实现

体绘制是科学计算可视化的重要手段,针对大规模数据场体绘制计算量大、效率低的问题,提出一种基于哈尔小波变换的三维规则网格数据场快速体绘制方法.采用整体描述、局部细化的策略对转换后的数据进行组织、管理和调度,实现了多尺度分析和快速随机存取,并有效解决了CPU在处理大规模数据集时纹理内存的局限;采用基于CUDA(计算统一设备架构)的GPU加速技术提高体绘制算法性能,很好的实现了大规模数据集的交互式可视化.     

体素分类与Phong光照模型GPU加速体绘制

为了提高体绘制的速度和效果,研究了体数据的分类和计算及其在图形处理单元上加速实现的体绘制算法.分别采用点体素先分类和预积分后分类方法为体数据分配颜色和不透明度,改进了利用不透明度对颜色加权改善绘制效果,根据Phong光照模型对体数据进行渲染.通过查找表软件加速和图形处理单元硬件加速两个方面分别实现并进行比较,实验结果表明,采用图形硬件加速的方法达到实时交互的效果,体绘制性能大大提高.     

体视化中LOD技术思想的应用与实现

在真实感图形学研究中,复杂模型的实时绘制与动态显示是研究的热点之一.细节层次是实时图形生成的一项重要技术.细节层次模型是指对同一个场景或场景中的物体,使用具有不同细节的方法得到一组模型,供绘制时使用.建立细节层次模型能很有效地降低数据量和复杂度,实现三维场景的实时处理.针对光线投射绘制算法图像质量高,但是速度较慢的特点,提出将LOD技术思想引入到光线投射算法以改善图像体绘制时的交互性能,该方法为以后在地形可视化、虚拟现实等领域的应用提供了理论依据.     

Volume and Isosurface Rendering with GPU‐Accelerated Cell Projection*

We present an efficient Graphics Processing Unit GPU‐based implementation of the Projected Tetrahedra (PT) algorithm. By reducing most of the CPU–GPU data transfer, the algorithm achieves interactive frame rates (up to 2.0 M Tets/s) on current graphics hardware. Since no topology information is stored, it requires substantially less memory than recent interactive ray casting approaches. The method uses a two‐pass GPU approach with two fragment shaders. This work includes extended volume inspection capabilities by supporting interactive transfer function editing and isosurface highlighting using a Phong illumination model.