Interactive volume rendering of large fields

We first present the volume-rendering pipeline and the most typical of the existing methods for each pipeline stage. The complexity of each stage in terms of computing time is analyzed for each method. Then the demands and the scope of interactive volume rendering are briefly summarized. Based on this analysis we examine alternate solutions to optimize each pipeline stage in order to allow interactive visualization while maintaining the image quality. The proposed method maximizes interactive manipulation possibilities and minimizes runtimes by sampling at the Nyquist rate and by flexibly trading off quality for performance at any pipeline level. Our approach is suitable for rendering large, scalar, discrete volume fields such as semitransparent clouds (or X-rays) on the fly.     

改进的交互式动态体绘制算法

针对交互式动态体绘制算法生成图像质量差的问题,提出一种改进算法,在减少使用插值的同时,通过增加采样点数和使用采样点间距离作为权值等方法进行图像合成。改进的算法使结果图像的质量有了明显改善,同时保持了较快的速度。     

Towards animating ray-traced volume visualization

Ray-tracing volumetric data may take several minutes to compute a single image from a fixed viewpoint. We present techniques that generate approximate ray-traced volumetric images in less than one second per image, after a lengthy initialization process is performed. These approximate images are based on methods that interpolate data sampled at locations on a sphere.     

An optimal parallel algorithm for volume ray casting

Volume rendering by ray casting is computationally expensive. For interactive volume visualization, rendering must be done in real time (30 frames/s). Since the typical size of a 3D dataset is 256³, parallel processing is imperative. In this paper, we present anO(logn) EREW algorithm for volume rendering. We useO(n ³) processors that can be optimized toO(log³ n) time withO(n ³/log³ n) processors. We have implemented our algorithm on a MasPar MP-1. The implementation results show that a frame of size 256³ is generated in 11 s by 4096 processors. This time can be further reduced by the use of large number of processors.     

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。     

Volumetric texture synthesis for non-photorealistic volume rendering of medical data

This paper presents a novel technique, called volumetric texture synthesis, for non-photorealistic volume rendering. It extends texture synthesis from 2D areas/3D surfaces to volumes. By selecting different texture samples, it allows for a wide variety of stylized rendering for the target volume. As a preprocessing step, volume data analysis is used to identify texture orientations for the volume. This is followed by volumetric texture synthesis, which generates 3D non-photorealistic textures along the identified texture orientations. Finally, standard volume rendering is applied to display the volume data decorated by the texture. Experimental results are provided in the paper.     

Error-controlled real-time cut updates for multi-resolution volume rendering

Multi-resolution techniques are required for rendering large volumetric datasets exceeding the size of the graphics card's memory or even the main memory. The cut through the multi-resolution volume representation is defined by selection criteria based on error metrics. For GPU-based volume rendering, this cut has to fit into the graphics card's memory and needs to be continuously updated due to the interaction with the volume such as changing the area of interest, the transfer function or the viewpoint. We introduce a greedy cut update algorithm based on split-and-collapse operations for updating the cut on a frame-to-frame basis. This approach is guided by a global data-based metric based on the distortion of classified voxel data, and it takes into account a limited download budget for transferring data from main memory into the graphics card to avoid large frame rate variations. Our out-of-core support for handling very large volumes also makes use of split-and-collapse operations to generate an extended cut in the main memory. Finally, we introduce an optimal polynomial-time cut update algorithm, which maximizes the error reduction between consecutive frames. This algorithm is used to verify how close to the optimum our greedy split-and-collapse algorithm performs.     

基于GPU的烟雾数据体面混合绘制技术研究

研究烟雾等大规模体数据在虚拟场景中实时可视化的技术是一种新的体面混合绘制技术,在灾害现象仿真中有着重要的应用。在处理体面混合绘制时,已有的绘制算法难以实时地处理体数据的遮挡和裁剪,并在内窥绘制中出现片元空洞。针对以上问题,提出一种基于GPU的体面混合绘制算法,将体数据视为参与介质,同时将面绘制的结果作为体绘制的积分域约束条件,从而把面绘制中的裁减算法推广到体数据的绘制中,实现了体面混合绘制的无缝融合。仿真结果表明算法能够实时地绘制虚拟场景中的大规模体数据,并且能够处理复杂的内窥效果。     

医学体数据三维可视化改进算法综述

医学体数据三维可视化技术有着广泛的应用前景。近年来为加快绘制速度,提高成像质量和节省存储空间提出了许多改进算法,本文总结了这些算法,为进一步研究奠定了基础。     

体绘制技术在医学可视化中的新发展

科学计算可视化体绘制算法能反映出体数据的内部信息,在医学,它已经从辅诊断发展成为辅助治疗的重要手段,体可视化技术是医学可视化的重要研究内容,其处理过程包括体数据的获取,模型的建立,数据的映射,绘制等操作,该文介绍了医学可视化中常使用的几种光照模型,针对基于图象空间和对象空间两种体绘制算法,介绍了它们的基本思想方法,并详细阐述了在近期的主要加速技术和提高图象质量方法的新进展,最后给出了实验数据和结论。     

Particle-based non-photorealistic volume visualization

Non-photorealistic techniques are usually applied to produce stylistic renderings. In visualization, these techniques are often able to simplify data, producing clearer images than traditional visualization methods. We investigate the use of particle systems for visualizing volume datasets using non-photorealistic techniques. In our VolumeFlies framework, user-selectable rules affect particles to produce a variety of illustrative styles in a unified way. The techniques presented do not require the generation of explicit intermediary surfaces.     

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.     

在Matlab环境下实现体绘制法的生物切片图象的三维重建

在生物学领域、如何将生物切片图象进行三维重建并显示,日益受到人们所重视。体绘制法能够避免重建过程所造成的伪象痕迹,缩短了在体数据中寻找、计算物体表面的时间和不丢失细节,更加准确地反映出体数据所包含的形状结构。Matlab提供了各种矩阵运算、操作和图象显现工具,文章利用Matlab工具箱有用体绘制法进行生物切片图象的三维重建,试验结果理想。     

A distance template for octree traversal in CPU-based volume ray casting

Several optimization techniques have been proposed to improve the speed of direct volume rendering. A hierarchical representation formed by an octree is a data structure to skip over transparent regions while requiring little preprocessing and data storage. However, in order to skip over an octant estimated to be transparent (a transparent octant), the distance from a boundary to another boundary of the octant should be calculated. Because the distance computation is expensive, we propose a precomputed data structure, the distance template, which stores direction and distance values from one boundary voxel on a face to all the boundary voxels on the remaining five faces. In the rendering step, if a ray reaches a transparent octant, it leaps over the octant by referring to the stored distance value.     

加速体绘制技术

根据体绘制成像的各个操作环节,对体绘制的加速技术进行了较全面且系统的介绍,包括色彩合成、光线与数据的求交、插值计算、排序及视见变换、对体绘制的基于硬件及系统方面的加速技术（如并行体绘制和漫游体绘制）也进行了一些讨论,在实际应用中,只有将各种加速技术进行有机地结合才能充分发挥体绘制的可视化作用。     

交互体绘制中的快速颜色合成

颜色合成是体绘制的重要组成部分,其中大量重复计算严重影响了绘制的实时性。为了减少颜色合成中的计算量,该文从体数据中分离出了与交互绘制无关的特征进行预处理,进而避免了交互绘制过程中的大量重复计算。对于稳定采样区间的颜色合成,提出了基于透明度标尺的颜色合成新算子,该方法对于类属较少的体数据,其绘制加速效果是十分明显的。     

三维医学图像的体绘制技术综述

在分析三维医学图形体绘制技术的基础上,描述了射线投射法、足迹法、剪切-曲变法、基于硬件的3D纹理映射、频域体绘制法和基于小波的体绘制等典型算法,给出了各类算法的性能评价,展望了体绘制技术研究的发展前景。     

Improved perspective visibility ordering for object-order volume rendering

Finding a correct a priori back-to-front (BTF) visibility ordering for the perspective projection of the voxels of a rectangular volume poses interesting problems. The BTF ordering presented by Frieder et al. [6] and the permuted BTF presented by Westover [14] are correct for parallel projection but not for perspective projection [12]. Swan presented a constructive proof for the correctness of the perspective BTF (PBTF) ordering [12]. This was a significant improvement on the existing orderings. However, his proof assumes that voxel projections are not larger than a pixel, i.e. voxel projections do not overlap in screen space. Very often the voxel projections do overlap, e.g. with splatting algorithms. In these cases, the PBTF ordering results in highly visible and characteristic rendering artefacts. In this paper we analyse the PBTF and show why it yields these rendering artefacts. We then present an improved visibility ordering that remedies the artefacts. Our new ordering is as good as the PBTF, but it is also valid for cases where voxel projections are larger than a single pixel, i.e. when voxel projections overlap in screen space. We demonstrate why and how our ordering works at fundamental and implementation levels.     

探地数据可视化研究

由于发展中国家经济增长的驱动,全球对石油、天然气体的需求在不断地增长,从而需要越来越纯熟的石油勘探技术.探地数据可视化在石油、天然气勘探过程中起着举足轻重的作用.文中主要从可视化的角度对探地数据的解释与展示进行了调研:首先介绍了以二维切片为主的探地数据可视化方法,包括二维切片纹理映射、二维断层可视化;其次讨论了以三维体绘制技术为主的探地数据可视化方法;最后总结了解释性与叙述性可视化,以及基于Sketch的交互式可视化和领域知识辅助的可视化.     

Normal estimation in 3 D discrete space

Three-dimensional voxel-based objects are inherently discrete and do not maintain any notion of a continuous surface or normal values, which are crucial for the simulation of light behavior. Thus, in volume rendering, the normal vector of the displayed surfaces must be estimated prior to rendering. We survey several methods for normal estimation and analyze their performance. One unique method, the context-sensitive approach, employs segmentation and segment-bounded operators that are based on object and slope discontinuities in order to achieve high fidelity normal estimation for rendering volumetric objects.