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题名:
三维数据场体绘制技术的研究和实现
作者: 王文成
答辩日期: 1998
专业: 计算机软件
授予单位: 中国科学院软件研究所
授予地点: 中国科学院软件研究所
学位: 博士
关键词: 可视化 ; 数据场 ; 体绘制 ; 光线投射方法 ; 投影成象方法 ; 色彩合成 ; 交互操作 ; 模板法 ; 光照 ; 排序 ; 混合绘制
摘要: 三维数据场是当前可视化研究的重点,也是实践中最常遇到的。体绘制技术是可视化一类重要的技术。与从数据场中抽取几何面进行可视化的方法相比,体绘制方法不生成中间几何元素,而是直接将数据进行整体的合成。这样,不同的内容可以在一幅图象中同时显示,便于人们对数据场进行全面综合的分析和研究。针对体绘制方法成象速度慢和图象对信息的表达比较模糊的弱点,本文提出了一些有效的方法,使体绘制技术能更好地进行可视化,提高人们分析理解数据的能力。这些方法如下:1)将数据场中各种体元的透明以一个透明度基本单元进行统一,形成一种透明度标尺。依此,将体绘制的最基本操作“色彩合成运算”转化到标尺上运行,使得这种运算只需进行加法操作,促进了成象速度的有效提高。2)根据作者以前提出的“基于虚拟面的色彩分布合成”方法,将数据场的一些三维信息、以及一些成象的中间结果保留在二维的虚拟面上,并推导出三种交互操作工具,使得体绘制可以进行快速的效互可视化,方便用户跟踪分析感兴趣的内容。3)模板法运用于非规则场的体绘制中时,往往是进行一种较粗糙的逼近,影响了图象对数据场的反映质量。对此,本文提出一种可变模板法,运用正弦函数对样点尺寸的统一度量,使得不同大小的样点均可以进行高精度的色彩累积运算,提高了图象质量。4)光照是增强可视性分析的重要手段。但体绘制中成象速度较快的投影成象方法,很难有效地使用光照提高图象的反映效果。本文运用球体重组数据场,将数据场中的物质分界面进行拟合,使得光照运算能够高效地与投影成象方法相结合,提高可视化的效率。5)在非规则场的体绘制中,由于体元的形状和大小不确定,其绘制速度和图象质量都很难令人满意。对此。我们提出一种方法,利用链表化解影响非规则场体绘制速度的关键问题“体元排序”,并且由此将光线投射和投影成象这两种体绘制方法有效地结合,使得非规则场的体绘制可以快速获得高质量的图象。6)数据场与几何形体的混合成象,一直是可视化中的重要研究内容。这方面的工作很多,但都没有彻底解决数据场与几何形体交界处的成象问题,并且没有利用投影成象这种较快的体绘制方法。我们深入分析了交界处的情况,提出一种链表方法,从根本上解决了交界处的成象问题,并结合投影成象方法的使用,使得数据场与几何形体的混合成象可以快速准确地进行。
英文摘要: Three-dimensional data fields are quite common in many applications, and visualization of 3D data fields is a hot research area in scientific visualization. Among all the visualization methods, direct rendering to 3D data is a fundamental and important approach. In comparison with the surface extraction approach, direct volume rendering processes all samples of data in making images, without necessity of producing the intermediate geometric elements. Therefore, more features inside data could be demonstrated in a single image, and more information of the data could be provided to investigators. Although the direct volume rendering has many advantages, the method is computationally extensive and the images produced by the method are in general blurred, which hinders scientists from understanding data in high efficiency. To solve the problems. several aspects are investigated and research on the problem solution has been conducted in the works associated with the thesis. 1) By establishment of a transparent degree unit to unify different transparent values of samples, a transparent degree ruler is set up to facilitate the transparency accumulation Based on such a ruler, the operation of color composition, the fundamental calculation in the volume rendering can be greatly simplified, through a replacement of summation operations provided in the method in stead of the original multiplication operations. 2) By distributing the accumulation colors along a ray over a 2D virtual plane, much 3D information of the data volume could be reflected on the plane. Through the color distribution in this novel proposal, a new interactive visualization method is put forward which allows the interactions being operated on the virtual plane. With the new interactive method, an investigator has the power of manipulating parts of data at his/her disposal which he/she is interested in. 3) As a special projection method in volume rendering, splatting works well for regular data volumes. However, the method performs poorly when irregular volumes are rendered. By using the triangular Sine function to uniformly scale samples in different sizes, a variable splatting algorithm is proposed to have different samples accumulate their effects in high precision. The method may greatly improve the image quality. 4) Shading is an important measure to help the expression of data features in visualization. However, it is difficult to produce shading effect in the projection approach. In this thesis, we present a shading technique by using sphere and ellipsoid surfaces to approximate the material interfaces in data volumes. As a result, shading effect may be easily performed on the material interfaces in the projection approach. 5) In irregular data volumes, as the shape and size of samples are not constant, the rendering speed is rather low and the quality of images produced are also far form satisfaction. In this theis, we put forward a method to solve the problem by setting up node links in queuing up cells at each pixel. Consequently, three-dimensional scan conversion & ray-casting are naturally combined, and the rendering process could be performed with high efficiency of projection approach and the image quality of ray-casting approach. 6) Rendering volume data with geometric objects together is an important subject in scientific visualization. Although many methods have been proposed, the problem of intersection between geometric objects and volume samples has not been completely solved yet, and no one has employed the projection approach in this aspect. After an investigation of the intersection situation, we present a method by setting up node links to integrate the projection approach. The method completely solves the intersection problem with high efficiency in rendering the geometric objects and volumes together.
语种: 中文
内容类型: 学位论文
URI标识: http://ir.iscas.ac.cn/handle/311060/7002
Appears in Collections:中科院软件所

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Recommended Citation:
王文成. 三维数据场体绘制技术的研究和实现[D]. 中国科学院软件研究所. 中国科学院软件研究所. 1998-01-01.
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