基于特征线条的三维模型检索方法

为了避免在三维模型检索中对输入源的限制,提出一种以自然图像为输入源、基于特征线条的三维模型检索方法.首先基于最优视点提取算法训练并获取三维模型较优视点集;然后在较优视点集下渲染三维模型混合轮廓线视图,并为各视点混合轮廓线视图提取Gabor边缘响应特征,建立特征库;最后对输入的自然图像提取相同的边缘响应特征,采用视觉词袋方法从特征库中检索相似模型,并根据相似度排序.实验结果表明,该方法利用自然图像与模型特征线视图的边缘相似性实现三维模型检索,降低了退化视图与自然图像纹理对三维模型检索的干扰,符合人类视觉辨识三维物体的机理,具有良好的检索效果.     

基于POVRAY的三维全景图像的计算机生成方法

三维全景图像技术（Integral Imaging,简称II）是一种采用微透镜阵列进行记录和显示的三维图像技术。该技术目前正成为最有希望实现下一代三维电视的方法,吸引着国际上三维技术领域的重多关注。本文提出了一种新的基于三维图形软件POVRAY的快速生成II图像的相机模型构造方法,详细阐述了该相机模型的实现算法,并采用该相机对虚拟的三维场景进行记录。实验结果表明,使用该相机模型能在保证图像质量的情况下,最大程度满足实时性要求。     

以目标为中心的MCRBR视点空间投影方法

三维目标的姿态随视点变化而不同,选择适当角度范围的多尺度投影图像为代表,建立三维目标的完备特征库,能够提高基于图像的三维目标识别率。以目标为观察中心,基于3ds MAX提出一种多摄像机旋转批量渲染的三维目标视点空间投影方法。首先建立目标的三维模型,设置目标模型位置和顶视图摄像机位置,然后利用max层级命令面板锁定其中一个轴向的角度,以等采样间隔复制摄像机,设置半球面运动路径,并约束到相应摄像机,最后设置投影图像的输出参数并建立批处理脚本,实现三维目标视点空间任意投影图像的自动保存。     

基于视点互信息的树叶实时简化方法

三维树木模型在虚拟地理环境, 三维城市场景等领域中应用广泛, 但由于树木中包含丰富的几何信息, 难以对大规模的森林场景进行有效的渲染. 为此我们设计了一种基于视点互信息(Viewpoint Mutual Information, VMI)的树木实时简化方法. 在预处理中按照树枝间的拓扑关系将树木划分为具有父子关系的节点, 然后根据VMI计算每片树叶在多个视点下的平均重要度并以此对树叶进行排序, 重要程度较小的树叶在简化过程中将会被优先删除. 实时简化过程中, 我们提出了一种视点依赖的简化方法, 大大降低了需要渲染的数据量. 为了提高渲染森林场景时的性能, 我们使用了多种渲染优化措施以避免不必要的细节层次(Level Of Detail, LOD)切换.     

基于视点的多分辨率纹理选择方法

MIP Mapping技术是纹理映射中一种有效的纹理反走样技术。但是MIP Mapping只是根据被渲染区域的大小来选择相应分辨率的纹理,在初始化的时候必须把所有的纹理细节层次调入内存,这种情况下会降低计算机的效率。提出了一种基于视点的三维地图控制方法,根据与视点相关的渲染区域大小以及视觉重要度来选择相应分辨率的纹理。试验证明该方法在不降低显示质量的同时能有效减少纹理的渲染量,提高了计算效率。     

手持式三维声纳实时成像系统设计

针对传统三维声纳成像系统集成度低、实时性差的问题,提出一种手持式三维声纳实时成像系统设计方案。利用DM8127实现声纳图像的处理,通过坐标转换数组预生成、自适应阈值的网格构建等方法实现实时高精度的三维建模,同时采用多线程并行处理架构改善网格构建时的系统处理性能,降低处理时延,并利用Open GL ES2.0实现三维声纳图像的渲染和显示。实验结果证明,该系统能清晰显示水下探测目标,且实时成像速率高达25帧/s,满足系统实时性要求。     

视频图像在三维模型中的渲染

视频监控是大型安防工作中最重要的一个环节,传统的视频监控系统展示给用户的只是独立的二维平面图像,图像脱离环境,整体性不足,为了解决该问题,提出了将视频图像渲染显示于三维模型的思路.研究了纹理映射技术并结合视频图像渲染的特殊性分析研究了Z缓冲算法、Shadow map算法,根据实际应用提出Extend Shadow map算法以实现将视频图像与三维场景无缝贴合.实验结果表明,视频图像渲染显示于三维模型中所体现的优越性.     

基于向量投影法的心肌缺血三维显示

提出了一种将一维心电信号的缺血信息转化为三维图像显示的方法。该方法使用便携式采集装置采集心电信号,自动获取信号特征。对各导联向量添加权重系数,通过逆投影合成ST损伤向量。并将ST损伤向量投影到心脏三维模型上,通过彩色编码显示出心肌缺血的位置和范围。实验结果表明,该方法对心肌缺血的检测与心电图诊断一致性极强,显示部位参考价值高。     

基于粒子群的三维可视化视点优化方法

通常三维可视化的最佳视点选择是通过人工试探,这样会导致反复迭代尝试的次数增加且效率低下,针对上述问题提出了一种基于粒子群的视点优化方法。该方法把视点利用多分辨率层级来表示,引入图像信息熵评价不同视点下绘制的三维图像的质量,熵值作为视点优化的依据和粒子群的适应度函数值。在三维可视化中利用粒子群算法进行视点的智能、自动的优化,从而实现最佳视点的选择。实验结果表明,该方法具有较快的收敛速度,有效地减少了评估次数,可提高三维可视化的绘制图像的质量和绘制效率。     

基于三层植物模型的大规模植物模拟方法*

针对在大规模植物模拟中基于三维几何网格模型的植物模拟方法内存消耗大,以及基于二维平面模型的植物模拟方法近视点模糊缺陷问题,提出了一种基于三层植物模型的大规模植物模拟方法。该方法将大规模植物分为三层：精度高的几何网格模型层、精度适中的Impostor模型层和精度低的Billboard模型层。根据植物到视点的距离,动态加载相应层中的模型,即当植物距视点较近时,加载精度高的几何网格模型层中的模型;当植物距视点较远时,加载精度适中的Impostor模型层中的模型;当植物距视点很远时,加载精度低的Billboard模型层中的模型。最后,利用Ogre图形引擎对三种植物模拟方法进行了渲染效果对比实验。由实验结果可知,该方法可以在低内存消耗情况下,取得与基于三维几何网格模型的植物模拟方法一样的逼真感,取得与基于二维平面模型的植物模拟方法相近的渲染速度。     

基于粒子系统的天气雷达资料三维显示

传统天气雷达资料为二维图像显示,随着科技的发展与应用的需求,三维显示成为必然。本文研究了一般粒子系统,并根据天气雷达资料特点,建立了适合天气雷达资料特点的粒子系统;在给出三维显示结果图的同时,对粒子绘制与面绘制进行了比较,结果表明粒子绘制能很好的显示雷达资料的三维信息,且在速度方面有一定的提高。     

Computer-Generated Graphite Pencil Rendering of 3D Polygonal Models

Researchers in non-photorealistic rendering have investigated the display of three-dimensional worlds using various display models. In particular, recent work has focused on the modeling of traditional artistic media and styles such as pen-and-ink illustration and watercolor painting. By providing 3D rendering systems that use these alternative display models users can generate traditional illustration renderings of their three-dimensional worlds. In this paper we present our graphite pencil 3D renderer. We have broken the problem of simulating pencil drawing down into four fundamental parts: (1) simulating the drawing materials (graphite pencil and drawing paper, blenders and kneaded eraser), (2) modeling the drawing primitives (individual pencil strokes and mark-making to create tones and textures), (3) simulating the basic rendering techniques used by artists and illustrators familiar with pencil rendering, and (4) modeling the control of the drawing composition. Each part builds upon the others and is essential to developing the framework for higher-level rendering methods and tools. In this paper we present parts 2, 3, and 4 of our research. We present non-photorealistic graphite pencil rendering methods for outlining and shading. We also present the control of drawing steps from preparatory sketches to finished rendering results. We demonstrate the capabilities of our approach with a variety of images generated from 3D models.     

基于三维纹理的实时流体模拟

本文描述了一种利用基于Open GL三维纹理实现的直接体绘制方式显示流体模拟结果的方法。以JosStam的二维流体模拟模型为基础，扩展出三维流体模拟的模型；然后通过将密度场映射到三维纹理空间，实现实时的显示；并通过引入全局光照模型，得到真实感的渲染效果。最后通过与粒子系统进行对比，分析了本方法的显示效果优势。     

Distributed real-time rendering for ultrahigh-resolution multiscreen 3D display

Large-scale autostereoscopic three-dimensional (3D) displays can give audiences a truly immersive feeling with strong visual impact. However, the traditional autostereoscopic 3D display systems are limited by the display hardware, making it difficult to directly achieve large-scale 3D displays with high resolution. Multiscreen splicing with laser backlights can be used for large-scale and ultrahigh-resolution 3D display, but it normally results in subscreen image asynchronization, view zone error, or obvious edge overlapping. To solve the problems mentioned above, a distributed real-time rendering system for ultrahigh-resolution multiscreen 3D display is proposed. Fifteen 3D LCD display devices are driven through a host, cooperating with laser backlights, a lenticular lens array (LLA), and a directional diffuser to display high resolution, high frame rate, large size, and wide-viewing angle 3D images. The resolution of the whole display system can reach 23,040 × 21,600. The rendering system provides a large-scale and real-time 3D scene image with an ultrahigh-definition resolution at a speed of 40 frames per second and high quality.     

Visualization and Computer Graphics on Isotropically Emissive Volumetric Displays

The availability of commodity volumetric displays provides ordinary users with a new means of visualizing 3D data. Many of these displays are in the class of isotropically emissive light devices, which are designed to directly illuminate voxels in a 3D frame buffer, producing x-ray-like visualizations. While this technology can offer intuitive insight into a 3D object, the visualizations are perceptually different from what a computer graphics or visualization system would render on a 2D screen. This paper formalizes rendering on isotropically emissive displays and introduces a novel technique that emulates traditional rendering effects on isotropically emissive volumetric displays, delivering results that are much closer to what is traditionally rendered on regular 2D screens. Such a technique can significantly broaden the capability and usage of isotropically emissive volumetric displays. Our method takes a 3D data set or object as the input, creates an intermediate light field, and outputs a special 3D volume data set called a lumi-volume. This lumi-volume encodes approximated rendering effects in a form suitable for display with accumulative integrals along unobtrusive rays. When a lumi-volume is fed directly into an isotropically emissive volumetric display, it creates a 3D visualization with surface shading effects that are familiar to the users. The key to this technique is an algorithm for creating a 3D lumi-volume from a 4D light field. In this paper, we discuss a number of technical issues, including transparency effects due to the dimension reduction and sampling rates for light fields and lumi-volumes. We show the effectiveness and usability of this technique with a selection of experimental results captured from an isotropically emissive volumetric display, and we demonstrate its potential capability and scalability with computer-simulated high-resolution results.     

一个基于 Google Earth 的交互式空间体数据可视化系统

三维空间体数据的可视化既需要同时展示数据多个属性的特征,又需要结合数据周边复杂地理地貌的特征。体绘制是当前最有效的三维数据可视化方法之一,但现有的体绘制方法尚没有考虑到数据场周围复杂的地理地貌特征。本文提出了一种基于 Google Earth (简称 GE) 地理信息的空间数据体绘制可视化方法,其基本思想是首先由三维纹理算法出发,对数据做沿高度法向的切片,多层渲染后组合为最终的体绘制效果,然后将渲染结果转换为 GE 支持的 KML 数据格式,充分利用 GE 中的复杂地形和三维建筑群模型信息,最后加入体感控制和 WEB 呈现功能。这为三维空间数据的可视化提供了一种全新的思路,取得了更好的可视化效果。最后利用数值模拟的大气雾霾数据论证了技术的可行性。     

Articulated Billboards for Video‐based Rendering

We present a novel representation and rendering method for free‐viewpoint video of human characters based on multiple input video streams. The basic idea is to approximate the articulated 3D shape of the human body using a subdivision into textured billboards along the skeleton structure. Billboards are clustered to fans such that each skeleton bone contains one billboard per source camera. We call this representation articulated billboards. In the paper we describe a semi‐automatic, data‐driven algorithm to construct and render this representation, which robustly handles even challenging acquisition scenarios characterized by sparse camera positioning, inaccurate camera calibration, low video resolution, or occlusions in the scene. First, for each input view, a 2D pose estimation based on image silhouettes, motion capture data, and temporal video coherence is used to create a segmentation mask for each body part. Then, from the 2D poses and the segmentation, the actual articulated billboard model is constructed by a 3D joint optimization and compensation for camera calibration errors. The rendering method includes a novel way of blending the textural contributions of each billboard and features an adaptive seam correction to eliminate visible discontinuities between adjacent billboards textures. Our articulated billboards do not only minimize ghosting artifacts known from conventional billboard rendering, but also alleviate restrictions to the setup and sensitivities to errors of more complex 3D representations and multiview reconstruction techniques. Our results demonstrate the flexibility and the robustness of our approach with high quality free‐viewpoint video generated from broadcast footage of challenging, uncontrolled environments.     

基于微机环境的三维数据场多等值面快速显示算法

直接体绘制技术能够利用半透明效果显示三维数据场，提供了比等值面绘制方法更为丰富的信息，但是，由于数据场中所有体素都参与了图象生成过程，使得该技术的计算开销昂贵，远远无法达到交互式操作的要求。事实上，如果用边界表示法来表示三维数据场，就可以利用三维空间连续性来大幅度缩短绘制时间。边界表示法只关心有值面穿过的边界体元，用Ｏ内存单元来表示大小的原始数据场，从而产生大规模数据压缩。本文在此基础上提出一种基     

Visualizing dynamic geosciences phenomena using an octree-based view-dependent LOD strategy within virtual globes

Geoscientists build dynamic models to simulate various natural phenomena for a better understanding of our planet. Interactive visualizations of these geoscience models and their outputs through virtual globes on the Internet can help the public understand the dynamic phenomena related to the Earth more intuitively. However, challenges arise when the volume of four-dimensional data (4D), 3D in space plus time, is huge for rendering. Datasets loaded from geographically distributed data servers require synchronization between ingesting and rendering data. Also the visualization capability of display clients varies significantly in such an online visualization environment; some may not have high-end graphic cards. To enhance the efficiency of visualizing dynamic volumetric data in virtual globes, this paper proposes a systematic framework, in which an octree-based multiresolution data structure is implemented to organize time series 3D geospatial data to be used in virtual globe environments. This framework includes a view-dependent continuous level of detail (LOD) strategy formulated as a synchronized part of the virtual globe rendering process. Through the octree-based data retrieval process, the LOD strategy enables the rendering of the 4D simulation at a consistent and acceptable frame rate. To demonstrate the capabilities of this framework, data of a simulated dust storm event are rendered in World Wind, an open source virtual globe. The rendering performances with and without the octree-based LOD strategy are compared. The experimental results show that using the proposed data structure and processing strategy significantly enhances the visualization performance when rendering dynamic geospatial phenomena in virtual globes.