面向移动设备的矢量图形绘制技术

在绘制资源受限的移动设备上研究了OpenVG标准中路径的绘制算法.该算法包括几何处理阶段的填充/描边算法、基于活性边的光栅化以及基于位图的缓冲区显示,实现了矢量图形的跨平台绘制.提出了基于曲率的曲线非均匀细分法,通过基于拐点的曲线预处理、求取曲率较大的区间和各区间均匀细分3个步骤,减少了曲线细分和光栅化的计算量,而且生成曲线的光滑程度更高.老虎头和贺卡实例验证了绘制算法在移动设备上的可行性,非均匀细分法的绘制时间更短     

大规模点云内外存调度绘制技术

为实现大规模点云的快速绘制,提出以部分内存访问机制为基础、以节点点数上限为叶节点形成条件的平衡八叉树存储结构。设计点云内外存调度绘制流程,包括节点可见性判断、内外存数据调度和点云绘制等环节。为提高可见性判断的效率,在视点与节点距离、夹角约束条件的基础上给出节点可视半径约束。利用实测大规模点云数据进行实验,结果证明,该技术可以在有限的内存资源条件下,以较小的内存消耗实现上亿级规模点云从整体到局部的流畅绘制。     

Adaptive Surface Visualization of Vessels with Animated Blood Flow

The investigation of hemodynamic information for the assessment of cardiovascular diseases (CVDs) gained importance in recent years. Improved flow measuring modalities and computational fluid dynamics (CFD) simulations yield in reliable blood flow information. For a visual exploration of the flow information, domain experts are used to investigate the flow information combined with its enclosed vessel anatomy. Since the flow is spatially embedded in the surrounding vessel surface, occlusion problems have to be resolved. A visual reduction of the vessel surface that still provides important anatomical features is required. We accomplish this by applying an adaptive surface visualization inspired by the suggestive contour measure. Furthermore, an illustration is employed to highlight the animated pathlines and to emphasize nearby surface regions. Our approach combines several visualization techniques to improve the perception of surface shape and depth. Thereby, we ensure appropriate visibility of the embedded flow information, which can be depicted with established or advanced flow visualization techniques. We apply our approach to cerebral aneurysms and aortas with simulated and measured blood flow. An informal user feedback with nine domain experts, we confirm the advantages of our approach compared with existing methods, e.g. semi‐transparent surface rendering. Additionally, we assessed the applicability and usefulness of the pathline animation with highlighting nearby surface regions.     

Flux‐Limited Diffusion for Multiple Scattering in Participating Media

For the rendering of multiple scattering effects in participating media, methods based on the diffusion approximation are an extremely efficient alternative to Monte Carlo path tracing. However, in sufficiently transparent regions, classical diffusion approximation suffers from non‐physical radiative fluxes which leads to a poor match to correct light transport. In particular, this prevents the application of classical diffusion approximation to heterogeneous media, where opaque material is embedded within transparent regions. To address this limitation, we introduce flux‐limited diffusion, a technique from the astrophysics domain. This method provides a better approximation to light transport than classical diffusion approximation, particularly when applied to heterogeneous media, and hence broadens the applicability of diffusion‐based techniques. We provide an algorithm for flux‐limited diffusion, which is validated using the transport theory for a point light source in an infinite homogeneous medium. We further demonstrate that our implementation of flux‐limited diffusion produces more accurate renderings of multiple scattering in various heterogeneous datasets than classical diffusion approximation, by comparing both methods to ground truth renderings obtained via volumetric path tracing.     

一种视点相关的实时海洋渲染算法“研究生论坛”

针对模拟仿真系统对海洋模拟效果实时性和真实性的严格要求,提出一种视点相关的海洋渲染算法。在实时性上,使用快速傅里叶变换的频谱统计模型计算视点近处的海洋运动细节,使用Perlin噪声扰动的方式模拟视点远处的海洋运动,并对远近过渡区域进行alpha混合处理;在真实性上,构建视点相关的海洋网格并通过实时坐标转换使其能够适用于全球漫游,并结合实时光照和水底折射渲染海水颜色。文章提供了能够适用全球范围海洋真实模拟的新方法。实验表明该算法在展现逼真海洋视觉效果的同时,具有较高的渲染帧率。     

研究基于并行渲染的虚拟现实开发平台设计与实现

在设计三维VR场景时需要依赖可视化的开发平台,设计开发平台时应注重提高软件运行速度,确保硬件接口与软件接口相互匹配,维持虚拟环境共享的一致性,能够及时更新网络协议与升级软件功能,保证VR系统具有兼容性的特点.     

基于视觉认知的汽车内饰造型效果图评价体系构建

目的基于视觉认知理论,构建普适性的汽车内饰造型效果图评价体系。方法根据视觉特征整合理论,建立造型的视觉认知评价框架,萃取相应的评价指标及其权重赋值,建立内饰造型方案效果图评价体系,并通过实证案例检测评价体系的有效性及可行性。结果汽车内饰造型方案效果图的认知存在递阶的层级关系,评价指标具有基础性指标与增益性指标两种属性。结论汽车内饰造型方案效果图评价体系可以辅助设计师有效处理方案评审和完善过程,同时辅助企业进行相关决策。     

面向具有重复结构的大规模CAD模型的快速渲染

目的 基于普通个人计算机快速渲染大规模计算机辅助设计（CAD）模型仍然是个挑战。针对由少量基本对象按一定规律排布而成的大规模CAD模型——重复结构CAD模型,提出一种快速渲染方法,能够在个人计算机上的快速渲染大规模重复结构CAD模型。方法 该方法首先利用重复结构CAD模型的层次结构特征,结合现代GPU的Render-To-Texture的功能进行快速视锥裁剪,节约视锥裁剪时间;然后利用重复结构CAD模型中对象按规律布置的特点,仅对少量基本对象进行面片化,其他对象的面片模型在渲染时根据对象排布规律由基本对象的面片模型实时变换生成,解决大规模CAD模型内存需求过多的问题。结果 基于超级蒙卡核模拟软件系统SuperMC,使用典型重复结构模型——HM（hoogenboom-martin）、ADS（accelerator driven sub-critical system）、DCA（deuterium critical assembly）全堆芯CAD模型进行测试,HM、ADS、DCA模型分别由1 114 384,113 952和20 808个实体组成。测试结果表明,裁剪算法能大幅减少待渲染对象数量,渲染速度明显提高,且模型规模越大,本文方法优势越明显,在远视角的情况下提升效果最为突出,能提升3倍左右;结论 针对任意大规模CAD模型的快速渲染仍然是一个挑战,但本文针对重复结构CAD模型的特点,针对性地提出一套专用渲染策略,在个人计算机上实现大规模重复结构CAD模型的快速渲染。使用多个典型重复结构模型——反应堆全堆芯模型进行测试,测试结果表明了本文方法的有效性。     

Reproducing Spectral Reflectances From Tristimulus Colours

Physically based rendering systems often support spectral rendering to simulate light transport in the real world. Material representations in such simulations need to be defined as spectral distributions. Since commonly available material data are in tristimulus colours, we ideally would like to obtain spectral distributions from tristimulus colours as an input to spectral rendering systems. Reproduction of spectral distributions given tristimulus colours, however, has been considered an ill‐posed problem since single tristimulus colour corresponds to a set of different spectra due to metamerism. We show how to resolve this problem using a data‐driven approach based on measured spectra and propose a practical algorithm that can faithfully reproduce a corresponding spectrum only from the given tristimulus colour. The key observation in colour science is that a natural measured spectrum is usually well approximated by a weighted sum of a few basis functions. We show how to reformulate conversion of tristimulus colours to spectra via principal component analysis. To improve accuracy of conversion, we propose a greedy clustering algorithm which minimizes reconstruction error. Using pre‐computation, the runtime computation is just a single matrix multiplication with an input tristimulus colour. Numerical experiments show that our method well reproduces the reference measured spectra using only the tristimulus colours as input.     

基于MAYA和Unity3D的在线定制鞋系统

针对传统制鞋企业无法满足个性化需求的问题,结合虚拟现实技术的交互性等特点,设计了基于MAYA和Unity3D在线定制鞋系统.首先采用MAYA建模软件中多边形与细分建模相结合的技术进行三维鞋建模;然后基于Unity3D引擎,采用Shader渲染技术实现打包纹理贴图并结合C#脚本语言,实现人机交互功能;最后,应用WebGL技术发布至网页,使用户通过浏览器即可进行在线三维定制鞋的设计及浏览.该系统可以实现用户在网页上个性化定制属于自己的鞋,满足人们个性化定制的理念,对制鞋企业的发展会产生很大的推动力.