支持嵌入式Web服务器的多层级力觉交互仿真

针对传统力觉交互操作过程复杂、模拟物理场景不真实的问题,提出支持嵌入式Web服务器的多层级力觉交互仿真研究方法.在嵌入式Web服务器的基础上添加离散LOD模型,计算相对交互速度,获得目标多层级的序列号进行碰撞计算,构建速度驱动模型.将碰撞检验离散速度驱动模型与SCP层级映射算法相结合,判定映射约束线段、映射约束包围盒单元,运用GHOST SDK计算二者的正交函数,确认满足模型的限制速度阈值条件,从而获得模型的速度参数值以及切换速度,完成力觉交互研究.仿真结果证明,所提方法可以有效解决力觉交互过程中出现的振动现象,提升场景真实感,并且计算简便,具有较高的稳定性与适用性.     

基于分形理论的三维地形场景的真实感绘制

如何在PC机上进行三维地形场景的真实感绘制一直是一个挑战性课题。三维地形场景的真实感绘制追求的两个目标是绘制的逼真度和绘制的实时性,需要在不明显降低图像质量的条件下保持较高的交互帧速率。该文运用分形理论生成三维地形场景,为了满足实时性的要求,采用连续LOD算法和其它技术来加速地形绘制;为了满足逼真度的需求,采用纹理映射和光照映射。这种方法可以在普通微机上基于分形理论实现三维场景的真实感绘制,达到实时性和逼真度的要求。     

LOD模型生成算法研究

细节层次模型(LOD)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LOD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.文中通过对LOD模型生成算法进行分析,研究了基于点删除算法的多分辨率模型生成方法、递进网格的简化算法、基于二次误差度量的几何简化算法等三种算法的实现步骤和误差计算方法.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.     

3D多层次模型简化算法的研究

细节层次模型(LOD)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LOD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.以研究多层次细节模型快速生成算法为目的,在分析当前多层次细节模型生成算法的基础上,构建了三角形面片的权值计算公式,设计和实现了基于面片删除操作的LOD算法,详细描述了算法的设计,给出了算法实现所需的关键公式,最后给出了算法的应用实例和对算法时间效率的分析.此算法的最大特点是在不同的层次细节模型之间快速地平滑过渡.从试验结果和分析可见,该算法可以满足大的3D模型快速生成和交互的需要,同时也证明了算法的正确性和实用性.     

交互式乐器演奏的六自由度力觉渲染方法

目的在进行虚拟乐器交互演奏时,需要模拟触力觉-视觉-听觉多通道同步反馈,其中触力觉反馈的难点在于模拟人手操作乐器的六自由度(6-Do F)力觉交互过程。方法提出一种基于混合模型和单边约束优化的六自由度力觉合成方法,实现了虚拟人手和琴弦的多点多区域接触力觉模拟。虚拟人手采用层次化球树模型表达,古琴采用混合模型表达,其中琴体和琴弦分别采用层次化球树模型和直线解析模型。提出了基于混合模型的离散碰撞检测算法,实时检测虚拟手和琴弦是否产生碰撞;基于发生碰撞的几何元素对建立单边不可穿透约束方程,通过Active Set方法求解约束优化后方程,获得6维位姿变量保证图形显示场景中的虚拟手不会和琴弦产生穿透。为模拟琴弦变形,提出变直径的圆柱体模型来模拟琴弦在不同振动幅度下的动力学响应;提出交互状态敏感的力计算模型以刻画人手在弹奏不同状态琴弦(静态、振动态)的力觉感受差异。结果基于力觉交互设备Phantom Premium 3.0建立了实验平台,实验结果表明,本文算法可以模拟单点、多点等不同接触状态,并能模拟6维力和力矩,操作者可以感受到琴弦振动时的细腻力感觉,力觉交互过程稳定,算法计算效率在1 k Hz以上。结论算法可模拟针对琴弦一类的超薄形状物体的多点接触力觉交互过程,算法计算效率高,包含碰撞检测、约束优化、琴弦变形仿真等计算回路的更新频率也能达到要求,该混合模型能为后续复杂形状物体的碰撞响应研究提供思路。     

三维地形场景的真实感绘制

三维地形场景的真实感绘制追求的两个目标是绘制的逼真度和绘制的实时性，需要在不明显降低图像质量的条件下保持较高的交互帧速率。为了满足实时性的需求，采用连续LOD算法和其它技术来加速地形绘制：为了满足逼真度的需求，采用SAR图像进行纹理映射，采用光照映射实现场景照明和明暗处理。     

基于运动捕获数据的运动LOD技术研究

通过运动捕获技术获得的动画具有高度的逼真性,但由于其数据量大,限制了虚拟场景中动画角色的数量,因此虚拟场景中角色简化的主要目的是在不影响视觉效果的基础上降低角色的渲染花费.将几何LOD思想引入角色运动,对运动LOD进行分类,提出利用关节点的旋转信道计算帧差距来生成和控制不同层次的运动LOD模型,分析不同运动行为选择LOD模型的标准,离散LOD模型和连续LOD模型都得到了很好的简化效果,运动LOD简化技术是提高渲染速度、增加角色数量的有效方法.     

面向牙科手术培训的力觉合成技术

虚拟现实系统的沉浸感和交互性是高性能系统的重要特征,对于医学应用的虚拟现实尤其如此.文中针对牙科手术培训中训练医生触力觉感受的需求,重点研究基于三角面片网格模型的真实感触力觉合成技术,包括基于多更新率的力觉渲染体系架构、基于均匀空间划分和时间连续性的实时碰撞检测算法、基于虚拟代理的接触碰撞响应算法、基于等效接触模型的切削力计算模型,以及滑动速度驱动的大规模数据多层次力觉渲染算法等.建立了力觉-视觉融合的牙科操作培训系统的原型物理样机,实现了龋齿探查、牙齿纵截面物理属性感知、牙体钻削制备等典型牙科手术操作模拟.文中的触力觉合成技术是构建虚拟现实培训系统的共性问题,不但适用于牙科手术操作领域,也可用于其他外科手术培训系统.     

基于四叉树分割的地形LOD技术综述

层次细节(Levels of Detail,LOD)技术是在大规模地形模型简化方面使用得最多的技术,它极大地提高了地形场景的漫游速度。在众多LOD模型中,应用最为广泛的是基于四叉树(Quadtree)分割的LOD算法。国内外学者对LOD模型做了大量的研究工作,文中对基于四叉树分割的LOD算法进行了系统的梳理与总结,对涉及到的核心算法进行了归类并详细分析了各自的优缺点,深入且全面地介绍了其研究现状。     

改进LOD的大规模三维漫游场景简化策略及分割算法

提出一种改进LOD的大规模三维漫游场景简化策略及分割算法,首先应用基于最小二乘粗糙度的节点简化策略对复杂场景网格进行简化,通过改进Lindstrom算法,增加简化准则来解决误差模型精确度下降和粗糙度值变化的问题;然后对简化后的模型采用多通道切割算法进化分割;分割后的场景数据,应用基于误差因子的评价系统来判断;最后实验,通过与传统算法分析比较,证明本文提出的简化策略和分割算法对降低大规模三维场景绘制复杂度,加快场景实时性显示等方面具有较明显的优势．     

面向磁悬浮视触觉交互的多速率系统框架

非接触式磁悬浮视触觉交互克服了机械式交互的固有摩擦,具有广阔应用前景,但存在交互过程中虚拟工具穿透物体、图形渲染与触觉渲染速率不一致等问题。针对上述问题,提出面向磁悬浮视触觉交互的多速率系统框架,通过扩展三自由度（3-DOF）单射线触觉渲染方法,利用多射线对虚拟工具进行建模,避免工具穿透,实现六自由度（6-DOF）触觉渲染;通过多速率并行,实现速率不一致模块间相互协同;通过构建映射滤波算法,实现视觉定位数据到虚拟工具位姿的稳定映射。实验结果表明,该系统能有效避免交互过程中的穿透现象,并提供稳定、真实的视触觉反馈。     

Building a virtual environment for endoscopic sinus surgery simulation

Advanced display technologies have made the virtual exploration of relatively complex models feasible in many applications. Unfortunately, only a few human interfaces allow natural interaction with the environment. Moreover, in surgical applications, such realistic interaction requires real-time rendering of volumetric data—placing an overwhelming performance burden on the system. We report on our advances towards developing a virtual reality system that provides intuitive interaction with complex volume data by employing real-time realistic volume rendering and convincing forece feedback (haptic) sensations. We describe our methods for real-time volume rendering, model deformation, interaction, and the haptic devices, and demonstrate the utilization of this system in the real-world application of Endoscopic Sinus Surgery (ESS) simulation.     

Six degree-of-freedom haptic rendering using spatialized normal cone search

This paper describes a haptic rendering algorithm for arbitrary polygonal models using a six degree-of-freedom haptic interface. The algorithm supports activities such as virtual prototyping of complex polygonal models and adding haptic interaction to virtual environments. The underlying collision system computes local extrema in distance between the model controlled by the haptic device and the rest of the scene. The haptic rendering computes forces and torques on the moving model based on these local extrema. The system is demonstrated on models with tens of thousands of triangles and developed in an accessibility application for finding collision-free paths.     

Stable adaptive algorithm for Six Degrees-of-Freedom haptic rendering in a dynamic environment

Recently, physically-based simulations with haptics interaction attracted many researchers. In this paper, we propose an adaptive Six Degrees-of-Freedom (6-DOF) haptic rendering algorithm based on virtual coupling, which can automatically adjust virtual coupling parameters according to mass values of the simulated virtual tools. The algorithm can overcome the virtual tool displacement problem caused by the large mass values of the virtual tool and can provide stable force/torque display. The force/torque magnitude is saturated to the maximum force/torque values of the haptic device automatically. The implemented algorithm is tested on the simple and complex standard benchmarks. The experimental results confirm that the proposed adaptive 6-DOF haptic rendering algorithm displays good stability and accuracy for haptic rendering of dynamic virtual objects with mass values.     

高度复杂拟凸体的实时触觉绘制

触觉绘制目前已成为虚拟现实的研究热点之一,其核心是触觉代理与目标物体的实时碰撞检测与距离计算,对高度复杂模型的触觉绘制仍然是虚拟现实领域的难题,原因是对模型复杂度敏感的算法均不能满足触觉绘制苛刻的时间要求.提出触觉包围盒概念,并针对拟凸体提出一种基于触觉包围盒的实时触觉绘制算法.触觉包围盒记录了离散的采样光线与目标物体的相交信息,进行触觉计算时,只需要执行1次线段与包围盒求交运算和5次双线性插值运算即可高速求出碰撞信息,且所得到的碰撞信息可直接用于反馈力计算.实验结果表明,该算法不仅快速有效,而且具有与触觉绘制模型复杂度不相关的优点.     

Haptic rendering for dental training system

Immersion and interaction are two key features of virtual reality systems, which are especially important for medical applications. Based on the requirement of motor skill training in dental surgery, haptic rendering method based on triangle model is investigated in this paper. Multi-rate haptic rendering architecture is proposed to solve the contradiction between fidelity and efficiency requirements. Realtime collision detection algorithm based on spatial partition and time coherence is utilized to enable fast contact determination. Proxy-based collision response algorithm is proposed to compute surface contact point. Cutting force model based on piecewise contact transition model is proposed for dental drilling simulation during tooth preparation. Velocity-driven levels of detail haptic rendering algorithm is proposed to maintain high update rate for complex scenes with a large number of triangles. Hapticvisual collocated dental training prototype is established using half-mirror solution. Typical dental operations have been realized including dental caries exploration, detection of boundary within dental cross-section plane, and dental drilling during tooth preparation. The haptic rendering method is a fundamental technology to improve immersion and interaction of virtual reality training systems, which is useful not only in dental training, but also in other surgical training systems. Supported by National Natural Science Foundation of China (Grant Nos. 60605027, 50575011), National High-Tech Research & Development Program of China (Grant No. 2007AA01Z310)     

Sensation-preserving haptic rendering

Most human-computer interactive systems focus primarily on the graphical rendering of visual information and, to a lesser extent, on the display of auditory information. Haptic interfaces have the potential to increase the quality of human-computer interaction by accommodating the sense of touch. They provide an attractive augmentation to visual display and enhance the level of understanding of complex data sets. A haptic rendering system generates contact or restoring forces to prevent penetration into the virtual objects and create a sense of touch. The system computes contact forces by first detecting if a collision or penetration has occurred. Then, the system determines the (projected) contact points on the model surface. Finally, it computes restoring forces based on the amount of penetration. Researchers have recently investigated the problem of rendering the contact forces and torques between 3D virtual objects. This problem is known as six-degrees-of-freedom (6-DOF) haptic rendering, as the computed output includes both 3-DOF forces and 3-DOF torques. This article presents an overview of our work in this area. We suggest different approximation methods based on the principle of preserving the dominant perceptual factors in haptic exploration.     

An information-theoretic treatment of passive haptic media

Haptic rendering has been long considered as the process of estimating the force that stems from the interaction of a user and an object. Even if this approach follows the principles of natural haptic interaction, it places severe limitations in processing haptic media. This paper presents an information theoretic framework that aims to provide a new view of haptic rendering that can accommodate for open-loop synthetic haptic media, where interaction-based rendering is a special case. As a result, using the proposed information-theoretic approach, the haptic signal can be precomputed as a force field, stored and then filtered by taking into account device and perceptual capabilities of the receiver in order to lower the required bandwidth of the resulting stream, thus opening new possibilities for the representation and processing of haptic media.     

Haptic rendering of dynamic volumetric data

With current methods for volume haptics in scientific visualization, features in time-varying data can freely move straight through the haptic probe without generating any haptic feedback the algorithms are simply not designed to handle variation with time but consider only the instantaneous configuration when the haptic feedback is calculated. This article introduces haptic rendering of dynamic volumetric data to provide a means for haptic exploration of dynamic behaviour in volumetric data. We show how haptic feedback can be produced that is consistent with volumetric data moving within the virtual environment and with data that, in itself, evolves over time. Haptic interaction with time-varying data is demonstrated by allowing palpation of a CT sequence of a beating human heart.     

虚拟体空间中的触觉雕刻

目前，在虚拟环境中大多数的信息获取是通过视觉、听觉等非接触感觉获得的。然而缺乏触觉反馈的信息减少了很大一部分的信息源。在看和听之外，能够触摸、感觉和操纵物体，在很大程度上提高了虚拟环境的真实性。该文研究了触觉绘制的基本模型，提出了采用虚平面作为中介实现体数据的实时触觉绘制。并在此基础上探讨了体的局部变形及结合触觉反馈模型，实现了具有触觉反馈的虚拟雕刻交互系统。该系统可应用于融化、燃烧、印记、构造和着色实时交互操作。