基于SIP的VoWLAN漫游时延优化方法研究

针对现有基于SIP的VoWLAN环境下漫游时延过长和漫游成功率不高的问题,本文提出了一种新的漫游管理服务器解决方案.此方案中由漫游控制服务器控制整个漫游过程,采用资源预申请和应用层预漫游以及对SIP_EYE的支持,减少漫游时延和提高漫游成功率,从而进一步减少漫游时延.通过网络仿真,证明了此方案在减少漫游时延和提高漫游成功率上的有效性和可行性,具有一定的实际应用价值.     

一种快速VoWLAN漫游切换机制研究

介绍经典的VoWLAN子网间漫游802.11r和域间漫游Mobile IP和Mobile SIP,针对它们漫游切换时延过长的缺点,本文提出一种全漫游解决方案FROAM,除了将802.11r和Mobile SIP机制有机结合外,增加一个漫游模式判断服务器,使得可以分别处理子网间漫游和域间漫游,并把域间漫游中的SIP协议信令控制过程提前到链路切换之前。仿真表明,FROAM大大降低了切换延迟,提高了漫游切换性能。     

基于Cardinal样条曲线的虚拟漫游路径优化

漫游路径不平滑和漫游相机视角方向固定是导致虚拟漫游沉浸感差的主要问题.基于此,提出一种基于Cardinal样条曲线拟合的漫游路径平滑过渡算法,解决漫游中由于漫游路径不平滑造成的视点跳跃问题;提出一种虚拟漫游相机视角方向动态更新算法,实现漫游相机视角方向沿路径方向动态更新,更加符合人们的观察习惯;最后,基于开源场景图形引擎(OpenSceneGraph,OSG)对上述算法进行了实现和实验验证.结果表明,基于所提方法生成的漫游路径平滑、漫游相机视角方向过渡自然,有效提高了漫游的虚拟沉浸感.     

视景仿真系统中以人机交互控制漫游模式

实施了一个民族博物馆视景仿真漫游系统的项目。在传统的漫游方式下,增加了特定的人机交互功能,如自由选择漫游方式、双通道观赏等,并使用线性样条解决了生成自动漫游路径的问题。实验结果表明,灵活的人机交互功能丰富了视景仿真系统的漫游方式。     

三维场景交互漫游的研究与实现

给出了一个三维场景交互漫游系统的框架,着重介绍了三维空间漫游的方法及实现,包括键盘漫游、路径漫游、记录漫游路径,记录场景动画,碰撞检测等,并提出按线性样条路径漫游时转角处抖动问题的解决方法,这些方法都已应用到作者开发的系统当中,收到了满意的效果。     

体感交互虚拟漫游的沉浸感评价

沉浸感是虚拟漫游的重要特征,目前体感交互的虚拟漫游存在严重的感知失真问 题,虚拟场景运动的视觉感知与人机交互的体感感知不能相互匹配,破坏了虚拟漫游的沉浸感。 基于Catmull-Rom 曲线的非等距插值算法、等距插值算法和实时插值算法,分别构建3 种不同 的虚拟漫游路径,评价体感交互虚拟漫游的沉浸感。主观评价实验和仿真实验的结果表明： Catmull-Rom 曲线的非等距插值漫游路径,无论是匀速漫游还是变速漫游,均存在明显的感知 失真现象;基于Catmull-Rom 曲线的等距插值漫游路径适用于匀速漫游,但不太适合用于变速 漫游;基于Catmull-Rom 曲线的实时插值漫游路径能实现真实运动速度与场景运动速度的匹配, 较好地解决虚拟漫游时视觉感知与身体运动感知不一致的问题,增强了虚拟漫游的沉浸感。     

基于信任度的对等实体间的网络用户漫游机制

针对网络应用中用户频繁注册、多账号多密码和反复登录的问题，该文提出了网络用户漫游机制，构造了相应的网络用户漫游模型。引入了漫游信任度、对等实体综合信任度、网络用户信任度来描述实体的可漫游性，给出了各个信任度的计算算法，讨论了网络用户漫游技术。分析和验证表明，基于信任度的对等实体间的网络用户漫游机制具备可行性。     

基于场景建模的虚拟漫游系统

介绍了基于场景建模的虚拟漫游系统,分析了通用漫游引擎开发中的相关技术,最后以实际应用为例说明该漫游引擎在场景漫游设计中的优越性以及需要注意的问题.     

三维数字技术在建筑漫游动画中的应用研究

在人们可视化要求越来越高、市场需求不断增加的数字媒体时代,建筑漫游动画的市场迅速发展起来.通过多年的教学和实践经验,分析了建筑漫游动画的特点、作用、需求和实现技术,研究了三维数字技术在建筑漫游动画中的应用,利用三维数字技术制作了潍坊职业学院滨海校区建筑漫游动画,总结了建筑漫游动画的制作要点、制作流程、技巧、注意事项和建筑漫游动画制作关键技术.指出了建筑漫游动画是未来建筑表现的一种新形式,也是三维数字技术新的应用领域.     

非跳跃式全景漫游算法及在X3D下的实现

针对目前全景漫游系统漫游在切换视点过程中产生跳跃感的问题提出了一种实用的全景漫游算法。该算法以摄影变焦原理为基础,结合人机工程学视觉原则方面的理论,通过对观察摄像机朝向和视角的操作模拟视点的运动过程,实现漫游效果。漫游过程避免了复杂的图像变换运算,有很好的实时性。并且创建了一个运用该算法控制全景漫游的X3D场景,实验验证了该算法的可行性。     

Accelerated Walkthroughs of Virtual Environments Based on Visibility Preprocessing and Simplification

This paper proposes a new preprocessing method for interactive rendering of complex polygonal virtual environments. The approach divides the space that observer can reach into many rectangular viewpoint regions. For each region, an outer rectangular volume (ORV) is established to surround it. By adaptively partitioning the boundary of the ORV together with the viewpoint region, all the rays that originate from the viewpoint region are divided into the beams whose potentially visible polygon number is less than a preset threshold. If a resultant beam is the smallest and intersects many potentially visible polygons, the beam is simplified as a fixed number of rays and the averaged color of the hit polygons is recorded. For other beams, their potentially visible sets (PVS) of polygons are stored respectively. During an interactive walkthrough, the visual information related to the current viewpoint is retrieved from the storage. The view volume clipping, visibility culling and detail simplification are efficiently supported by these stored data. The rendering time is independent of the scene complexity.     

包含整体镜面反射的虚拟场景实时漫游算法

针对复杂多边形场景,提出了一种基于层面叠加技术并能处理整体镜面反射分量的漫游算法.此算法将整体镜面反射分量预处理和整个场景的预消隐紧密结合,把整体镜面反射的计算问题转化为求取光束PVS(potentially visible set)的问题.算法通过预处理,建立镜面PVS映射G和可能镜面入射光束集合;在漫游阶段,则通过执行G映射并调用其他层面的光亮度计算过程,实时地合成整体镜面反射分量.     

虚平面映射:深度图像内部视点的绘制技术

首先推导与归纳了图像三维变换中像素深度场的变换规律,同时提出了基于深度场和极线原则的像素可见性别方法,根据上述理论和方法,提出一种基于深度图像的建模与绘制(image-based modeling and rendering,简称IBMR)技术,称为虚平面映射.该技术可以基于图像空间内任意视点对场景进行绘制.绘制时,先在场景中根据视线建立若干虚拟平面,将源深度图像中的像素转换到虚平面上,然后通过对虚平面上像素的中间变换,将虚平面转换成平面纹理,再利用虚平面的相互拼接,将视点的成像以平面纹理映射的方式完成.新方法还能在深度图像内侧,基于当前视点快速获得该视点的全景图,从而实现视点的实时漫游.新方法视点运动空间大、存储需求小,且可以发挥图形硬件的纹理映射功能,并能表现物体表面的三维凹凸细节和成像视差效果,克服了此前类似算法的局限和不足.     

复杂模型的视点依赖简化算法

为了达到在虚拟环境的漫游系统中对复杂模型进行实时绘制的目的，通常采用多层次细节模型来解决这一问题，给出一种即与视点相关又无须对原来的复杂模型进行预处理的网格简化算法，该算法采用精细(refinement)法．每次绘制前都从最粗糙的模型开始，根据视点位置、视方向和模型的每个部分产生的误差，对影响视觉效果大的部分进行细分(subdivision)，逐步产生可显示的模型，实验表明，本文提出的网格简化算法能在对视觉效果影响不大的前提下大大降低需要绘制的三角形数量。     

基于纹理数组的大规模地形绘制算法

将Shader Model 4.0引入的纹理数组技术同顶点纹理拾取技术、瓦片块四叉树算法和地形分块技术等相结合,提出了一种基于GPU的大规模地形绘制方法。将整个大规模地形数据分割成地形块,按照金字塔模型保存在CPU内存里,将地形中潜在的可见部分以纹理数组形式驻留在GPU Cache里;在CPU上发送瓦片块四叉树平面网格,利用存储在GPU Cache里的高程值生成相应的地形;GPU Cache随着视点运动而连续更新。实验证明该方法充分利用了现代GPU的特性,适合于大规模地形的漫游。     

FastV: From-point Visibility Culling on Complex Models

We present an efficient technique to compute the potentially visible set (PVS) of triangles in a complex 3D scene from a viewpoint. The algorithm computes a conservative PVS at object space accuracy. Our approach traces a high number of small, volumetric frusta and computes blockers for each frustum using simple intersection tests. In practice, the algorithm can compute the PVS of CAD and scanned models composed of millions of triangles at interactive rates on a multi-core PC. We also use the visibility algorithm to accurately compute the reflection paths from a point sound source. The resulting sound propagation algorithm is 10–20X faster than prior accurate geometric acoustic methods.     

Spherical Visibility Sampling

Many 3D scenes (e.g. generated from CAD data) are composed of a multitude of objects that are nested in each other. A showroom, for instance, may contain multiple cars and every car has a gearbox with many gearwheels located inside. Because the objects occlude each other, only few are visible from outside. We present a new technique, Spherical Visibility Sampling (SVS), for real‐time 3D rendering of such – possibly highly complex – scenes. SVS exploits the occlusion and annotates hierarchically structured objects with directional visibility information in a preprocessing step. For different directions, the directional visibility encodes which objects of a scene's region are visible from the outside of the regions' enclosing bounding sphere. Since there is no need to store a separate view space subdivision as in most techniques based on preprocessed visibility, a small memory footprint is achieved. Using the directional visibility information for an interactive walkthrough, the potentially visible objects can be retrieved very efficiently without the need for further visibility tests. Our evaluation shows that using SVS allows to preprocess complex 3D scenes fast and to visualize them in real time (e.g. a Power Plant model and five animated Boeing 777 models with billions of triangles). Because SVS does not require hardware support for occlusion culling during rendering, it is even applicable for rendering large scenes on mobile devices.     

Interactive direct rendering of trivariate B-spline scalarfunctions

This paper presents a direct rendering paradigm of trivariate B-spline functions that is able to incrementally update complex volumetric data sets in the order of millions of coefficients at interactive rates of several frames per second on modern workstations. This incremental rendering scheme can hence be employed in modeling sessions of volumetric trivariate functions, offering interactive volumetric sculpting capabilities. The rendering is conducted from a fixed viewpoint and in two phases. The first, preprocessing stage accumulates the effect that the coefficients of the trivariate function have on the pixels in the image. This preprocessing stage is conducted offline and only once per trivariate and viewing direction. The second stage conducts the actual rendering of the trivariate functions. As an example, during a volumetric sculpting operation, the artist can sculpt the volume and get a displayed feedback, in interactive rates     

虚拟环境漫游系统绘制优化技术的集成框架

In the walkthrough of virtual environments, the number of polygons consisting the virtualenvironments often far exceeds the rendering capacity of graphics pipeline with interactive frame rates.One solution is to reduce the number of primitives before they are sent into the graphics pipeline by ex-ploiting various optimal rendering techniques. Since no single such technique can achieve satisfactoryframe rate, frameworks for integrating several optimal rendering techniques are needed to solve theproblem. In this paper ,some frameworks and the data structures needed by them are discussed in detail.And one kind of proposed framework suitable for PC is presented 1in this paper.     

Tone Reproduction for Interactive Walkthroughs

When a rendering algorithm has created a pixel array of radiance values the task of producing an image is not yet completed. In fact, to visualize the result the radiance values still have to be mapped to luminances, which can be reproduced by the used display. This step is performed with the help of tone reproduction operators. These tools have mainly been applied to still images, but of course they are just as necessary for walkthrough applications, in which several images are created per second. In this paper we illuminate the physiological aspects of tone reproduction for interactive applications. It is shown how tone reproduction can also be introduced into interactive radiosity viewers, where the tone reproduction continuously adjusts to the current view of the user. The overall performance is decreased only moderately, still allowing walkthroughs of large scenes.