数字人切片数据的硬件加速体绘制

实现了一个PC平台下的体绘制硬件加速算法，并对中国数字人、美国可视化人数据集进行可视化．预处理去除图像背景时，将图像从RGB颜色空间转换到YCbCr颜色空间，然后对Cb分量进行Otsu阈值化处理，用生成的二值图像作为掩码图像去除背景．为支持任意大小的体数据，采取了分块策略，并使用BSP树组织数据块，以生成正确的绘制顺序．此外还设计了一种基于图像的CIELUV颜色空间L分量的梯度向量场的传输函数，并取得了良好的绘制效果．     

Volume-preserving free-form solids

Some important trends in geometric modeling are the reliance on solid models rather than surface-based models and the enhancement of the expressive power of models, by using free-form objects in addition to the usual geometric primitives and by incorporating physical principles. An additional trend is the emphasis on interactive performance. In this paper, we integrate all of these requirements into a single geometric primitive by endowing the tri-variate tensor-product free-form solid with several important physical properties, including volume and internal deformation energy. Volume preservation is of benefit in several application areas of geometric modeling, including computer animation, industrial design and mechanical engineering. However, previous physics-based methods, which have usually used some form of “energy”, have neglected the issue of volume (or area) preservation. We present a novel method for modeling an object composed of several tensor-product solids while preserving the desired volume of each primitive and ensuring high-order continuity constraints between the primitives. The method utilizes the Uzawa algorithm for non-linear optimization, with objective functions based on deformation energy or least squares. We show how the algorithm can be used in an interactive environment by relaxing exactness requirements while the user interactively manipulates free-form solid primitives. On current workstations, the algorithm runs in real-time for tri-quadratic volumes and close to real-time for tri-cubic volumes     

基于可见性预处理和细节简化的虚拟环境快速漫游算法

本文针对复杂多边形场早的漫游提出了一个新的预处理方法，并给出了相应的快速漫游算法。     

Live path: adaptive agent navigation in the interactive virtual world

We present a novel approach to adaptive navigation in the interactive virtual world by using data from the user. Our method constructs automatically a navigation mesh that provides new paths for agents by referencing the user movements. To acquire accurate data samples from all the user data in the interactive world, we use the following techniques: an agent of interest (AOI), a region of interest (ROI) map, and a discretized path graph (DPG). Our method enables adaptive changes to the virtual world over time and provides user-preferred path weights for smart-agent path planning. We have tested the usefulness of our algorithm with several example scenarios from interactive worlds such as video games. In practice, our framework can be applied easily to any type of navigation in an interactive world. In addition, it may prove useful for solving previous pathfinding problems in static navigation planning.     

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。     

A General Version of Crow's Shadow Volumes

In 1977 Frank Crow introduced a new class of algorithm for the generation of shadows. His technique, based on the concept of shadow volumes, assumes a polygonal database and a constrained environment. For example, polyhedrons must be closed, and polygons must be planar. This article presents a new version of Crow's algorithm, developed at the Universite de Montreal, which attempts a less constrained environment. The method has allowed the handling of both open and closed models and nonplanar polygons with the viewpoint anywhere, including any shadow volume. It does not, however, sacrifice the essential features of Crow's original version: penetration between polygons is allowed and any number of light sources can be defined anywhere in 3D space, including the view volume and any shadow volume. The method has been used successfully in the film Tony de Peltrie and is easily incorporated into an existing scan-line, hidden-surface algorithm.     

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.     

面向互动式网络场景再现的流速控制系统与方法

互动式网络场景再现是一种重要的真实网络流量产生方法.然而,由于流量产生过程的复杂性,基于精确的数学模型对该过程产生流速进行控制是一个较为困难的新问题.文中设计实现了一个面向互动式网络场景再现的流速控制系统,并将网络场景再现过程中的流速控制问题转化为目标跟踪控制问题进行求解.该系统采用一种基于函数近似器的流速控制方法,利用函数近似器对系统的输入输出关系进行描述,通过动态调整系统输入流量来对回放过程输出流量进行跟踪.最后,利用真实网络流量实验考察了文中系统和方法在不同丢包、传输延迟以及会话阻断环境下的实际控制效果,并从收敛时间、产生输入输出、控制误差等角度对系统的控制性能进行了分析.     

Error-controlled real-time cut updates for multi-resolution volume rendering

Multi-resolution techniques are required for rendering large volumetric datasets exceeding the size of the graphics card's memory or even the main memory. The cut through the multi-resolution volume representation is defined by selection criteria based on error metrics. For GPU-based volume rendering, this cut has to fit into the graphics card's memory and needs to be continuously updated due to the interaction with the volume such as changing the area of interest, the transfer function or the viewpoint. We introduce a greedy cut update algorithm based on split-and-collapse operations for updating the cut on a frame-to-frame basis. This approach is guided by a global data-based metric based on the distortion of classified voxel data, and it takes into account a limited download budget for transferring data from main memory into the graphics card to avoid large frame rate variations. Our out-of-core support for handling very large volumes also makes use of split-and-collapse operations to generate an extended cut in the main memory. Finally, we introduce an optimal polynomial-time cut update algorithm, which maximizes the error reduction between consecutive frames. This algorithm is used to verify how close to the optimum our greedy split-and-collapse algorithm performs.     

Visual guided navigation for image retrieval

In this work, we are interested in technologies that will allow users to actively browse and navigate large image databases and to retrieve images through interactive fast browsing and navigation. The development of a browsing/navigation-based image retrieval system has at least two challenges. The first is that the system's graphical user interface (GUI) should intuitively reflect the distribution of the images in the database in order to provide the users with a mental picture of the database content and a sense of orientation during the course of browsing/navigation. The second is that it has to be fast and responsive, and be able to respond to users actions at an interactive speed in order to engage the users. We have developed a method that attempts to address these challenges of a browsing/navigation based image retrieval systems. The unique feature of the method is that we take an integrated approach to the design of the browsing/navigation GUI and the indexing and organization of the images in the database. The GUI is tightly coupled with the algorithms that run in the background. The visual cues of the GUI are logically linked with various parts of the repository (image clusters of various particular visual themes) thus providing intuitive correspondences between the GUI and the database contents. In the backend, the images are organized into a binary tree data structure using a sequential maximal information coding algorithm and each image is indexed by an n-bit binary index thus making response to users’ action very fast. We present experimental results to demonstrate the usefulness of our method both as a pre-filtering tool and for developing browsing/navigation systems for fast image retrieval from large image databases.