保留细节特征的轮廓线远程绘制算法

目前,智能掌上电脑、个人数字助理和智能手机等移动终端因为其便携性和可移动性,越来越多地被应用于分布式虚拟环境中,但是因为移动终端自身的局限性,在移动终端上的3维模型实时绘制问题仍未得到很好的解决。结合多分辨率网格模型和基于轮廓线的远程绘制的优点,提出了一种保留细节特征的轮廓线远程绘制算法。该算法预处理阶段,在原始精细网格模型上提取细节特征线,并进行多分辨率网格模型的预处理;运行时阶段,根据视点、帧率等交互信息使用选取策略对细节特征线进行选取,然后构建合适的多分辨率网格模型,并在该模型上提取出外围轮廓线,最后发送这两种轮廓线到移动终端进行绘制。实验结果表明,该算法在基于轮廓线的远程绘制中较好地保留了模型的细节特征,并保证了在移动终端的实时绘制。     

视相关地形多分辨率模型在飞行仿真中的应用

对于飞行仿真中海量地形数据,现有的软硬件无法直接对其进行实时连续的绘制,采用视点相关的层次细节模型可以有效地提高实时绘制的性能.该文针对飞行仿真中大地形实时显示问题,对现有的视点相关多分辨率模型算法进行了改进,采用四叉树结构来表示地形,给出了节点的数据结构和构建四叉树的算法;提出了一种新的细节层次选择误差度量标准;实现了视点相关的连续多分辨率地形网格的简化和实时绘制.     

大型三维网格模型的简化及基于视点的LOD控制

传统的三维网格简化及多分辨率建模方法对数据量超出内存限制的大型网格模型已不适用．提出一种基于外存的网格简化和基于视点的细节层次控制方法．该方法建立在网格分割的基础上，利用分割边界的对应性，在一次遍历中对所有的网格分块进行简化，从而克服了通常的网格分割简化方法需要多次分割、重复简化的缺点；同时实现了针对大型网格模型的基于视点的选择件绘制．对模型进行绘制时，模型局部细节可以被快速抽取出来，并且网格的分辨率在整个模型表面呈连续分布．     

基于混合多细节层次技术的实时绘制算法

细节层次是实时图形生成的一项重要技术.提出一种把视点无关和视点相关两类多细节层次技术结合起来的网格模型实时绘制算法.该算法首先根据应用领域的不同要求或用户给出的误差范围,对模型进行与视点无关的预处理简化,然后把简化后得到的模型用在与视点相关的实时简化算法中.实验表明,这种网格模型简化和绘制算法能在损失很小的屏幕像素误差的前提下大大提高绘制速度.     

基于限制四叉树的网格递进算法

提出基于限制四叉树的不同分辨率网络模型之间的网格递进方法,实现了在模型误差控制下视点相关的多分辨网格的实时正确构网.实验证明,该方法对于实时控制大规模地形模型的细节层次,增强大规模地形模型的绘制效率是非常有效的.     

基于边优化的三角网格简化算法

在渐进网格算法的基础上,提出一种新的基于边优化的三角网格简化算法。在该方法重建出的多分辨率模型表面上,模型的细节层次呈连续分布,并且能跟随视点位置的变化发生动态变化。实验结果表明,该算法运算速度快,显示效果较好,能有效支持细节层次模型的表示。     

一种基于视点的网格模型简化算法

在计算机图形学中,经常采用网格模型对物体和场景进行描述,而网格模型的大数据量成为实时绘制的瓶颈.因此,必须对网格模型进行简化,目前的简化算法,主要是以网格模型几何误差的最小化为准则,而忽略了模型的视觉特征.本文提出了一种基于视点的网格模型简化算法,其简化准则是视觉特征的最优化,利用视点相关,建立视点与网格精度的对应关系,对距离视点较近的部分采用较密网格,对距视点较远的部分采用稀疏网格.实验结果表明,该算法能够在保证高度真实感视觉效果的前提下,实现模型较大幅度的简化.     

大型网格模型简化和多分辨率技术综述

网格简化和多分辨率绘制是2种对于提高绘制性能非常有效的技术,但对于大型网格模型,这2种技术的设计和实现本身也存在诸多难点.文中综述了大型网格模型简化和多分辨率技术的研究进展,首先分析和比较基于网格分割、基于外存数据结构和基于流式策略的大型网格模型简化方法,然后介绍和比较大型网格模型多分辨率表示的设计、构建和绘制技术.最后总结并展望了该研究领域的发展趋势.     

基于分形维数的地表模型多分辨率动态绘制

以基于分形维数的树状结构组织三维地表网格模型,实现了与视点相关的连续多分辨率地表模型简化及实时绘制.算法分为预处理和实时绘制两个阶段.在预处理阶段,通过分形维数评价地表的复杂度,建立自适应的树状结构,计算出所有顶点的误差值.在绘制阶段,则根据视距、视角等因素动态地确定需保留的顶点集,并采用受限四叉树方法实时三角化得到所需分辨率下的三角网格近似模型.该算法具有两个优点:一个是地表模型的分层区域划分考虑了地形本身的复杂度;另一个是建立了视点相关各参数与所采用的分辨率表示的直接关系.实验表明,此算法简单、有效,支持对地表模型的交互式实时动态绘制.     

距离加权的二次误差测度多分辨率网格简化

为了有效显示复杂的三维物体网格模型,基于边折叠操作与二次误差测度,给出了建立与视点相关的多分辨率模型的网格简化算法.该方法引入了距离因子与三角形形态品质因子:网格顶点到视点的距离因子使得产生了与视点位置相关的符合观察需要的网格;三角形形态品质因子的引入,提高了简化后新生成的三角形的形态品质.同时,在构造候选边队列时,采取了邻域冻结办法,避免了对模型的某个部位过度简化与过大三角形的出现.实验结果表明,在保证效率的前提下,简化速度快,但显示并无明显失真,简化后的三角形形态品质较好.该算法适应于三角形网格模型的简化、优化及建立多分辨率细节模型.     

基于Hamiltonian三角剖分的三角网格多分辨率表示

三角网格模型的多分辨率表示是几何模型绘制与传输的基础，本文通过三角形之间的拓扑相邻关系将三角网格划分为广义三角形带的集合，然后利用Hamiltonian三角剖分的性质构造三角网格的多分辨率表示。该方法统一了单分辨率网格和多分辨率网格的表示方法，当模型有c个不同分辨率表示时，其编码效率为（logc＋5）bit／vertex。     

Displacement patches for view-dependent rendering

In this paper we present a new approach for interactive view-dependent rendering of large polygonal data sets which relies on advanced features of modern graphics hardware. Our preprocessing algorithm starts by generating a simplified representation of the input mesh. It then builds a multiresolution hierarchy for the simplified model. For each face in the hierarchy, it generates and assigns a displacement map that resembles the original surface represented by that face. At runtime, the multiresolution hierarchy is used to select a coarse view-dependent level-of-detail representation, which is sent to the graphics hardware. The GPU then refines the coarse representation by replacing each face with a planar tile, which is elevated according to the assigned displacement map. Our results show that our implementation achieves quality images at high frame rates.     

Perception-motivated multiresolution rendering on sole-cube maps

This paper presents a novel GPU-based multiresolution rendering on sole-cube maps (SCMs), which is a variant of geometry images built upon spherical parameterization. Given spherical parametrization of a manifold mesh, the sphere domain is gnomonically projected to a closed cube, which constitutes the 6-chart sole-cube maps. A quadtree structure of SCMs and normal map atlas are then constructed by using the regular re-sampling. Then, by packing the quadtree nodes into the SCMs texture atlas, a new parallel multiresolution rendering is processed on the latest GPU in two rendering passes: the multiresolution node selection in fragment shader; the triangulation in vertex shader followed by the node culling operation in geometry shader. The proposed approach generates adaptive mesh surfaces dynamically, and can be fully implemented in GPU parallelization. The proposed scheme alleviates the computing load of multiresolution mesh refinement on CPU, and our GPU-based multiresolution rendering is demonstrated with a variety of examples. Our user study confirmed that the visual quality of the SCMs multiresolution rendering, in comparison with the meshes/geometry images rendering, is also highly efficient especially for complex models in large-scale virtual environment.     

体积保持的多分辨率多边形网格的光顺造型

给出了一个高效的多边形网格的多分辨率光顺造型算法。该算法首先通过引入体积保持约束,快速地实现稠密多边形网格的多分辨率表示,然后结合一个有效的无收缩光顺算法,对网格执行高效的多分辨率光顺编辑,与传统编辑方法不同,该方法利用体积保持约束及优化技术,来自动恢复编辑区域中相应的细节,而无需引入非常损耗资源的局部标架。实验结果表明,该算法计算稳定、高效,能产生复杂的模型。     

个性化三维人脸模型的特征约束多分辨率绘制

给出了一种有效支持个性化变形的三维人脸模型结构和一种特征约束的实时连续多分辨率绘制方法。为方便变形中特征点及相关区域的移动，模型结构的设计体现了人脸特征及模型中点、边、面的邻接关系。基于这种模型结构的多分辨率绘制方法给出了特征约束的有序递减网格设计，实现了视距相关的快速模型简化，在保持模型视觉特征的同时保证了实时连续绘制。     

一种新的基于顶点聚类的网格简化算法

在计算机图形学中,经常采用多边形网格来描述物体模型.由于绘制时间和存储量 与多边形的数量成正比,过于庞大的物体网格模型通常是不实用的.模型简化在计算机动画、 虚拟现实和交互式可视化等计算机图形应用领域有着广阔的应用前景.为此提出一种新的基 于顶点聚类的网格简化算法.该算法利用八叉树对网格进行自适应划分,给出了一种基于点 到平面距离的有效的误差控制方法,并能在用户指定的误差范围内通过使原始网格中的顶点 聚类达到大量简化的目的.该算法实现简单,速度快且能很好地保持边界特征.给出的一组图 例说明了该算法的有效性.     

An algorithm for converting the boundary representation of a CAD model to its octree representation

Present CAD systems store the solid model of an object using a convenient representation. Boundary models and CSG (Constructive Solid Geometry) models are the most frequently used representations. Based on recent research findings, octree representation of an object presents a promising approach in solving problems in the areas of Computer Graphics, Manufacturing and Robotics. The most notable use of octree representations is in CAD-based robotic path planning problems. Octree models have also been used in fast rendering of 3-D solid models using ray tracing methods. This paper presents an algorithm for converting the boundary representation of polyhedral models to its octree representation. Such an algorithm would provide the link between an object generated using a solid modelling system and the application involving an octree representation of an object. The algorithm is demonstrated by converting a polyhedral boundary model of a sample object to its octree representation.     

A single-pass GPU ray casting framework for interactive out-of-core rendering of massive volumetric datasets

We present an adaptive out-of-core technique for rendering massive scalar volumes employing single-pass GPU ray casting. The method is based on the decomposition of a volumetric dataset into small cubical bricks, which are then organized into an octree structure maintained out-of-core. The octree contains the original data at the leaves, and a filtered representation of children at inner nodes. At runtime an adaptive loader, executing on the CPU, updates a view and transfer function-dependent working set of bricks maintained on GPU memory by asynchronously fetching data from the out-of-core octree representation. At each frame, a compact indexing structure, which spatially organizes the current working set into an octree hierarchy, is encoded in a small texture. This data structure is then exploited by an efficient stackless ray casting algorithm, which computes the volume rendering integral by visiting non-empty bricks in front-to-back order and adapting sampling density to brick resolution. Block visibility information is fed back to the loader to avoid refinement and data loading of occluded zones. The resulting method is able to interactively explore multi-gigavoxel datasets on a desktop PC.     

Efficient implementation of real-time view-dependent multiresolution meshing

In this paper, we present an efficient (topology preserving) multiresolution meshing framework for interactive level-of-detail (LOD) generation and rendering of large triangle meshes. More specifically, the presented approach, called FastMesh, provides view-dependent LOD generation and real-time mesh simplification that minimizes visual artifacts. Multiresolution triangle mesh representations are an important tool for reducing triangle mesh complexity in interactive rendering environments. Ideally, for interactive visualization, a triangle mesh is simplified to the maximal tolerated visible error and, thus, mesh simplification is view-dependent. This paper introduces an efficient hierarchical multiresolution triangulation framework based on a half-edge triangle mesh data structure and presents optimized implementations of several view-dependent or visual mesh simplification heuristics within that framework. Despite being optimized for performance, these error heuristics provide conservative error bounds. The presented framework is highly efficient both in space and time cost and needs only a fraction of the time required for rendering to perform the error calculations and dynamic mesh updates.