基于视向LOD算法在三维雷达终端的应用

本文提出了一种新的基于视向LOD自动生成算法,该算法结合DEM均匀网格模型,以"块"为模型简化的空间单位,结合实际视觉效果中观察点位置和角度对场景细节程度的影响,以一个包含视点视向相关因子的尺度作为简化标准.简化过程中采取基于点删除的网格简化算法的思想.建立了多层次LOD数据模型,有效地简化了地形的绘制,提高了生成效率.并将该算法应用于三维雷达终端仿真系统中,取得了良好的效果.     

一种基于视觉特性的三角网格简化算法

在计算机图形学和几何造型中,实体模型经常采用多边形网格描述,由于绘制时间和存储量与网格的数量成正比,因此复杂的网格模型通常并不实用,从而必须进行模型简化。因为任意多边形可以很方便地被剖分为三角形,由此该文提出一种新的基于视觉特性的三角形网格简化算法。该算法基于人类的视觉特性对三角形网格进行重要性分析,模型细节的选择取决于整个模型对视觉效果的贡献程度,在用户指定的尺度范围内,通过采用收缩三角形以达到迅速简化的目的,以较小的图形生成代价获取丰富的图形视觉效果。实验结果表明,该算法具有实现简单,速度快的特点,能有效地支持细节层次模型的表示。     

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.     

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。     

虚拟环境中多细节层次模型自动生成算法

虚拟环境是限时计算和限时图形绘制技术的典型应用．本文对用于限时图形绘制的多细节层次模型表示进行研究，提出了基于三角形网格简化的多细节层次模型自动生成算法．该算法多次遍历现有三角形网格模型的每一个顶点，使用局部几何和拓扑特征移去满足简化标准的顶点，对移去顶点后产生的多边形区域进行局部三角化．多次执行上述过程，结果形成不同细节层次的三角形网格模型．文中给出的实例说明了该算法的有效性．     

一种基于视点的LOD生成方法

总结LOD自动生成的一般算法，结合渐进网格模型与实际视觉效果中视点位置和角度对场景细节程度的影响，以与视点相关的因子作为简化标准，根据视点的参数对二叉顶点树的节点进行合并或展开调整模型个部分的细节层次。简化过程采用渐进网格结构，建立了多层次LOD数据模型，有效的简化了地形模型的绘制，提高了生成效率，使得生成的三维地形有较高的可视性和真实感。     

基于OpenGL的三维地形的模拟

三维地形模拟一直是虚拟现实、地理信息系统(GIS)等领域的研究热点.提出了一种基于不同层次的多边形网格模型的地形生成算法,采用多重纹理映射技术,通过插值对应网格基本元素的位置实现模型之间的平滑过渡并生成地形连续LOD模型.通过该技术可以简化场景的复杂度,并对图形的真实感程度损失比较小.该算法是在VC++6.0平台上利用OpenGL编程技术实现的.实验表明:该算法具有较低的时间和空间开销,适合大规模三维地形的模拟.     

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.     

一种三角形折叠网格模型简化的改进算法

目前提出的网格简化算法中,三角形折叠简化方法是一种主要的简化方法,在网格压缩、多细节层次模型生成、递进网格构造中得到了广泛地应用。提出一种基于三角形折叠的网格模型简化改进算法,在基于三角形折叠的基础上,在计算三角形折叠误差代价时引入局部区域面积度量参数,有效控制简化模型的三角形折叠顺序。实验表明,采用该文算法简化后的模型更逼近原始模型。     

一种具有边界自适应能力的蒙皮网格生成算法

根据图像生成网格是骨骼蒙皮动画生成的关键步骤，网格质量直接影响动画效果，但网格优化工作量大且严重依赖制作者本身技能。对此，本文提出一种能够自适应图像边界的蒙皮网格生成算法。首先，利用图像轮廓的法向量变换计算得到包围图像的均匀近似多边形；接着使用信息熵作为衡量图形内部灵活性的权重，结合改进的重心Voronoi算法对图形内部采样，获得按权重分布均匀的内部采样点；最后，结合边界多边形顶点与内部点进行带边界约束的Delaunay三角剖分，得到可用于骨骼蒙皮动画的三角网格。实验结果表明本文所提出的算法可生成高质量网格，且高度匹配原图像边界，可用于骨骼蒙皮动画制作。     

面向装配的飞行器超大模型实时可视化技术

针对飞行器大数据量CAD模型实时绘制困难的问题,提出一种LOD自动批处理生成以及实时自适应绘制方法.以零部件为处理对象以保留装配树信息,结合模型分割完成超大模型简化,并根据计算机存储能力、实时绘制能力以及CAD模型特点,实现了定量的LOD自动批处理生成;以精确遮罩查询为基础,根据计算机实时绘制负载和CAD模型面片密度,动态地调整LOD精度等级,使得各个模型的精度基本一致,避免了传统算法的弊端,实现了LOD实时自适应绘制,并进行了优化.实验结果表明:采用文中技术处理千万级三角面片的模型约1h完成LOD生成,并可在普通计算机上实现实时的自适应绘制.     

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.     

Out‐of‐Core Simplification and Crack‐Free LOD Volume Rendering for Irregular Grids

We propose a novel out‐of‐core simplification and level‐of‐detail (LOD) volume rendering algorithm for large irregular grids represented as tetrahedral meshes. One important feature of our algorithm is that it creates a space decomposition as required by I/O‐efficient simplification and volume rendering, and simplifies both the internal and boundary portions of the sub‐volumes progressively by edge collapses using the (extended) quadric error metric, while ensuring any selected LOD mesh to be crack‐free (i.e., any neighboring sub‐volumes in the LOD have consistent boundaries, and all the cells in the LOD do not have negative volumes), with all computations performed I/O‐ejficiently. This has been an elusive goal for out‐of‐core progressive meshes and LOD visualization, and our novel solution achieves this goal with a theoretical guarantee to be crack‐free for tetrahedral meshes. As for selecting a desirable LOD mesh for volume rendering, our technique supports selective refinement LODs (where different places can have different error bounds), in addition to the basic uniform LODs (where the error bound is the same in all places). The proposed scalar‐value range and view‐dependent selection queries for selective refinement are especially effective in producing images of the highest quality with a much faster rendering speed. The experiments demonstrate the efficacy of our new technique.     

结合视点变换的三维地形无缝绘制算法

针对传统地形裂缝消除技术普遍存在构网速度慢,层次约束强等问题,提出了一种结合视点变换的地形无缝绘制算法。该方法首先根据精度生成LOD粗模型,然后利用纹理映射技术生成精细网格,并根据视点动态调整顶点位置以消除因层次细节过渡产生的T型裂缝。此外,通过CPU-GPU协同工作的方式,将批量构网及渲染的工作从CPU移植到GPU中,提升了整个系统的处理速度。实验结果表明,该方法可以有效消除地形裂缝,保证网格平滑过渡。     

A strategy of automatic hexahedral mesh generation by using an improved whisker-weaving method with a surface mesh modification procedure

One of the demands for three dimensional (3D) finite element analyses is the development of an automatic hexahedral mesh generator. For this problem, several methods have been proposed by many researchers. However, reliable automatic hexahedral mesh generation has not been developed at present. In this paper, a new strategy of fully automatic hexahedral mesh generation is proposed. In this strategy, the prerequisite for generating a hexahedral mesh is a quadrilateral surface mesh. From the given surface mesh, combinatorial dual cycles (sheet loops for the whisker-weaving algorithm) are generated to produce a hexahedral mesh. Since generating a good quality hexahedral mesh does not depend only on the quality of quadrilaterals of the surface mesh but also on the quality of the sheet loops generated from it, a surface mesh modification method to remove self-intersections from sheet loops is developed. Next, an automatic hexahedral mesh generator by the improved whisker-weaving algorithm is developed in this paper. By creating elements and nodes on 3D real space during the weaving process, it becomes possible to generate a hexahedral mesh with fewer bad-quality elements. Several examples will be presented to show the validity of the proposed mesh generation strategy.     

Generating high-quality discrete LOD meshes for 3D computer games in linear time

The real-time interactive 3D multimedia applications such as 3D computer games and virtual reality (VR) have become prominent multimedia applications in recent years. In these applications, both visual fidelity and degree of interactivity are usually crucial to the success or failure of employment. Although the visual fidelity can be increased using more polygons for representing an object, it takes a higher rendering cost and adversely affects the rendering efficiency. To balance between the visual quality and the rendering efficiency, a set of level-of-detail (LOD) meshes has to be generated in advance. In this paper, we propose a highly efficient polygonal mesh simplification algorithm that is capable of generating a set of high-quality discrete LOD meshes in linear run time. The new algorithm adopts memoryless vertex quadric computation, and suggests the use of constant size replacement selection min-heap, pipelined simplification, two-stage optimization, and a new hole-filling scheme, which enable it to generate very high-quality LOD meshes using relatively small amount of main memory space in linear runtime.     

基于限制性四叉树LOD大规模地形预处理算法

LOD（Level Of Detail,层次细节）技术是解决大规模地形实时渲染的关键技术之一,通过这种技术可以较好地简化场景的复杂度,减少图形显示的失真度,满足一定的实时性要求。传统的算法将四叉树和LOD技术相结合将大规模数字高程模型数据（DEM）进行分块,并对块内数据按照分辨率的大小分层存储。通过对四叉树的研究,在限制性四叉树的基础上引入预处理算法,提高了地形读取速度,增强了实时显示效果。该算法是基于限制性四叉树的一种高效的规则网格划分方法,内存开销少,降低了CPU的负担。实验结果表明该算法提高了地形导入的效率,能实现大规模地形的实时漫游。     

基于能量评估的网格简化算法及其应用

网格简化是曲面重构和多细节层次构造中的一个重要步骤，本文提出了一个基于局部能量评估的网格简化算法，能够大量地删除密集网格的三角形面片．为了加速算法的执行还提出了一种简单有效的采样方法．算法自动化程度高，能有效地支持多细节层次模型的建立．