战场环境三维地形快速生成算法研究

针对庞大战场环境三维地形数据限制地形绘制速度问题展开研究.在确定仿真视野剪裁区域的基础上,提出一种新的实时调度算法;对可见数据区域,通过连续细节层次(Level of Detail, LOD)建立分块四叉树和设计基于距离空间误差方法的自适应节点评估系统,通过三角平面判据剔除背面三角形,实现连续LOD模型的快速动态构建;仿真数据表明,该方法在保证显示效果的前提下,剔除多余三角形,取得较高的帧数,较好地实现了大规模战场三维地形的实时快速漫游.     

三维GIS大规模地形实时渲染技术的研究

本文针对三维GIS大规模地形的实时渲染问题,研究了基于四叉树的LOD算法的设计.首先,建立了简单高效地节点评价系统和裁剪体系统,然后对网格的渲染过程可能出现的问题,给出了可行的解决方案,以及如何保证四叉树的合法性和筛选合适的节点.最后程序运行结果表明,该算法可以很好地解决三维GIS大规模地形渲染的性能问题,并对本算法的实现存在的不足进行了分析和建议.     

一种大规模地形简化的算法

在地形可视化领域,实时绘制复杂地形场景的最有效工具是LOD技术。结合四叉树数据结构与不规则三角网数据结构的优点,提出一种混合数据结构的地形简化算法。算法通过使用不同的误差阈值,实现了视点相关的地形简化。同时通过有效的误差控制原则,解决了不规则三角网分块之间的拼接问题,消除了地形裂缝。实验结果证明了算法能高效地生成地形的连续多分辨率模型,实现地形场景的平滑绘制。     

一种基于视点的大规模三维地形实时渲染算法

针对大规模三维地形的实时渲染问题,提出一种基于顶点法向量的模型简化算法。渲染过程中利用视图体的投影方式快速裁剪数据块,丢弃与视图体相离的数据块,将部分可见和完全可见的数据块全部加载到内存,根据视点到节点的距离和地形的粗糙程度构造了节点分辨率评价函数,最后采用加点的方法消除裂缝。仿真结果表明,该算法能有效减少渲染地形所需的三角形数目和时间,且对地形的逼真度影响较小。     

一种基于LOD的大规模地形生成算法

文中在前人的基础上,改进了基于四叉树的LOD模型,通过该模型管理和组织地形数据,建立节点判断准则来决定当前视区的细节程度,最终通过程序编译证明该算法能生成连续的多分辨率地形模型,提高了地形漫游的运行效率和实现不同分辨率地形模型之间的平滑过度.     

基于LOD算法的大规模地形实时渲染技术优化

大规模室外地形渲染是数字战场仿真领域的关键技术之一。文中使用四叉树的LOD算法来进行大规模地形渲染,并针对地形渲染容易出现地形裂缝现象,给出了一种四叉树节点依据细节等级向四周扩展再分割的方法来解决裂缝现象。该方法基本上可以实现不同分辨率地形模块间的平滑过渡。     

电力巡线直升机激光扫描数据的高效组织与显示

为了提高激光扫描数据的后处理速度和显示效率，采用了并行化阈值分割构建八叉树结构、对海量点云进行分块处理的方法。基于高差的数据抽稀方法，逐层精简八叉树叶节点中的数据，保存在八叉树外存结构中，构建点云多分辨率细节层次模型。采用视点变化与分页数据库结合的内外存调度策略，对一组电力巡线直升机获取的激光扫描点云数据进行实验验证。结果表明，该方法在八叉树构建速度和海量点云数据显示效率上的优越性，可以很好地满足电力巡线的时效性需求。     

基于高度图、多层纹理混合的大规模地形系统

一、引言 在实时渲染系统中,地形系统的研究一直是图形学的热点.虚拟地形漫游系统和主流游戏中基本上有以下几种解决方法:高度图、分形、Voxel等,然后综合采用CLOD、可变分辨率、GeoMipmap、二叉树/四叉树/BSP树等几种不同算法获得更快速更大的地形场景,比如Blueberry3D与MultiGen-Paradigm采用高级分形运算与程序几何体混合的方法,对GIS数据进行处理等.不同于学院派算法的是,游戏开发者的算法通常更加的简洁和快速,大量游戏使用的是基于高度图地形配合LOD算法进行场景处理的,比如游戏<孤岛惊魂>使用1025×1025大小的高度图和4级LOD生成地形.     

大规模地形实时绘制算法研究

在大规模场景的地形简化中,海量数据的内外存调度算法一直是热点研究问题。提出了一种高效的大规模地形数据调度算法,算法设计了一种有效的地形网格数据的多分辨率存储方法,减少了简化过程中实时数据调度量,同时算法对地形分块与内存分块进行了优化处理,从而提高了大数据量地形数据的实时调度效率。实验结果证明了算法的有效性。     

基于图模型的多边形自动构建算法

为了克服线拓扑造区效率低的问题,根据图模型中有向闭合环的特点,提出了一种基于图模型的鲁棒性较强的多边形构建方案.该方案首先将线数据构成图模型,并对图模型进行预处理;然后根据图模型生成环,再依据有向环的构成方向,判断有效环是洞还是壳;最后,把生成的洞分配给其对应的壳.壳的个数即为生成多边形的个数.该算法可较好地解决大规模线性数据生成区的效率问题,同时用其与混合模型,要素模型和简单要素模型进行了比较,实验中采用了四叉树索引和R树索引,都具有较高的效率,其中四叉树索引在实验中对于93664大小的线数据生成区数据,比要素模型快了5.400 s,比简单要素模型快了3.641 s.实验结果说明该算法性能优于其他的同类算法.     

基于ROAM算法的数字地面模型研究与实现

针对规则网格的数据量过大问题,采用了基于分块的ROAM算法进行多分辨率渲染,根据地形粗糙程度和视点位置,对地形进行有选择的细化,将庞大的三角形二叉树分为多个小二叉树,提高了地形构建效率,在此基础上建立地物要素模型,完成了数字地面模型的构建与多分辨率渲染.     

Multiview vision-based human crowd localization for UAV fleet flight safety

This paper presents a centralized, vision-based method for robust, on-the-fly 3D localization and mapping of human crowds in large-scale outdoor environments, assuming their independent visual detection on the camera feed of multiple UAVs. The proposed method aims at enhancing vision-assisted human crowd avoidance, in line with common UAV safety regulations, since the resulting 3D crowd annotations may be employed by other algorithms for on-line mission/path replanning during deployment of a UAV fleet. Initially, 2D crowd heatmaps are assumed to be derived per video frame on-board each UAV separately, using deep neural human crowd detectors, which indicate the probability of each pixel depicting a human crowd. The UAV-mounted cameras are assumed to be covering the same large-scale outdoor area over time. The heatmaps of each time instance are transmitted to a central computer and back-projected onto the common 3D terrain/map of the navigation environment, utilizing the intrinsic and extrinsic camera parameters. The projected crowd heatmaps derived from the different drones/cameras are fused by exploiting a Bayesian filtering approach that favors newer crowd observations over older ones. Thus, during flight, an area is marked as crowded (therefore, a no-fly zone) if all, or most, individual UAV-mounted visual detectors have recently and confidently indicated crowd existence on it. In order to calculate prior probabilities for Bayesian fusion, the method also proposes and exploits a simple, but efficient image processing-based algorithm for identifying flat terrain areas (under the assumption that people do not gather on highly curved or inclined terrain), relying on a priori available ground elevation data for the mapped area. Evaluation on both synthetic and real-world multiview video sequences depicting human crowds in outdoor environments verifies the effectiveness of the proposed method.     

基于小波分析的多分辨率地形构建

地形建模是虚拟战场构建的一个重要方面,DEM和正射影像是地形可视化的主要数据来源,他们可看作是表示地形信息的二维信号。首先论述了小波分析的基本原理,利用多次二进制小波对DEM和影像进行压缩,构建了一个多分辨率地形模型。实践证明,该方法具有压缩比高、压缩速度快等优点,同时还解决了不同分辨率子块之间的"裂缝"问题,可以满足大规模地形数据实时无缝漫游的需要。     

行星地形激光测高可视化仿真系统的设计

建立行星地形激光测高的可视化仿真系统对于卫星探测中行星地形信息的处理具有重要的意义。采用分形技术仿真了行星数字地形,计算了卫星轨道数据和测量点信息。对测量的高程信息通过插值算法得到了规则的DEM,动态地三维展示了整个探测过程的卫星轨道和测量点分布情况,并通过基于LOD的地形生成算法显示了原始的行星地形和测得的地形对比。     

基于区域聚合的栅格地形数据简化算法

针对规则网格地形数据存在的数据冗余,提出了一种基于区域聚合的地形数据简化算法,区域聚合是将共面或近似共面的若干地形栅格点用这组栅格点的边界点代替。该算法用面元间最大法向量夹角余弦值作为简化度量误差,通过递归过程完成数据简化,结合简化后存留散列点的特点进行地形绘制且经过消除地形裂缝处理,避免了离散点Delaunay三角化过程。实验结果表明,算法数据结构简单,便于使用,简化精度可控,简化效果好。     

Web and personal image annotation by mining label correlation with relaxed visual graph embedding

The number of digital images rapidly increases, and it becomes an important challenge to organize these resources effectively. As a way to facilitate image categorization and retrieval, automatic image annotation has received much research attention. Considering that there are a great number of unlabeled images available, it is beneficial to develop an effective mechanism to leverage unlabeled images for large-scale image annotation. Meanwhile, a single image is usually associated with multiple labels, which are inherently correlated to each other. A straightforward method of image annotation is to decompose the problem into multiple independent single-label problems, but this ignores the underlying correlations among different labels. In this paper, we propose a new inductive algorithm for image annotation by integrating label correlation mining and visual similarity mining into a joint framework. We first construct a graph model according to image visual features. A multilabel classifier is then trained by simultaneously uncovering the shared structure common to different labels and the visual graph embedded label prediction matrix for image annotation. We show that the globally optimal solution of the proposed framework can be obtained by performing generalized eigen-decomposition. We apply the proposed framework to both web image annotation and personal album labeling using the NUS-WIDE, MSRA MM 2.0, and Kodak image data sets, and the AUC evaluation metric. Extensive experiments on large-scale image databases collected from the web and personal album show that the proposed algorithm is capable of utilizing both labeled and unlabeled data for image annotation and outperforms other algorithms.     

一种基于随机文件的C#与非托管C代码交互模式

在大型科学计算过程中往往会出现海量中间数据,需要在不同开发平台或语言之间传递,此时中间数据会消耗大量系统资源,引起系统性能急剧下降;此外,中间数据长度的不确定性和跨平台的移植性都对科学计算算法提出了较高的接口要求;为保证系统的稳定性和可移植性,文中提出一种基于随机文件读写进行数据传递的简单实用方法,来实现在C#．NET平台下的托管代码中调用C语言开发的非托管代码的交互模式。     

Study of Millimeter-Wave Radar for Helicopter Assisted-Landing System

Landing helicopters on rough unprepared terrain has always been considered hazardous, since the massive dust cloud generated by wind drafts from the helicopter's rotors completely obstructs the pilot's view of the landing area. This article presents a performance assessment of a proposed millimeter-wave (MMW) three-dimensional imaging radar system, specifically meant for helicopter assisted landing. The assessment includes simulation of radar backscattering from the underlying rough terrain, in addition to the signal attenuation and scattering from dust clouds generated by the helicopter's rotors. Terrain scattering is simulated in two steps: 1) generation of a two-scale random rough surface according to prescribed statistics of a large-scale undulation and a small-scale surface roughness; and 2) simulation of the returned signal, including the effects of the real-aperture radar parameters and the terrain-backscatter response. Details of the three-dimensional imaging algorithm are presented. Single-scattering theory is used to simulate the effects of a dust cloud - including signal attenuation and backscatter clutter generation - on the radar's performance. It is shown that operating in the upper millimeter-wave regime (70 GHz-220 GHz) is the most practical solution for a compact, high-resolution, three-dimensional imaging system for this problem.     

Early termination algorithm for 2BT block motion estimation

A simple algorithm to reduce the computational complexity of two bit transform (2BT) block motion estimation is presented. The difference between pixel intensity and the mean value is added and compared to a certain threshold value. The proposed algorithm is much faster than the conventional 2BT algorithm, while maintaining visual quality.     

图像纹理合成的研究应用

在此介绍了纹理和纹理合成的基本概念,给出了纹理合成常见的几种算法,通过分析块拼接纹理合成算法,对块拼接纹理合成算法进行改进,将块拼接的原理应用到图像拼接上,并对象素加入与人视觉有关的权值进行接缝处理。实验结果表明,该方法简单实用,对于基本的由不同方位拍摄的图像都可以通过该算法进行拼接,并通过对接缝处的处理,取得了较好的结果。