基于DEM数据库的可视域算法

可视性分析在军事和工程领域有着广泛的应用,可视域计算是可视性分析的重要因子.首先讨论了可视域计算的常用算法,分析了各个常用算法的优劣.并针对大数据量的DEM数据库,在Xdraw算法的基础上提出了一种改进的Xdraw算法,大大减少了访问数据库的次数.然后在实验的基础上从正确性和效率两个方面对该算法进行了分析,并给出了继续研究的方向.     

城市作战环境中可视性算法研究及模型构建

城市可视性在城市作战中具有重要的作用,可视性情况是指挥员必须要考虑的作战要素之一。首先从城市作战行动、武器装备运用和作战人员三个方面探讨了可视性对城市作战的影响,研究了基于城市RSG高程数据的LOS可视算法、平面视域算法,并扩展到立体视域计算,利用三维视球法建立了城市可视性衡量的指标模型,提出城市作战可视性专题图的设计思路,分别以观察哨、城市可视性分布为例,制作了专题图实例。     

利用最大仰角插值技术的通视性分析算法研究

针对点对区域的通视性分析问题,提出了一种算法．该算法只需对前沿边界点进行点对点通视性分析;而对内部点的可视性,根据地形空间连续性的原理,采用插值技术,利用前方点的最大仰角和可视性信息来判断．实验表明,该算法基本满足实时性的要求,同时具有较高的稳定性和精确性。     

从外存中计算地形可视域的高效算法

可视性分析广泛应用于GIS的各个方面,视线和视域是其最基本的两个因子。视域的计算方法有很多种,在计算时因为采用的算法和实现算法所运用的编程方法不同,导致效率和精度有很大差异。为了解决由内存受限而无法存储和处理海量区域地理信息数据的问题,提出一种在外部存储器上计算地形视域的高效算法,对该算法进行了分析,并进行了实验验证,表明该算法明显优于现有的其他算法。     

RSG地形的矢量视域改进算法

针对视域分析改进算法及其矢量化进行研究,提出了一种基于局部最优检测和高程限制的改进通视性算法。介绍了空间中两点通视性问题的基本算法;给出了局部最优单调区间的定义;通过分析视线方向与地形遮挡点之间的关系,提出了基于局部最优区间和最大高程限制的通视性改进算法,给出了算法的实现方法;改进算法只对一般高程点进行局部最优判断,而只对点序列中相对较少的一部分点进行完整的通视性计算,因此改进算法在收敛速度方面得到了明显改善;最后,通过程序仿真对改进算法进行了验证,并利用改进算法进行了视域分析与矢量化仿真。     

一种顾及地形特征的布料模拟滤波改进方法

为了提高激光点云滤波算法在地形复杂区域的精度、效率以及自适应性,基于布料模拟滤波算法,提出了一种面向大范围复杂场景的顾及地形特征的点云滤波方法。该方法首先采用基于坡度的动态格网分割方法,对剔除粗差后的点云建立格网索引;其次利用每个格网的邻域格网中的最低点建立曲面方程拟合高程值,通过计算真实高程与拟合高程差值实现高程归一化;然后使用布料模拟算法模拟布料下降过程得到地形布料的最终形态,进而通过阈值限定实现地面点提取。在地形复杂的测试区使用相同滤波参数进行算法改进前后对比测试,结果表明:改进算法的正确率由原CSF算法的88.9%提高到改进后算法的95.19%;I类误差、II类误差分别由9.71%、1.39%下降到4.57%、0.24%,且滤波时长由164 s缩减至60.9 s。本文提出的改进算法在保证大范围复杂场景区域滤波正确率的基础上,对不同地形具有较强的自适应性,且提高了滤波计算效率。     

一种顾及地形特征的布料模拟滤波改进方法

为了提高激光点云滤波算法在地形复杂区域的精度、效率以及自适应性，基于布料模拟滤波算法，提出了一种面向大范围复杂场景的顾及地形特征的点云滤波方法。该方法首先采用基于坡度的动态格网分割方法，对剔除粗差后的点云建立格网索引；其次利用每个格网的邻域格网中的最低点建立曲面方程拟合高程值，通过计算真实高程与拟合高程差值实现高程归一化；然后使用布料模拟算法模拟布料下降过程得到地形布料的最终形态，进而通过阈值限定实现地面点提取。在地形复杂的测试区使用相同滤波参数进行算法改进前后对比测试，结果表明：改进算法的正确率由原CSF算法的88.9%提高到改进后算法的95.19%；I类误差、II类误差分别由9.71%、1.39%下降到4.57%、0.24%，且滤波时长由164 s缩减至60.9 s。本文提出的改进算法在保证大范围复杂场景区域滤波正确率的基础上，对不同地形具有较强的自适应性，且提高了滤波计算效率。     

一种顾及地形特征的布料模拟滤波改进方法

为了提高激光点云滤波算法在地形复杂区域的精度、效率以及自适应性，基于布料模拟滤波算法，提出了一种面向大范围复杂场景的顾及地形特征的点云滤波方法。该方法首先采用基于坡度的动态格网分割方法，对剔除粗差后的点云建立格网索引；其次利用每个格网的邻域格网中的最低点建立曲面方程拟合高程值，通过计算真实高程与拟合高程差值实现高程归一化；然后使用布料模拟算法模拟布料下降过程得到地形布料的最终形态，进而通过阈值限定实现地面点提取。在地形复杂的测试区使用相同滤波参数进行算法改进前后对比测试，结果表明：改进算法的正确率由原CSF算法的88.9%提高到改进后算法的95.19%；I类误差、II类误差分别由9.71%、1.39%下降到4.57%、0.24%，且滤波时长由164 s缩减至60.9 s。本文提出的改进算法在保证大范围复杂场景区域滤波正确率的基础上，对不同地形具有较强的自适应性，且提高了滤波计算效率。     

一种面向流体仿真的场景处理方法

在流体仿真中,场景处理是将场景模型转化为可计算流体边界的重要途径.针对传统算法效率低的问题,提出一种面向流体仿真的场景处理方法.通过挖掘流体仿真计算的规律,定义面向流体计算特征的场景语义;利用该语义建立最优场景图来组织仿真场景,并对场景进行高效的处理.将文中方法应用到火灾仿真和流体动画中的实验结果表明,该方法能够提高场景处理效率,满足流体仿真计算的需求.     

基于DEM的地形可视域分析关键技术

地形可视域分析是空间分析中很重要的内容,基于DEM地形数据,目前的算法存在计算复杂、通用性不强等问题,尤其是针对多分辨率的海量DEM数据,算法还不成熟.从底层的地形数据组织入手,以可视域遮蔽角分析的必要性为出发点,考虑数据结构对算法的影响,详细讨论了遮蔽角计算的原理以及可视域分析过程中的关键技术,提出了基于金字塔模型的四叉树索引结构,在可视域计算中引入了“优化矩阵”,提高了可视域分析的效率,并在此基础上实现了基于DEM的地形可视域分析系统.     

Scalable visibility color map construction in spatial databases

Recent advances in 3D modeling provide us with real 3D datasets to answer queries, such as “What is the best position for a new billboard?” and “Which hotel room has the best view?” in the presence of obstacles. These applications require measuring and differentiating the visibility of an object (target) from different viewpoints in a dataspace, e.g., a billboard may be seen from many points but is readable only from a few points closer to it. In this paper, we formulate the above problem of quantifying the visibility of (from) a target object from (of) the surrounding area with a visibility color map (VCM). A VCM is essentially defined as a surface color map of the space, where each viewpoint of the space is assigned a color value that denotes the visibility measure of the target from that viewpoint. Measuring the visibility of a target even from a single viewpoint is an expensive operation, as we need to consider factors such as distance, angle, and obstacles between the viewpoint and the target. Hence, a straightforward approach to construct the VCM that requires visibility computation for every viewpoint of the surrounding space of the target is prohibitively expensive in terms of both I/Os and computation, especially for a real dataset comprising thousands of obstacles. We propose an efficient approach to compute the VCM based on a key property of the human vision that eliminates the necessity for computing the visibility for a large number of viewpoints of the space. To further reduce the computational overhead, we propose two approximations; namely, minimum bounding rectangle and tangential approaches with guaranteed error bounds. Our extensive experiments demonstrate the effectiveness and efficiency of our solutions to construct the VCM for real 2D and 3D datasets.     

诱导维修中的局部视点优选方法

在诱导维修过程中,为了使维修者能够快速准确地找到待维修目标区域,并提供一个最佳的观察视角来提高对维修目标和场景的认知,需要构建视点规划模型.为此提出一种诱导维修中局部视点的优选方法,在目标区域周围建立候选视点区域,根据约束条件,从目标的可见性、观察质量及视点舒适度几个方面来制定视点评价函数,通过离散寻优的方式进行了视点优选.实验结果表明,应用该方法所选出的最优视点比其他视点观察质量更好,对比结果论证了方法的有效性.     

Multimodal selection techniques for dense and occluded 3D virtual environments

Object selection is a primary interaction technique which must be supported by any interactive three-dimensional virtual reality application. Although numerous techniques exist, few have been designed to support the selection of objects in dense target environments, or the selection of objects which are occluded from the user's viewpoint. There is, thus, a limited understanding on how these important factors will affect selection performance. In this paper, we present a set of design guidelines and strategies to aid the development of selection techniques which can compensate for environment density and target visibility. Based on these guidelines, we present new forms of the ray casting and bubble cursor selection techniques, which are augmented with visual, audio, and haptic feedback, to support selection within dense and occluded 3D target environments. We perform a series of experiments to evaluate these new techniques, varying both the environment density and target visibility. The results provide an initial understanding of how these factors affect selection performance. Furthermore, the results showed that our new techniques adequately allowed users to select targets which were not visible from their initial viewpoint. The audio and haptic feedback did not provide significant improvements, and our analysis indicated that our introduced visual feedback played the most critical role in aiding the selection task.     

Dynamic Polygon Visibility Ordering for Head-Slaved Viewing in Virtual Environments

This paper presents an approach to visibility called the Viewpoint Movement Space (VpMS) algorithm which supports the concept of dynamic polygon visibility orderings for head-slaved viewing in virtual environments (VE). The central idea of the approach is that the visibility, in terms of back-to-front polygon visibility ordering, does not change dramatically as the viewpoint moves. Moreover, it is possible to construct a partition of the space into cells, where for each cell the ordering is invariant. As the viewpoint moves across a cell boundary typically only a small and predictable change is made to the visibility ordering. The cost to perform this operation represents a notable reduction when compared with the cost of resolving the visibility information from the BSP tree where the classification of the viewpoint with every node plane has to be performed. The paper demonstrates how the subdivision into such cells can represent the basic source for an acceleration of the rendering process. We also discuss how the same supportive data structure can be exploited to solve other tasks in the graphics pipeline.     

Time-optimal visibility-related algorithms on meshes with multiplebroadcasting

Given a collection of objects in the plane along with a viewpoint ω, the visibility problem involves determining the portion of each object that is visible to an observer positioned at ω. The visibility problem is central to various application areas including computer graphics, image processing, VLSI design, and robot navigation, among many others. The main contribution of this work is to provide time-optimal solutions to this problem for several classes of objects, namely ordered line segments, disks, and iso-oriented rectangles in the plane. In addition, our visibility algorithm for line segments is at the heart of time-optimal solutions for determining, for each element in a given sequence of real numbers, the position of the nearest larger element within that sequence, triangulating a set of points in the plane, determining the visibility pairs among a set of vertical line segments, and constructing the dominance and visibility graphs of a set of iso-oriented rectangles in the plane. All the algorithms in this paper involve an input of size n and run in O(log n) time on a mesh with multiple broadcasting of size n×n. This is the first instance of time-optimal solutions for these problems on this architecture     

Time-space Viewpoint Planning for Guard Robot with Chance Constraint

This paper presents a novel movement planning algorithm for a guard robot in an indoor environment, imitating the job of human security. A movement planner is employed by the guard robot to continuously observe a certain person. This problem can be distinguished from the person following problem which continuously follows the object. Instead, the movement planner aims to reduce the movement and the energy while keeping the target person under its visibility. The proposed algorithm exploits the topological features of the environment to obtain a set of viewpoint candidates, and it is then optimized by a cost-based set covering problem. Both the robot and the target person are modeled using geodesic motion model which considers the environment shape. Subsequently, a particle model-based planner is employed, considering the chance constraints over the robot visibility, to choose an optimal action for the robot. Simulation results using 3D simulator and experiments on a real environment are provided to show the feasibility and effectiveness of our algorithm.

     

结构化骨架求取和内窥可见性计算

提出了包含距离和拓扑信息的结构化骨架提取方法和骨架指导的内窥可见性计算方法,并将其有机地应用于虚拟漫游系统中.结构化骨架提取算法结合了并行细化算法和距离变换算法,使得骨架能够有效地控制虚拟内窥镜的视点移动和漫游位置的跟踪,有利于准确地观察病变位置.内窥可见性算法利用人体器官的封闭管状特征,将其分割成许多网格单元,并在预处理中使用深度缓存计算单元间的可见性,同时对每个单元建立可见性树.虚拟漫游时,通过当前视点信息可进一步动态地删减所在单元的可见性树,从而得到实时可见性,最终实现实时漫游并保持漫游图像的质量.     

改进的基于图像边缘的能见度反演方法

针对现有的基于图像边缘的能见度计算方法效果不理想的问题,提出一种改进的基于图像边缘检测求能见度的方法。相对于原有的方法,该方法首先选取目标图像并用sift算法对其进行模板匹配,然后利用离散Shearlet变换提取边缘特征,再将这些特征和前向散射式能见度仪测量的数据进行线性拟合,建立它们之间的关系式,从而求出能见度。实验结果表明,该算法相对于sobel算法和小波变换算法,相对误差减少了2.761%和1.607%,计算的准确性和有效性明显得到改善。     

曲线通视分析算法初探

通视分析是常用的重要地理信息系统分析方法,在各种系统的空间分析功能中,用得较多的是直线通视,而在许多现实情况中,通视路径是一条曲线。作者根据军事上的应用需求,以炮弹弹道计算数字地形模型上的着落点为例,来初步探讨曲线通视的算法,并用实例进行了验证。     

基于可见性约束的自动表面重构算法研究

提出了一种基于可见性约束的自动表面重构算法.此算法首先介绍了一种通过插入法实现的3维Delaunay三角网自动重构算法,然后利用给定的离散点,构建包围所有点的凸包.在完成初始的Delaunay三角剖分基础上,提出了利用特征点在影像中的可见性信息,对初始的3维模型进行修正,从而得到物体的实际表面模型.实验结果表明,该方法是有效的.