移动对象索引方法研究

传统空间索引结构因无法适应大量的更新操作而不能应用于移动对象的存储和检索。本文介绍了三种主要移动时象索引方法的基本思想，即R树及其变形树、四叉树及其变形树以及网格文件及其变形算法，并进行了分析时比，在此基础上提出了混合索引结构，比已知的索引结构效率更高。     

MOQ-QR:基于QR-树的连续K近邻查询算法研究*

综合分析了R-树和四叉树在处理移动对象的连续K近邻（简称CKNN）查询算法中的不足,提出了一种基于R树和四叉树索引结构,去解决移动对象连续K近邻查询算法。该算法通过对移动对象分配静态空间,并在研究区域内利用QR-树和hash表作为索引去存储移动对象以此计算查询点与移动对象之间的空间距离。实验证明,该算法与现有算法相比,不仅提高了数据的查询效率,而且降低了系统资源的消耗。     

基于线性四叉树的快速邻域查询算法

邻域查询是位置服务系统的核心技术,它的实现取决于空间对象数据模型.根据空间对象分布构建的四叉树模型,以及线性四叉树中位置码的使用,提出了一种新的基于线性四叉树的快速邻域查询算法.该算法根据满四叉树结点编码思想对线性四叉树的Morton码进行了改进,并增加了表示四叉树所有结点状态的序列,通过网格模型的邻域查询算法实现了线性四叉树的快速邻域查询.     

空间数据库中的一种混合索引结构的研究

空间索引是实现空间查询的关键技术,其性能的好坏直接决定着空间数据的存储效率及空间查询的性能。为了提高空间查询效率,提出一种混合空间索引结构松散QR-树：LQR-tree。针对已有的QR-树索引结构在节点分配中,可能存在较小的对象落入较大的节点中的问题,将松散四叉树和R-树相结合,能够实现节点下移,优化处理移动空间对象的查询,给出LQR-tree的结构和插入删除算法,并提出对应算法的相关定理和证明。     

边界约束的非相交球树实体对象多维统一索引

针对现有空间索引剖分结构复杂、节点重叠率高及对多维实体对象检索及运算支撑较弱等问题,构建了一种边界约束的非相交球实体对象多维统一空间索引;利用球的几何代数外积表达,提出了基于求交算子的直线-平面和直线-球面的相交判定与交点提取方法,建立了多维实体对象体元化剖分方法及包含边界约束的非相交离散球实体填充算法,实现了实体对象空间均匀、非重叠的分割,并在填充球的个数、重叠率以及对象逼近近似度等约束条件上获得了较好的平衡.定义了最小外包球生成与更新的迭代算法与包含球体积修正的批量Neural Gas层次聚类算法,在尽可能保证球树各分支平衡性的前提下,实现了索引层次体系的稳健构建.利用几何代数下球对象间几何关系计算的内蕴性与参数更新的动态性,实现了索引结构的动态生成与更新,进而设计了实体对象表面及其内部任意位置及区域的检索策略及基于实体索引的空间关系计算方法.基于不同实体对象的模拟实验显示,基于几何代数的实体对象索引可以有效实现多维实体对象表面及其内部任意位置及区域的快速检索,并能在有限时间内以较高的精度实现多维实体对象最近邻距离和动态实体对象相交状态的检索.相对于常用球树索引,所提出的索引方法在填充率、节点重叠率、填充误差、体元个数、层次球个数、体积百分比和时间占用等方面均具有明显优势,且不同分辨率剖分条件下的索引结构及空间关系计算精度具有更高的稳健性,可运用于具有较强时间约束下复杂多维动态场景中对象检索与空间关系计算.     

HBase中基于时空特征的监测视频大数据关联查询研究

针对传统的时空索引构建、维护困难且实时查询效率低等问题,首先提出基于HBase的时空索引构造方法。该方法采用HBase作为监测视频大数据时空特征索引结构,通过Z填充曲线对空间特征进行降维存储,并利用时间、空间和属性特征之间的关联及依赖规则来安排rowkey索引键,可有效解决传统的时空索引构建、维护困难的缺陷。此外,针对传统的时空索引实时查询效率低的问题,进一步提出了基于Z曲线的时空关联查询算法,该算法对查询空间计算Z值范围和建立空间划分子集,利用划分后的时空特征进行列索引查询得到候选数据集并反查HBase索引表完成关联查询。实验结果表明,与传统的R树索引算法相比,提出的基于HBase的时空索引构造方法索引插入效率更高,提出的基于Z曲线的时空关联查询算法能够快速高效地处理时空关联查询。     

GAPI:GPU加速的移动对象并行索引方法

为减少加锁操作对移动对象数据库并行性能的影响并提高其吞吐量,提出一种由GPU加速的网格结合四叉树的索引方法。采用由GPU对出入节点对象进行计数并持续计算节点拆分/合并条件的方式,在不影响CPU计算能力的前提下,将存在性能瓶颈的网格节点转化为四叉树,从而减少对象数据更新时加锁操作造成的其他线程等待时间。该方法结构简单且更适用于对象不均匀分布的场景,避免了现有索引方式或在热点区域存在性能瓶颈,或需花费大量计算资源进行结构平衡等缺点。实验结果表明,该方法与现有移动对象索引方式相比具有数据吞吐量大、响应速度快等特点,在移动对象空间分布不均匀的场景下其优势更为明显。     

基于八叉树GIS算法森林建模方法研究

研究森林资源真实形态建模问题.由于森林树数值特征和机体形态千变万化,数学模型很难表达真实性,传统的三维空间数据模型方法难以真实反映森林资源的复杂形态.为解决上述问题,采用了八叉树算法有效解决了森林模型的计算复杂性,同时又提出了多尺度八叉树细分算法,结合地理信息系统(GIS),构建真实三维森林形态模型.根据八叉树细分算法的形态对象,满足了数据多尺度组织和划分的需求,以空间体元建立起了各种树木对象之间的联系,为空间分析和森林资源的可视化提供了数据支持.仿真结果表明提出改进算法算法能准确高效地实现森林图像真实感,并能适合常见复杂条件下三维复杂森林形态模型的构建.     

基于数据空间网格划分的PK-树索引结构

在大规模高维数据挖掘研究中,数据存储与索引方法的有效性是决定算法时空效率的重要因素。将数据空间网格划分策略与高效率的树型索引结构结合起来,可以充分发挥两者在数据组织上的综合优势,将复杂问题转换为结构化的简单重复问题：在统一的框架下给出了各种数据空间网格划分的定义,讨论了两种适用于实现网格化数据索引的R-树和PK-树索引结构：试验结果表明,PK-树在数据存储和索引上具有更高的效率,与网格化数据组织方法结合起来,对于降低大规模高维数据分析问题的时空复杂度具有重要意义。     

基于数据空间网格划分的PK 树索引结构*

在大规模高维数据挖掘研究中,数据存储与索引方法的有效性是决定算法时空效率的重要因素。将数据空间网格划分策略与高效率的树型索引结构结合起来,可以充分发挥两者在数据组织上的综合优势,将复杂问题转换为结构化的简单重复问题。在统一的框架下给出了各种数据空间网格划分的定义,讨论了两种适用于实现网格化数据索引的R树和PK树索引结构。试验结果表明,PK树在数据存储和索引上具有更高的效率,与网格化数据组织方法结合起来,对于降低大规模高维数据分析问题的时空复杂度具有重要意义。     

Geometry-shader-based real-time voxelization and applications

This work proposes a new voxelization algorithm based on newly available GPU functionalities and designs several real-time applications to render complex lighting effects with the voxelization result. The voxelization algorithm can efficiently transform a highly complex scene in a surface-boundary representation into a set of voxels in one GPU pass using the geometry shader. Newly available 3D textures are used to directly record the surficial and volumetric properties of objects such as opaqueness, refraction, and transmittance. In the first, the usage of 3D textures can remove those strenuous efforts required to modify the encoding and decoding scheme when adjusting the voxel resolution. Second, surficial and volumetric properties recorded in 3D textures can be used to interactively compute and render more realistic lighting effects including the shadow of objects with complex occlusion and the refraction and transmittance of transparent objects. The shadow can be rendered with an absorption coefficient which is computed according to the number of surfaces drawing in each voxel during voxelization and used to compute the amount of light passing through partially occluded complex objects. The surface normal, transmittance coefficient and refraction index recorded in each voxel can be used to simulate the refraction and transmittance lighting effects of transparent objects using our multiple-surfaced refraction algorithm. Finally, the results demonstrate that our algorithm can transform a dynamic scene into a set of voxels and render complex lighting effects in real time without any pre-processing.     

Frame-sliced voxel representation: An accurate and memory-efficient modeling method for workpiece geometry in machining simulation

This paper presents a new and enhanced voxel representation format for modeling the machined workpiece geometry in simulating machining operations involving repeated update of the workpiece model volume. The modeling format is named as the Frame-Sliced Voxel representation (FSV-rep) as it uses a novel concept of frame-sliced voxels to represent the boundary of the workpiece volume. The FSV-rep uses a multi-level surface voxel representation for sparse and memory-efficient implementations. The utilization of frame-sliced voxels enables approximation of the workpiece surface to only loosely depend on the grid resolution but achieve sub-voxel resolution updates for the model volume. It can, thus, provide a boundary representation of the workpiece model at an accuracy that is much higher than a basic voxel model of the same grid resolution and a similar model size. Quantitative comparisons of the FSV-rep with the traditional voxel representations at the same finest grid resolution show improvement up to two orders of magnitude in accuracy with only marginal increases in the model size. This confirms the effectiveness of the FSV-rep in simulating machined workpiece geometry in complex machining processes such as multi-axis milling.     

Free Path Sampling in High Resolution Inhomogeneous Participating Media

This paper presents efficient algorithms for free path sampling in heterogeneous participating media defined either by high‐resolution voxel arrays or generated procedurally. The method is based on the concept of mixing ‘virtual’ material or particles to the medium, augmenting the extinction coefficient to a function for which the free path can be sampled in a straightforward way. The virtual material is selected such that it modifies the volume density but does not alter the radiance. We define the total extinction coefficient of the real and virtual particles by a low‐resolution grid of super‐voxels that are much larger than the real voxels defining the medium. The computational complexity of the proposed method depends just on the resolution of the super‐voxel grid and does not grow with the resolution above the scale of super‐voxels. The method is particularly efficient to render large, low‐density, heterogeneous volumes, which should otherwise be defined by enormously high resolution voxel grids and where the average free path length would cross many voxels.     

基于量子粒子群优化的DAG并行任务调度研究*

任务调度是网络并行计算系统的核心问题之一。在有向无环图(DAG)描述问题的基础上,提出了一种进行并行任务调度的量子粒子群优化算法。首先对DAG并行任务调度问题作出定义,并给出了优化问题的目标;然后分别讨论了问题的编码表示、解码方案、位置向量的计算方法、离散问题连续化、算法的总体流程等;最后给出算法的仿真实验情况及分析,实验结果表明,该算法有良好的全局寻优性能和快捷的收敛速度,调度效果优于遗传算法和粒子群优化算法。     

Efficient sparse voxel octrees

In this paper, we examine the possibilities of using voxel representations as a generic way for expressing complex and feature-rich geometry on current and future GPUs. We present in detail a compact data structure for storing voxels and an efficient algorithm for performing ray casts using this structure. We augment the voxel data with novel contour information that increases geometric resolution, allows more compact encoding of smooth surfaces, and accelerates ray casts. We also employ a novel normal compression format for storing high-precision object-space normals. Finally, we present a variable-radius postprocess filtering technique for smoothing out blockiness caused by discrete sampling of shading attributes. Based on benchmark results, we show that our voxel representation is competitive with triangle-based representations in terms of ray casting performance, while allowing tremendously greater geometric detail and unique shading information for every voxel. Our voxel codebase is open sourced and available at http://code.google.com/p/efficient-sparse-voxel-octrees/.     

结合体元数据结构的机载LIDAR建筑物检测

目的 目前,点云、栅格格网及不规则三角网等建筑物检测中常用的离散机载激光雷达（LIDAR）点云数据表达方式存在模型表达复杂、算法开发困难、结果表达不准确及难以表达多返回数据等缺点。为此,针对LIDAR点云体元结构模型构建及在此基础上的建筑物检测展开研究,提出一种基于体元的建筑物检测算法。方法 首先将点云数据规则化为二值（即1、0值,分别表示体元中是否包含有激光点）3D体元结构。然后利用3D滤波算法将上述体元结构中表征数据点的体元分类为地面和非地面体元。最后,依据建筑物边缘的接近直线、跳变特性从非地面体元中搜寻建筑物边缘作为种子体元进而标记与其3D连通的非地面体元集合为建筑物体元。结果 实验基于ISPRS（international society for photogrammetry and remote sensing）提供的包含了不同的建筑物类型的城区LIDAR点云数据测试了"邻域尺度"参数的敏感性及提出算法的精度。定量评价的结果表明：56邻域为最佳邻域尺度;建筑物的检测质量可达到95%以上——平均完整度可达到95.61%、平均正确率可达95.97%。定性评价的结果表明：对大型、密集、不规则形状、高低混合及其他屋顶类型比较特殊的复杂建筑物均可成功检测。结论 本文提出的建筑物检测算法采用基于体元空间邻域关系的搜索标记方式,可有效实现对各类建筑目标特别是城市建筑目标的检测,检测结果易于建模3D建筑物模型。     

Reconstruction of opaque inclusions in objects with high refractive index

The problem of reconstruction of inclusions in rough diamonds occupies an important place in the entire technological process of extraction and cutting precious stones. Inclusions are foreign objects that are naturally formed in raw stock during the formation of diamond (see Fig. 1). The algorithm proposed in the present paper performs a full reconstruction of three-dimensional models of inclusions from photo images. Three-dimensional models of inclusions are based on a voxel representation. The algorithm performs the coloring of voxels and the segmentation of a voxel grid and constructs polygonal models of inclusions. Experiments carried out on real and synthetic data show that the algorithm can reconstruct three-dimensional models of medium- and large-size inclusions, which may serve as a first approximation for the methods of refinement of the shape of inclusions.     

Binary volume rendering using Slice-based Binary Shell

This paper presents a new data structure, Slice-based Binary Shell (SBS), for efficient manipulation and rendering of binary volume data. Since SBS stores only surface voxels with selected attributes of the voxels in a slice-based data structure that allows direct access to the voxels, it shows high storage and computational efficiency. This efficiency becomes more prominent when representing multiple binary objects. We also present an efficient rendering algorithm for SBS. The algorithm, based on the shear-warp technique, provides high-speed interactive rendering for binary volumes of many objects on a PC with no specialized hardware.     

Shell rendering

A structure model for volume rendering, called a shell, is introduced. Roughly, a shell consists of a set of voxels in the vicinity of the structure boundary together with a number of attributes associated with the voxels in this set. By carefully choosing the attributes and storing the shell in a special data structure that allows random access to the voxels and their attributes, storage and computational requirements can be reduced drastically. Only the voxels that potentially contribute to the rendition actually enter into major computation. Instead of the commonly used ray-casting paradigm, voxel projection is used. This eliminates the need for render-time interpolation and further enhances the speed. By having one of the attributes as a boundary likelihood function that determines the most likely location of voxels in the shell to be on the structure boundary, surface-based measurements can be made. The shell concept, the data structure, the rendering and measurement algorithms, and examples drawn from medical imaging that illustrate these concepts are described     

A distance template for octree traversal in CPU-based volume ray casting

Several optimization techniques have been proposed to improve the speed of direct volume rendering. A hierarchical representation formed by an octree is a data structure to skip over transparent regions while requiring little preprocessing and data storage. However, in order to skip over an octant estimated to be transparent (a transparent octant), the distance from a boundary to another boundary of the octant should be calculated. Because the distance computation is expensive, we propose a precomputed data structure, the distance template, which stores direction and distance values from one boundary voxel on a face to all the boundary voxels on the remaining five faces. In the rendering step, if a ray reaches a transparent octant, it leaps over the octant by referring to the stored distance value.