Data structures for encoding triangulated irregular networks

Triangulated Irregular Networks are the most common form of digital surface model. They are based on a decomposition of the surface into a set of non-overlapping triangular patches. In the paper, we consider the problem of the internal representation of triangular subdivisions. We describe four different data structures, which are especially well-suited to represent triangular grids. Algorithms for solving three basic problems on triangulated irregular networks, namely the point-in-triangulation, the vertex-neighbor and the edge-neighbor problems, are described, and their time complexity is evaluated.     

Multiresolution analysis on irregular surface meshes

Wavelet-based methods have proven their efficiency for visualization at different levels of detail, progressive transmission, and compression of large data sets. The required core of all wavelet-based methods is a hierarchy of meshes that satisfies subdivision-connectivity. This hierarchy has to be the result of a subdivision process starting from a base mesh. Examples include quadtree uniform 2D meshes, octree uniform 3D meshes, or 4-to-1 split triangular meshes. In particular, the necessity of subdivision-connectivity prevents the application of wavelet-based methods on irregular triangular meshes. In this paper, a “wavelet-like” decomposition is introduced that works on piecewise constant data sets over irregular triangular surface meshes. The decomposition/reconstruction algorithms are based on an extension of wavelet-theory allowing hierarchical meshes without property. Among others, this approach has the following features: it allows exact reconstruction of the data set, even for nonregular triangulations, and it extends previous results on Haar-wavelets over 4-to-1 split triangulations     

基于三角形不规则网模型的快速体素化方法

为了改善在大数据量时体素化效率不高的缺点,针对三角形不规则网（TIN）模型的三角网特性,提出了一种快速简单的体素化算法。首先通过细划三角面片,将面体素化转换为简单的点体素化生成体表面模型,然后利用深度缓存原理快速寻找初始种子体素进行体内填充。实验结果表明,对于精细复杂的大规模TIN模型,算法能确实有效地生成逼近原模型的26-连通的体素模型,且具有高效的时间效率。     

三维不规则三角网格的精确裁剪算法

给出了一种基于约束Delaunay三角剖分的三维不规则三角网格的精确裁剪算法。算法结合TIN数据的生成特点,首先将TIN投影到二维平面,然后利用约束Delaunay三角剖分把裁剪多边形的每条边嵌入三角网中,再利用边-三角形的拓扑关系删除裁剪多边形外部多余三角形,最后利用边-点的拓扑关系对裁剪多边形顶点高程进行插值,使生成裁剪后的TIN模型。对不同复杂程度的三维TIN模型进行裁剪实验,发现二维投影策略极大地提高了三维TIN裁剪效率。算法的程序实现简单,且符合工程需求。     

Filtering LiDAR data based on adjacent triangle of triangulated irregular network

Multimedia Tools and Applications - The filtering of LiDAR points cloud data is a fundamental procedure in the production of Digital Elevation Model. Against the lack of using the relationship...     

Semantic indexing in structured peer-to-peer networks

The past few years have seen tremendous advances in distributed storage infrastructure. Unstructured and structured overlay networks have been successfully used in a variety of applications, ranging from file-sharing to scientific data repositories. While unstructured networks benefit from low maintenance overhead, the associated search costs are high. On the other hand, structured networks have higher maintenance overheads, but facilitate bounded time search of installed keywords. When dealing with typical data sets, though, it is infeasible to install every possible search term as a keyword into the structured overlay.     

Layered routing in irregular networks

Freedom from deadlock is a key issue in cut-through, wormhole, and store and forward networks, and such freedom is usually obtained through careful design of the routing algorithm. Most existing deadlock-free routing methods for irregular topologies do, however, impose severe limitations on the available routing paths. We present a method called layered routing, which gives rise to a series of routing algorithms, some of which perform considerably better than previous ones. Our method groups virtual channels into network layers and to each layer it assigns a limited set of source/destination address pairs. This separation of traffic yields a significant increase in routing efficiency. We show how the method can be used to improve the performance of irregular networks, both through load balancing and by guaranteeing shortest-path routing. The method is simple to implement, and its application does not require any features in the switches other than the existence of a modest number of virtual channels. The performance of the approach is evaluated through extensive experiments within three classes of technologies. These experiments reveal a need for virtual channels as well as an improvement in throughput for each technology class.     

Update-efficient indexing of moving objects in road networks

Recent advances in wireless sensor networks and positioning technologies have boosted new applications that manage moving objects. In such applications, a dynamic index is often built to expedite evaluation of spatial queries. However, the development of efficient indexes is a challenge due to frequent object movement. In this paper, we propose a new update-efficient index method for moving objects in road networks. We introduce a dynamic data structure, called adaptive unit, to group neighboring objects with similar movement patterns. To reduce updates, an adaptive unit captures the movement bounds of the objects based on a prediction method, which considers road-network constraints and the stochastic traffic behavior. A spatial index (e.g., R-tree) for the road network is then built over the adaptive unit structures. Simulation experiments, carried on two different datasets, show that an adaptive-unit based index is efficient for both updating and querying performances.

SAR imaging simulation for an inhomogeneous undulated lunar surface based on triangulated irregular network

Based on the statistics of the lunar cratered terrain, e.g., population, dimension and shape of craters, the terrain feature of cratered lunar surface is numerically generated. According to the inhomogeneous distribution of the lunar surface slope, the triangulated irregular network (TIN) is employed to make the digital elevation of lunar surface model. The Kirchhoff approximation of surface scattering is then applied to simulation of lunar surface scattering. The synthetic aperture radar (SAR) image for comprehensive cratered lunar surface is numerically generated using back projection (BP) algorithm of SAR imaging. Making use of the digital elevation and Clementine UVVIS data at Apollo 15 landing site as the ground truth, an SAR image at Apollo 15 landing site is simulated. The image simulation is verified using real SAR image and echoes statistics. Supported by the National Matural Science Foundation of China (Grant No. 40637033)     

不规则网络拓扑结构下的多棵树路由算法研究

为了提高不规则网络拓扑结构的路由效率,提出了一种新型路由算法-多棵树路由算法.考虑了原始路由算法的不足,平均了网络中各个通道的利用率,降低路由表的平均路径长度,同时在死锁发生时能够及时有效的进行死锁恢复,解决了先前路由算法中通道负载集中、通道利用率低、路由表平均路径长度过长的问题.通过模拟真实硬件环境的模拟器软件,表明了在不同规模、不同负载下的不规则网络下多棵树路由算法具有更高的效率.     

Film segmentation and indexing using autoassociative neural networks

In this paper, Autoassociative Neural Network (AANN) models are explored for segmentation and indexing the films (movies) using audio features. A two-stage method is proposed for segmenting the film into sequence of scenes, and then indexing them appropriately. In the first stage, music and speech plus music segments of the film are separated, and music segments are labelled as title and fighting scenes based on their position. At the second stage, speech plus music segments are classified into normal, emotional, comedy and song scenes. In this work, Mel frequency cepstral coefficients (MFCCs), zero crossing rate and intensity are used as audio features for segmentation and indexing the films. The proposed segmentation and indexing method is evaluated on manual segmented Hindi films. From the evaluation results, it is observed that title, fighting and song scenes are segmented and indexed without any errors, and most of the errors are observed in discriminating the comedy and normal scenes. Performance of the proposed AANN models used for segmentation and indexing of the films, is also compared with hidden Markov models, Gaussian mixture models and support vector machines.     

路网中移动对象轨迹索引的研究

索引结构对有效保存和查询移动对象的运动轨迹是至关重要的.根据交通网络中移动对象的轨迹特点,讨论了目前具有代表性的几种索引结构,重点分析了MON-Tree索引结构,将它与3D-Rtree进行了性能比较.在此基础上,提出并实现了一种基于MON-Tree的网络中移动对象轨迹数据库原型.     

道路网络中移动对象的索引研究

为了能有效地实现网络中移动对象的过去、当前和将来轨迹的查询,提出了一种L2R索引,它由两层R树和一个链表结构组成。两层R树用以索引道路网络和移动对象过去的运动,对象当前的位置和将来的预测轨迹信息保存在链表中。L2R索引不仅可以支持网络中的移动对象的轨迹查询,尤其是可方便的在纵向链表中查询在同条路线上的所有对象。在此索引基础上文中实施了对移动对象的范围查询和点查询,最后通过实验表明L2R结构的索引和查询性能均要优越于TPR树。     

Designing efficient irregular networks for heterogeneous systems-on-chip

Networks-on-chip will serve as the central integration platform in future complex systems-on-chip (SoC) designs, composed of a large number of heterogeneous processing resources. Most researchers advocate the use of traditional regular networks like meshes, tori or trees as architectural templates which gained a high popularity in general-purpose parallel computing. However, most SoC platforms are special-purpose tailored to the domain-specific requirements of their application. They are usually built from a large diversity of heterogeneous components which communicate in a very specific, mostly irregular way.

In this work, we propose a methodology for the design of customized irregular networks-on-chip, called INoC. We take advantage of a priori knowledge of the communication characteristic of the application to generate an optimized network topology and routing algorithm. We show that customized irregular networks are clearly superior to traditional regular architectures in terms of performance at comparable implementation costs for irregular workloads. Even more, they inherently offer a high degree of scalability and expansibility which allows to adapt the network to an arbitrary number of nodes with a given communication demand. This can normally not be accomplished by traditional approaches.     

分布式P2P网络基于索引的资源发现研究

基于DHT的P2P网络很大程度地增加了网络的可扩展性和健壮性,但是它也带来了新的问题,在结构化的p2p DHT网络中,在事先知道所要搜索资源的全部关键字的情况下,通过DHT很容易定位到对应资源,但是,实际应用中,用户有时在搜索资源的过程中只给出了部分关键字,这时即使网络中存在相关资源也不能被发现.本文研究的重点就是如何在县现有可用的DHT网络模型的基础之上对其进行扩展,提出一种分布式的树型索引结构,使其能有效支持部分关键字匹配查询.     

iNet: visual analysis of irregular transition in multivariate dynamic networks

Multivariate dynamic networks indicate networks whose topology structure and vertex attributes are evolving along time. They are common in multimedia applications. Anomaly detection is one of the essential tasks in analyzing these networks though it is not well addressed. In this paper, we combine a rare category detection method and visualization techniques to help users to identify and analyze anomalies in multivariate dynamic networks. We conclude features of rare categories and two types of anomalies of rare categories. Then we present a novel rare category detection method, called DIRAD, to detect rare category candidates with anomalies. We develop a prototype system called iNet, which integrates two major visualization components, including a glyph-based rare category identifier, which helps users to identify rare categories among detected substructures, a major view, which assists users to analyze and interpret the anomalies of rare categories in network topology and vertex attributes. Evaluations, including an algorithm performance evaluation, a case study, and a user study, are conducted to test the effectiveness of proposed methods.     

Multiresolution Tiling

This paper describes an efficient method for constructing a tiling between a pair of planar contours. The problem is of interest in a number of domains, including medical imaging, biological research and geological reconstructions. Our method, based on ideas from multiresolution analysis and wavelets, requires O(n) space and appears to require O(n log n) time for average inputs, compared to the O(n²) space and O(n² log n) time required by the optimizing algorithm of Fuchs, Kedem and Uselton¹. The results computed by our algorithm are in many cases nearly the same as those of the optimizing algorithm, but at a small fraction of the computational cost. The performance improvement makes the algorithm usable for large contours in an interactive system. The use of multiresolution analysis provides an efficient mechanism for data compression by discarding wavelet coefficients smaller than a threshold value during reconstruction. The amount of detail lost can be controlled by appropriate choice of the threshold value. The use of lower resolution approximations to the original contours yields significant savings in the time required to display a reconstructed object, and in the space required to store it.     

TDMA scheduling for event-triggered data aggregation in irregular wireless sensor networks

Multi-hop wireless sensor networks often use a TDMA schedule to collect data periodically from multiple locations within a large area. If the measurements from neighboring sensors are cross-correlated, they can be aggregated and compressed as they travel to the data sink. In order for data aggregation to occur quickly, the TDMA schedule must arrange time slot assignments in a certain order. The existing scheduling protocols cannot quickly obtain a schedule with this order, high concurrency, and no collisions. We propose a distributed TDMA scheduling protocol for data aggregation called DATP. In DATP, the sensor nodes transmit dummy packets in order to determine whether they can tolerate the interference from the other nodes that are assigned the same time slot. In this way, time slot allocations are empirically verified to be collision-free. In contrast, the existing protocols obtain schedules with collisions because they use unrealistic interference models such as neglecting interference generated more than two hops away. Furthermore, our simulations reveal that DATP achieves similar concurrency and lower execution time than comparable protocols. These simulations are executed for different network sizes, node densities, and data compression models. In addition, we show that, in networks with fluctuating links, DATP’s main advantage is its execution speed.     

Tree-turn routing: an efficient deadlock-free routing algorithm for irregular networks

In this paper, we propose a general turn model, called a Tree-turn model, for tree-based routing algorithms on irregular topologies. In the Tree-turn model, links are classified as either a tree link or a cross link and six directions are associated with the channels of links. Then we can prohibit some of the turns formed by these six directions such that an efficient deadlock-free routing algorithm, Tree-turn routing, can be derived. There are three phases to develop the Tree-turn routing. First, a coordinated tree for a given topology is created. Second, a communication graph is constructed based on the topology and the corresponding coordinated tree. Third, the forwarding table is set up by using all-pairs shortest path algorithm according to the prohibited turns in the Tree-turn model and the directions of the channels in the communication graph. To evaluate the performance of the proposed Tree-turn routing, we develop a simulator and implement Tree-turn routing along with up*/down* routing, L-turn routing, and up*/down* routing with DFS methodology. The simulation results show that Tree-turn routing outperforms other routing algorithms for all the test cases.     

An optimal scheduling algorithm for an agent-based multicast strategy on irregular networks

This paper describes an agent-based approach for scheduling multiple multicast on wormhole switch-based networks with irregular topologies. Multicast/broadcast is an important communication pattern, with applications in collective communication operations such as barrier synchronization and global combining. Our approach assigns an agent to each subtree of switches such that the agents can exchange information efficiently and independently. The entire multicast problem is then recursively solved with each agent sending message to those switches that it is responsible for. In this way, communication is localized by the assignment of agents to subtrees. This idea can be easily generalized to multiple multicast since the order of message passing among agents can be interleaved for different multicasts. The key to the performance of this agent-based approach is the message-passing scheduling between agents and the destination processors. We propose an optimal scheduling algorithm, called ForwardInSwitch to solve this problem. We conduct extensive experiments to demonstrate the efficiency of our approach by comparing our results with SPCCO, a highly efficient multicast algorithm reported in literature. We found that SPCCO suffers link contention when the number of simultaneous multiple multicast becomes large. On the other hand, our agent-based approach achieves better performance in large cases.