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T-Drive: Enhancing Driving Directions with Taxi Drivers' Intelligence

IEEE TRANSACTIONS ON KNOWLEDGE AND DATA ENGINEERING 2013年第1期25卷 220-232页

作者： Yuan, Jing Zheng, Yu Xie, Xing Sun, Guangzhong Univ Sci & Technol China Hefei 230026 Anhui Peoples R China Microsoft Res Asia Beijing 100080 Peoples R China

This paper presents a smart driving direction system leveraging the intelligence of experienced drivers. In this system, GPS-equipped taxis are employed as mobile sensors probing the traffic rhythm of a city and taxi drivers' intelligence in choosing driving directions in the physical world. We propose a time-dependent landmark graph to model the dynamic traffic pattern as well as the intelligence of experienced drivers so as to provide a user with the practically fastest route to a given destination at a given departure time. Then, a Variance-Entropy-Based Clustering approach is devised to estimate the distribution of travel time between two landmarks in different time slots. Based on this graph, we design a two-stage routing algorithm to compute the practically fastest and customized route for end users. We build our system based on a real-world trajectory data set generated by over 33,000 taxis in a period of three months, and evaluate the system by conducting both synthetic experiments and in-the-field evaluations. As a result, 60-70 percent of the routes suggested by our method are faster than the competing methods, and 20 percent of the routes share the same results. On average, 50 percent of our routes are at least 20 percent faster than the competing approaches.

关键词： spatial databases and gis data mining GPS trajectory driving directions driving behavior

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Topological operators: a relaxed query processing approach

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GEOINFORMATICA 2012年第1期16卷 67-110页

作者： Belussi, Alberto Catania, Barbara Podesta, Paola Univ Genoa Dipartimento Informat & Sci Informaz I-16146 Genoa Italy Univ Verona Dipartimento Informat I-37134 Verona Italy

Relaxation and approximation techniques have been proposed as approaches for improving the quality of query results, in terms of completeness and accuracy, in environments where the user may not be able to specify the query in a complete and exact way, since data are quite heterogeneous or she may not know all the characteristics of data at hand. This problem, mainly addressed for relational and XML data, is nowadays quite relevant also for geo-spatial data, due to their increasing usage in highly critical decisional processes. Among geo-spatial queries, those based on spatial and more precisely topological relations are currently used in an increasing number of applications. As far as we know, no approach has been proposed so far for relaxing queries based on topological predicates when they return an empty or insufficient answer, in order to improve result quality and user satisfaction. In this paper, we consider this problem and we present a general relaxation strategy for, possibly multi-domain, topological selection and join queries. Two specific semantics are also provided: the first applies the minimum amount of relaxation in order to get an acceptable answer;the second relaxes the given query of a certain fixed amount, depending on the considered topological predicate. Index-based processing algorithms, for efficiently executing relaxed queries based on the proposed semantics, are also presented and a specific topological similarity function, to be used for relaxation purposes, is proposed. Experimental results show that the overhead given by query relaxation is acceptable.

关键词： Information technology and systems Database management Database applications spatial databases and gis

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Redistricting Using Constrained Polygonal Clustering

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IEEE TRANSACTIONS ON KNOWLEDGE AND DATA ENGINEERING 2012年第11期24卷 2065-2079页

作者： Joshi, Deepti Soh, Leen-Kiat Samal, Ashok Univ Nebraska Dept Comp Sci & Engn Lincoln NE 68588 USA

Redistricting is the process of dividing a geographic area consisting of spatial units-often represented as spatial polygons-into smaller districts that satisfy some properties. It can therefore be formulated as a set partitioning problem where the objective is to cluster the set of spatial polygons into groups such that a value function is maximized [ 1]. Widely used algorithms developed for point-based data sets are not readily applicable because polygons introduce the concepts of spatial contiguity and other topological properties that cannot be captured by representing polygons as points. Furthermore, when clustering polygons, constraints such as spatial contiguity and unit distributedness should be strategically addressed. Toward this, we have developed the Constrained Polygonal spatial Clustering (CPSC) algorithm based on the A* search algorithm that integrates cluster-level and instance-level constraints as heuristic functions. Using these heuristics, CPSC identifies the initial seeds, determines the best cluster to grow, and selects the best polygon to be added to the best cluster. We have devised two extensions of CPSC-CPSC* and CPSC*-PS-for problems where constraints can be soft or relaxed. Finally, we compare our algorithm with graph partitioning, simulated annealing, and genetic algorithm-based approaches in two applications-congressional redistricting and school districting.

关键词： spatial clustering polygonal clustering constraint-based processing data mining spatial databases and gis

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Processing of Continuous Location-Based Range Queries on Moving Objects in Road Networks

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IEEE TRANSACTIONS ON KNOWLEDGE AND DATA ENGINEERING 2011年第7期23卷 1065-1078页

作者： Wang, Haojun Zimmermann, Roger Univ So Calif Dept Comp Sci Los Angeles CA 90089 USA Natl Univ Singapore Dept Comp Sci Sch Comp Singapore 117417 Singapore Natl Univ Singapore IDMI Singapore 117417 Singapore

With the proliferation of mobile devices, an increasing number of urban users subscribe to location-based services. This trend has led to significant research interest in techniques that address two fundamental requirements: road network-based distance computation and the capability to process moving objects as points of interests. However, there exist few techniques that support both requirements simultaneously. To address these challenges, we propose a novel approach to process continuous range queries. We build on our previous work of an infrastructure that supports location-based snapshot queries on MOVing objects in road Networks (MOVNet). We introduce several significant features to enable continuous queries. The dual index structure that we proposed for MOVNet has been appropriately modified. We further appoint a number of connecting vertices in each cell and precompute the distances among them to expedite query processing. Most importantly, to alleviate the effects of frequent object updates, we introduce a Shortest-Distance-based Tree (SD-Tree). We illustrate that the network connectivity and distance information can be preserved and reused by the SD-Tree when the query point location is updated;hence, reducing the continuous query update cost. Our experimental results demonstrate that our method yields excellent performance with a very large number of moving objects.

关键词： spatial databases and gis location-dependent and sensitive

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Location-Based Data Dissemination for spatial Queries in Wireless Broadcast Environments

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Journal of Computer Science & Technology 2010年第2期25卷 330-346页

作者： Kwangjin Park Hyunseung Choo School of Electrical Electronics and Information Engineering Wonkwang University School of Information and Communication Engineering Sungkyunkwan University

Most current research on Location-Based Services （LBSs, for short） assumes point-to-point wireless commu- nication, where the server processes a query and returns the query result to the user via a point-to-point wireless channel. However, LBSs via point-to-point wireless channel suffer from a tremendous amount of tramc and service requests from the user and thereby result in poor performance. In this paper, we present broadcast-based spatial query processing algorithms designed to support k-NN （k-Nearest Neighbor） and range queries via a wireless network. The task of the query processor is to selectively monitor the wireless broadcast channel, when the data items are disseminated by the server, according to their locations. Experiments are conducted to evaluate the performance of the proposed algorithms. Comprehensive experiments illustrate that the presented algorithms are highly scalable and are more efficient than the previous techniques in terms of both access time and energy consumption.

关键词： distributed databases indexing methods information storage and retrieval spatial databases and gis

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Bichromatic Reverse Nearest-Neighbor Search in Mobile Systems

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IEEE SYSTEMS JOURNAL 2010年第2期4卷 230-242页

作者： Tran, Quoc Thai Taniar, David Safar, Maytham Monash Univ Clayton Sch Informat Technol Melbourne Vic 3004 Australia Kuwait Univ Dept Comp Engn Safat Kuwait

In traditional reverse nearest-neighbor (RNN) search, the goal is to find the set of interest objects taking the query object as the nearest neighbor given that the interest objects and the query object have the same type. However, when the interst objects and the query object are of different types, this problem is called bichromatic reverse nearest neighbor (BRNN) search. The BRNN query has an increasing number of mobile applications and requires efficient algorithms for processing. In this paper, we present a novel approach for the BRNN search in the context of spatial network databases (SNDB). The main idea behind our approaches is to use Euclidean-based range search to prune the search space and use Euclidean distance in addition to network distance to minimize processing time. Finally, the experimental results confirm that our proposed algorithm have good performance on different network densities.

关键词： Mobile systems nearest neighbor searches network Voronoi diagrams query processing spatial databases and gis

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Placegram: A Diagrammatic Map for Personal Geotagged Data Browsing

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IEEE TRANSACTIONS ON VISUALIZATION AND COMPUTER GRAPHICS 2010年第2期16卷 221-234页

作者： Jo, Hyungeun Ryu, Jung-hee Korea Adv Inst Sci & Technol Grad Sch Culture Technol Taejon 305701 South Korea

Geotagging personal data such as photos and videos are continuously becoming easier and more popular. Nevertheless, browsing such data on general purpose maps can be difficult, due to the frequent zoom and pan operations as well as visual components unnecessary for the task. This paper presents Placegram, a compact diagrammatic map visualization for personal geotagged data browsing based on cognitive map theories. An evaluation using real-life data sets shows that the speed of finding and pointing to places from the participants' own data increased by a factor of 2.1-2.9, and the number of interesting places discovered from others' data within a time limit increased by 48.8 percent in Placegram compared to a general purpose map. Placegram was even slightly faster than a simple text list, while at the same time, preserving the geographic senses of direction and location. Subjective ratings and comments from participants support these results, indicating that Placegram is significantly preferred over both a general map and a text list.

关键词： Information visualization graphical user interfaces spatial databases and gis multimedia information systems

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A link-based storage scheme for efficient aggregate query processing on clustered road networks

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INFORMATION SYSTEMS 2010年第1期35卷 75-93页

作者： Demir, Engin Aykanat, Cevdet Cambazoglu, B. Barla Bilkent Univ Dept Comp Engn Ankara Turkey Yahoo Res Barcelona Spain

The need to have efficient storage schemes for spatial networks is apparent when the volume of query processing in some road networks (e.g., the navigation systems) is considered. Specifically, under the assumption that the road network is stored in a central server, the adjacent data elements in the network must be clustered on the disk in such a way that the number of disk page accesses is kept minimal during the processing of network queries. In this work, we introduce the link-based storage scheme for clustered road networks and compare it with the previously proposed junction-based storage scheme. in order to investigate the performance of aggregate network queries in clustered road networks, we extend our recently proposed clustering hypergraph model from junction-based storage to link-based storage. We propose techniques for additional storage savings in bidirectional networks that make the link-based storage scheme even more preferable in terms of the storage efficiency. We evaluate the performance of our link-based storage scheme against the junction-based storage scheme both theoretically and empirically. The results of the experiments conducted on a wide range of road network datasets show that the link-based storage scheme is preferable in terms of both storage and query processing efficiency. (C) 2009 Elsevier B.V. All rights reserved.

关键词： Storage management spatial databases and gis Road networks Link-based storage Clustering Hypergraphs

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Dictionary-Based Compression for Long Time-Series Similarity

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IEEE TRANSACTIONS ON KNOWLEDGE AND DATA ENGINEERING 2010年第11期22卷 1609-1622页

作者： Lang, Willis Morse, Michael Patel, Jignesh M. Univ Wisconsin Dept Comp Sci Madison WI 53706 USA MITRE Washington Mitre Corp Innovat Informat Engn & Biometr Mclean VA 22102 USA

Long time-series data sets are common in many domains, especially scientific domains. Applications in these fields often require comparing trajectories using similarity measures. Existing methods perform well for short time series but their evaluation cost degrades rapidly for longer time series. In this work, we develop a new time-series similarity measure called the Dictionary Compression Score (DCS) for determining time-series similarity. We also show that this method allows us to accurately and quickly calculate similarity for both short and long time series. We use the well-known Kolmogorov Complexity in information theory and the Lempel-Ziv compression framework as a basis to calculate similarity scores. We show that off-the-shelf compressors do not fair well for computing time-series similarity. To address this problem, we developed a novel dictionary-based compression technique to compute time-series similarity. We also develop heuristics to automatically identify suitable parameters for our method, thus, removing the task of parameter tuning found in other existing methods. We have extensively compared DCS with existing similarity methods for classification. Our experimental evaluation shows that for long time-series data sets, DCS is accurate, and it is also significantly faster than existing methods.

关键词： spatial databases and gis database management

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Visualization of Spatiotemporal Behavior of Discrete Maps via Generation of Recursive Median Elements

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IEEE TRANSACTIONS ON PATTERN ANALYSIS AND MACHINE INTELLIGENCE 2010年第2期32卷 378-384页

作者： Sagar, B. S. Daya Indian Stat Inst Bangalore Ctr Syst Sci & Informat Unit Bangalore 560059 Karnataka India

spatial interpolation is one of the demanding techniques in Geographic Information Science (gisci) to generate interpolated maps in a continuous manner by using two discrete spatial and/or temporal data sets. Noise-free data (thematic layers) depicting a specific theme at varied spatial or temporal resolutions consist of connected components either in aggregated or in disaggregated forms. This short paper provides a simple framework: 1) to categorize the connected components of layered sets of two different time instants through their spatial relationships and the Hausdorff distances between the companion-connected components and 2) to generate sequential maps (interpolations) between the discrete thematic maps. Development of the median set, using Hausdorff erosion and dilation distances to interpolate between temporal frames, is demonstrated on lake geometries mapped at two different times and also on the bubonic plague epidemic spread data available for 11 consecutive years. We documented the significantly fair quality of the median sets generated for epidemic data between alternative years by visually comparing the interpolated maps with actual maps. They can be used to visualize (animate) the spatiotemporal behavior of a specific theme in a continuous sequence.

关键词： gisci spatial interpolation mathematical morphology thematic maps dilation erosion interpolation formulas spatial databases and gis cartography morphological image representation visualization techniques and methodologies geometrical problems and computations set theory

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