3D GIS中线性八叉树空间索引的建立与查询算法研究

三维地理信息系统空间数据库具有数据量大、空间实体关系复杂、空间操作计算量大等特点。为了提高检索效率,必须建立高效的空间索引机制。八叉树空间索引是对二维GIS中四叉树索引进行扩展的一种三维空间数据结构,具有思路简单、容易理解和实现、查询速度快的优点。本文首先阐述了线性八叉树空间索引的原理,然后重点介绍了线性八叉树空间索引的建立和查询算法。     

Predictors of user perceptions of web recommender systems: How the basis for generating experience and search product recommendations affects user responses

One critical question suggested by Web 2.0 is as follows: When is it better to leverage the knowledge of other users vs. rely on the product characteristic-based metrics for online product recommenders? Three recent and notable changes of recommender systems have been as follows: (1) a shift from characteristic-based recommendation algorithms to social-based recommendation algorithms; (2) an increase in the number of dimensions on which algorithms are based; and (3) availability of products that cannot be examined for quality before purchase. The combination of these elements is affecting users’ perceptions and attitudes regarding recommender systems and the products recommended by them, but the psychological effects of these trends remain unexplored. The current study empirically examines the effects of these elements, using a 2 (recommendation approach: content-based vs. collaborative-based, within)×2 (dimensions used to generate recommendations: 6 vs. 30, between)×2 (product type: experience products (fragrances) vs. search products (rugs), between) Web-based study (N=80). Participants were told that they would use two recommender systems distinguished by recommendation approach (in fact, the recommendations were identical). There were no substantive main effects, but all three variables exhibited two-way interactions, indicating that design strategies must be grounded in a multi-dimensional understanding of these variables. The implications of this research for the psychology and design of recommender systems are presented.     

Coupling and comparing a spatially- and temporally-detailed eutrophication model with an ecosystem network model: An initial application to Chesapeake Bay

Coastal waters are modeled for a variety of purposes including eutrophication remediation and fisheries management. Combining these two approaches provides insights which are not available from either approach independently. Coupling is confounded, however, by differences in model formulations and “currencies.” We present here an initial coupling of a spatially- and temporally-detailed eutrophication model, CE-QUAL-ICM, with a network fisheries model, Ecopath. We list commonalities between the models and present algorithms and software for the exchange of information. The models are applied to the central portion of Chesapeake Bay for a contemporary summer period. After comparison of the representations of Chesapeake Bay by the two models, an illustrative example one-way, off-line, coupling is presented. In an initial examination of a 20% increase in predation on phytoplankton by a small, highly-exploited fish (Atlantic menhaden, Brevoortia tyrannus), computed reduction in phytoplankton biomass is accompanied by increased production due to enhanced nutrient recycling. Minimal impact on the structure of the food web or on biomass of higher-trophic level organisms is computed. The algorithms and software can be adapted to alternate eutrophication models and Ecopath applications and provide the first, necessary, steps for subsequent coupling with the time-variable Ecosim model.     

Urban Rainwater Utilization and its Role in Mitigating Urban Waterlogging Problems—A Case Study in Nanjing, China

With the acceleration of the urbanization process, urban waterlogging problems are becoming more and more serious in Nanjing, China. In order to mitigate the urban waterlogging problems, it is necessary to reduce surface runoff from the source by rainwater harvesting and utilization. An urban residential district with an area of 0.58?km² in Nanjing was selected as the study area. Based on a large-scale topographic map data and the long term rainfall data (1951?C2008), the types of underlying surfaces were classified. The potentiality of collectable rainwater and the possibility of runoff volume reduction were calculated. The results showed that exploitation of rainwater harvesting from rooftops and other underlying surfaces has high potential. The annual collectable rainwater is approximately 372,284?m³, 314,034?m³ and 275,180?m³ under different cumulative frequency of rainfall at 20?%, 50?% and 75?%, respectively. The total capacity of cisterns under assumptions of return period of rainfall and rainfall duration with 5?years and 20?min is 11,022?m³. The cistern??s capacity which is used for roof rainwater harvesting is 4,083?m³, the cistern capacity for per unit roof area (1?m²) is 0.0267?m³. The results of the feasibility analysis of setting up above-ground cisterns showed that 55?% of the total roof areas in the study area are available for setting up cisterns. In the three building types, 16?% of the commercial building??s roof areas and 77?% of that of the residential and the ??others?? buildings are available for setting up cisterns. Urban waterlogging problems can be effectively reduced through rainwater harvesting by 13.9?%, 30.2?% and 57.7?% of runoff volume reduction in three cases of the maximum daily rainfall (207.2?mm), the average annual maximum daily rainfall (95.5?mm) and the critical rainfall of rainstorm (50?mm).     

黄河信息资源共享服务系统设计与实现

为了有效组织和管理黄委局域网内各类分布异构的数据资源,解决在网络环境下的异构信息资源整合问题,促进信息共享与利用,开发建设了黄河信息资源共享服务系统。黄河信息资源具有内容形式复杂多样、异构、海量与分布式存储的特征,因此在系统的开发过程中,通过采用统一标准,引入基于语义的信息资源管理和信息服务机制,把本体的语义推理能力有效地与元数据信息相结合,从而建立语义统一的全局模式,达到屏蔽底层数据库异构现象的目的。该系统由应用系统、应用支撑平台、中心节点和分节点构成,具有数据汇交、查询浏览、数据下载、数据目录服务、用户管理和访问统计等功能。     

Search product and experience product online reviews: An eye-tracking study on consumers' review search behavior

This study uses eye-tracking method to investigate consumers' online review search behavior by suggesting that it needs to consider the type of product reviewed. A review-product congruity proposition was testified through a self-report survey and an eye-tracking experiment. The proposition states that consumers of search products expect to seek attribute based reviews, while consumers shopping for experience products tend to seek experience based reviews. Two experiments were conducted in the human factors & ergonomics laboratory of Beihang University, China and all subjects are college students. The results of our first empirical experiment support our hypotheses by showing consumers' more active and positive responses to attribute based reviews when shopping for search products and to experience based reviews when purchasing experience products. The second experiment was conducted with eye tracking method to gain further insights. We found that consumers of search products are attracted and engaged more deeply by attribute based reviews. However, when they browse experience products, the difference of their fixations on experience based reviews and attribute based reviews is not significant, and thus the proposition is partially supported. This study extends our current understanding of consumers' online review search behavior by subsuming product type, which is necessary and helpful, and provides references on the classification and presentation of reviews to facilitate consumers' product judgement and decision making. Moreover, comparison of traditional empirical method and eye-tracking method can help deepen our understanding of complex consumer online shopping behavior.     

Multi-agent based path planning for first responders among moving obstacles

Natural or man-made disasters can cause different kinds of moving obstacles (e.g., fires, plumes, floods), which make some parts of the road network temporarily unavailable. After such incidents occur, responders have to go to different destinations to perform their tasks in the environment affected by the disaster. Therefore they need a path planner that is capable of dealing with such moving obstacles, as well as generating and coordinating their routes quickly and efficiently. In this paper, we present a novel approach for using a multi-agent system for navigating one or multiple responders to one or multiple destinations in the presence of moving obstacles. Our navigation system supports information collection from hazard simulations, spatio-temporal data processing and analysis, connection with a geo-database, and route generation in dynamic environments affected by disasters. We design and develop a set of software geospatial agents that assist emergency actors in dealing with the spatio-temporal data required for emergency navigation, based on their roles in the disaster response. One of the key components of the system is the path planning module, which combines the modified A* algorithm, insertion heuristics, and auction algorithm to calculate obstacle-avoiding routes for multiple responders with multiple destinations. A spatial data model is designed to support the storage of information about the tasks and routes produced during the disaster response. Our system has been validated using four navigation cases. Some preliminary results are presented in this paper and show the potential of the system for solving more navigation cases.     

近40年来长江口沉积物粒度变化及其对底床冲淤的响应

在全球变化和人类活动的双重驱动下,长江口的沉积物来源、输运和河床冲淤正在经历持续性调整。为了探索近40年长江口沉积物输运和海底冲淤时空变化趋势,基于1980—2020年长江口海底沉积物粒度和水下地形数据,采用沉积物粒径趋势模型和多种空间分辨率网格统计分析方法开展研究。结果表明,长江口北支沉积物总体向河道中下部汇聚,南支则在南、北港分流处靠近崇明岛区域形成沉积中心,该结果与基于2012—2020年地形计算的冲淤变化基本相符,沉积中心具有较大的淤积幅度。多年统计结果表明:1980—2003年为高强度输沙时期,整个河口区处于淤积状态,沉积物粒径变细但整体变幅较小;2003—2012年河流输沙量快速降低背景下,2009年前河口区整体依然处于淤积状态,粒径变化不显著;2009—2012年是由淤积转为冲刷的过渡期,口外区域首先出现了小范围侵蚀和沉积物粗化现象;2012—2020年,河口区整体出现大面积侵蚀和粒径粗化现象,粒径与侵蚀变化间呈显著相关。研究发现,高分辨统计网格可以更有效地捕捉到小范围地貌由淤转冲的信号。总体而言,近40年来,长江口已经由显著淤积转为局部侵蚀,未来可能面临持续性的海岸侵蚀灾害。     

基于IHA/RVA法的修水流域上游大型水库影响下的枯水变异研究

根据水文变异指标法及变化范围法(IHA/RVA),对江西修水流域上游两个大型水库启用日期差异进行组合,定量计算、分析了水利工程影响下的修水流域上游枯水流量的时序变异特征,探讨了水利工程建设前后导致的水文变异程度,揭示了对河流生态系统至关重要的低流量范围内多个枯水情势高改变度的存在,为水库生态调度与河流生态保护提供了有益的参考。     

水利工程对河网连通性的影响研究——以太湖西苕溪流域为例

河网连通性对维护河流生态系统的结构和功能具有重要作用,水利工程可改变天然河网的连通性,直接威胁到河流生态系统的健康与稳定。利用空间分析、连续性指标以及树状河网连通性指数等方法,深入探讨了闸坝对河网连通性的影响。结果表明,树状河网连通性指数能够较为全面地分析不同数量、可通过性及地理位置的闸坝对河网连通性的影响,可以广泛应用于流域规划过程中不同方案的比较,从而为水利工程设施的选址及设计提供参考。