一种基于WMS服务的地图应用方法

网络地图服务(WMS)是基于开放地理信息系统协会(OGC)规范的网络地图服务,实现了对多源异构地理空间数据的封装和转换,通过返回地图图像的方式满足客户端的地图请求。在对WMS规范的技术原理进行分析研究的基础上,提出了一种访问WMS服务目录列表,从WMS下载地图图像进行应用的方法以及使用该方法时的要点,对既有系统进行了应用改造,实现了对多种格式海量地理空间数据的支持。技术方法思路清晰,功能边界清楚,通用性强,能方便相关应用的集成。     

云框架下的WMS服务实现研究

传统WMS服务基于集中或者离散分布B/S模式,单台服务器既要承担地图发布的任务,也要承担地图绘制的任务,当大量客户端并发访问服务器时,服务器响应速度明显降低甚至宕机。针对传统WMS服务模式的不足,将WMS服务构建于自主开发的云平台之上,详细阐述了实现的关键技术,包括WMS云服务框架的设计、空间数据的组织方法和任务调度策略。并且对B/S模式和云模式下的WMS服务性能进行了测试,证明了在同等服务器硬件环境下,云模式的WMS服务具有相对较高的处理效率,其研究具有十分重要的实践应用价值。     

一种Web地图服务搜索器的设计

借助于Web地图服务技术,大量的Web地图服务得以开发并发布到网络上.由于Web地图服务缺乏有机联系,用户很难有效地获取和利用这些服务.本文提出了一种Web地图服务搜索器框架,包括URL搜索器、Capabilities数据库和Capabilities响应文档解析器等.搜索器采用一个高效的Robot对互联网中所有的URL进行搜索,然后判断一个URL地址是否符合WMS规范,再向该地址发送WMS的GetCapabilites服务请求,通过对响应文档的分析来判定该服务是否是Web地图服务,从而提取WMS服务器信息并存储.测试验证,该Web地图服务搜索器可以实现Web地图服务的搜索、共享与服务.     

基于百度地图Web API技术的WEBGIS气象服务研究及系统设计

针对传统专业用户气象服务网站开发周期长,产品展示形式单一等问题,采用基于百度地图Web API技术,研究各类气象数据在WEBGIS地图上的叠加显示,设计陕西省气象服务中心专业用户气象信息服务网站系统。利用模块化开发方式,划分基础数据、天气预报、天气实况、气象服务、后台文件处理系统、后台管理平台等六个模块,通过后台功能模块参数的灵活配置,实现网站快速搭建、功能定制化、图形化及可视化、信息精准推送等功能。     

WMS服务的缓存策略研究

随着开放式GIS的发展,基于WMS服务来集成异构空间数据技术日渐广泛.为了提高WMS服务的效率,有效地减轻WebGIS服务器的负载,本文分析了传统的缓存策略和当前流行的地图瓦片缓存策略,剖析了开源的缓存工具TileCache的基本原理和切片索引机制,并基于 TileCache进行应用开发.实验表明经过缓存后的WMS服务速度明显示提高.     

地理Web服务集成技术及其原型实现

为有效利用网络上不断增多的地理Web服务功能,使它们协调工作,该文通过分析当前网络上流行的基于WSRP规范的门户技术和语义服务,探讨地理Web服务的集成原理,并实现了对基于OGC规范的网络地图服务WMS集成的一个原型,为使用分布式地理Web服务提供了统一的接口和界面操作。     

云平台上海洋服务流定制的可视化建模研究

利用已有的海洋信息处理模型及相关资源,开展基于云平台的海洋服务流架构设计,实现个性化的海洋服务流定制.通过可视化建模技术实现服务流定义,模型分析,服务流的交互式执行.用户只需要通过网络即可访问云平台中提供的各种模型服务.其中服务流页面作为定制服务流的唯一访问点,可视化地提供了云平台上的海洋数据模型资源和图形化的定制方法,将服务流描述提交给云平台,完成用户的个性化的服务定制执行.     

可扩展的电子地图符号体系的设计与实现

随着地理信息技术的快速发展和电子地图应用领域的不断拓展,电子地图可视化成为目前GIS和地图学的研究热点之一,而地图符号化处理则是其中的核心问题.应用面向对象及组件化的方法,给出了一种可扩展的地图符号体系的设计方案.基于这种体系结构,可以方便地扩展地图符号类型,实现多种地图符号化方法,从而使电子地图的内容表现及绘制效果达到对丰富性、美观性、艺术性的要求.     

高性能互操作的OGC WMS系统的研究与实现*

针对遥感数据量大、多时空分辨率等特点,提出了一种基于Tile影像金字塔存储结构的、符合OGC WMS规范的、高性能可扩展的网络地图服务实现方法,并实现了原型系统。该方法的主要思想是通过预处理技术将遥感图像切割成规则的Tile小块;然后将其存储在分布式存储系统中,地图服务器只返回用户请求地理区域的Tiles,这样减少了数据传输量。经过性能测试,与传统的方法相比,该方法提高了WMS系统的性能,缩短了系统的响应时间。     

Web服务图中基于知识地图的服务关系建模与应用

随着Web环境下服务数量的快速增长,如何高效快速地发现服务成为迫切需要解决的问题.基于Web服务图的服务发现方法,利用Web服务之间的语义关系来进行服务发现,仿真实验证明这种方法能极大的提高Web服务的发现效率.但是目前的研究还未涉及到Web服务组合流的网络传输、服务组合流的可视化表示以及多服务组合流的客户自主与交互选择.而这些是基于Web服务图的服务发现方法得以实现和应用的重要环节.本文以知识地图为基础,通过对服务关系进行建模来解决这些问题,从而进一步完善基于Web服务图的服务发现理论与方法.     

地图符号的XML Web Services共享方法

分析当前两种主要地图符号共享方法的优点与不足。针对地图符号设计方式的差异问题,总结地图符号构图规律,引入PS成像模型,设计面向共享的地图符号数据结构及其XML表达模式;针对地图符号使用环境和符号化接口的差异,提出基于Web Services的地图符号数据分布式共享框架。构建符号共享原型系统,验证了所提技术路线的可行性。     

用描述逻辑实现语义主题Web服务组合的方法

针对面向服务计算所具有的分散性、不确定性等因素的影响,以及服务发现、选择和组合存在技术和高效应用上的瓶颈,提出一种用描述逻辑实现主题服务组合的方法。该方法将主题图与Web服务用描述逻辑进行融合,并在融合过程借助本体实现主题图与Web服务间的描述,进而形成一种语义主题Web服务。最后用基于SHOIQ的Tableau决策算法实现语义Web主题服务组合。案例分析表明该方法可行且有效。     

Process-context aware matchmaking for web service composition

Web service composition can help software developer design more powerful and flexible applications according to requirements of enterprise. But during compositing, how to discover suitable web services is a critical problem in design and implementing application-oriented web service technologies. The traditional keyword-based matchmaking approach is difficult to help developer to find suitable service. Current researches find that to attaching semantics to each registered service can help improve the precision of matchmaking. The improvement can help developer find more suitable service for business process. This paper proposes a novel approach of semantics-based matchmaking, which is named process-context aware matchmaking. The process-context aware matchmaking discovers the suitable service during web service composite modeling. During matchmaking, the approach utilizes not only semantics of technical process but also that of business process of a registered service, thus further improving the precision of matchmaking. We integrate the process-context aware matchmaking with business-process-driven web service composition in an integrated development environment based on Eclipse. The performance evaluation shows that performance overhead of this novel approach is acceptable.     

Semantic web service composition testbed

A huge amount of web services are deployed on the Web, nowadays. These services can be used to fulfill online requests. Requests are getting more and more complicated over time. So, there exists a lot of frequent request that cannot be fulfilled using just one web service. For using web services, composing individual services to create the added-value composite web service to fulfill the user request is necessary in most cases. Web services can be composed manually but it is a too tedious and time consuming task. The ability of automatic web service composition to create a new composite web service is one of the key enabling features for the future for the semantic web. There are some successful methods for automatic web service composition, but the lack of standard, open, and lightweight test environment makes the comparison and evaluation of these composition methods impossible. In this paper we propose an architecture for a light weight and scalable testbed to execute, test and evaluate automatic web service composition algorithms. The architecture provides mandatory components for implementing and evaluation of automatic web service composition algorithms. Also, this architecture provides some extension mechanisms to extend its default functionalities. We have also given reference implementations for web service matchmaking and composition. Also, some scenarios for testing and evaluating the testbed are given. We have found that the performance of the composition method will dramatically decrease as the number of web services increases.     

Quality-of-service oriented web service composition algorithm and planning architecture

In the next few decades, it is expected that web services will proliferate, many web services will offer the same services, and the clients will demand more value added and informative services rather than those offered by single, isolated web services. As the result, the problem of synthesizing web services of high quality will be raised as a prominent issue. The clients will face the trouble of choosing or creating composition plans, among numerous possible plans, that satisfy their quality-of-service (QoS) requirements. Typical QoS properties associated with a web service are the execution cost and time, availability, successful execution rate, reputation, and usage frequency. In engineering perspective, generating the composition plan that fulfills a client’s QoS requirement is a time-consuming optimization problem. To resolve the problem in a timely manner, we propose a constraint satisfaction based web service composition algorithm that combines tabu search and simulated annealing meta-heuristics. As an implementation framework of the algorithm, we suggest a QoS-oriented web service composition planning architecture. The architecture maintains expert made composition schemas in a service category and assists the client as pure user to choose the one he/she wants to use. The main modules of the architecture are composition broker and execution plan optimizer. With the aid of the UDDI server, the composition broker discovers candidate outsourced web services for each atomic process of the selected schema and gathers QoS information on the web services. After that, the execution plan optimizer runs the web service composition algorithm in order to generate a QoS-oriented composition plan. The performance of the algorithm was tested in a simulated environment.     

RESTful风格地图瓦片服务的研究

综合当前主流的WebGIS产品和瓦片缓存技术,对地图瓦片服务的重要性和未来WebGIS产品应用的趋势进行了分析.详细阐述了OGC地图瓦片服务执行规范1.0.0版本的重点内容;并且介绍了RESTful风格服务的设计原则.充分利用现有的Web基础设施,从实现的角度给出了地图瓦片服务的体系架构,整体流程,按目录存储地图瓦片的具体结构,以及地图库访问引擎模块的功能接口的实现,完成基于RESTful风格的OGC地图瓦片服务的实现.     

Computing performance requirements for web service compositions

In order to produce service compositions, modern web applications now combine both in-house and third-party web services. Therefore, their performance depends on the performance of the services that they integrate. At early stages, it may be hard to quantify the performance demanded from the services to meet the requirements of the application, as some services may not be available or may not provide performance guarantees. The authors present several algorithms that compute the required performance for each service from a model of a service composition at an early stage of development. This is also helpful when testing service compositions and selecting candidate web services, enabling performance-driven recommendation systems for web services that could be integrated into service discovery. Domain experts can annotate the model to include partial knowledge on the expected performance of the services. We develop a throughput computation algorithm and two time limit computation algorithms operating on such a model: a baseline algorithm, based on linear programming, and an optimised graph-based algorithm. We conduct theoretical and empirical evaluations of their performance and capabilities on a large sample of models of several classes. Results show that the algorithms can provide an estimation of the performance required by each service, and that the throughput computation algorithm and the graph-based time limit computation algorithm show good performance even in models with many paths.     

Monitoring and evaluating the quality of Web Map Service resources for optimizing map composition over the internet to support decision making

Over the past 10 years, there have been great advances in the interoperability technologies in geographic information science. More than 10,000 map layers are available online today through Open Geospatial Consortium (OGC) specified interfaces, such as Web Map Service (WMS), Web Feature Service (WFS), and Web Coverage Service (WCS). These map layers are persistently serving the geospatial communities; however, our empirical study found that their potential value has not been fully exploited. Frequently, a targeted map cannot be composed because some published map servers are unavailable. This problem becomes more serious when a map is composed of several layers from different servers. These services are geographically distributed and maintained by various hosts; therefore, simply waiting for service improvement on the host side cannot solve this problem. In this paper, we proposed a new approach and developed a mechanism that allows clients to select the best map layers at run-time. The selection is based on the results of continuous monitoring and evaluation of the quality of WMSs. Based on Service Oriented Architecture (SOA), this approach includes quality monitoring and evaluation modules. Quality factors are taken into account during the process of registration, search, and bind. The OGC capability document is extended to include WMS quality information. Three prototype systems were developed in this study to demonstrate: (a) how WMS layers are monitored and evaluated, (b) how the subjective evaluation of WMS quality by a user is collected, and (c) how this can be a feasible method to fuse WMS resources suitable for decision making.     

一种基于杂草优化的全局Web服务选择算法

随着网络中的Web服务数量的暴增,基于QoS的服务选择成为保证组合服务质量和可靠性的关键环节。针对当前服务选择算法全局优化能力弱的问题,将服务选择建模为带约束的非线性最优化问题,并提出一种基于杂草优化的服务选择算法。首先随机产生一组服务选择可行解并将其编码为杂草个体,进而根据个体的QoS效用值确定个体的繁殖数,最后以高斯分布方式指导种群的扩散完成对解空间的快速搜索。理论分析与实验结果表明,该算法有效性和鲁棒性强,可获得相较于已有文献更优的全局解。