网络地图可以快捷地提供海量空间数据,用户可通过其提供的API方便地将其嵌入到定制的网络应用中,同样,将其集成到功能丰富的GIS桌面系统中是必要的、有益的。但目前主流的网络地图如Google地图、Bing地图等,与主流GIS桌面系统所支持的OGC的WFS、WMS、WCS等空间数据服务发布规范不兼容,因而不能被GIS桌面系统直接使用。为了解决这一问题,本文提出了一种将二者集成的思路与方法,即利用网络地图的可下载性和GIS桌面系统的可扩展性,采用配置机制实现统一编程接口,将不同站点、不同类型的网络地图作为GIS桌面系统的自定义图层处理。在实验验证中,我们采用ArcGIS Desktop作为实验平台,以自定义扩展模块实现功能,以自定义工具条实现用户访问界面,将Google中文和英文地图、Bing地图、Esri在线地图等4类12种大型网络地图以自定义图层的形式实时、动态、全比例尺地加载到ArcGIS Desktop中,供显示、利用,实现了独立桌面系统和独立网站之间的连接。本文提出的方法具有一定的实用价值和较广泛的应用前景,对实现类似的集成和定义网络地图访问接口标准具有参考价值。
It is desirable that massive data of Web maps can be incorporated into desktop GIS systems for use and analysis.But Web maps can not be added into desktop GIS systems directly,because Web maps don't conform to the geospatial service standard published by OGC.Fortunately,the tile of Web maps can be downloaded and advanced desktop GIS has a built-in extension mechanism.Those together make it possible to integrate desktop GIS applications and Web Maps.This paper presents a generic method for the integration.Most Web maps consist of sets of tiles of multiple scales,covering the entire surface of the Earth at each zoom level.A key of the method is the acquisition of dynamic information of Web maps,such as the extent and zoom level of the right set of tiles and the URL of each tile,from the projection and resolution of Web maps and the extent of the active view in the desktop GIS system.In order to accelerate the process of downloading the tiles and to make it not interfere with other operations of desktop GIS system,the process of tiles downloading should be asynchronous and Multi-Threaded.After fetching the tiles,the tiles may be cached.By tagging spatial reference information to the tiles,the tile images can be turned into raster layers supported by most GIS platforms.The custom layers control the drawing properties and the actual drawing of the set of tiles.Furthermore,different Web maps can be accessed using a uniform interface through the introduced configuration mechanism for dealing with multiple data source.To test and verify the proposed method,we choose ArcGIS Desktop as the test platform.Custom extension and custom toolbar have been employed in the implementation of custom layers.With the developed extension and its associated toolbar,Web maps can be added into and displayed instantly and dynamically in ArcGIS Desktop.Four categories of Web maps are supported,which amount to twelve layers,including Google maps,Bing maps and Esri map services.The advantages and limitations of the method are discussed.The p