PRODUCT COMPARISON FOR GIS OVER THE WEB: ESRI’s ArcIMS vs Intergraph’s GeoMedia WebMap Political Economy 6383 Management & Implementation of GIS Dr. R. Briggs November 8, 2001 By: James Janning Michael Wallace Justin Johnson Web-based GIS 1 INTRODUCTION Web-based GIS is fast becoming the way to distribute geographic data to users without the need of GIS software or specialized training for the end user. With nothing more than a standard Internet browser, users from different organizations and departments can view and manipulate geographic data from multiple sources that was once only available to a select few (people who new how to use GIS data browsers and had access to one). This paper will examine both basic principles of web-based GIS, the software requirements of both the server and the end user, what types of data can be used, and the data format that the client will receive. It will then take a detailed look at two products being offered by the industry leaders in the GIS market. The first product, ArcIMS, is the latest incarnation from ESRI for serving data over the Internet or an intranet. The other product, GeoMedia WebMap is Intergraph’s first foray into the web-based GIS Market. BASICS OF WEB-BASED GIS A successful implementation of web GIS requires the incorporation of clients, middleware (application server connectors and web server software), web GIS software (ArcIMS or WebMap), data, and physical server(s). The web GIS software provides the tools necessary to manage GIS data so that it is accessible to clients through the Internet and intranet connections. It does not directly interact with the client. An application is necessary to act as a mediator between the user who is requesting information and ArcIMS or WebMap, which retrieves it. Middleware, the web GIS software, and data all reside on one or more physical servers. The client accesses the Internet or intranet using Web-based GIS 2 a web browser via http and TCP/IP technology. They can then contact the server and request data from ArcIMS or WebMap through the middleware tier. When a client requests information over the web, the middleware applications will process this request and pass it to the web GIS software. The web GIS software will query a spatial database for the appropriate spatial and/or attribute information and pass it back to the application. The application translates the information to a format that the client can read and passes it back over the intranet or Internet. The responsibilities of the Map Serving application include sending and receiving data between the client and application, organizing requests made by multiple clients, managing data transmission and maximizing the efficiency of the server tier. The application also determines what information is available to be distributed. The application sets what colors and line weights each feature will be. It also determines in what order the features will be drawn. In addition, the application will set the coordinate system and units that the data will be viewed in. Web pages can be custom written to suit the needs of the individual organizations using web-based GIS. Both ArcIMS and WebMap also come with application generators that can be used to create generic templates for a quick implementation. DATA OUTPUT ESRI’s and Intergraph’s web products can send data to clients over the web in one of two ways, raster or vector. Each of these formats has advantages and disadvantages and it must be decided at the time of coding which format will be served. Web-based GIS 3 When data is transmitted over the web in a vector format it has a “static” connection back to the source. A picture is taken of the features that the client wants to see and sent to them in a JPG, PNG, or GIF format. If the user does anything to change the data (such as turning on additional features or zooming in on a specific area of the map) the server must then request new data and another static picture taken and sent to the client. Raster based websites are more server intensive because each request made by the client requires the server to render a new image and temporarily store the image. The main advantage, however, is that the communication between the browser and the server is simplified and the middleware can execute these procedures rather quickly. When data is transmitted over the web in a vector format it has a “live” connection back to the source. Features can be turned on and off and display scales can be changed on the fly. Vector maps contain intelligent features linked to records in the database, as do Raster maps. Vector based websites are less server intensive than raster based websites, due to the use of vector data streaming. With vector data streaming, Internet bandwidth and traffic will determine data rendering efficiency. In order for a client to utilize a site designed to stream vector data, they must have a program locally installed that is designed to render the data being sent to them by the server. ESRI’S ARCIMS Introduction Since 1996, ESRI has honed a software product enabling GIS professionals the functionality of gathering, viewing, manipulating, and disseminating GIS data layers via a web browser. In May of 2000, ArcIMS (Internet Map Server) became the primary ESRI Web-based GIS 4 product for web-mapping solutions, replacing, combining, and extending the power of two earlier products - MapObjects IMS and the ArcView IMS extension. This extremely robust software product allows users to provide GIS solutions over an intranet, via the Internet, or through a network (if ESRI client software is used as a browser in the place of a standard web browser). Application There are four connectors available for use as middleware: ActiveX connector, Cold Fusion connector, Java servlet connector and WMS connector. The Java servlet connector is the default connector that will automatically be selected during installation unless one of the other three connectors is manually selected. The page developer might select one of the other three connectors, which would work in conjunction with already existing web development software. The ArcIMS software is comprised of four separate software tools. Together these tools manage spatial data, process requests from the middleware, return responses to the middleware and provide an interface for the administrator to develop web pages. The first three tools are ArcIMS Author, ArcIMS Administrator and ArcIMS Designer. Together they are used to create a web page that contains an interactive map made up of GIS data layers. Within these tools, decisions are made about what specific GIS data appear in each map, what symbology will be assigned to the data layers, the level of usability that will be offered to the end user as well as the layout of the web page. The fourth tool is ArcIMS Manager. This tool utilizes Internet Explorer to provide the developer access to the other three tools. Manager is only available if IMS Application Web-based GIS 5 Server is loaded on a Windows platform and allows for remote administration of ArcIMS. Data Input Arc IMS can utilize GIS data in ESRI, such as shape files and coverages, or from an ArcSDE layer. Also ArcIMS can render images including aerial photographs and satellite imagery. If a user wishes to incorporate GIS data in a non-ESRI format, the data must be converted first. Further, ArcGIS desktop products can utilize as a data source a data layer from an ArcIMS website. Data Output Raster: Distributed in JPG, PNG, or GIF format Requires no additional client-side software Vector: Distributed with vector data streaming using ArcXML Requires that the clients web browser can interpret ArcXML and handle java scripting Advantages Out-of-the-box usability Capability of administering server software from remote location Can act as a data source for other ESRI GIS software products ArcIMS is not limited to a Windows platform. Web-based GIS 6 Disadvantages Inability to use non-ESRI data sources without conversion Limited customizability without for-knowledge of Web-programming technologies Server Requirements Microsoft WindowsNT, Windows2000, UNIX, or AIX Appropriate web serving software, such as IIS or Apache for the operating system selected Servlet engine Client Requirements Microsoft Windows platforms, UNIX, or AIX Browsers that can handle java code, such as: IE 4, 5, 5.5, and Netscape 6 (for IMS 3.1) Plug-in to handle ArcXML (extendable markup language) Pricing $7,500 for 1st CPU $5,000 for each additional CPU INTERGRAPH’S GEOMEDIA WEBMAP Introduction Intergraph provides two powerful products used to disseminate geographic data over the Web, GeoMedia WebMap and the more robust GeoMedia WebEnterprise. GeoMedia WebMap allows the user to create web-based mapping applications that Web-based GIS 7 combine, analyze, and distribute GIS information from multiple sources over an intranet or Internet. With WebMap the user can select what data is viewed over the web and print maps. WebEnterprise combines all the functions of WebMap with the added feature of manipulating geographic data. Application An application generator is provided with both WebMap and WebEnterprise. The application generator creates templates used to distribute data over the web. Applications can also be custom written to meet the specific needs of an organization. These custom applications may be written in a number of programming languages such as Java and Visual Basic. Data Input WebMap and WebEnterprise are able to view any data regardless of data format or coordinate system. They use no proprietary data types or languages. WebMap and WebEnterprise have the ability to view multiple data types with multiple coordinate systems at the same time. Data in different formats are translated and reprojected at the same time and viewed all at once in a coordinate system defined by the application. Both products are also ideal for integrating aerial and satellite images. Data Output Raster: Distributed in JPG, PNG or GIF format Requires no additional client-side software Vector: Web-based GIS 8 Distributed in CGM (computer graphics metafile) format Requires ActiveCGM plug-in on the client-side. This program must be downloaded and installed by the user. The plug-in is limited to a Windows platform using IE or Netscape Advantages Open GIS solution that uses no proprietary languages or data formats Ability to customize applications for specific clients Disadvantages The CGM plug-in is a major component of WebMap (when viewing vector) but Intergraph (the maker of WebMap) does not own it The CGM plug-in is necessary to view vector data. The plug-in must be actively downloaded and installed by the client. If the client is not very computer savvy, this can cause problems CGM plug-in only works on Windows platform Limited customizability without for-knowledge of Web-programming technologies Server Requirements Microsoft WindowsNT, Windows2000, or WindowsXP Microsoft IIS for the appropriate operating system Client Requirements Windows98 or greater Microsoft Internet Explorer 4.0 or later Web-based GIS 9 Netscape 4.7 or later InterCAP ActiveX control for ActiveCGM (for MS Internet Explorer browser) InterCAP ActiveCGM plug-in (for Netscape browsers) Pricing $10,000 for two CPUs using GeoMedia WebMap $24,000 for two CPUs using GeoMedia WebEnterprise CONCLUDING REMARKS There are many software applications available for the distribution of GIS images over the Internet; among them are Intergraph’s GeoMedia WebMap and ESRI’s ArcIMS, which by far hold the most significant market share. Pricing of each package is similar on the surface; however, many hours of programming are required just for the basic operation of WebMap. Conversely, a great deal of man-hours can be saved with WebMap’s elimination of the need for data conversion. Each of the aforementioned issues needs to be addressed from a cost/benefit analysis standpoint prior to deciding which product to purchase. WebMap must be programmed prior to use, whereas ArcIMS, although it too can be programmed and customized, comes with templates for out-of-the-box usage, which can be extremely beneficial for an organization without the budget for a full-time programmer.
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