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Track: Information Access and the Internet
John Alexander
WPTC
3305 Hancock Drive
Austin, TX 78731
Telephone: 512-459-9027
Fax: 512-452-1655
E-mail: john@wptc.com
Valerie Warwick
Writing GIS Applications for the WWW
Defining Issue: Historically, GIS applications have been written for specific vendor architectures. Client/server designs and distributed object technologies offer an environment for developing open systems solutions for GIS. The goal is to allow a wide variety of client configurations to utilize GIS servers with significantly different underlying implementations. Methodology: The development described in this paper is for a GIS on the Internet system built with MapObjects, ArcView, and SDE as potential servers. Distributed objects are the key design element. For example, the client, using Java and/or JavaScript, understands the concept of a map display with multiple map layers. Individual layers may be visible, invisible, or drawn in a variety of orders. To redraw the map display, for a pan or zoom operation, the browser drawing services invoke methods in distributed objects on different servers. Each server, with a different implementation of the requested method, returns a transparent gif. The
servers are sensitive to the target coordinate system and, for a limited set of projections, make the appropriate coordinate transformations. The Java client then renders the final map display from the layers produced by the servers. This is a networked application using object technologies. The example is not fully CORBA compliant, but it certainly derives much of its motivation from the OMG's work on distributed objects. Three examples are discussed. 1) A core WWW GIS server design implemented for multiple servers with different architectures, object models, and method implementations 2) Defining interfaces for application-specific capabilities to allow their use by Web clients: ArcView/Address Matching and ArcView/Network Analyst 3) A simple application involving client data, address matching services from one server and map rendering from another server Software: The application was written using HTML, Java, JavaScript, Avenue, Visual Basic, and PERL. It relies heavily on the GD library for gif
rendering and MapObjects Internet Mapping Server.
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