World Wide Web Access to ArcInfo Databases

Brian Biggs
Kimberly Patraw
R. Douglas Ramsey
Allan Falconer
Department of Geography and Earth Resources
Utah State University
Logan, UT 84322-5240
Telephone: (801)797-3783
Fax: (801)797-4048
E-mail: ned@nr.usu.edu

Abstract: With the advent of the global information society there is a need to efficiently transfer user-specified spatial information over the Internet. To satisfy this need, a prototype data server for ArcInfo formatted geographic databases was compiled and is accessible through the World Wide Web via its Universal Resource Locator: http://www.nr.usu.edu/ned. The server is a hypertext markup language FORMS interface which sends user-specified criteria to a PERL script which parses the request and posts it to a file. The file is then read by another PERL program during off-peak hours, and sends each request to an ArcInfo Arc Macro Language (AML) program which creates a map and posts it to a file to be retrieved on the next day by the user.

Background

The Army National Guard Bureau (NGB) has initiated an Integrated Training Area Management (ITAM) program in order to both facilitate environmental monitoring, and to assist trainers in maintaining quaility training land for continued success in troop development. NGB is working in collaboration with the Department of Geography and Earth Resources at Utah State University to develop a multi-scale national environmental database as a significant part of the ITAM program. The Department of Geography and Earth Resources is responsible for the population of the national, state, and installation level database, as well as integrating the programs that manage and display the data. Since the NGB installations are located throughout the country, access to the database has become a concern. This paper describes a system that enables selected groups to access the database through the World Wide Web (WWW). In this manner, NGB personnel can make requests to the database and download maps of the data they require.

Database

The associated database consists of national, state, and installation data. National level data consists of ARCUSA(TM) coverages which include 1:2 Million scale roads, rivers, railroads, state boundaries, and socioeconomic data, as well as EROS Data Center produced land characteristics data including AVHRR imagery, maximum NDVI, 30 year average climatic data, and land cover data. State level data consists of the above data sets and includes Gap Analysis data where available, as well as 3 arc-second DEM data from the Defense Mapping Agency. Installation level data is inconsistent depending upon the site, but generally includes: installation, training area, and range boundaries; roads, rivers, soils and vegetation.

Overall WWW/ARC Interface Design

The interface consists consists of three components. The first component is the WWW FORMS interface, a hypertext markup language (HTML) document that enables the user to identify variables such as scale, data layers, and output format. The output of this page is passed to a PERL script which parses the output and appends it to a file. At a predetermined time each evening, a batch process is started that initiates the second component of the interface. The batch begins a second PERL script which reads the request file and parses it into individual requests. The requests are processed one at a time and sent to the third component: an ArcInfo AML. The AML processes each request sent by the PERL program by creating a map for each in the format specified, and posts each map to a Hypertext Transfer Protocol (HTTP) directory with the specified filename to be retrieved on the next day by the user.

WWW Interface

The WWW interface is a FORMS based interface with selection buttons that give options for scale, data layers and colors, and output type, (See Figure 1). Currently, the user can select from a base layer menu, arc overlays, and polygon overlays, type in a filename, and select an output format type. Different FORMS menus are used depending upon the request items. For example, there can only be one base layer, so the SELECT pull-down menu option is used. There may be multiple overlays, so the CHECKBOX option is used allowing several overlays to be used. Where only one item in a list may be specified, as with the output format, RADIO buttons are employed. Finally, the default INPUT text entry box is used when a text response is required from the user as with the filename. The POST action is used with the submission of the request. The interface can be easily updated and modified to add functionality and to change as the database evolves. The request submission calls a PERL script in the HTTP bin directory which processes the request. The PERL script checks for duplicate filenames, changes the name if needed, appends the request string to a file, and returns information on how to retrieve the output map with the final filename.

Batch Process

The batch is stated by the UNIX 'AT' command which runs indefinitely. The batch is started at a specific time nightly. This method is chosen as a cost reduction so that an arc license is not used with each request and as a reduction in CPU usage during peak hours. The batch calls a PERL script that first reads the request file. If the file is empty (i.e., no requests were made that day), the script ends. If the file has requests, the script reads each request string and stores it as a variable. The script then initiates ArcInfo and passes the request string to be processed by an AML. After the AML completes its process, the script sends the next request string, until all requests have been processed, and then empties the request file to be filled the next day.

Arc Macro Language Program

The AML accepts the arguments passed by the PERL script, and sets up the mapping environment using DISPLAY 1040 in order to create maps without a live display. Options are used on the DISPLAY 1040 to provide different types of output. Any output types not supported by DISPLAY are created later by translation. The AML then calls a different program, depending on the type of base coverage desired, an image or avhrr data. In these programs, keys and titles are created, and the scalar level (national, state or base) is decided. Returning to the main program, each of the overlays are processed and an output map is produced. The output map is saved with a filename chosen by the user and can be retrieved by the user the next day via Mosaic.

Conclusion

The World Wide Web is an excellent system for the sharing of data with groups in diverse locations. The creation and delivery of maps on an individual basis requires a large amount of personnel time. This system takes advantage of the World Wide Web's data sharing capabilities and reduces personnel time by handling requests for maps automatically. It also balances system load by processing requests at night, especially by using an ARC license after peak demand times.