Augmenting an Internet Map Server with an ArcInfo Product Generator

Author: Kent Lethcoe
Organization: USGS EROS Data Center

Mundt Federal Building
Sioux Falls, SD 57198
USA

Phone: 605 594 6502
Fax: 605 594 2592
lethcoe@edcmail.cr.usgs.gov

A Java-based Internet Map Server (IMS) makes map products available to customers over the Internet. In addition, some customers need downloaded data sets for analysis and generation of derived output products. A product generator is needed that processes IMS-defined customer requests for data and produces data sets, running as an application separate from the IMS.

The IMS allows a user to browse data layers, define a study area, and specify products that are needed. This information is stored in a database table that is read by a product generator daemon. The daemon selects orders placed in the database table by the IMS, establishes a workspace for each order, and initiates a product generator Arc session in each order's workspace. Then the triggering order database record is set to an in-process status. The daemon monitors system resources such as the available disk space and the number of available Arc licenses. This information, along with the order requests, is used to intelligently regulate the initiation of product generator sessions, balancing order demands with available processing resources.

Each product generator Arc session retrieves its order's list of requested products and study area footprint from supporting database tables. ARC Macro Language (AML) routines extract data and make products for each requested data layer. Completed products are copied to designated directories for transfer to media or for file transfer protocol (ftp) retrieval. Appropriate metadata are generated for the order. When ftp delivery is requested, e-mail is sent to the requestor instructing how the data can be retrieved. The requestor is responsible for retrieving the data within a time period specified in the e-mail notification. The product generator Arc session marks the order status in the order database table as complete and terminates. A subsequent run of the product generator daemon selects completed orders and deletes their workspaces.

Future implementations of the product generator Arc session will have more capabilities. These capabilities are expected to include projecting output products into a requested map projection or datum, generating derivative products such as a shaded relief view of elevation data, and resampling raster data to a different cell size.