The new system, developed by the San Diego Sector’s Enforcement Technology Department (ETD), gives agents a host of previously unavailable data in an easy-to-use format.  The website features a mapping interface, which allows the US Border Patrol agents to interactively enter information about each day's events, and to query the database which builds maps of specific event types, locations and frequencies.

Use of High Resolution Imagery Data

From the beginning, use of high resolution imagery such as 1-meter aerial photography was made a high priority.  With 1000’s of miles of borders to monitor, imagery is critical to providing a “real world” context for agents using the system and helps them visualize terrain and landcover features.  Traditionally, efficient use of high resolution imagery in Internet-based mapping systems has been difficult due to the extremely large file sizes, correspondingly slow delivery speeds and heavy server loads to process imagery.  To overcome this problem, ETD decided to use a tandem solution of ESRI’s ArcIMS as the Intranet web-based interface for display and analysis of the geographic data coupled with the Image Web Server software from Earth Resource Mapping to provide high speed delivery of the imagery components.

Typically, ETD develops a website for each geographic area along the border, such as a county or other regional area. The process involves preparation of the imagery data, and development of the website to house the image and vector data that agents will use analysis and reporting.

Preparation of Imagery Data

The first task is to prepare the imagery data for use with Image Web Server.  This involves mosaicking and enhancing the images required to cover the area of interest, then exporting the mosaic image to the ECW (Enhanced Compressed Wavelet) image file format used by Image Web Server.  Using the ER Mapper software from Earth Resource Mapping, ETD first runs a wizard to automatically display several hundred separate images in a “virtual” mosaic on screen. 

Next, color balancing, contrast enhancements and other image processing operations are interactively applied and adjusted as needed to make the overall mosaic image more seamless and visually pleasing.  The mosaic is saved within ER Mapper as an ECW image file on disk for serving over the Internet.  For the San Diego County website, for example, 576 2-ft resolution color infrared TIFF orthophotos covering the county were mosaicked, converted to “natural color” (so vegetation looked green instead of red), and then compressed from 87GB to a single 4GB ECW file.  All this was accomplished without creating any intermediate image files. 

Website Development

The next task is to develop an ArcIMS website for display and analysis of the vector and point data  along with the imagery data.  Once the ArcIMS site is built, the free I-Wizard application is run to modify the website to use the Image Web Server.  The site is then tested in-house and externally by various US Border Patrol users around the country, and brought online when validation is completed.

Benefits of the Tandem Approach

The tandem of ArcIMS and Image Web Server provides a powerful Internet-based mapping application with very high speed display.  Imagery appears immediately when users zoom or pan through the maps, which reduces frustration and enhances the user’s experience.  In addition, Image Web Server’s design dramatically reduces the server side processing needed to serve imagery, so very high performance can be gained from a single multi-processor PC web server.  Finally, the imagery for each geographic area is archived as a single highly compressed ECW file rather than 100s of TIFF image files, which saves large amounts of disk space.

Architecture of implementing imagery into an ESRI environment with Image Web Server

By integrating ArcIMS® and Image Web Server they have been able to bring a comprehensive GIS component to their field agents and command and control staff in a fast and interactive manner.

Article by Eric Augenstein, Earthstar Geographics - entire article copyright (c) 2004