By Brian Davis, Software Development Engineer, SAIC and USGS Earth Resources Observation Systems Data Center

If a picture is worth a thousand words, then a digital picture must be worth a thousand and twenty-four words (or one kilobyte). If that is true, then how much would a 3D digital picture be worth—2,048 words? The value of a 3D digital picture becomes apparent when data is transformed into interactive illustrations. Until recently, the idea of 3D visualization aiding scientists was one that brought the limitations of expensive equipment and software.

ArcGIS 3D Analyst displaying NASA's ASTER satellite imagery of the San Bernardino wildfire of 2003 in stereo.

In February 2001, individuals from the University of Illinois, Chicago, Electronic Visualization Laboratory (EVL); the University of Michigan's Department of Earth Sciences; the University of Minnesota's Department of Geology and Geophysics; and the United States Geological Survey's Earth Resources Observation System (EROS) Data Center (EDC) met to discuss the feasibility of 3D display systems. The group, which later became known as the GeoWall Consortium, outlined a strategy to overcome financial and proprietary hardware and software restrictions that often accompany 3D display systems. Staff at EVL had been researching virtual reality and immersive display environments for a decade. They were looking for a way to configure low-cost, commodity components into stereo 3D display systems. Eventually, graphics cards were available that were compatible with motherboards of commodity PCs and could produce dual monitor output. EVL staff installed the Linux operating system on just such a computer and ported their CAVE Automatic Virtual Environment (CAVE) projection-based virtual environments library of software to this platform, making the total sum of components very inexpensive—less than $10,000.

The resulting product was named GeoWall, for Geology Wall. The system takes the output from a dual video graphics card and routes it to a pair of projectors. The light from the projectors is polarized separately to produce two independent views. Special projection screen material is required to retain this light wave polarization. Readily available polarized glasses, such as those used at theme parks, are used to filter the light for each eye. The glasses allow each eye to see only one of two projected images. OpenGL software capable of creating two separate views for the two ports of the graphics card cause the user's eyes to deceive the brain into believing it is seeing two separate views from two distinct angles.

The public enjoying the GeoWall at the Chicago Museum of Science and Industry.

Geology departments from the University of Michigan and the University of Minnesota were represented at the February 2001 meeting, and efforts at those institutions and at EVL soon resulted in open source software not only for Linux but also for the Windows and Mac OS-X operating systems. Shortly thereafter, the University of Michigan offered Web server resources to host software, data, and information in the same spirit of openness, and the official GeoWall Consortium was born. The group's Web site (GeoWall.org) has evolved over time and contains all the information necessary to implement a GeoWall as well as several stereo viewing applications and example data sets. Some GeoWall applications now have the capability to add the fourth dimension of time for 3D animations.

While academic consortium members were redesigning geology curriculum to incorporate GeoWall visualizations, staff at EDC were working with Esri and Esri Business Partner Leica Geosystems to determine how to use a GeoWall to assist remote sensing and GIS applications for earth scientists. Esri software is robust enough to be compatible with bleeding edge technology developments arising from academic research efforts such as those of the GeoWall Consortium. EDC scientists require interactive access to data layers from sources such as The National Map. EDC also hosts the National Satellite Land Remote Sensing Data Archive, the National Elevation Data Set, the National Land Cover Dataset, and many other data sources. To analyze this data interactively in 3D, GIS applications would need to run on a GeoWall. Working with Esri developers, EDC integrated stereo viewing into their existing software that enabled single perspective views.

With ArcGIS 9 and Leica Geosystems' Stereo Analyst, ArcGIS 3D Analyst functioned on GeoWall with minimal effort. Settings for a graphics card must be configured to enable dual horizontal display, and users must select the stereo view setting. Anything normally done in ArcGIS 3D Analyst can now be viewed in stereo. This capability helps users new to GeoWall technology overcome the major stumbling block of data translations. All earth science GIS users have data they know and care about, but it is often not in a format required by viewing software provided by GeoWall Consortium members. Significant time and effort can be spent converting and transferring data between computers, operating systems, and software packages. These conversion steps can prohibit interactive data access within the viewing application. ArcGIS 3D Analyst helps solve these problems by enabling 3D interaction with data that is already imported into ArcGIS.

With news of a successful ArcGIS 3D Analyst implementation on a GeoWall, EDC staff were invited by the U.S. Department of the Interior to represent it at a federal interagency GIS Day event held at Environmental Protection Agency headquarters in Washington, D.C., in November 2003. ArcGIS 3D Analyst was demonstrated on a GeoWall to people from all federal agencies, congressional staffers, and elementary school students. Since its launch, the popularity of GeoWall has continued to soar.

GeoWall Consortium members hear success stories almost every day, emphasizing the value of the 3D system. In less than three years since the initial inception of the GeoWall concept, more than 300 systems have sprung up around the world so quickly that they are difficult to keep track of accurately. However, in the spirit of openness advocated by the consortium, GIS users are encouraged to take the technology and use it in new and different ways, so keeping track of GeoWall's use is not pertinent. The 3D display technology is now affordable, so uses that were never practical or possible before are now. For example, the Archaeology Department at the University of South Dakota in Vermillion used a GeoWall to view and analyze data from soundings of archaeological sites before beginning to dig, greatly reducing the chance of the accidental destruction of priceless artifacts.

For more information, visit the GeoWall Web site at GeoWall.org.