Geo-VRML Visualization: A Tool for Spatial Data Mining

(*now at Nortel (Northern Telecom) Corporation)

Introduction:

At the United States Environmental Protection Agency (US EPA), efforts are underway to examine the use of the Virtual Reality Modeling Language (VRML) for the interactive exploration of geographically spatial data sets. The EPA's National GIS Program Office is the focal point of EPA's efforts to implement a consistent Agency-wide spatial data management infrastructure. One result of these efforts is the EPA Spatial Data Library System (ESDLS) which is currently accessible via the Web at (http://www.epa.gov/ngispr/). ESDLS utilizes the Environmental Systems Research Institute's (ESRI) ARC/INFO data management software (entitled Librarian) and complies with Spatial Data Transfer Standards. The ESDLS is EPA's node on the Federal Geographic Data Committee (FGDC) 's National Geospatial Data Clearinghouse (see: (http://nsdi.epa.gov/nsdi)).

Designing Java User Interfaces for Geo-VRML Visualization & Animation:

During mid - 1997, we began to develop user interfaces that would allow for selection of spatial data and automatic conversion into VRML 2.0/97 file formats for 3D viewing and interaction on the Web. Prototype Java user interfaces were designed to allow for: (a) selecting digital elevation model (DEM) data sets and establishing color maps and (b) Creating customized fly-bys of DEM data sets.

Initially, we built a pilot web server system for spatial data handling. Using the United States' National Geospatial Data Clearinghouse and some European Web sites, we obtained public domain DEM data for regions in the United States and Europe. We then created Javascripts that converted these DEM data sets into ARC/INFO format. Java code was also developed to support transparent file conversion from the ARC/INFO format to the final VRML 2.0/97 formats for 3D viewing and interaction on the Web. These research efforts were recently shown to be compatible with the existing EPA Spatial Data Library System (ESDLS).

Figure # 1: User Interface to a prototype Terrain Modeling Web Page. The user can obtain Digital Elevation Models (DEMs) for prescribed geographic regions with this system. Using Java and Javascript, VRML files of the specified DEM are created. With a VRML Web browser, the user can then interactively explore the specified terrain model. See: (http://www.epa.gov/gisvis/).

Components of the Parameters Selection Page:

To build any Terrain VRML Model, like the example shown in Figure #1, the user first begins with the parameters selection page. There are eight components for the user to establish. The first component allows the user to select the desired Digital Elevation Model (DEM) data set. The second parameter provides for color map settings. The third button allows the user to select between four VRML parameters: a) a VRML 1.0 file; b) a VRML 2.0 file; c) a VRML 2.0 file where the Z axis can change when the user clicks on the 3-D VRML model; and c) a pre-computed flyby of the VRML 2.0 model. The fourth option allows for the selection of the Z Axis (height field) scaling factors while the fifth parameter allows for viewer altitude selections. The background color can be selected with the sixth option. Parameters 1 - 6 are executed by pushing the "Execute Form" button under the seventh option. Finally, we have a "Reset" button as option eight.

Figure # 2: Parameters Selection Web Page. The specific options selected in this example yielded the image shown in Figure #1.

Building the Selected Terrain VRML Model:

After the user selects the "Excute Form" button, a set of Javascripts are automatically activitated. The first Javascript triggers a Java applet to search the Arc/Info spatial data base to find the desired DEM. Once the DEM is found, a second Javascript establishes the color map selections. Next, a Java applet builds the desired VRML file and automatically loads the VRML file into the user's VRML browser plug-in. The VRML browser plug-in must already be pre-established by the HTML Web Browser perferences. Finally, the last Javascript automatically transfers the user from the Parameters Selection Web Page into the VRML browser with the Terrain Model already loaded. The user is then able to explore the 3-D DEM world with the VRML browser.

The Interaction Model for VRML browsers:

The interaction model of 3-D VRML browsers is a client-server approach, similar to most other Web browsers. 3-D browsers are usually embedded into 2-D browsers (e.g. Netscape or Microsoft Internet Explorer) or launched as helper applications when connecting to a 3-D site. A VRML source file is down loaded from the Internet server to the Web client requesting to view the 3-D VRML "world". The user interacts with this 3-D world on their own (client) workstation or personal computer. This client-server approach has limitations when it comes to multiple user interactions with a single VRML world.

In order for VRML to scale to many simultaneous users, peer to peer interactions are necessary in addition to the existing client-server query response mechanisms. Efforts are underway in the VRML community to define a conceptual framework to support collaborative information discovery and visual exploration.

One approach to collaborative VRML involves the development and construction of a networking protocol called the Virtual Reality Transfer Protocol (vrtp). Vrtp would support VRML just as the hypertext transfer protocol (http) supports HTML. This initiative is based on the premise that the underlying network support provided by the existing hypertext transfer protocol (http) is insufficient for large scaled virtual environments (LSVEs). The vrtp would be optimized for performance on individual desktop computers and across the Internet. More information on vrtp is available on the Web at: (http://www.stl.nps.navy.mil/~brutzman/vrtp/).

Collaborative VRML will allow for the interactive real-time sharing of Geo-VRML files generated from a spatial data base. This will assist with geographic exploration and discovery via the Internet.

Future Directions:

We are currently expanding our horizons to explore the 3-D visual display and animation of data mined from ESRI's recently released Spatial Database Engine (SDE) product. For more information on SDE see: (http://www.esri.com/base/products/sde/sde.html). We anticipate using SDE in conjunction with the Advanced Visual Systems (AVS) Inc.'s to be released interface to SDE and AVS Express, see: (http://www.avs.com). Work will continue on our VRML 97 efforts for ESRI ARC/INFO and SDE data sets. Discussions are underway with the EPA National GIS Program Office to provide for the integration of their EPA Spatial Data Library System (ESDLS) with our geographic visualization techniques. We hope to provide general users with utilities that allow for creating VRML worlds from interactive queries of ESDLS data. Our Java based Web interfaces to support this integration and to provide for the technology transfer of these new geographic visualization techniques are currently under Intranet testing within EPA. We hope to release these tools on the EPA Public Internet Server in late 1998.

References:

1) US EPA GIS-VIS Integration Web Site: (http://www.epa.gov/gisvis)