Distributing 3D information over the internet using VRML

Distributing 3D information over the internet using VRML

D. Brent Henderson
Smallworld Systems, Inc.
5600 Greenwood Plaza Blvd, Suite 300
Englewood, CO 80111, USA

Background of VRML
The Virtual Reality Modeling Language (VRML) is a three-dimensional (3D) interchange format. It is simply a file format specification to allow 3D information to be communicated over the Internet and viewed using common Web browsers with VRML controls. The VRML file format provides basic geometric modeling features. It also provides semantics for specifying advanced computer graphics effects such as hierarchical transformations, light sources, viewpoints, geometry, animation, fog, material properties, and texture mapping.

VRML first came into existence in 1994 with the development of the initial specification, VRML 1.0, which was released in 1995. The following year the VRML 2.0 specification was produced and was submitted to the International Standards Organization (1S0) as a draft (Bell, 1996). In December, 1997, the 1S0 approved the VRML specification and released it as ISO/IEC 14772- 1:1997, commonly called VRML 97. VRML 97 was based on the VRML 2.0 specification and is 98°/0 compatible with VRML 2.0. The current VRML specification may be found at the VRML Repository web site whose address is http: //www.vrml.org/Specifications/VRML97.

The development of the VRML specification has been the result of a collaboration of many individuals and companies. In 1996, a group of companies formed the VRML Consortium to develop and promote the specification. Charter members of the Consortium include 3Dlabs, Inc., Apple Computer, blaxxun Interactive, Cosmo Software, IBM Corp,, INTEL Corp., Intervista Software, Inc., Micrsoft Corp., Mitsubishi Electric Corp., Oracle Corp., PLATINUM Tech., Samsung Electronics Co., Sony Corp., and Superscape Inc. Today there are over 50 organizations in the non-profit Consortium. The Consortium is lead by a Board of Directors. The Consortium also elects a VRML Review Board (VRB) with eight members who oversee the Working Groups. The VRB members are volunteers who are recognized technical experts in 3D Web technologies. The Working Groups help guide the future of VRML by providing proposals to the VRB recommending practices and modifications to the standard.

Recently the VRML Consortium announced a proposed expansion of its charter to include all 3D Web technologies. One thrust of this expansion will be to integrate VRML with other 3D technologies and features such as Java3D. Java3D provides an application programming interface (API) for drawing 3D graphics. One example of how Java3D and VRML can be integrated is a recently released Java3D-based VRML 97 viewer applet from Sun Microsystems.

Structure of VRML files
VRML files maybe created from scratch using a simple text editor or through authoring tools and data translators. VRML files consist of four components: a header, prototypes, shapes (including nodes, interpolators, sensors, and scripts), and routes. Of these four main components only the header is required. The header specifies that the file is a VRML type file, the VRML version, and type of character set used. Prototypes allow the addition of new node types that specify the shape, appearance, or behavior of a structure that may be reused elsewhere in the file. Shapes are provided to buildup scenes from standard geometries and controls. Finally, routes are mechanisms for sending messages between nodes to enable dynamic 3D scenes and animations (Ames, 1997).

Typically VRML filenames use "wrl" for their extension. Building a 3D scene is done by speci~ing shapes and nodes. The VRML standard provides over 50 different nodes types for speci~ing geometric shapes, animations, and effects. Standard shapes include box, sphere, cylinder, text, and cone. Control of the position and orientation of shapes is provided through transform commands. A simple VRML file is shown below. This file defines a box object which is rotated 0.785 radians about the X-axis.


#VRIVILIV2 .0 utf8
Transform {
rotation 1.0 0.0 0.0 0.785
children [
        Shape {
               appearance Appearance {
                        material Material { }
                 }
                 geometry Box { }
          }
    }
}

A screen shot of the above VRML file is shown in Figure 1. The VRML file is displayed using Internet Explorer using a Microsoft VRML viewer.

Figure 1. Screen shot of a simple VRML file using Internet Explorer

For specifying surfaces, the ElevationGrid maybe used. The ElevationGrid may be used to display terrain generated from digital terrain models (DEMs). An example of an ElevationGrid is shown in Figure 2.

Figure 2. An example of a VRML ElevationGrid node displayed in a VRML viewer.

For additional information on VRML developments, specifications, viewers, and working groups see the web site http: //www.vrml.org. Another popular site for finding information on the VRML technology and whereto find VRML files on the Internet is the VRML Repository web site http:lhnvw.sdsc. edu/vrml.

Applications of VRML
VRML maybe used for educational, entertainment, and scientific purposes. Some examples of how VRML files are being used today include simulators, games, 3D visualizations, design, and 3D user interfaces. Examples of how VRML maybe used by utilities include line-of-site analyses, visualizations of 3D structures, and sewer pipe design using digital terrain models.

One of the official VRML Working Groups is examining ways to use VRML for displaying georeferenced data. This Working Group, called the GeoVRML Working Group, was formed to determine if modifications to the VRML specification will be necessary. The GeoVRML Working Group is currently focusing on several key areas such as coordinate systems, time referencing, terrain representation, levels of detail, resolution and accuracy, and data interchange. Additional information on the GeoVRML Working Group maybe found at the VRML Consortium web site (http://www.vrml.org).

Conclusion
VRML provides a means for communicating 3D scenes and information over the Internet. VRML scenes can be created using a simple text editor or authoring or data translation tools. These scenes, which are called worlds, may be viewed in common Web browsers with compatible VRML viewers. Although the VRML standard is fairly new, many examples of how it can be used have been developed for educational, entertainment, user interface, and visualization purposes. One area of active research is how to apply VRML for representing georeferenced data in accurate and practical ways. Several challenges are being examined including how to specifi coordinate systems, resolution and accuracy of coordinates, and data interchange methods. As these issues are addressed and worked into the VRML standard, VRML could become a very popular and effective means for sharing 3D information over the Internet.

References

Abernathy, M. and Shaw, S., 1998, Integrating Geographic Information in VRML Models, VRML'98 Conference, Monteray, California.
Ames, A. L., Nadeau, D. R., and Moreland, J.L., 1997, VRML 2.0 Sourcebook, Second Edition, John Wiley & Sons, Inc.
Bell, G. and Carey, R., 1997, The Annotated VRML 2.0 Reference Manual, Addison Wesley Developers Press.