Picture this: using your Web browser to fly through a spacetime diagram of colliding black holes, to spin a molecule and view it from all sides, or to navigate the Web by walking from room to room.
Industry-wide adoption of VRML -- the Virtual Reality Modeling Language -- makes it possible to share 3D graphics over the World Wide Web. VRML is a specification language that lets the author of a VRML world define objects and specify parameters for how they should be rendered. VRML-capable browsers interpret the VRML document and draw the scene. Browsers are interactive, allowing the user to move around and visit different parts of the world or view from different vantage points. Browsers are available for PCs, Macintoshes, and all major UNIX platforms, making it possible to use the Web to provide interactive 3D graphics in a platform-independent manner.
VRML 2.0 extends the functionality of the early standard to incorporate animated behaviors into a VRML world. A variety of vendor groups advanced proposals for achieving animated VRML. Moving Worlds, a specification proposed by a group of about a dozen organizations and spearheaded by Silicon Graphics Inc. (SGI), has emerged as dominant and is now endorsed by more than 50 organizations. VRML 2.0 browsers will become available this summer, dramatically extending the possibilities for sharing and exploring 3D worlds.
In Moving Worlds, geometry objects include input fields. The VRML author connects these input ports to entities that supply new values. Imagine being able to download a virtual flow field— when you click Go, tracer particles move along their appropriate paths to reveal the characteristics of the flow. Moving Worlds makes this possible by attaching the particles' positions to Interpolator objects—animators that modify object positions by interpolating through a set of control points.
Moving Worlds also supports event-driven animation using Sensor objects. For example, the hands of a clock could be driven by a TimeSensor. At regular intervals, the TimeSensor generates events that are then forwarded to the clock's geometry.
More complicated behaviors can be accomplished by using Scripts. Scripts are C programs or Java applets using the Java package vrml. Writing scripts in Java provides complete platform-independence—the applet can simply be downloaded along with the VRML file.
In addition to behaviors, Moving Worlds extends VRML to include sound. A VRML author can specify the URL of an audio clip to be played. Sounds have locations, and the VRML author can control how the sound should change as a user moves closer or farther away.
In its basic capabilities, VRML mimics the functionality found in contemporary graphics systems. In fact, the VRML language is based on the file format used in OpenInventor, an object-oriented software system for graphics programming developed by SGI and licensed by many major vendors. SGI fully endorses the development of VRML as an open standard within the Web community.
VRML is distinguished from non-Web graphics systems by the addition of the WWWAnchor object. Any piece of VRML geometry can serve as a hyperlink, by bundling the geometry and a URL into a WWWAnchor. In the browser, when a user's mouse moves over the geometry, it highlights in some fashion, perhaps by changing color. Clicking on the geometry activates the link and loads the associated Web document. The link might connect to a text file or audio document explaining some aspect of the VRML world or to a new VRML world. For example, in a world composed of a central foyer and multiple rooms, clicking on a door could usher the user into the new room by loading the appropriate VRML file.
One of the most widely used external browsers for VRML 1.0 is WebSpace, pictured in Figure 1. CosmoPlayer is a VRML 2.0 browser available from SGI for UNIX and Windows platforms. WebSpace is a shared-development project between SGI and Template Graphics Software Inc. (TGS), a leading supplier of graphics software for UNIX machines and for PCs. Browsers for SGI, Sun, and IBM AIX, as well as Windows 95 and Windows NT are currently downloadable at the TGS Web site. Other VRML browsers, both commercial and public domain, are available. An up-to-date source of information about browsers (and all things VRML) is the comprehensive VRML repository maintained by the San Diego Supercomputer Center.
Figure 1 shows a VRML file from the Digital Image Library that depicts two related datasets, the work of A. Dayal and J. H. Bieging from the University of Arizona. The image shows the star IRC+10216 -- a red giant nearing the end of its life as a star. As part of this life stage, it is expelling its outer layers in a massive wind. As the material in the wind cools, molecules such as CN (cyanide), HCN (hydrogen cyanide), and HCO+ (which doesn't exist on Earth) can form. Astronomers observe the spectral line emission from these molecules to study the chemical processes at work, as well as how the mass loss affects the evolution of the star. This particular image shows that CN is found in the shell surrounding the central star, while the HCN is found concentrated toward the center of the envelope.
The VRML file shown in Figure 1 was generated with a beta version of NCSA DataView. DataView is a tool for desktop visualization and VRML-generation. DataView reads HDF files [see access, Spring 1996] and represents the data as slices, contour plots, surfaces, and isosurfaces. Built using SGI's OpenInventor, DataView can capture the current state of a work session as a VRML file, which can then be downloaded to any platform's VRML browser. A companion application, DataCAVE, has the same visualization capabilities as DataView but operates in NCSA's virtual environments and provides physically immersive user control. Like DataView, DataCAVE can record the current state of the CAVE visualization as a VRML file. This snapshot of the CAVE session is useful for later display on the desktop or for sharing with colleagues over the Web. Developed within the Applications and Virtual Environments Graphics divisions, DataView and DataCAVE are scheduled for release this fall.
A variety of other strategies for producing VRML worlds of scientific content are being pursued. One easy approach is using the freely available conversion programs that translate the Wavefront geometry format or AutoDesk files to VRML. NCSA's numerical relativity and cosmology teams produce their VRML scenes using custom-built shell scripts to translate to VRML the output of popular visualization programs, such as IRIS Explorer and IDL (Interactive Data Language). For example, Figure 2 shows the spacetime diagram of the embedding of the event horizon of two colliding black holes. Figure 3 presents the Teukolsky wave evolution, with negative amplitudes shown as red surfaces and positive amplitudes shown as blue.
VRML has numerous applications in business and commerce. Sears and NCSA are collaborating to build a Virtual Sears Store using VRML (see Figure 4). The VRML file can be viewed in the CAVE or in the desktop WebSpace browser. In either case, store personnel can wander the store's aisles evaluating product displays and traffic patterns and experimenting with alternate arrangements.
In addition to science and business, VRML has obvious applications in education. Because it is platform-independent and sharable over the Web, VRML lowers the traditional barriers to 3D animated graphics that have existed for decades. NCSA researchers and educators welcome and intend to pursue aggressively this new opportunity to share animated 3D worlds with the Web community.
More information about VRML is available at the following Web
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NCSA: The National Center for Supercomputing
access / Summer 1996
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