Artwork by Kevin Hughes, kevinh@eit.com, Enterprise Integration Technologies.
Artwork by Kevin Hughes, kevinh@eit.com,
Enterprise Integration Technologies.
Marco A. Calamari
We first need to thanks the people that turn the VRML from a vision to reality for the rest of us; the gurus of VRML Brian Behlendorf, Gavin Bell, Tony Parisi, Mark Pesce, and also the keepers of the VRML Repository (an invaluable source of information) Charles Eubanks, John Moreland, and Dave Nadeau. A special thanks to Mark Owens of InterVista Software, to the assistance that is providing to everyone. My hat goes off to all of them. We, and a lot of people around the world, that maybe never heard about VRML, we all have a big debt to all of them an to a lot of other people that spent their time hard working about VRML specification and software.
VRML is a language to describe 3D objects and their behavior, that sometime is said to be for the three-dimensional space what the HTML is for a two-dimensional page; in fact, this is true, but only from a general point of view. From a technical perspective, the differences are big.
The HTML language is an ASCII, tag-based language derived from SGML; SGML is a language created to allow quite general text based information, as books or databases, to be transferred from an archival system to another.
The VRML language is also ASCII, but is not tag based, but slightly object oriented, with a syntax similar to C or C++ language; there is no inheritance, but complex object can be built from group of simpler ones. The basis for VRML were not built from scratch, but using Silicon Graphics Open Inventor, a format for an SGI product that (once more an intelligent action!) was put in the public domain.
(Excerpts from VRML 1.0 Specification)
The Virtual Reality Modeling Language (VRML) is a language for describing multi-participant interactive simulations -- virtual worlds networked via the global Internet and hyperlinked with the World Wide Web. All aspects of virtual world display, interaction and internetworking can be specified using VRML. It is the intention of its designers that VRML become the standard language for interactive simulation within the World Wide Web.
The first version of VRML allows for the creation of virtual worlds with limited interactive behavior. These worlds can contain objects which have hyperlinks to other worlds, HTML documents or other valid MIME types. When the user selects an object with a hyperlink, the appropriate MIME viewer is launched. When the user selects a link to a VRML document from within a correctly configured WWW browser, a VRML viewer is launched. Thus VRML viewers are the perfect companion applications to standard WWW browsers for navigating and visualizing the Web. Future versions of VRML will allow for richer behaviors, including animations, motion physics and real-time multi-user interaction.
The history of the development of the Internet has had three distinct phases; first, the development of the TCP/IP infrastructure which allowed documents and data to be stored in a proximally independent way; that is, Internet provided a layer of abstraction between data sets and the hosts which manipulated them. While this abstraction was useful, it was also confusing; without any clear sense of "what went where", access to Internet was restricted to the class of sysops/net surfers who could maintain internal cognitive maps of the data space.
Next, Tim Berners-Lee's work at CERN, where he developed the hypermedia system known as World Wide Web, added another layer of abstraction to the existing structure. This abstraction provided an "addressing" scheme, a unique identifier (the Universal Resource Locator), which could tell anyone "where to go and how to get there" for any piece of data within the Web. While useful, it lacked dimensionality; there's no there there within the web, and the only type of navigation permissible (other than surfing) is by direct reference. In other words, I can only tell you how to get to the VRML Forum home page by saying, "http://www.wired.com/", which is not human-centered data. In fact, I need to make an effort to remember it at all. So, while the World Wide Web provides a retrieval mechanism to complement the existing storage mechanism, it leaves a lot to be desired, particularly for human beings.
Finally, we move to "perceptualized" Internetworks, where the data has been sensualized, that is, rendered sensually. If something is represented sensually, it is possible to make sense of it. VRML is an attempt (how successful, only time and effort will tell) to place humans at the center of the Internet, ordering its universe to our whims. In order to do that, the most important single element is a standard that defines the particularities of perception. Virtual Reality Modeling Language is that standard, designed to be a universal description language for multi-participant simulations.
These three phases, storage, retrieval, and perceptualization are analogous to the human process of consciousness, as expressed in terms of semantics and cognitive science. Events occur and are recorded (memory); inferences are drawn from memory (associations), and from sets of related events, maps of the universe are created (cognitive perception). What is important to remember is that the map is not the territory, and we should avoid becoming trapped in any single representation or world-view. Although we need to design to avoid disorientation, we should always push the envelope in the kinds of experience we can bring into manifestation!
This document is the living proof of the success of a process that was committed to being open and flexible, responsive to the needs of a growing Web community. Rather than re-invent the wheel, we have adapted an existing specification (Open Inventor) as the basis from which our own work can grow, saving years of design work and perhaps many mistakes. Now our real work can begin; that of rendering our noospheric space.
VRML was conceived in the spring of 1994 at the first annual World Wide Web Conference in Geneva, Switzerland. Tim Berners-Lee and Dave Raggett organized a Birds-of-a-Feather (BOF) session to discuss Virtual Reality interfaces to the World Wide Web. Several BOF attendees described projects already underway to build three dimensional graphical visualization tools which interoperate with the Web. Attendees agreed on the need for these tools to have a common language for specifying 3D scene description and WWW hyperlinks -- an analog of HTML for virtual reality. The term Virtual Reality Markup Language (VRML) was coined, and the group resolved to begin specification work after the conference. The word 'Markup' was later changed to 'Modeling' to reflect the graphical nature of VRML.
Shortly after the Geneva BOF session, the www-vrml mailing list was created to discuss the development of a specification for the first version of VRML. The response to the list invitation was overwhelming: within a week, there were over a thousand members. After an initial settling-in period, list moderator Mark Pesce of Labyrinth Group announced his intention to have a draft version of the specification ready by the WWW Fall 1994 conference, a mere five months away. There was general agreement on the list that, while this schedule was aggressive, it was achievable provided that the requirements for the first version were not too ambitious and that VRML could be adapted from an existing solution. The list quickly agreed upon a set of requirements for the first version, and began a search for technologies which could be adapted to fit the needs of VRML.
The search for existing technologies turned up a several worthwhile candidates. After much deliberation the list came to a consensus: the Open Inventor ASCII File Format from Silicon Graphics, Inc. The Inventor File Format supports complete descriptions of 3D scenes with polygonally rendered objects, lighting, materials, ambient properties and realism effects. A subset of the Inventor File Format, with extensions to support networking, forms the basis of VRML. Gavin Bell of Silicon Graphics has adapted the Inventor File Format for VRML, with design input from the mailing list. SGI has publicly stated that the file format is available for use in the open market, and have contributed a file format parser into the public domain to bootstrap VRML viewer development.
At the highest level of abstraction, VRML is just a way for objects to read and write themselves. Theoretically, the objects can contain anything -- 3D geometry, MIDI data, JPEG images, anything. VRML defines a set of objects useful for doing 3D graphics. These objects are called Nodes.
Nodes are arranged in hierarchical structures called scene graphs. Scene graphs are more than just a collection of nodes; the scene graph defines an ordering for the nodes. The scene graph has a notion of state -- nodes earlier in the scene can affect nodes that appear later in the scene. For example, a Rotation or Material node will affect the nodes after it in the scene. A mechanism is defined to limit the effects of properties (Separator nodes), allowing parts of the scene graph to be functionally isolated from other parts.
VRML 1.0 is designed to meet the following requirements:
As with HTML, the above are absolute requirements for a network language standard; they should need little explanation here.
Early on the designers decided that VRML would not be an extension to HTML. HTML is designed for text, not graphics. Also, VRML requires even more finely tuned network optimizations than HTML; it is expected that a typical VRML scene will be composed of many more "inline" objects and served up by many more servers than a typical HTML document. Moreover, HTML is an accepted standard, with existing implementations that depend on it. To impede the HTML design process with VRML issues and straightjacket the VRML design process with HTML compatibility concerns would be to do both languages a disservice. As a network language, VRML will succeed or fail independent of HTML.
It was also decided that, except for the hyperlinking feature, the first version of VRML would not support interactive behaviors. This was a practical decision intended to streamline design and implementation. Design of a language for describing interactive behaviors is a big job, especially when the language needs to express behaviors of objects communicating on a network. Such languages do exist; if we had chosen one of them, we would have risked getting into a "language war." People don't get excited about the syntax of a language for describing polygonal objects; people get very excited about the syntax of real languages for writing programs. Religious wars can extend the design process by months or years. In addition, networked inter-object operation requires brokering services such as those provided by CORBA or OLE, services which don't exist yet within WWW; we would have had to invent them. Finally, by keeping behaviors out of Version 1, we have made it a much smaller task to implement a viewer. We acknowledge that support for arbitrary interactive behaviors is critical to the long-term success of VRML; they will be included in Version 2.
Marco Calamari (marcoc@dada.it) works in Elea FP on new technologies applied to vocational training.