With a carefully chosen, representative set of articles, this monograph presents the state-of-the-art in the field of virtual environments, including theoretical and practical aspects of the latest developments in this area.

There are many definitions of the expression virtual environment (VE) in literature (in this monograph the terms virtual environment, environment, virtual world, and world will be used indistinctly). Some definitions are highly restrictive while others are more open. Generally the restrictive approaches define virtual environments as three-dimensional (3D), multi-sensorial, immersive, real time, and interactive simulations of a space that can be experienced by users via three-dimensional input and output devices. The more open approaches to virtual environments define them as a computer representation of a space. According to the latter definition a text-based role-playing environment would be a virtual environment.

In this monograph, a virtual environment is considered to be somewhere in the continuum between those two extremes. We would define it as a three-dimensional computer representation of a space in which users can move their viewpoint freely in real time. We therefore consider that the following cases, among others, are virtual environments: 3D multi-user chats (such as Active Worlds, the Palace, etc), first person 3D videogames (such as Quake, Unreal Tournament, etc) and 3D virtual spaces in the web (such as those created with VRML, Adobe Atmosphere, FlatLand 3DML, etc).There is no unified definition of virtual environments. This is partly due to the fact that they have been used (and they have proved to be useful) in a variety of fields such as videogames, interactive narrative and collaborative environments, to mention just a few. Virtual environments are already being used in the present and will play a very importantrole in a number of different media in the future.

Overview of This Monograph

One interesting and fairly direct approach to get to know the state-of-the-art of a field such as virtual environments is to review the most salient features of the latest technologies currently being used. Among others, the following questions arise:

• What concepts lie behind these technologies?
• What functionalities do they provide?
• What hardware is required?
• How much budget is required?

Nowadays the majority of environments programmed in 3D use systems based on the scene graph concept which abstracts the application from specific aspects of the graphic cards. It also allows environments to be managed via flexible and extensible libraries that help to write applications which will work on a variety of platforms. Meanwhile, the virtual environment industry has also seen some notable changes, affecting both software and hardware. Big SGI systems have been replaced by clustered PCs and commercial software libraries have been replaced by Open Source systems.

The creator of OpenSG, Dirk Reiners, in his article "Open Source Tools for Virtual Environments: OpenSG and VRJuggler" describes the main features of the principal Open Source components for virtual environments such as the ones mentioned in the title. The author shows how these scene graph based components support the use of clustered PCs. The design and development of virtual environments needs to take into account more aspects than those purely related to their rendering and graphic quality.

Whenever the decision to design a virtual environment is taken, the first step is to plan its design. While tools do exist to help the designer construct the application of the virtual environment, there are still no formal guidelines or methodologies to guide the design process. This makes the design process long and costly, especially when the application is a virtual world for the Internet and is therefore aimed at a large audience with a wide range of profiles. In his article "Methods and Tools for Designing VR Applications for The Internet", Frederic Kleinermann discusses the design of Virtual Reality (VR) applications for the Net. The article proposes a series of design stages, showing the importance of following a number of steps that help define a document with all the details of the application. The article also introduces a set of tools that help model the scenes with all their objects, behaviours, interactions, navigation, and sounds. Finally, the article mentions some research work that may be used in the near future.

Now that we are starting to move in real time aroundimpressively realistic virtual environments, other difficulties and limitations are beginning to appear when we interact with virtual environments during a certain length of time. While the worlds are visually impressive, they lack other aspects of reality that require a certain degree of intelligence and, above all, another kind of information representation. These aspects need to be taken into account in order to arrive at more interactive and user-friendly environments.

With regard to the above, in their article "Virtual Environments and Semantics", Jesús Ibáñez-Martínez and Carlos Delgado-Mata present different aspects and applications of virtual environments. The focus here is on the relationship and integration of these virtual environments with semantic information. They show how virtual worlds can benefit from an additional layer of semantic information that makes it possible to enhance user interaction with these worlds. They also demonstrate how the worlds themselves are a powerful tool to show the semantics associated with the information they represent from other domains. These aspects are described using specific examples that show the direct application and usefulness of the presented ideas.

Probably the most extensive virtual environments nowadays are collaborative environments. This may be due to the fact that, rather than being oriented towards user interaction with virtual environments, they focus on interaction and collaboration among the users themselves. Based on virtual worlds and distributed collaborative environments, collaborative VEs provide collaborative tools with a very realistic and close to the user approach, thanks to the degree of immersion and interaction of the systems. In their article "Tracking The Evolution of Collaborative Virtual Environments", Rubén Mondéjar-Andreu, Pedro García-López, Carles Pairot-Gavaldà and Antonio F. Gómez-Skarmeta review the bases of collaborative virtual environments while analysing the requirements and frameworks that are needed to build them. They also show environments within their field of application (collaborative work, education, training).

The video games industry is to a large extent responsible for the progress seen in the field of VE in recent years. The industry’s quest for more realistic, faster, and more credible products in order to expand their market share prompts them to invest a huge amount of (economic and human) resources in order to optimize existing technology. Meanwhile, the technological progress seen in recent years has brought about major changes in the videogames industry. The new generation of consoles, PCs and PDAs allows closer integration between art and science, fosters a wide range of research areas, and facilitates the creation of increasingly impressive virtual environments and societies.

In his article "A Quick Look at the Videogame Industry – Technology and Future Challenges", from his privileged position in the videogames industry at BioWare Corp., Daniel Torres-Guízar, tells us about the latest developments and the most significant trends in the industry - not just those that we can enjoy already, but also new products in the pipeline.

A growing body of work is oriented towards the creation of virtual characters and their inclusion, animation, and interaction in virtual worlds. Applications of this type of work are very varied and range from the purely pedagogical to more commercial products in which virtual characters assist the user in e-commerce processes. The virtual presenter is another common application of these systems (e.g. the public TV channel of Catalonia has just launched SAM, the virtual weather man shown in Figure 1). Michael Nischt, Helmut Prendinger, Elisabeth André and Mitsuru Ishizuka, in their article "Creating Three-Dimensional Animated Characters: An Experience Report and Recommendations of Good Practice", provide an overview of state of-the-art techniques and tools for modelling and animating highly realistic and expressive characters. Based on their experience, they also suggest good practice methods and provide a number of recommendations. VEs have recently been attracting growing interest as a story-telling media.

Figure 1: SAM (The Virtual Weather Man of The Public TV Channel of Catalonia).

These systems are generally based on intelligent systems that are able to automatically direct everything that happens within a virtual environment in order to adapt a story to the application’s objectives and the particular characteristics of each interactor. In his article "Interactive Digital Storytelling: Automatic Direction of Virtual Environments", Federico Peinado-Gil presents an up to date review of implemented systems while outlining the tasks that are yet to be addressed in this line of research.

Finally, we would like to express our sincerest thanks to the authors for their efforts (the fantastic results of which are the articles we can all enjoy in this monograph), to the Editor of UPGRADE and Novática for offering us the chance to edit this monograph, and to Leticia Lipp-Ramírez for generously providing her English proofreading skills.

Translation by Jesús Ibáñez-Martínez and Carlos Delgado-Mata