Tim Tutenel

A Survey on Procedural Modelling for Virtual Worlds

Procedural modelling deals with (semi‐)automatic content generation by means of a program or procedure. Among other advantages, its data compression and the potential to generate a large variety of detailed content with reduced human intervention, have made procedural modelling attractive for creating virtual environments increasingly used in movies, games and simulations. We survey procedural methods that are useful to generate features of virtual worlds, including terrains, vegetation, rivers, roads, buildings and entire cities. In this survey, we focus particularly on the degree of intuitive control and of interactivity offered by each procedural method, because these properties are instrumental for their typical users: designers and artists. We identify the most promising research results that have been recently achieved, but we also realize that there is far from widespread acceptance of procedural methods among non‐technical, creative professionals. We conclude by discussing some of the most important challenges of procedural modelling.

The role of semantics in games and simulations

Powerful graphics hardware is enabling strong improvements in both the appearance and the complexity of virtual worlds for games and simulations. However, current practices in the design and development of virtual worlds mostly resemble high-tech variants of traditional handcrafts, resulting in increasingly unbearable design costs. In this article we state that an essential key to overcoming these problems lies in the enrichment of object models with several kinds of semantic data. We discuss numerous and promising uses for semantic information in virtual worlds, and show, for many of them, how previous results of recent research can be successfully applied. We also identify the fundamental challenges in this new cross-disciplinary area, and point out a number of open issues lying ahead, including the need for (i) a suitable way of specifying semantic data, providing a powerful vocabulary that is useful and usable for all disciplines involved in game design and development; (ii) a seamless integration of semantic data integrated with procedural generation techniques, in order to provide designers with a new and powerful generation of tools; and (iii) a consistency maintenance among evolving objects in a changeable environment, for which powerful constraint-solving methods will be instrumental. We conclude that, as the expectancy for future games and simulations steadily shifts from improved graphics and appearance towards improved character behavior, plausible realism and coherent gameplay, embedding the game world and its objects with richer semantics is going to play a crucial role. We can therefore expect that, in the near future, increasing research efforts and influential results will be emerging in this new exciting area.

Semantic 3D Media and Content: A declarative approach to procedural modeling of virtual worlds

With the ever increasing costs of manual content creation for virtual worlds, the potential of creating it automatically becomes too attractive to ignore. However, for most designers, traditional procedural content generation methods are complex and unintuitive to use, hard to control, and generated results are not easily integrated into a complete and consistent virtual world. We introduce a novel declarative modeling approach that enables designers to concentrate on stating what they want to create instead of on describing how they should model it. It aims at reducing the complexity of virtual world modeling by combining the strengths of semantics-based modeling with manual and procedural approaches. This article describes two of its main contributions to procedural modeling of virtual worlds: interactive procedural sketching and virtual world consistency maintenance. We discuss how these techniques, integrated in our modeling framework SketchaWorld, build up to enable designers to create a complete 3D virtual world in minutes. Procedural sketching provides a fast and more intuitive way to model virtual worlds, by letting designers interactively sketch their virtual world using high-level terrain features, which are then procedurally expanded using a variety of integrated procedural methods. Consistency maintenance guarantees that the semantics of all terrain features is preserved throughout the modeling process. In particular, it automatically solves conflicts possibly emerging from interactions between terrain features. We believe that these contributions together represent a significant step towards providing more user control and flexibility in procedural modeling of virtual worlds. It can therefore be expected that by further reducing its complexity, virtual world modeling will become accessible to an increasingly broad group of users.

Integrating procedural generation and manual editing of virtual worlds

Because of the increasing detail and size of virtual worlds, designers are more and more urged to consider employing procedural methods to alleviate part of their modeling work. However, such methods are often unintuitive to use, difficult to integrate, and provide little user control, making their application far from straightforward. In our declarative modeling approach, designers are provided with a more productive and simplified virtual world modeling workflow that matches better with their iterative way of working. Using interactive procedural sketching, they can quickly layout a virtual world, while having proper user control at the level of large terrain features. However, in practice, designers require a finer level of control. Integrating procedural techniques with manual editing in an iterative modeling workflow is an important topic that has remained relatively unaddressed until now. This paper identifies challenges of this integration and discusses approaches to combine these methods in such a way that designers can freely mix them, while the virtual world model is kept consistent during all modifications. We conclude that overcoming the challenges mentioned, for example in a declarative modeling context, is instrumental to achieve the much desired adoption of procedural modeling in mainstream virtual world modeling.

Declarative terrain modeling for military training games

Military training instructors increasingly often employ computer games to train soldiers in all sorts of skills and tactics. One of the difficulties instructors face when using games as a training tool is the creation of suitable content, including scenarios, entities, and corresponding terrain models. Terrain plays a key role in many military training games, as for example, in our case game Tactical Air Defense. However, current manual terrain editors are both too complex and too time-consuming to be useful for instructors; automatic terrain generation methods show a lot of potential, but still lack user control and intuitive editing capabilities. We present a novel way for instructors to model terrain for their training games: instead of constructing a terrain model using complex modeling tools, instructors can declare the required properties of their terrain using an advanced sketching interface. Our framework integrates terrain generation methods and manages dependencies between terrain features in order to automatically create a complete 3D terrain model that matches the sketch. With our framework, instructors can easily design a large variety of terrain models that meet their training requirements.

Designing Semantic Game Worlds

Current game worlds often fall short in providing consistency between the visual representation of the world and the way it feels, behaves, and reacts. This problem partly originates from the goal-oriented and cost-effective nature of the game development process, which mostly favors ad hoc solutions for one particular game, rather than investing in concepts like reusability and emergent gameplay. In broader terms, we observe that game worlds miss semantics, and we argue that its deployment has the potential to bring about the consistency missing in their content. Therefore, we present a novel approach aimed at enriching virtual entities in game worlds with information about their roles, how they relate to others, and how they can affect and interact with players, NPCs, and with each other. We discuss several requirements to achieve these goals, and introduce a semantic model to represent game worlds. In order to support and validate this model, we have developed Entika, a framework to facilitate the deployment of semantics during game development, as well as its maintenance during run-time. Furthermore, we briefly discuss several applications that demonstrate the power of this semantic model for game worlds. After careful evaluation of our semantic game world model and framework, we conclude that a semantically rich world representation can substantially assist designers in creating much more consistent game worlds.

Interactive Creation of Virtual Worlds Using Procedural Sketching

Procedural modelling is an attractive alternative to cut down the costs of manual content creation for virtual worlds. We discuss our declarative modelling approach to the creation of 3D virtual worlds, which integrates a variety of procedural techniques in order to enable a non-specialist user to interactively create a complete 3D virtual world in minutes. In particular, we introduce procedural sketching, a novel paradigm which allows designers to quickly specify and see the effects of their procedural modelling operations, and describe its main features as implemented in our prototype system SketchaWorld. Two main interaction modes are described, for specifying the landscape and terrain features, respectively. Our approach automatically fits all generated terrain features with their surroundings, for example by smoothing out rough terrain for roads, or creating a bridge to cross a river. It is concluded that this approach provides designers with the productivity gain of procedural methods, while still allowing for fine user control and actively supporting iterative modelling.

Generating Consistent Buildings: A Semantic Approach for Integrating Procedural Techniques

Computer games often take place in extensive virtual worlds, attractive for roaming and exploring. Unfortunately, current virtual cities can strongly hinder this kind of gameplay, since the buildings they feature typically have replicated interiors, or no interiors at all. Procedural content generation is becoming more established, with many techniques for automatically creating specific building elements. However, the integration of these techniques to form complete buildings is still largely unexplored, limiting their application to open game worlds. We propose a novel approach that integrates existing procedural techniques to generate such buildings. With minimal extensions, individual techniques can be coordinated to create buildings with consistently interrelated exteriors and interiors, as in the real world. Our solution offers a framework where various procedural techniques communicate with a moderator, which is responsible for negotiating the placement of building elements, making use of a library of semantic classes and constraints. We demonstrate the applicability of our approach by presenting several examples featuring the integration of a façade shape grammar, two different floor plan layout generation techniques, and furniture placement techniques. We conclude that this approach allows one to preserve the individual qualities of existing procedural techniques, while assisting the consistency maintenance of the generated buildings.

An interactive simulation and visualization tool for flood analysis usable for practitioners

Developing strategies to mitigate or to adapt to the threats of floods is an important topic in the context of climate changes. Many of the world’s cities are endangered due to rising ocean levels and changing precipitation patterns. It is therefore crucial to develop analytical tools that allow us to evaluate the threats of floods and to investigate the influence of mitigation and adaptation measures, such as stronger dikes, adaptive spatial planning, and flood disaster plans. Up until the present, analytical tools have only been accessible to domain experts, as the involved simulation processes are complex and rely on computational and data-intensive models. Outputs of these analytical tools are presented to practitioners (i.e., policy analysts and political decision-makers) on maps or in graphical user interfaces. In practice, this output is only used in limited measure because practitioners often have different information requirements or do not trust the direct outcome. Nonetheless, literature indicates that a closer collaboration between domain experts and practitioners can ensure that the information requirements of practitioners are better aligned with the opportunities and limitations of analytical tools. The objective of our work is to present a step forward in the effort to make analytical tools in flood management accessible for practitioners to support this collaboration between domain experts and practitioners. Our system allows the user to interactively control the simulation process (addition of water sources or influence of rainfall), while a realistic visualization allows the user to mentally map the results onto the real world. We have developed several novel algorithms to present and interact with flood data. We explain the technologies, discuss their necessity alongside test cases, and introduce a user study to analyze the reactions of practitioners to our system. We conclude that, despite the complexity of flood simulation models and the size of the involved data sets, our system is accessible for practitioners of flood management so that they can carry out flood simulations together with domain experts in interactive work sessions. Therefore, this work has the potential to significantly change the decision-making process and may become an important asset in choosing sustainable flood mitigations and adaptation strategies.

Using gameplay semantics to procedurally generate player-matching game worlds

The use of procedural content generation to support adaptive games is starting to gain momentum in current research. However, there are still many open issues to tackle, namely the reusability of methodologies. Our research focuses on reusable and generic methods for linking the procedural generation of 3D game worlds with gameplay, as measured by player modelling techniques. As the interface for that link, we propose the use of gameplay semantics, a knowledge representation technique that allows our case-based generator to match content to player models. We present and discuss the implementation of our proposed method in an existing game, Stunt Playground. Gameplay semantics is created by designers in a generic way and is then used to procedurally generate player-matching Stunt Playground game worlds, both at the design and game stage. Current results show that our approach can automatically create such adaptive game content, thus effectively bridging game world designers, procedural generation and gameplay.