Klaas Jan de Kraker

Representation and management of feature information in a cellular model

Many limitations in current feature modelling systems are inherited from the geometric representation they use for the product model. Both a very rigid and a very extensive representation are unsuitable for feature applications, at least if no convenient support is provided to manage the data. This paper describes a cellular representation for feature models that contains all the relevant information to effectively solve a variety of current problems in feature modelling. Much benefit is gained from a coherent integration between shapes of a feature model and cells in the cellular model. Every feature shape has an explicit volumetric representation in terms of cells. Specific subsets of its boundary are also distinguished in terms of cell faces and edges. Feature interactions are maintained in attributes of cells, cell faces and cell edges. Methods for modifying and querying the cellular model are presented, and their application is illustrated for feature validity maintenance, feature interaction management, feature conversion between multiple views, and feature visualization.

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.

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.

Maintaining multiple views in feature modeling

A new feature modeling concept and its implementation are presented. In the multiple-view modeling concept, a set of open feature views of a product is maintained. The implementation does not rely on the existence of certain views, but instead is generic since generic view specifications are used. Views are maintained using feature conversion techniques, including constraint techniques. For adding a view to the set of open views, an open view function has been developed. This function uses the specified view properties, including its feature definitions. It derives a meaningful feature interpretation for the opened view. Geometric constraint solving is used to propagate feature parameter changes between views, and a priority mechanism is used in case of conflicting constraints. In case of a conflict, a new incremental version of the open view function is invoked, which updates the feature model of the reopened view efficiently.

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.

Multiple-View Feature Modelling and Conversion

A product model containing information for all product life cycle activities is central to concurrent engineering. Preferably each activity has its own view on the product model, with information relevant to that activity. In this paper, a feature modelling approach is outlined in which each view consists of a specific feature model, containing features relevant to the corresponding activity. Attention is paid to the product model, feature validation, feature conversion and specific assembly features. Feature validation is the basis for maintaining the meaning of features. Feature conversion is used to convert features from one view to other views; multiple-way conversions are possible. As an example of view-specific features, it is shown which assembly-specific features can be included in a feature model for the assembly planning view.

Multiple-way feature conversion—opening a view

A new approach to feature modeling is presented. It supports multiple feature views of a product, each with its own feature model. Consistency between the views is maintained by performing multiple-way feature conversion. A product model has been defined that contains the different views and their feature models. The feature models of the different views are linked by the product geometry, which is represented by a cellular model.

Semantic constraints for procedural generation of virtual worlds

Procedural generation of virtual worlds is a promising alternative to classical manual modelling approaches, which usually require a large amount of effort and expertise. However, it suffers from a number of issues; most importantly, the lack of user control over the generation process and its outcome. Because of this, the result of a procedural method is highly unpredictable, rendering it almost unusable for virtual world designers. This paper focuses on providing user control to deliver an outcome consistent with designers intent. For this, we introduce semantic constraints, a flexible concept to express high-level designers intent in intuitive terms as e.g. line of sight. Our constraint evaluation method is capable of detecting the context in which such a constraint is specified, automatically adapting to surrounding features of the virtual world. From experiments performed within our prototype modelling system, we can conclude that semantic constraints are another step forward in making procedural generation of virtual worlds more controllable and accessible to non-specialist designers.