Scientific Work

Improving Usability in Procedural Modeling

River Networks for Instant Procedural Planets

Realistic terrain models are required in many applications, especially in computer games. Commonly, procedural models are applied to generate the corresponding models and let users experience a wide variety of new environments. Existing algorithms generate landscapes immediately with view-dependent resolution and without preprocessing. Unfortunately, landscapes generated by such algorithms lack river networks and therefore appear unnatural. Algorithms that integrate realistic river networks are computationally expensive and cannot be used to generate a locally adaptive high resolution landscape during a fly-through. In this paper, we propose a novel algorithm to generate realistic river networks. Our procedural algorithm creates complete planets and landscapes with realistic river networks within seconds. It starts with a coarse base geometry of a planet without further preprocessing and user intervention. By exploiting current graphics hardware, the proposed algorithm is able to generate adaptively refined landscape geometry during fly-throughs.

1-2-tree: Semantic Modeling and Editing of Trees

In computer graphics, procedural methods and L-systems are common approaches to model complex botanical trees. In contrast to previous tree modeling systems, we propose linking rules, parameters and geometry to semantic entities. This has the avantage that when an entity is clicked in the viewport, its parameters can be displayed immediately, and viewport editing operations can be reflected in the parameter set. Furthermore, we store the entities in a hierarchical data structure and allow the user to activate recursive traversal via selection options for all editing operations. Therefore, viewport or parameter changes can be applied to a single entity or many entities at once, and only the geometry for the affected entities needs to be updated. The proposed user interface aims at simplifying the modeling process.

An Integrated Framework for Procedural Modeling

This paper proposes a new type of visual language to integrate the features of previous procedural modeling systems into a single modeling environment. As in a visual dataflow pipeline, we let nodes wrap operations, but instead of using pipelines to define dataflow, we use edges to define the order of execution. Models can be created efficiently without needing time-consuming compilation runs or learning an unintuitive syntax, and the new system offers a mechanism that can alter procedural models in the viewport. An example demonstrates how to use the new system to create complex models consisting of buildings, plants and landscapes procedurally without resorting to external tools.

Effiziente Algorithmen zur bildbasierten Beleuchtung von Kleidung
(Efficient Algorithms for image-based lighting of clothes)

Several algorithms for computing shadows are discussed and new algorithms for calculating the radiance arriving at selected points of the geometry are proposed. A new model for surface lighting suitable for objects with concavities based on a paper by James Stewart is introduced. In order to accomplish this, so-called visibility maps are used. A visibility map is an image of a scene from the point of view of a vertex of that scene. In particular, the discussed algorithms allow for image-based lighting in combination with self-shadowing. Finally, we demonstrate how to use the visibility maps to calculate shadow boundaries und how to use digital camera pictures for illuminating a scene. This makes it possible to calculate soft shadows for extended light sources.

Realtime shading of folded surfaces

In this paper we present a new, simple, and efficient way to illuminate folded surfaces with extended light sources in realtime including shadows. In a preprocessing step we compute the parts of the surrounding environment that are visible from a set of points on the surface and represent this information in a binary visibility map. The illumination of the scene, i.e., incoming light from different directions, is encoded in an environment map. This way, extended light sources and complex illumination conditions of the surface can be simulated. The binary visibility information stored in the visibility maps is used during runtime to calculate the incoming and outgoing radiance in the direction of the viewer for each sample point. Various reflection models like the Phong or Lafortune model can be incorporated into these calculations. After computing the radiance values in each sample point, the surface is shaded using simple Gouraud interpolation. Using the pre-computed visibility information, the whole shading and even the change of lighting conditions can be simulated in realtime by modifying the environment map. As an extension to the environment map we support additional point light sources whose parameters and positions can also be manipulated in realtime. Several examples of mesh illumination and shading are demonstrated.

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