NPH05: Natural Phenomena 2005

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https://diglib.eg.org/handle/10.2312/412

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Extreme Model Simplification for Forest Rendering
(The Eurographics Association, 2005) Fuhrmann, Anton L.; Umlauf, Eike; Mantler, Stephan; Pierre Poulin and Eric Galin
Models of large forest scenes are of a geometric complexity that surpasses even the capabilities of current high end graphics hardware. We propose an extreme simplification method which allows us to render such scenes in realtime. Our work is an extension of the image based-simplification method of Billboard Clouds. We automatically generate tree model representations of 15-50 textured polygons. In this paper, we focus on the algorithmic details to improve the simplification process for foliage. We use the simplified models as static levels-of-detail in the medium to far field and demonstrate how our approach yields real-time rendering of dense forest scenes for walkthroughs and flyovers.
Interactive physically based Fluid and Erosion Simulation
(The Eurographics Association, 2005) Neidhold, B.; Wacker, M.; Deussen, O.; Pierre Poulin and Eric Galin
Realistically eroded terrain is a base of almost every outdoor visualization for simulators or computer games. In order to achieve convincing results physically based erosion algorithms are necessary. We present a new method that combines a non-expensive fluid simulation with an erosion algorithm. Both parts are running at interactive rates so the artist is able to influence the erosion process in real-time by changing simulation parameters or applying additional water to the scene. In this way, we support realism as well as design aspects during the terrain creation process. To simplify the three dimensional fluid simulation we use a newtonian physics approach that works on a two dimensional grid storing acceleration, velocity and mass. The method provides all features that are important for simulation of erosion e.g. moving, non-moving water (rivers, lakes) and evaporation. This allows us to support effects like dissolving, transportation and sedimentation of material in the erosion process.
FlowFixer: Using BFECC for Fluid Simulation
(The Eurographics Association, 2005) Kim, ByungMoon; Liu, Yingjie; Llamas, Ignacio; Rossignac, Jarek; Pierre Poulin and Eric Galin
Back and Forth Error Compensation and Correction (BFECC) was recently developed for interface computation by using the level set method. We show that it can be applied to reduce dissipation and diffusion encountered in various advection steps in uid simulation such as velocity, smoke density and image advections. BFECC can be implemented easily on top of the r st order upwinding or semi-Lagrangian integration of advection equations, while providing second order accuracy both in space and time. When applied to level set evolution, BFECC reduces volume loss signi cantly . We combine these techniques with variable density projection and show that they yield a realistic animations of two-phase ows. We demonstrate the bene ts of this approach on the image advection and on the simulation of smoke, of bubbles in water, and of a highly dynamic interaction between water, a solid, and air.
Realistic and Interactive Visualization of High-Density Plant Ecosystems
(The Eurographics Association, 2005) Dietrich, Andreas; Colditz, Carsten; Deussen, Oliver; Slusallek, Philipp; Pierre Poulin and Eric Galin
Modeling and visualization of natural and realistic outdoor ecosystems like forests or meadows remains a highly challenging task in computer graphics. Convincing and non-artificial scenes require many thousands to millions of plants, each modeled with a high degree of geometric, shading, and lighting detail. At the same time many applications demand interactive rendering at high fidelity. In this paper we demonstrate a ray tracing based approach that does not rely on geometric simplification. Using real-time ray tracing technology, we are able to directly render the highly complex original models with advanced shading and lighting, including pixel-accurate shadows, and even high dynamic range lighting from environment maps. On high-end PCs we obtain interactive performance with reduced quality that quickly converges to high quality in static situations. On clusters of PCs high quality can be sustained even at interactive rates. We demonstrate these results using a highly complex forest model.
A Preliminary Approach of 3D Simulation of Soil Surface Degradation by Rainfall
(The Eurographics Association, 2005) Valette, Gilles; Herbin, Michel; Lucas, Laurent; Léonard, Joël; Pierre Poulin and Eric Galin
Soil surface structure and morphology deeply in uence a lot of processes of high agronomic and environmental relevance, such as mass and heat transfer through the soil-atmosphere interface, runoff and erosion, seed germination and seedling emergence. The soil surface structure of agricultural eld is in continuous evolution: it is strongly affected by tillage, and in between tillage operations, erosion by rainfall and runoff causes a progressive degradation of the structure whose intensity and speed partly depend on the initial state associated to tillage modalities. A soil surface degradation model could allow to predict this evolution of the soil surface structure, and even to help choosing adequate tillage practices and sowing dates. Erosion modelling has been addressed by soil scientists but also by computer graphic scientists in order to add realism to virtual landscapes. Mixing both of these points of view would be interesting to simulate and visualize the evolution of the soil surface of a cultivated soil. In this paper, we present our project of a simulator of soil surface degradation by rainfall at a small spatial scale (1 m2 or less), including visualization, and which is mainly based on a 3D cellular automata approach with a speci c type of cell. The choices made for the implementation of our model are discussed in the light of the results found in the literature with different modelling approaches.
Synthesis of Material Drying History: Phenomenon Modeling, Transferring and Rendering
(The Eurographics Association, 2005) Lu, Jianye; Georghiades, Athinodoros S.; Rushmeier, Holly; Dorsey, Julie; Xu, Chen; Pierre Poulin and Eric Galin
We consider the problem of the spatio-temporal variations in material appearance due to the wetting and drying of materials. We conducted a series of experiments that capture the appearance history of surfaces drying. We reduce this history to two parameters that control the shape of a drying curve. We relate these drying parameters to the shape of the original wetted area and the surface geometry. Using these relationships, we generate new time-varying spatial patterns of drying on synthetic shapes.
Modeling and Visualization of symmetric and asymmetric plant competition
(The Eurographics Association, 2005) Alsweis, M.; Deussen, O.; Pierre Poulin and Eric Galin
In this paper we describe a new method for the visual simulation of evolving plant communities, which involves, aside from the known symmetric competition for resources also asymmetric competition. Asymmetric competition takes place if plants differ in their size and/or species. The discrete simulation methods proposed in this work help to visually simulate complex plant ecosystems for computer graphics.
Point-based Rendering of Trees
(The Eurographics Association, 2005) Gilet, Guillaume; Meyer, Alexandre; Neyret, Fabrice; Pierre Poulin and Eric Galin
The goal of this paper is the interactive and realistic rendering of 3D trees covering a landscape. The landscape is composed by instantiating one or more block of vegetation on the terrain. A block of vegetation is composed by a single or a compact group of trees. For these blocks of vegetation, we propose a new representation based on triangle+point primitives organized into a regular spatial structure (grid). This structure is de ned onto easily adapt the level of details (LOD) of each subpart (cell) of the vegetation element. During the rendering process, we determine a global level of details for each block of vegetation. Then, we re ne it for each cell according to the following heuristic: leaves or branches on the rear of tree or inside the forest are statistically less visible than front ones and then can be rendered coarsely. As a result, our method greatly decrease the number of rendered primitives by preserving realism. This allows rendering of large landscape in interactive time, for a camera far away until inside.
Table Mountains by Virtual Erosion
(The Eurographics Association, 2005) Bene , B.; Arriaga, X.; Pierre Poulin and Eric Galin
We present an ef cient algorithm for visual modeling table mountains (mesas) using erosion simulation. The method uses techniques from Computer Graphics to closely model the phenomenon, without relying on physically correct modeling. Our main goal is to devise an ef cient algorithm that is geologically inspired and simulates visually plausible results in a reasonable time with certain user control over the process. The algorithm models a terrain as composed of two different materials, the hard one (rock) and the soft one (sand). The hard material is exposed to moisture and thermal changes that erode the side parts (the rimrock) of the table mountain. The eroded parts fall and change into the soft material. This material is subject of a different type of erosion. The soft material moves as sand or gravel with high inner friction. It moves slowly trying to reach an equilibrium and forms characteristic hillside of table mountains. We simulate this slow motion of soft material by a diffusion algorithm. The algorithm presented here achieves visually plausible results in reasonable time. The results are in tune with mountains observed in nature, and are comparable to the existing terrain modeling and displaying techniques.
Phenomenological Simulation of Efflorescence in Brick Constructions
(The Eurographics Association, 2005) Shahidi, S.; Merillou, S.; Ghazanfarpour, D.; Pierre Poulin and Eric Galin
In human constructions, repetitive patterns can be handled by different texturing methods. However, almost all techniques do not consider weathering phenomena, missing a very important visual effect for realistic rendering. Among a great number of weathering effects occurring on constructions - in particular on fired-clay brick walls - efflorescence implies important visual changes and their removal (surface cleaning) is an economic problem in numerous countries. Due to the complexity of the physics involved, we propose in this paper an original phenomenological simulation of this weathering process on fired-clay bricks. In this case, efflorescence is materialized by a thin white powdery deposit of water-soluble salts on the surface or in the pores of masonry. We propose a method to generate the texture of efflorescence-affected fired-clay brick. First, we synthesize a brick solid texture from digital photographs using a classical solid texturing technique. Then, we add efflorescence by a phenomenological algorithm representing salt transport and crystallization in porous building materials for each brick separately. We can build aged walls by changing the parameters of efflorescence for each brick.

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