NPH: Natural Phenomena

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https://diglib.eg.org/handle/10.2312/408

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Now showing 1 - 20 of 33

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.
Effective Multi-resolution Rendering and Texture Compression for Captured Volumetric Trees
(The Eurographics Association, 2006) Linz, Christian; Reche-Martinez, Alex; Drettakis, George; Magnor, Marcus; Norishige Chiba and Eric Galin
Trees can be realistically rendered in synthetic environments by creating volumetric representations from photographs. However, volumetric tree representations created with previous methods are expensive to render due to the high number of primitives, and have very high texture memory requirements. We address both shortcomings by presenting an efficient multi-resolution rendering method and an effective texture compression solution. Our method uses an octree with appropriate textures at intermediate hierarchy levels and applies an effective pruning strategy. For texture compression, we adapt a vector quantization approach in a perceptually accurate color space, and modify the codebook generation of the Generalized Lloyd Algorithm to further improve texture quality. In combination with several hardware acceleration techniques, our approach achieves a reduction in texture memory requirements by one order of magnitude; in addition, it is now possible to render tens or even hundreds of captured trees at interactive rates.
Physically-based Driven Tree Animations
(The Eurographics Association, 2006) Haevre, William Van; Fiore, Fabian Di; Reeth, Frank Van; Norishige Chiba and Eric Galin
Simulating dynamic natural wind effects on trees remains a challenging task in Computer Graphics. From an animator s point of view it is a cumbersome and tedious task to create this effect due to the complexity of the tree shape, the numerous protruding branches and the wide variety of foliage. In this paper we present a novel method to create controllable animations of trees. Our approach borrows from several ideas from video textures, computer-assisted animation and motion graphs. It combines re-sequencing of existing material with the automatic generation of new data. Furthermore, the animator can direct the animation at each arbitrary moment using a goal based motion algorithm. First, a small set of motion data is gathered from a physically-based driven tree animation. Next, an optimised motion graph is constructed from the acquired data indicating all possible transitions from one tree pose to another. By creating in-between frames for all pairs of keyframes we ensure smooth transitions. Finally, by walking on the motion graph new non-identical animations are synthesised. The resulting animations are smooth, controllable by the animator and suitable for different production targets including 3D virtual environments (e.g., games) and 2D stylised animation.
Simulating Caustics due to Liquid-Solid Interface Menisci
(The Eurographics Association, 2006) Bourque, Eric; Dufort, Jean-François; Laprade, Michelle; Poulin, Pierre; Norishige Chiba and Eric Galin
A solid partially immersed in a liquid creates a local deformation of the liquid surface at their interface. This deformation, called a meniscus, exhibits high curvature, and as such, produces very intriguing caustic patterns. However, this natural phenomena has been neglected in almost all previous liquid simulation techniques. We propose a complete solution to model and render meniscal illumination effects. First, we outline a physicallymotivated approach to approximating the geometry of the meniscus. We then describe the targeted photon map, an adapted photon map which facilitates efficient sampling of the finely tessellated menisci. This technique, which integrates well within traditional photon mapping, allows for automatically rendering illumination effects for complex solid-liquid interfaces. Several images rendered using this technique are presented and are compared to their real-world counterparts.
Realistic Water Volumes in Real-Time
(The Eurographics Association, 2006) Baboud, Lionel; Décoret, Xavier; Norishige Chiba and Eric Galin
We present a real-time technique to render realistic water volumes. Water volumes are represented as the space enclosed between a ground heightfield and an animable water surface heightfield. This representation allows the application of recent GPU-based heightfield rendering algorithms. Our method is a simplified raytracing approach which correctly handles reflections and refractions and allows us to render complex effects such as light absorption, refracted shadows and refracted caustics. It runs at high framerates by exploiting the power of the latest graphic cards, and could be used in real-time applications like video games, or interactive simulation.
Physically-Based Realistic Fire Rendering
(The Eurographics Association, 2006) Pegoraro, Vincent; Parker, Steven G.; Norishige Chiba and Eric Galin
Accurately rendering fires is a challenging problem due to the various subtle ways in which the electromagnetic waves interact with this complex participating medium. We present a new method for physically-based rendering of flames from detailed simulations of flame dynamics which accounts for their unique characteristics. Instead of relying on ad-hoc models, we build on fundamental molecular physics to compute the spectrally dependent absorption, emission and scattering properties of the various chemical compounds found in the fire. Combined with a model of the refractive process, and with tone-mapping techniques simulating the visual adaptation of a human observer, we are able to generate highly realistic renderings of various types of flames, including colorful flames containing chemical species with very characteristic spectral properties.
Time-Varying BRDFs
(The Eurographics Association, 2006) Sun, Bo; Sunkavalli, Kalyan; Ramamoorthi, Ravi; Belhumeur, Peter; Nayar, Shree; Norishige Chiba and Eric Galin
The properties of virtually all real-world materials change with time, causing their BRDFs to be time-varying. However, none of the existing BRDF models and databases take time variation into consideration; they represent the appearance of a material at a single time instance. In this work, we address the acquisition, analysis, modeling and rendering of a wide range of time-varying BRDFs. We have developed an acquisition system that is capable of sampling a material's BRDF at multiple time instances, with each time sample acquired within 36 seconds. We have used this acquisition system to measure the BRDFs of a wide range of time-varying phenomena which include the drying of various types of paints (watercolor, spray, and oil), the drying of wet rough surfaces (cement, plaster, and fabrics), the accumulation of dusts (household and joint compound) on surfaces, and the melting of materials (chocolate). Analytic BRDF functions are fit to these measurements and the model parameters' variations with time are analyzed. Each category exhibits interesting and sometimes non-intuitive parameter trends. These parameter trends are then used to develop analytic time-varying BRDF (TVBRDF) models. The analytic TVBRDF models enable us to apply effects such as paint drying and dust accumulation to arbitrary surfaces and novel materials.
Real-time Realistic Illumination and Shading of Stratiform Clouds
(The Eurographics Association, 2006) Bouthors, Antoine; Neyret, Fabrice; Lefebvre, Sylvain; Norishige Chiba and Eric Galin
Realistic rendering of clouds involves solving the complex interaction of light within the cloud and with its environment. Interactive methods achieve efficient cloud rendering by ignoring several lighting effects. However, these effects are visually important, and removing them strongly reduces realism. We present a novel approach for capturing the important effects of multiple anisotropic Mie scattering within cloud layers (i.e., stratiform clouds), and the inter-reflections between the ground and the cloud base under sun and sky illumination. Our model maps well to graphics hardware, enabling the real-time rendering of animated cloud skies over landscapes.
Artist-Directable Real-Time Rain Rendering in City Environments
(The Eurographics Association, 2006) Tatarchuk, Natalya; Isidoro, John; Norishige Chiba and Eric Galin
Photorealistic rain greatly enhances the scenes of outdoor reality, with applications including computer games and motion pictures. Rain is a complex atmospheric natural phenomenon. It consists of numerous interacting visual effects. We present a comprehensive real-time system for the realistic rendering of rain effects in complex environments in real-time. Our system is intuitive, flexible and provides a high degree of artistic control for achieving the desired look. We describe a number of novel GPU-based algorithms for rendering the individual components of rain effects, such as a hybrid system of an image-space approach for rainfall and the particle-based effects for dripping raindrops and splashes; water surface simulation for ripples; animation and rendering of water droplets trickling down on transparent glass panes; view-dependent warped reflections and a number of additional effects. All our techniques respond dynamically and correctly to the environment lighting and viewpoint changes as well as the atmospheric illumination due to lightning. Our effects can be rendered at interactive rates on consumer graphics hardware and can be easily integrated into existing game and interactive application pipelines or offline rendering.
A Generalized Cracks Simulation on 3D-Meshes
(The Eurographics Association, 2006) Valette, Gilles; Prévost, Stéphanie; Lucas, Laurent; Norishige Chiba and Eric Galin
This article describes a method for simulating the formation and the development of cracks on the surface of a shrinking volume. The simulated cracks are applied afterwards to any surface provided with a parameterization. The 2D path of the cracks is automatically precalculated by an appropriate algorithm which gives a graph of discrete ways. We newly propose to take into account a possibly inhomogeneous thickness of the shrinking layer by using a watershed transformation to compute this path. The propagation of one crack is then based on the respect of the primary orientation of the crack. Another originality of our method is the calculation of the enlargement of each crack by a discrete shrinkage volume propagation. We consider the shrinking layer as a set of cubic cells which contain volumes of matter and pores. During the dessiccation process, the matter shrinks, creating what we call a shrinkage volume . We propagate this shrinkage volume among the cells up to the cracked ones, and we deduce the width of the cracks from the resulting shrinkage volume in these cells. In this paper, this method is presented in detail and we give images obtained from different simulations. Initially designed to help for the prediction of seedlings emergence in an agronomic environment, the method we present can also be applied to enhance the realism of virtual 3D objects.
Eulerian Motion Blur
(The Eurographics Association, 2007) Kim, Doyub; Ko, Hyeong-Seok; D. Ebert and S. Merillou
This paper describes a motion blur technique which can be applied to rendering fluid simulations that are carried out in the Eulerian framework. Existing motion blur techniques can be applied to rigid bodies, deformable solids, clothes, and several other kinds of objects, and produce satisfactory results. As there is no specific reason to discriminate fluids from the above objects, one may consider applying an existing motion blur technique to render fluids. However, here we show that existing motion blur techniques are intended for simulations carried out in the Lagrangian framework, and are not suited to Eulerian simulations. Then, we propose a new motion blur technique that is suitable for rendering Eulerian simulations.

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