NPH: Natural Phenomena

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

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Animating Corrosion and Erosion
(The Eurographics Association, 2007) Wojtan, Chris; Carlson, Mark; Mucha, Peter J.; Turk, Greg; D. Ebert and S. Merillou
In this paper, we present a simple method for animating natural phenomena such as erosion, sedimentation, and acidic corrosion. We discretize the appropriate physical or chemical equations using finite differences, and we use the results to modify the shape of a solid body. We remove mass from an object by treating its surface as a level set and advecting it inward, and we deposit the chemical and physical byproducts into simulated fluid. Similarly, our technique deposits sediment onto a surface by advecting the level set outward. Our idea can be used for off-line high quality animations as well as interactive applications such as games, and we demonstrate both in this paper.
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.
Convective Clouds
(The Eurographics Association, 2007) Geist, Robert; Steele, Jay; Westall, James; D. Ebert and S. Merillou
A new technique for rendering convective clouds is suggested. The technique uses two lattice-Boltzmann (LB) models, one for generating the spatial and temporal distribution of water density and the other for photon transport, that is, lighting the water density with correct anisotropic scattering. The common LB structure is easily mapped to parallel execution environments such as a GPU or multiple CPUs connected via the Message Passing Interface (MPI), thereby providing sub-minute execution times on commodity hardware.
Corotated SPH for Deformable Solids
(The Eurographics Association, 2009) Becker, Markus; Ihmsen, Markus; Teschner, Matthias; Eric Galin and Jens Schneider
Smoothed Particle Hydrodynamics (SPH) is a powerful technique for the animation of natural phenomena. While early SPH approaches in Computer Graphics have mainly been concerned with liquids or gases, recent research also focuses on the dynamics of deformable solids using SPH. In this paper, we present a novel corotational SPH formulation for deformable solids. The rigid body modes are extracted from the deformation field which allows to use a linear strain tensor. In contrast to previous rotationally invariant meshless approaches, we show examples using coplanar and collinear particle data sets. The presented approach further allows for a unified meshfree representation of deformable solids and fluids. This enables the animation of sophisticated phenomena, such as phase transitions. The versatility and the efficiency of the presented SPH scheme for deformable solids is illustrated in various experiments.
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.
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.
Expressive Illumination of Foliage Based on Implicit Surfaces
(The Eurographics Association, 2007) Luft, Thomas; Balzer, Michael; Deussen, Oliver; D. Ebert and S. Merillou
This paper presents an approach for vivid representations of foliage based on implicit surfaces. It approximates the complex lighting interaction within the foliage and enables a clear illustration of its general shape and local density, thus supporting the three-dimensional depth cue of the viewer. Due to its straightforward implementation as a preprocessing step that only adjusts the normal vectors of the geometry, this method has no additional memory requirements during the rendering process, and is especially applicable to real-time visualizations.
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.
Fast Fluid Simulation Using Residual Distribution Schemes
(The Eurographics Association, 2007) Sewall, Jason; Mecklenburg, Paul; Mitran, Sorin; Lin, Ming; D. Ebert and S. Merillou
We present a fast method for physically-based animation of fluids on adaptive, unstructured meshes. Our algo- rithm is capable of correctly handling large-scale fluid forces, as well as their interaction with elastic objects. Our adaptive mesh representation can resolve boundary conditions accurately while maintaining a high level of efficiency.
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.
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.
A Geometric Algorithm for Snow Distribution in Virtual Scenes
(The Eurographics Association, 2009) Festenberg, Niels v.; Gumhold, Stefan; Eric Galin and Jens Schneider
Freshly fallen snow is a popular natural phenomenon able to evoke great beauty in all kinds of scenes. However, there still does not exist an all-purpose algorithm for automated snow distribution in virtual worlds. Previous works modelled snow either relying on costly particle simulations or oversimplified surface displacements. In this paper we develop a novel geometric snow model. In a first step, we propose a statistical snow deposition model inspired by real world observations. This statistical model is used to derive a geometric snow shape formulation. The geometric scheme is implemented with an enhanced height span map. Scene geometry is expressed with two parameter fields that enable us to efficiently compute snow cover geometry. A selection of snow covered scenes demonstrates the realism that can be achieved with this new method.
Goblins by Spheroidal Weathering
(The Eurographics Association, 2007) Beardall, Mathew; Farley, Mckay; Ouderkirk, Darius; Smith, Jeremy; Jones, Michael; Egbert, Parris; D. Ebert and S. Merillou
Height map models of terrain are computationally efficient but can not represent terrain with concave surfaces. We present an algorithm for generating sandstone goblins using a simulation of spheroidal weathering. Sandstone goblins are a kind of hoodoo which are characterized by rounded concave shapes. The weathering simulation uses bubbles centered on axis aligned voxels to approximate geometry-dependent effects of spheroidal weathering. We demonstrate that the algorithm, together with appropriate surface textures, produces visually plausible goblins at near interactive speeds for most simulation parameters.
Interactive Modeling of Virtual Ecosystems
(The Eurographics Association, 2009) Benes, Bedrich; Andrysco, Nathan; Stava, Ondrej; Eric Galin and Jens Schneider
We present a novel technique for interactive, intuitive, and efficient modeling of virtual plants and plant ecosystems. Our approach is biologically-based, but shades the user from overwhelming input parameters by simplifying them to intuitive controls. Users are able to create scenes that are populated by virtual plants. Plants communicate actively with the environment and attempt to generate an optimal spatial distribution that dynamically adapts to neighboring plants, to user defined obstacles, light, and gravity. We demonstrate simulations of ecosystems composed of up to 140 trees that are computed in less than two minutes. Various phenomena previously available for non-realtime procedural approaches are created interactively, such as plants competing for space, topiary, plant lighting, virtual forests, etc. Results are aimed at architectural modeling, the entertainment industry, and everywhere that quick and fast creation of believable biological plant models is necessary.
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.
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.
Modeling Trees with a Space Colonization Algorithm
(The Eurographics Association, 2007) Runions, Adam; Lane, Brendan; Prusinkiewicz, Przemyslaw; D. Ebert and S. Merillou
We extend the open leaf venation model by Runions et al. [RFL*05] to three dimensions and show that it generates surprisingly realistic tree structures. Model parameters correspond to visually relevant tree characteristics identified in landscaping, offering convenient control of tree shape and structure.
Multi-layered Indirect Texturing for Tree Rendering
(The Eurographics Association, 2007) García, Ismael; Patow, Gustavo; Szirmay-Kalos, László; Sbert, Mateu; D. Ebert and S. Merillou
This paper presents a technique to render in real time complex trees using billboard clouds as an impostor simplification for the original polygonal tree, combined with a new texture-based representation for the foliage. The technique provides several new contributions with respect to previous approaches. The new algorithm allows progressive level of detail both at the geometric and at the shader levels. It also preserves the parallax effects of the original polygonal model keeping leaf positions, orientations, and preserving the overlapping of the leaves as seen from any view point. In addition, the texture-based representation provides high-definition close views without introducing high memory requeriments. We adapted a realistic lighting model with soft shadows and a global illumination precomputation, allowing to render highly complex scenes with thousands of trees in real time.
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.
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.

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