51 research outputs found
A hybrid representation for modeling, interactive editing, and real-time visualization of terrains with volumetric features
Cataloged from PDF version of article.Terrain rendering is a crucial part of many real-time applications. The easiest way to process and visualize terrain data in real time is to constrain the terrain model in several ways. This decreases the amount of data to be processed and the amount of processing power needed, but at the cost of expressivity and the ability to create complex terrains. The most popular terrain representation is a regular 2D grid, where the vertices are displaced in a third dimension by a displacement map, called a heightmap. This is the simplest way to represent terrain, and although it allows fast processing, it cannot model terrains with volumetric features. Volumetric approaches sample the 3D space by subdividing it into a 3D grid and represent the terrain as occupied voxels. They can represent volumetric features but they require computationally intensive algorithms for rendering, and their memory requirements are high. We propose a novel representation that combines the voxel and heightmap approaches, and is expressive enough to allow creating terrains with caves, overhangs, cliffs, and arches, and efficient enough to allow terrain editing, deformations, and rendering in real time
Diamond-based models for scientific visualization
Hierarchical spatial decompositions are a basic modeling tool in a variety of application domains including scientific visualization, finite element analysis and shape modeling and analysis. A popular class of such approaches is based on the regular simplex bisection operator, which bisects simplices (e.g. line segments, triangles, tetrahedra) along the midpoint of a predetermined edge. Regular simplex bisection produces adaptive simplicial meshes of high geometric quality, while simplifying the extraction of crack-free, or conforming, approximations to the original dataset. Efficient multiresolution representations for such models have been achieved in 2D and 3D by clustering sets of simplices sharing the same bisection edge into structures called diamonds. In this thesis, we introduce several diamond-based approaches for scientific visualization. We first formalize the notion of diamonds in arbitrary dimensions in terms of two related simplicial decompositions of hypercubes. This enables us to enumerate the vertices, simplices, parents and children of a diamond. In particular, we identify the number of simplices involved in conforming updates to be factorial in the dimension and group these into a linear number of subclusters of simplices that are generated simultaneously. The latter form the basis for a compact pointerless representation for conforming meshes generated by regular simplex bisection and for efficiently navigating the topological connectivity of these meshes. Secondly, we introduce the supercube as a high-level primitive on such nested meshes based on the atomic units within the underlying triangulation grid. We propose the use of supercubes to associate information with coherent subsets of the full hierarchy and demonstrate the effectiveness of such a representation for modeling multiresolution terrain and volumetric datasets. Next, we introduce Isodiamond Hierarchies, a general framework for spatial access structures on a hierarchy of diamonds that exploits the implicit hierarchical and geometric relationships of the diamond model. We use an isodiamond hierarchy to encode irregular updates to a multiresolution isosurface or interval volume in terms of regular updates to diamonds. Finally, we consider nested hypercubic meshes, such as quadtrees, octrees and their higher dimensional analogues, through the lens of diamond hierarchies. This allows us to determine the relationships involved in generating balanced hypercubic meshes and to propose a compact pointerless representation of such meshes. We also provide a local diamond-based triangulation algorithm to generate high-quality conforming simplicial meshes
Modeling of erosion impact on geometric objects
Simulace eroze je dĹŻleĹžitĂ˝m problĂŠmem v oblasti poÄĂtaÄovĂŠ grafiky. NejvĂ˝znamnÄjĹĄĂmi eroznĂmi procesy v pĹĂrodÄ jsou zvÄtrĂĄvĂĄnĂ a hydraulickĂĄ eroze. Mnoho metod se tÄmito problĂŠmy zabĂ˝vĂĄ, ale vÄtĹĄinou jsou tyto metody zaloĹženy na výťkovĂ˝ch mapĂĄch nebo volumetrickĂ˝ch datech. VýťkovĂŠ mapy neumoĹžĹujĂ simulaci sloĹžitĂ˝ch plnÄ trojrozmÄrnĂ˝ch scĂŠn, zatĂmco volumetrickĂĄ data majĂ vysokĂŠ pamÄĹĽovĂŠ nĂĄroky. Tato disertaÄnĂ prĂĄce zkoumĂĄ vĂ˝hody reprezentace erodovanĂ˝ch objektĹŻ pomocĂ trojĂşhelnĂkovĂ˝ch sĂtĂ a navrhuje ĹeĹĄenĂ problĂŠmĹŻ, kterĂŠ vznikajĂ v dĹŻsledku pouĹžitĂ tĂŠto datovĂŠ struktury. TrojĂşhelnĂkovĂŠ sĂtÄ se ukĂĄzaly bĂ˝t vhodnou datovou strukturou pro pouĹžitĂ pĹi simulaci eroze dĂky jejich adaptivitÄ a moĹžnosti modelovat sloĹžitĂŠ konkĂĄvnĂ prvky scĂŠny. PouĹžitĂ trojĂşhelnĂkovĂ˝ch sĂtĂ vĹĄak pĹinĂĄĹĄĂ novĂŠ problĂŠmy, napĹĂklad problĂŠm vzniku nekonzistence sĂtÄ v dĹŻsledku silnĂŠ eroze nebo problĂŠm simulace sloĹžitĂ˝ch scĂŠn sloĹženĂ˝ch z vĂce materiĂĄlĹŻ. Tato prĂĄce zkoumĂĄ zmĂnÄnĂŠ problĂŠmy a navrhuje jejich moĹžnĂĄ ĹeĹĄenĂ.ObhĂĄjenoErosion simulation is an important problem in the field of computer graphics. The most prominent erosion processes in nature are weathering and hydraulic erosion. Many methods address these problems but they are mostly based on height fields or volumetric data. Height fields do not allow the simulation of complex fully 3D scenes while the volumetric data have high memory requirements. This thesis explores the advantages of representing the eroded objects as triangular meshes and proposes solutions to problems that arise due to the use of this data structure. Triangular meshes prove to be an advantageous data structure for erosion simulations due to their adaptivity and the possibility to model complex concave features. However, the use of the triangular meshes brings new problems to the erosion simulation, such as the problem of creation of an inconsistency in the mesh due to heavy erosion or the problem of simulation of complex scenes composed of multiple materials. This thesis explores these problems and suggests possible solutions
Parallel Computation of Piecewise Linear Morse-Smale Segmentations
This paper presents a well-scaling parallel algorithm for the computation of
Morse-Smale (MS) segmentations, including the region separators and region
boundaries. The segmentation of the domain into ascending and descending
manifolds, solely defined on the vertices, improves the computational time
using path compression and fully segments the border region. Region boundaries
and region separators are generated using a multi-label marching tetrahedra
algorithm. This enables a fast and simple solution to find optimal parameter
settings in preliminary exploration steps by generating an MS complex preview.
It also poses a rapid option to generate a fast visual representation of the
region geometries for immediate utilization. Two experiments demonstrate the
performance of our approach with speedups of over an order of magnitude in
comparison to two publicly available implementations. The example section shows
the similarity to the MS complex, the useability of the approach, and the
benefits of this method with respect to the presented datasets. We provide our
implementation with the paper.Comment: Journal: IEEE Transactions on Visualization and Computer Graphics /
Submitted: 22-Jun-2022 / Accepted: 13-Mar-202
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A framework for local terrain deformation based on diffusion theory
Terrains have a key role in making outdoor virtual scenes believable and immersive as they form the support for every other natural element in the scene. Although important, terrains are often given limited interactivity in real-time applications. However, in nature, terrains are dynamic and interact with the rest of the environment changing shape on different levels, from tracks left by a person running on a gravel soil (micro-scale), to avalanches on the side of a mountain (macro-scale).
The challenge in representing dynamic terrains correctly is that the soil that forms them is vastly heterogeneous and behaves differently depending on its composition. This heterogeneity introduces difficulties at different levels in dynamic terrains simulations, from modelling the large amount of different elements that compose the oil to simulating their dynamic behaviour.
This work presents a novel framework to simulate multi-material dynamic terrains by taking into account the soil composition and its heterogeneity. In the proposed framework soil information is obtained from a material description map applied to the terrain mesh. This information is used to compute deformations in the area of interaction using a novel mathematical model based on diffusion theory. The deformations are applied to the terrain mesh in different ways depending on the distance of the area of interaction from the camera and the soil material. Deformations away from the camera are simulated by dynamically displacing normals. While deformations in a neighbourhood of the camera are represented by displacing the terrain mesh, which is locally tessellated to better fit the displacement. For gravel based soils the terrain details are added near the camera by reconstructing the meshes of the small rocks from the texture image, thus simulating both micro and macro-structure of the terrain.
The outcome of the framework is a realistic interactive dynamic terrain animation in real-time
Procedural generation of features for volumetric terrains using a rule-based approach.
Terrain generation is a fundamental requirement of many computer graphics simulations, including computer games, flight simulators and environments in feature films. Volumetric representations of 3D terrains can create rich features that are either impossible or very difficult to construct in other forms of terrain generation techniques, such as overhangs, arches and caves. While a considerable amount of literature has focused on procedural generation of terrains using heightmap-based implementations, there is little research found on procedural terrains utilising a voxel-based approach. This thesis contributes two methods to procedurally generate features for terrains that utilise a volumetric representation. The first method is a novel grammar-based approach to generate overhangs and caves from a set of rules. This voxel grammar provides a flexible and intuitive method of manipulating voxels from a set of symbol/transform pairs that can provide a variety of different feature shapes and sizes. The second method implements three parametric functions for overhangs, caves and arches. This generates a set of voxels procedurally based on the parameters of a function selected by the user. A small set of parameters for each generator function yields a widely varied set of features and provides the user with a high degree of expressivity. In order to analyse the expressivity, this thesisâ third contribution is an original method of quantitatively valuing a result of a generator function. This research is a collaboration with Sony Interactive Entertainment and their proprietary game engine PhyreEngineTM. The methods presented have been integrated into the engineâs terrain system. Thus, there is a focus on real-time performance so as to be feasible for game developers to use while adhering to strict sub-second frame times of modern computer games
Parallel Mesh Processing
Die aktuelle Forschung im Bereich der Computergrafik versucht den zunehmenden AnsprĂźchen der Anwender gerecht zu werden und erzeugt immer realistischer wirkende Bilder. Dementsprechend werden die Szenen und Verfahren, die zur Darstellung der Bilder genutzt werden, immer komplexer. So eine Entwicklung ist unweigerlich mit der Steigerung der erforderlichen Rechenleistung verbunden, da die Modelle, aus denen eine Szene besteht, aus Milliarden von Polygonen bestehen kĂśnnen und in Echtzeit dargestellt werden mĂźssen.
Die realistische Bilddarstellung ruht auf drei Säulen: Modelle, Materialien und Beleuchtung. Heutzutage gibt es einige Verfahren fßr effiziente und realistische Approximation der globalen Beleuchtung. Genauso existieren Algorithmen zur Erstellung von realistischen Materialien. Es gibt zwar auch Verfahren fßr das Rendering von Modellen in Echtzeit, diese funktionieren aber meist nur fßr Szenen mittlerer Komplexität und scheitern bei sehr komplexen Szenen.
Die Modelle bilden die Grundlage einer Szene; deren Optimierung hat unmittelbare
Auswirkungen auf die Effizienz der Verfahren zur Materialdarstellung und Beleuchtung, so dass erst eine optimierte Modellrepräsentation eine Echtzeitdarstellung ermÜglicht. Viele der in der Computergrafik verwendeten Modelle werden mit Hilfe der Dreiecksnetze repräsentiert. Das darin enthaltende Datenvolumen ist enorm, um letztlich den Detailreichtum der jeweiligen Objekte darstellen bzw. den wachsenden Realitätsanspruch bewältigen zu kÜnnen. Das Rendern von komplexen, aus Millionen von Dreiecken bestehenden
Modellen stellt selbst fĂźr moderne Grafikkarten eine groĂe Herausforderung dar.
Daher ist es insbesondere fßr die Echtzeitsimulationen notwendig, effiziente Algorithmen zu entwickeln. Solche Algorithmen sollten einerseits Visibility Culling1, Level-of-Detail, (LOD), Out-of-Core Speicherverwaltung und Kompression unterstßtzen. Anderseits sollte diese Optimierung sehr effizient arbeiten, um das Rendering nicht noch zusätzlich zu behindern. Dies erfordert die Entwicklung paralleler Verfahren, die in der Lage sind, die enorme Datenflut effizient zu verarbeiten.
Der Kernbeitrag dieser Arbeit sind neuartige Algorithmen und Datenstrukturen, die speziell fßr eine effiziente parallele Datenverarbeitung entwickelt wurden und in der Lage sind sehr komplexe Modelle und Szenen in Echtzeit darzustellen, sowie zu modellieren. Diese Algorithmen arbeiten in zwei Phasen: Zunächst wird in einer Offline-Phase die Datenstruktur erzeugt und fßr parallele Verarbeitung optimiert. Die optimierte Datenstruktur wird dann in der zweiten Phase fßr das Echtzeitrendering verwendet.
Ein weiterer Beitrag dieser Arbeit ist ein Algorithmus, welcher in der Lage ist, einen sehr realistisch wirkenden Planeten prozedural zu generieren und in Echtzeit zu rendern
Simulation of a flowing snow avalanche using molecular dynamics
Ankara : The Department of Computer Engineering and the Institute of Engineering and Science of Bilkent University, 2010.Thesis (Master's) -- Bilkent University, 2010.Includes bibliographical references leaves 45-50.This thesis presents an approach for modeling and simulation of a flowing snow avalanche, which is formed of dry and liquefied snow that slides down a slope, by using molecular dynamics and discrete element method. A particle system is utilized as a base method for the simulation and marching cubes with real-time shaders are employed for rendering. A uniform grid based neighbor search algorithm is used for collision detection for inter-particle and particle-terrain interactions. A mass-spring model of collision resolution is employed to mimic compressibility of snow and particle attraction forces are put into use between particles and terrain surface. In order to achieve greater performance, general purpose GPU language and multi-threaded program-ming is utilized for collision detection and resolution. The results are dis-played with different combinations of rendering methods for the realistic re-presentation of the flowing avalanche.Gßçer, DenizhanM.S
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