219 research outputs found
Visualization and inspection of the geometry of particle packings
Gegenstand dieser Dissertation ist die Entwicklung von effizienten Verfahren zur Visualisierung und
Inspektion der Geometrie von Partikelmischungen. Um das Verhalten der Simulation für die
Partikelmischung besser zu verstehen und zu überwachen, sollten nicht nur die Partikel selbst, sondern auch
spezielle von den Partikeln gebildete Bereiche, die den Simulationsfortschritt und die räumliche Verteilung
von Hotspots anzeigen können, visualisiert werden können. Dies sollte auch bei großen Packungen mit
Millionen von Partikeln zumindest mit einer interaktiven Darstellungsgeschwindigkeit möglich sein. . Da
die Simulation auf der Grafikkarte (GPU) durchgeführt wird, sollten die Visualisierungstechniken die Daten
des GPU-Speichers vollständig nutzen.
Um die Qualität von trockenen Partikelmischungen wie Beton zu verbessern, wurde der
Korngrößenverteilung große Aufmerksamkeit gewidmet, die die Raumfüllungsrate hauptsächlich
beeinflusst und daher zwei der wichtigsten Eigenschaften des Betons bestimmt: die strukturelle Robustheit
und die Haltbarkeit. Anhand der Korngrößenverteilung kann die Raumfüllungsrate durch
Computersimulationen bestimmt werden, die analytischen Ansätzen in der Praxis wegen der breiten
Größenverteilung der Partikel oft überlegen sind. Eine der weit verbreiteten Simulationsmethoden ist das
Collective Rearrangement, bei dem die Partikel zunächst an zufälligen Positionen innerhalb eines Behälters
platziert werden. Später werden Überlappungen zwischen Partikeln aufgelöst, indem überlappende Partikel
voneinander weggedrückt werden. Durch geschickte Anpassung der Behältergröße während der Simulation,
kann die Collective Rearrangement-Methode am Ende eine ziemlich dichte Partikelpackung generieren.
Es ist jedoch sehr schwierig, den gesamten Simulationsprozess ohne ein interaktives Visualisierungstool zu
optimieren oder dort Fehler zu finden.
Ausgehend von der etablierten rasterisierungsbasierten Methode zum Darstellen einer großen Menge von
Kugeln, bietet diese Dissertation zunächst schnelle und pixelgenaue Methoden zur neuartigen
Visualisierung der Überlappungen und Freiräume zwischen kugelförmigen Partikeln innerhalb eines
Behälters.. Die auf Rasterisierung basierenden Verfahren funktionieren gut für kleinere Partikelpackungen
bis ca. eine Million Kugeln. Bei größeren Packungen entstehen Probleme durch die lineare Laufzeit und
den Speicherverbrauch. Zur Lösung dieses Problems werden neue Methoden mit Hilfe von Raytracing
zusammen mit zwei neuen Arten von Bounding-Volume-Hierarchien (BVHs) bereitgestellt. Diese können
den Raytracing-Prozess deutlich beschleunigen --- die erste kann die vorhandene Datenstruktur für die
Simulation wiederverwenden und die zweite ist speichereffizienter. Beide BVHs nutzen die Idee des Loose
Octree und sind die ersten ihrer Art, die die Größe von Primitiven für interaktives Raytracing mit häufig
aktualisierten Beschleunigungsdatenstrukturen berücksichtigen. Darüber hinaus können die
Visualisierungstechniken in dieser Dissertation auch angepasst werden, um Eigenschaften wie das
Volumen bestimmter Bereiche zu berechnen.
All diese Visualisierungstechniken werden dann auf den Fall nicht-sphärischer Partikel erweitert, bei denen
ein nicht-sphärisches Partikel durch ein starres System von Kugeln angenähert wird, um die vorhandene
kugelbasierte Simulation wiederverwenden zu können. Dazu wird auch eine neue GPU-basierte Methode
zum effizienten Füllen eines nicht-kugelförmigen Partikels mit polydispersen überlappenden Kugeln
vorgestellt, so dass ein Partikel mit weniger Kugeln gefüllt werden kann, ohne die Raumfüllungsrate zu
beeinträchtigen. Dies erleichtert sowohl die Simulation als auch die Visualisierung.
Basierend auf den Arbeiten in dieser Dissertation können ausgefeiltere Algorithmen entwickelt werden, um
großskalige nicht-sphärische Partikelmischungen effizienter zu visualisieren. Weiterhin kann in Zukunft
Hardware-Raytracing neuerer Grafikkarten anstelle des in dieser Dissertation eingesetzten Software-Raytracing verwendet werden. Die neuen Techniken können auch als Grundlage für die interaktive
Visualisierung anderer partikelbasierter Simulationen verwendet werden, bei denen spezielle Bereiche wie
Freiräume oder Überlappungen zwischen Partikeln relevant sind.The aim of this dissertation is to find efficient techniques for visualizing and inspecting the geometry of
particle packings. Simulations of such packings are used e.g. in material sciences to predict properties of
granular materials. To better understand and supervise the behavior of these simulations, not only the
particles themselves but also special areas formed by the particles that can show the progress of the
simulation and spatial distribution of hot spots, should be visualized. This should be possible with a frame
rate that allows interaction even for large scale packings with millions of particles. Moreover, given the
simulation is conducted in the GPU, the visualization techniques should take full use of the data in the GPU
memory.
To improve the performance of granular materials like concrete, considerable attention has been paid to the
particle size distribution, which is the main determinant for the space filling rate and therefore affects two
of the most important properties of the concrete: the structural robustness and the durability. Given the
particle size distribution, the space filling rate can be determined by computer simulations, which are often
superior to analytical approaches due to irregularities of particles and the wide range of size distribution in
practice. One of the widely adopted simulation methods is the collective rearrangement, for which particles
are first placed at random positions inside a container, later overlaps between particles will be resolved by
letting overlapped particles push away from each other to fill empty space in the container. By cleverly
adjusting the size of the container according to the process of the simulation, the collective rearrangement
method could get a pretty dense particle packing in the end. However, it is very hard to fine-tune or debug
the whole simulation process without an interactive visualization tool.
Starting from the well-established rasterization-based method to render spheres, this dissertation first
provides new fast and pixel-accurate methods to visualize the overlaps and free spaces between spherical
particles inside a container. The rasterization-based techniques perform well for small scale particle
packings but deteriorate for large scale packings due to the large memory requirements that are hard to be
approximated correctly in advance. To address this problem, new methods based on ray tracing are provided
along with two new kinds of bounding volume hierarchies (BVHs) to accelerate the ray tracing process ---
the first one can reuse the existing data structure for simulation and the second one is more memory efficient.
Both BVHs utilize the idea of loose octree and are the first of their kind to consider the size of primitives
for interactive ray tracing with frequently updated acceleration structures. Moreover, the visualization
techniques provided in this dissertation can also be adjusted to calculate properties such as volumes of the
specific areas.
All these visualization techniques are then extended to non-spherical particles, where a non-spherical
particle is approximated by a rigid system of spheres to reuse the existing simulation. To this end a new
GPU-based method is presented to fill a non-spherical particle with polydisperse possibly overlapping
spheres efficiently, so that a particle can be filled with fewer spheres without sacrificing the space filling
rate. This eases both simulation and visualization.
Based on approaches presented in this dissertation, more sophisticated algorithms can be developed to
visualize large scale non-spherical particle mixtures more efficiently. Besides, one can try to exploit the
hardware ray tracing of more recent graphic cards instead of maintaining the software ray tracing as in this
dissertation. The new techniques can also become the basis for interactively visualizing other particle-based
simulations, where special areas such as free space or overlaps between particles are of interest
Object Hierarchies for Efficient Rendering
This thesis covers the efficient visualization of complex 3d scenes using various rendering methods such as photo-realistic and real-time rendering. Especially the important role of bounding volume hierarchies is discussed in detail in the context of illumination and visibility algorithms. We present a novel approach for automatic generation of object hierarchies and apply the resulting data structure to several rendering techniques. In the field of ray tracing we describe a novel ray acceleration method that combines objects hierarchies and regular grids. We demonstrate how radiosity computations may benefit from available scene hierarchies to determine the radiant flux between object clusters. Finally, we present an adaptive interactive rendering algorithm that may dramatically reduce the number of visibility tests in an occlusion culling framework for interactive real-time visualization.Diese Dissertation untersucht unterschiedliche Verfahren zur effizienten Visualisierung grosser dreidimensionaler Szenengeometrien, sowohl im Bereich des Photorealismus wie auch bei der Echtzeit-Visualisierung. Hierbei wird insbesondere die Nützlichkeit von Hüllkörperhierarchien bei der Beleuchtungsrechnung und bei der Beantwortung von Sichtbarkeitsfragen herausgearbeitet. Ein neuartiges, kostenbasiertes Verfahren zur automatischen Konstruktion von Objekthierarchien wird präsentiert sowie dessen Anwendung für alle gängigen Darstellungsverfahren. Zusätzlich beschreibt diese Disseration im Bereich Ray Tracing ein neues Verfahren zur Szenenstrukturierung, welches die Vorteile von Hüllkörperhierarchien und regulären Gittern kombiniert. Im Bereich der Radiosity wird gezeigt, wie sich Szenenhierarchien ideal zur Berechnung des Lichtflusses zwischen Objekt-Clustern nutzen lassen und im Bereich Echtzeit-Rendering wird ein adaptives Verfahren vorgestellt, dass die Zahl teurer Sichtbarkeitstests beim Occlusion-Culling deutlich reduziert
Ray Tracing Methods for Point Cloud Rendering
State of the art scanning and capturing devices are able to produce surface point cloud models of a wide range of real world objects. The visualization and rendering of enormous point clouds with millions or billions of points is demanding. VR- and AR-applications can utilize embedded real world objects in generating visually pleasing and immersive virtual worlds. In order to achieve convincing real life equivalents in VR, rendering techniques that can replicate realistic material and lighting effects are needed. This can be achieved by utilizing ray tracing methods to render the virtual world onto a monitor or a head-mounted display.
Virtual reality applications need real-time stereoscopic rendering with high frame rates and resolution to produce a realistic and comfortable experience. This sets high demands on a point cloud ray tracing pipeline, which needs efficient intersection testing between rays and point cloud models. An easily intersectable global surface can be reconstructed from the point cloud model with, e.g., triangle mesh reconstruction. However, this can be computationally demanding and even wasteful if parts of the model are out of view or occluded. Direct point cloud ray tracing methods consider local features of the point cloud to generate intersectable surfaces only when needed.
In this thesis, we survey and compare different methods for directly ray tracing point cloud models without global surface reconstruction. Methods are compared with asymptotic complexity analysis and it is concluded that direct ray tracing of point clouds can be computationally more efficient compared to global surface reconstruction
Ray Tracing Structured AMR Data Using ExaBricks
Structured Adaptive Mesh Refinement (Structured AMR) enables simulations to
adapt the domain resolution to save computation and storage, and has become one
of the dominant data representations used by scientific simulations; however,
efficiently rendering such data remains a challenge. We present an efficient
approach for volume- and iso-surface ray tracing of Structured AMR data on
GPU-equipped workstations, using a combination of two different data
structures. Together, these data structures allow a ray tracing based renderer
to quickly determine which segments along the ray need to be integrated and at
what frequency, while also providing quick access to all data values required
for a smooth sample reconstruction kernel. Our method makes use of the RTX ray
tracing hardware for surface rendering, ray marching, space skipping, and
adaptive sampling; and allows for interactive changes to the transfer function
and implicit iso-surfacing thresholds. We demonstrate that our method achieves
high performance with little memory overhead, enabling interactive high quality
rendering of complex AMR data sets on individual GPU workstations
AMM: Adaptive Multilinear Meshes
We present Adaptive Multilinear Meshes (AMM), a new framework that
significantly reduces the memory footprint compared to existing data
structures. AMM uses a hierarchy of cuboidal cells to create continuous,
piecewise multilinear representation of uniformly sampled data. Furthermore,
AMM can selectively relax or enforce constraints on conformity, continuity, and
coverage, creating a highly adaptive and flexible representation to support a
wide range of use cases. AMM supports incremental updates in both spatial
resolution and numerical precision establishing the first practical data
structure that can seamlessly explore the tradeoff between resolution and
precision. We use tensor products of linear B-spline wavelets to create an
adaptive representation and illustrate the advantages of our framework. AMM
provides a simple interface for evaluating the function defined on the adaptive
mesh, efficiently traversing the mesh, and manipulating the mesh, including
incremental, partial updates. Our framework is easy to adopt for standard
visualization and analysis tasks. As an example, we provide a VTK interface,
through efficient on-demand conversion, which can be used directly by
corresponding tools, such as VisIt, disseminating the advantages of faster
processing and a smaller memory footprint to a wider audience. We demonstrate
the advantages of our approach for simplifying scalar-valued data for commonly
used visualization and analysis tasks using incremental construction, according
to mixed resolution and precision data streams
Ray tracing geometric models and parametric surfaces
Ankara : The Department of Computer Engineering and Information Sciences and the Institute of Engineering and Science of Bilkent Univ. , 1989.Thesis (Master's) -- Bilkent University, 1989.Includes bibliographical references leaves 42-46.In many computer graphics applications such as CAD, realistic displays
have very important and positive effects on designers using the system. There
axe several techniques to generate realistic images with the computer. Ray
tracing gives the most effective results by simulating the interaction of light
with its environment. Furthermore, this technique can be easily adopted to
many physical phenomena such as reflection, refraction, shadows, etc. by
which the interaction of many different objects with each other could be
realistically simulated. However, it may require excessive amount of time
to generate an image. In this thesis , we studied the ray tracing algorithm
arid the speed problem associated with it and several methods developed to
overcome this problem. We also implemented a ray tracer system that could
be used to model a three dimensional scene and And out the lighting effects
on the objects.İşler, VeysiM.S
Sparse Volumetric Deformation
Volume rendering is becoming increasingly popular as applications require realistic solid shape representations with seamless texture mapping and accurate filtering. However rendering sparse volumetric data is difficult because of the limited memory and processing capabilities of current hardware. To address these limitations, the volumetric information can be stored at progressive resolutions in the hierarchical branches of a tree structure, and sampled according to the region of interest. This means that only a partial region of the full dataset is processed, and therefore massive volumetric scenes can be rendered efficiently.
The problem with this approach is that it currently only supports static scenes. This is because it is difficult to accurately deform massive amounts of volume elements and reconstruct the scene hierarchy in real-time. Another problem is that deformation operations distort the shape where more than one volume element tries to occupy the same location, and similarly gaps occur where deformation stretches the elements further than one discrete location. It is also challenging to efficiently support sophisticated deformations at hierarchical resolutions, such as character skinning or physically based animation. These types of deformation are expensive and require a control structure (for example a cage or skeleton) that maps to a set of features to accelerate the deformation process. The problems with this technique are that the varying volume hierarchy reflects different feature sizes, and manipulating the features at the original resolution is too expensive; therefore the control structure must also hierarchically capture features according to the varying volumetric resolution.
This thesis investigates the area of deforming and rendering massive amounts of dynamic volumetric content. The proposed approach efficiently deforms hierarchical volume elements without introducing artifacts and supports both ray casting and rasterization renderers. This enables light transport to be modeled both accurately and efficiently with applications in the fields of real-time rendering and computer animation. Sophisticated volumetric deformation, including character animation, is also supported in real-time. This is achieved by automatically generating a control skeleton which is mapped to the varying feature resolution of the volume hierarchy. The output deformations are demonstrated in massive dynamic volumetric scenes
Automatische Erstellung von Objekthierarchien zum Ray Tracing von dynamischen Szenen
Ray tracing acceleration techniques most often consider only static scenes, neglecting the processing time needed to build the acceleration data structure. With the development of interactive ray tracing systems, this reconstruction time becomes a serious bottleneck if concerned with dynamic scenes. In this paper, we describe two strategies for effcient updating of bounding volume hierarchies (BVH) for scenarios with arbitrarily moving objects. The first exploits spatial locality in the object distribution for faster reinsertion of the moved objects. The second allows insertion and deletion of objects at almost constant time by using a hybrid system, which combines benefits from both spatial subdivision and BVHs. Depending on the number of moving objects, our algorithms adjust a dynamic BVH six to one hundred times faster than it would take to rebuild the complete hierarchy, while rendering times of the resulting hierarchy remain almost untouched.Beschleunigungstechniken für Ray Tracing (Strahlverfolgung) sind meist lediglich für statische Szenen ausgelegt, und wenig Aufmerksamkeit wird auf die Zeit gelegt, welche zur Erstellung der Beschleunigungsdatenstruktur benötigt wird. Mit der Entwicklung interaktiver Ray Tracing Systeme wird dieser Rekonstruktionszeit jedoch zum Flaschenhals, falls man mit dynamischen Szenen arbeitet. In diesem Report werden zwei Strategien für eine effiziente Aktualisierung von Bounding Volume Hierarchien vorgestellt, ausgelegt auf Szenarien mit beliebig bewegten Objekten. Die erste nutzt räumliche Lokalitäten in der Objektverteilung um den Einfügeprozess für bewegten Objekte zu verkürzen. Die zweite Methode erlaubt das Einfügen und Löschen von Objekten in nahezu konstanter Zeit, indem ein hybrides System verwendet wird, welches die Vorteile spatialer Datenstrukturen und Bounding Volume Hierarchien miteinander verknüpft. Abhängig von der Anzahl an bewegten Objekten, können unsere Algorithmen eine bestehende Bounding Volume Hierarchie sech bis hundertmal so schnell anpassen, wie ein kompletter Neuaufbau benötigen würde. Die benötigte Zeit zum Rendern der Szene bleibt jedoch nahezu unberührt im Vergleich
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