10 research outputs found
Hybrid Hierarchical Collision Detection Based on Data Reuse
To improve the efficiency of collision detection between rigid bodies in complex scenes, this paper proposes a method based on hybrid bounding volume hierarchies for collision detection. In order to improve the simulation performance, the method is based on weighted oriented bounding box and makes dense sampling on the convex hulls of the geometric models. The hierarchical bounding volume tree is composed of many layers. The uppermost layer adopts a cubic bounding box, while lower layers employ weighted oriented bounding box. In the meantime, the data of weighted oriented bounding box is reused for triangle intersection check. We test the method using two scenes. The first scene contains two Buddha models with totally 361,690 triangle facets. The second scene is composed of 200 models with totally 115, 200 triangle facets. The experiments verify the effectiveness of the proposed method
A Broad Phase Collision Detection Algorithm Adapted to Multi-cores Architectures
International audienceRecent years have seen the impressive evolution of graphics hardware and processors architecture from single core to multi and many-core architectures. Confronted to this evolution, new trends in collision detection optimisation consist in proposing a solution that maps on the runtime architecture. We present, in this paper, two contributions in the field of collision detection in large-scale environments. We present a first way to parallelise, on a multi-core architecture, the initial step of the collision detection pipeline: the broad-phase. Then, we describe a new formalism of the collision detection pipeline that takes into account runtime architecture. The well-known broadphase algorithm used is the ”Sweep and Prune” and it has been adapted to a multi-threading use. To handle one or more thread per core, critical writing sections and threads idling must be minimised. Our model is able to work on a n-core architecture reducing computation time to detect collision between 3D objects in a large-scale environment
Improvements to physically based cloth simulation
Physically based cloth simulation in computer graphics has come a long way since the 1980s. Although extensive methods have been developed, physically based cloth animation remains challenging in a number of aspects, including the efficient simulation of complex internal dynamics, better performance and the generation of more effects of friction in collisions, to name but a few. These opportunities motivate the work presented in this thesis to improve on current state of the art in cloth simulation by proposing methods for cloth bending deformation simulation, collision detection and friction in collision response. The structure of the thesis is as follows. A literature review of work related to physically based cloth simulation including aspects of internal dynamics, collision handling and GPU computing for cloth simulation is given in Chapter 2. In order to provide a basis for understanding of the work of the subsequent chapters of the thesis, Chapter 3 describes and discusses main components of our physically based cloth simulation framework which can be seen as the basis of our developments, as methods presented in the following chapters use this framework. Chapter 4 presents an approach that effectively models cloth non-linear features in bending behaviour, such as energy dissipation, plasticity and fatigue weakening. This is achieved by a simple mathematical approximation to an ideal hysteresis loop at a high level, while in textile research bending non-linearity is computed using complex internal friction models at the geometric structure level. Due to cloth flexibility and the large quantity of triangles, in a robust cloth system collision detection is the most time consuming task. The approach proposed in Chapter 5 improves performance of collision detection using a GPU-based approach employing spatial subdivision. It addresses a common issue, uneven triangle sizes, which can easily impair the spatial subdivision efficiency. To achieve this, a virtual subdivision scheme with a uniform grid is used to virtually subdivide large triangles, resulting in a more appropriate cell size and thus a more efficient subdivision. The other common issue that limits the subdivision efficiency is uneven triangle spatial distributions, and is difficult to tackle via uniform grids because areas with different triangle densities may require different cell sizes. In order to address this problem, Chapter 6 shows how to build an octree grid to adaptively partition space according to triangle spatial distribution on a GPU, which delivers further improvements in the performance of collision detection. Friction is an important component in collision response. Frictional effects include phenomena that are velocity dependent, such as stiction, Stribeck friction, viscous friction and the stick-slip phenomenon, which are not modelled by the classic Coulomb friction model adopted by existing cloth systems. Chapter 7 reports a more comprehensive friction model to capture these additional effects. Chapter 8 concludes this thesis and briefly discusses potential avenues for future work
The application of three-dimensional mass-spring structures in the real-time simulation of sheet materials for computer generated imagery
Despite the resources devoted to computer graphics technology over the last 40 years,
there is still a need to increase the realism with which flexible materials are simulated.
However, to date reported methods are restricted in their application by their use of
two-dimensional structures and implicit integration methods that lend themselves to
modelling cloth-like sheets but not stiffer, thicker materials in which bending moments
play a significant role.
This thesis presents a real-time, computationally efficient environment for simulations
of sheet materials. The approach described differs from other techniques principally
through its novel use of multilayer sheet structures. In addition to more accurately
modelling bending moment effects, it also allows the effects of increased temperature
within the environment to be simulated. Limitations of this approach include the
increased difficulties of calibrating a realistic and stable simulation compared to
implicit based methods.
A series of experiments are conducted to establish the effectiveness of the technique,
evaluating the suitability of different integration methods, sheet structures, and
simulation parameters, before conducting a Human Computer Interaction (HCI) based
evaluation to establish the effectiveness with which the technique can produce credible
simulations. These results are also compared against a system that utilises an
established method for sheet simulation and a hybrid solution that combines the use of
3D (i.e. multilayer) lattice structures with the recognised sheet simulation approach.
The results suggest that the use of a three-dimensional structure does provide a level of
enhanced realism when simulating stiff laminar materials although the best overall
results were achieved through the use of the hybrid model
Real-time simulation and visualisation of cloth using edge-based adaptive meshes
Real-time rendering and the animation of realistic virtual environments and characters
has progressed at a great pace, following advances in computer graphics hardware
in the last decade. The role of cloth simulation is becoming ever more important in
the quest to improve the realism of virtual environments.
The real-time simulation of cloth and clothing is important for many applications
such as virtual reality, crowd simulation, games and software for online clothes shopping.
A large number of polygons are necessary to depict the highly
exible nature of
cloth with wrinkling and frequent changes in its curvature. In combination with the
physical calculations which model the deformations, the effort required to simulate
cloth in detail is very computationally expensive resulting in much diffculty for its
realistic simulation at interactive frame rates. Real-time cloth simulations can lack
quality and realism compared to their offline counterparts, since coarse meshes must
often be employed for performance reasons.
The focus of this thesis is to develop techniques to allow the real-time simulation of
realistic cloth and clothing. Adaptive meshes have previously been developed to act as
a bridge between low and high polygon meshes, aiming to adaptively exploit variations
in the shape of the cloth. The mesh complexity is dynamically increased or refined to
balance quality against computational cost during a simulation. A limitation of many
approaches is they do not often consider the decimation or coarsening of previously
refined areas, or otherwise are not fast enough for real-time applications.
A novel edge-based adaptive mesh is developed for the fast incremental refinement
and coarsening of a triangular mesh. A mass-spring network is integrated into
the mesh permitting the real-time adaptive simulation of cloth, and techniques are
developed for the simulation of clothing on an animated character
Simulation inkompressibler deformierbarer Körper
Die computergestützte Simulation von Bewegungsabläufen wird immer wichtiger in vielen Anwendungsgebieten. Einsatzgebiete von dynamischen Simulationen sind beispielsweise die Erstellung von Computeranimationen für Filme, Anwendungen in der virtuellen Realität oder für Computerspiele. In diesen Gebieten genügen oft plausible Ergebnisse, die dem Anwender das Gefühl einer realistischen Bewegung vermitteln. Hier kann die Simulation volumenerhaltender Körper zur Verbesserung der visuellen Plausibilität
New geometric algorithms and data structures for collision detection of dynamically deforming objects
Any virtual environment that supports interactions between virtual objects and/or a user and objects,
needs a collision detection system to handle all interactions in a physically correct or plausible way. A
collision detection system is needed to determine if objects are in contact or interpenetrates. These
interpenetrations are resolved by a collision handling system. Because of the fact, that in nearly all
simulations objects can interact with each other, collision detection is a fundamental technology, that
is needed in all these simulations, like physically based simulation, robotic path and motion planning,
virtual prototyping, and many more. Most virtual environments aim to represent the real-world as
realistic as possible and therefore, virtual environments getting more and more complex. Furthermore,
all models in a virtual environment should interact like real objects do, if forces are applied to the
objects. Nearly all real-world objects will deform or break down in its individual parts if forces are
acted upon the objects. Thus deformable objects are becoming more and more common in virtual
environments, which want to be as realistic as possible and thus, will present new challenges to the
collision detection system. The necessary collision detection computations can be very complex and this
has the effect, that the collision detection process is the performance bottleneck in most simulations.
Most rigid body collision detection approaches use a BVH as acceleration data structure. This
technique is perfectly suitable if the object does not change its shape. For a soft body an update step
is necessary to ensure that the underlying acceleration data structure is still valid after performing a
simulation step. This update step can be very time consuming, is often hard to implement and in most
cases will produce a degenerated BVH after some simulation steps, if the objects generally deform.
Therefore, the here presented collision detection approach works entirely without an acceleration data
structure and supports rigid and soft bodies. Furthermore, we can compute inter-object and intraobject
collisions of rigid and deformable objects consisting of many tens of thousands of triangles in a
few milliseconds. To realize this, a subdivision of the scene into parts using a fuzzy clustering approach
is applied. Based on that all further steps for each cluster can be performed in parallel and if desired,
distributed to different GPUs. Tests have been performed to judge the performance of our approach
against other state-of-the-art collision detection algorithms. Additionally, we integrated our approach
into Bullet, a commonly used physics engine, to evaluate our algorithm.
In order to make a fair comparison of different rigid body collision detection algorithms, we propose
a new collision detection Benchmarking Suite. Our Benchmarking Suite can evaluate both the performance
as well as the quality of the collision response. Therefore, the Benchmarking Suite is subdivided
into a Performance Benchmark and a Quality Benchmark. This approach needs to be extended to
support soft body collision detection algorithms in the future.Jede virtuelle Umgebung, welche eine Interaktion zwischen den virtuellen Objekten in der Szene
zulässt und/oder zwischen einem Benutzer und den Objekten, benötigt für eine korrekte Behandlung der
Interaktionen eine Kollisionsdetektion. Nur dank der Kollisionsdetektion können Berührungen zwischen
Objekten erkannt und mittels der Kollisionsbehandlung aufgelöst werden. Dies ist der Grund für die weite
Verbreitung der Kollisionsdetektion in die verschiedensten Fachbereiche, wie der physikalisch basierten
Simulation, der Pfadplanung in der Robotik, dem virtuellen Prototyping und vielen weiteren. Auf Grund
des Bestrebens, die reale Umgebung in der virtuellen Welt so realistisch wie möglich nachzubilden,
steigt die Komplexität der Szenen stetig. Fortwährend steigen die Anforderungen an die Objekte, sich
realistisch zu verhalten, sollten Kräfte auf die einzelnen Objekte ausgeübt werden. Die meisten Objekte,
die uns in unserer realen Welt umgeben, ändern ihre Form oder zerbrechen in ihre Einzelteile, wenn
Kräfte auf sie einwirken. Daher kommen in realitätsnahen, virtuellen Umgebungen immer häufiger
deformierbare Objekte zum Einsatz, was neue Herausforderungen an die Kollisionsdetektion stellt. Die
hierfür Notwendigen, teils komplexen Berechnungen, führen dazu, dass die Kollisionsdetektion häufig
der Performance-Bottleneck in der jeweiligen Simulation darstellt.
Die meisten Kollisionsdetektionen für starre Körper benutzen eine Hüllkörperhierarchie als Beschleunigungsdatenstruktur.
Diese Technik ist hervorragend geeignet, solange sich die Form des Objektes
nicht verändert. Im Fall von deformierbaren Objekten ist eine Aktualisierung der Datenstruktur nach
jedem Schritt der Simulation notwendig, damit diese weiterhin gültig ist. Dieser Aktualisierungsschritt
kann, je nach Hierarchie, sehr zeitaufwendig sein, ist in den meisten Fällen schwer zu implementieren
und generiert nach vielen Schritten der Simulation häufig eine entartete Hüllkörperhierarchie, sollte
sich das Objekt sehr stark verformen. Um dies zu vermeiden, verzichtet unsere Kollisionsdetektion vollständig
auf eine Beschleunigungsdatenstruktur und unterstützt sowohl rigide, wie auch deformierbare
Körper. Zugleich können wir Selbstkollisionen und Kollisionen zwischen starren und/oder deformierbaren
Objekten, bestehend aus vielen Zehntausenden Dreiecken, innerhalb von wenigen Millisekunden
berechnen. Um dies zu realisieren, unterteilen wir die gesamte Szene in einzelne Bereiche mittels eines
Fuzzy Clustering-Verfahrens. Dies ermöglicht es, dass alle Cluster unabhängig bearbeitet werden und
falls gewünscht, die Berechnungen für die einzelnen Cluster auf verschiedene Grafikkarten verteilt werden
können. Um die Leistungsfähigkeit unseres Ansatzes vergleichen zu können, haben wir diesen gegen
aktuelle Verfahren für die Kollisionsdetektion antreten lassen. Weiterhin haben wir unser Verfahren in
die Physik-Engine Bullet integriert, um das Verhalten in dynamischen Situationen zu evaluieren.
Um unterschiedliche Kollisionsdetektionsalgorithmen für starre Körper korrekt und objektiv miteinander
vergleichen zu können, haben wir eine Benchmarking-Suite entwickelt. Unsere Benchmarking-
Suite kann sowohl die Geschwindigkeit, für die Bestimmung, ob zwei Objekte sich durchdringen, wie
auch die Qualität der berechneten Kräfte miteinander vergleichen. Hierfür ist die Benchmarking-Suite
in den Performance Benchmark und den Quality Benchmark unterteilt worden. In der Zukunft wird
diese Benchmarking-Suite dahingehend erweitert, dass auch Kollisionsdetektionsalgorithmen für deformierbare
Objekte unterstützt werden
Efficient configuration space construction and optimization
The configuration space is a fundamental concept that is widely used in algorithmic robotics. Many applications in robotics, computer-aided design, and related areas can be reduced to computational problems in terms of configuration spaces. In this dissertation, we address three main computational challenges related to configuration spaces: 1) how to efficiently compute an approximate representation of high-dimensional configuration spaces; 2) how to efficiently perform geometric, proximity, and motion planning queries in high dimensional configuration spaces; and 3) how to model uncertainty in configuration spaces represented by noisy sensor data. We present new configuration space construction algorithms based on machine learning and geometric approximation techniques. These algorithms perform collision queries on many configuration samples. The collision query results are used to compute an approximate representation for the configuration space, which quickly converges to the exact configuration space. We highlight the efficiency of our algorithms for penetration depth computation and instance-based motion planning. We also present parallel GPU-based algorithms to accelerate the performance of optimization and search computations in configuration spaces. In particular, we design efficient GPU-based parallel k-nearest neighbor and parallel collision detection algorithms and use these algorithms to accelerate motion planning. In order to extend configuration space algorithms to handle noisy sensor data arising from real-world robotics applications, we model the uncertainty in the configuration space by formulating the collision probabilities for noisy data. We use these algorithms to perform reliable motion planning for the PR2 robot.Doctor of Philosoph