28 research outputs found
Energy-precision tradeoffs in the graphics pipeline
The energy consumption of a graphics processing unit (GPU) is an important factor in its design, whether for a server, desktop, or mobile device. Mobile products, such as smart phones, tablets, and laptop computers, rely on batteries to function; the less the demand for power is on these batteries, the longer they will last before needing to be recharged. GPUs used in servers and desktops, while not dependent on a battery for operation, are still limited by the efficiency of power supplies and heat dissipation techniques. In this dissertation, I propose to lower the energy consumption of GPUs by reducing the precision of floating-point arithmetic in the graphics pipeline and the data sent and stored on- and off-chip. The key idea behind this work is twofold: energy can be saved through a systematic and targeted reduction in the number of bits 1) computed and 2) communicated. Reducing the number of bits computed will necessarily reduce either the precision or range of a floating point number. I focus on saving energy by way of reducing precision, which can exploit the over-provisioning of bits in many stages of the graphics pipeline. Reducing the number of bits communicated takes several forms. First, I propose enhancements to existing compression schemes for off-chip buffers to save bandwidth. I also suggest a simple extension that exploits unused bits in reduced-precision data undergoing compression. Finally, I present techniques for saving energy in on-chip communication of reduced-precision data. By designing and simulating variable-precision arithmetic circuits with promising energy versus precision characteristics and tradeoffs, I have developed an energy model for GPUs. Using this model and my techniques, I have shown that significant savings (up to 70% in computation in the vertex and pixel shader stages) are possible by reducing the precision of the arithmetic. Further, my compression approaches have enabled improvements of 1.26x over past work, and a general-purpose compressor design has achieved bandwidth savings of 34%, 87%, and 65% for color, depth, and geometry data, respectively, which is competitive with past work. Lastly, an initial exploration in signal gating unused lines in on-chip buses has suggested savings of 13-48% for the tested applications' traffic from a multiprocessor's register file to its L1 cache
Atmospheric cloud representation methods in computer graphics: A review
Cloud representation is one of the important components in the atmospheric cloud visualization system. Lack of review papers on the cloud representation methods available in the area of computer graphics has directed towards the difficulty for researchers to understand the appropriate solutions. Therefore, this paper aims to provide a comprehensive review of the atmospheric cloud representation methods that have been proposed in the computer graphics domain, involving the classical and the current state-of-the-art approaches. The reviewing process was conducted by searching, selecting, and analyzing the prominent articles collected from online digital libraries and search engines. We highlighted the taxonomic classification of the existing cloud representation methods in solving the atmospheric cloud-related problems. Finally, research issues and directions in the area of cloud representations and visualization have been discussed. This review would be significantly beneficial for researchers to clearly understand the general picture of the existing methods and thus helping them in choosing the best-suited approach for their future research and development
Particle based modeling and simulation of natural phenomena
Ankara : The Department of Computer Engineering and the Institute of Engineering and Science of Bilkent University, 2010.Thesis (Ph. D.) -- Bilkent University, 2010.Includes bibliographical references leaves 92-108.This thesis is about modeling and simulation of fluids and cloth-like deformable
objects by the physically-based simulation paradigm. Simulated objects are modeled
with particles and their interaction with each other and the environment is
defined by particle-to-particle forces. We propose several improvements over the
existing particle simulation techniques. Neighbor search algorithms are crucial
for the performance efficiency and robustness of a particle system. We present a
sorting-based neighbor search method which operates on a uniform grid, and can
be parallelizable. We improve upon the existing fluid surface generation methods
so that our method captures surface details better since we consider the relative
position of fluid particles to the fluid surface. We investigate several alternatives
of particle interaction schema (i.e. Smoothed Particle Hydrodynamics, the Discrete
Element Method, and Lennard-Jones potential) for the purpose of defining
fluid-fluid, fluid-cloth, fluid-boundary interaction forces. We also propose a practical
way to simulate knitwear and its interaction with fluids. We employ capillary
pressureābased forces to simulate the absorption of fluid particles by knitwear.
We also propose a method to simulate the flow of miscible fluids. Our particle
simulation system is implement to exploit parallel computing capabilities of the
commodity computers. Specifically, we implemented the proposed methods on
multicore CPUs and programmable graphics boards. The experiments show that
our method is computationally efficient and produces realistic results.Bayraktar, SerkanPh.D
Shape deformations based on vector fields
This thesis explores applications of vector field processing to shape deformations. We present a novel method to construct divergence-free vector fields which are used to deform shapes by vector field integration (Chapter 2). The resulting deformation is volume-preserving and no self-intersections occur. We add more controllability to this approach by introducing implicit boundaries (Chapter 3), a shape editing method which resembles the well-known boundary constraint modeling metaphor. While the vector fields are originally defined in space, we also present a surface-based version of this approach which allows for more exact boundary selection and deformation control (Chapter 4). We show that vectorfield- based shape deformations can be used to animate elastic motions without complex physical simulations (Chapter 5). We also introduce an alternative approach to exactly preserve the volume of skinned triangle meshes (Chapter 6). This is accomplished by constructing a displacement field on the mesh surface which restores the original volume after deformation. Finally, we demonstrate that shape deformation by vector field integration can also be used to visualize smoke-like streak surfaces in dynamic flow fields (Chapter 7).In dieser Dissertation werden verschiedene Anwendungen der Vektorfeldverarbeitung im Bereich Objektdeformation untersucht. Wir prƤsentieren eine neuartige Methode zur Konstruktion von divergenzfreien Vektorfeldern, welche mittels Integration zum Deformieren von Objekten verwendet werden (Kapitel 2). Die so entstehende Deformation ist volumenerhaltend und keine SelbstĆ¼berschneidungen treten auf. Inspiriert von etablierten, auf Randbedingungen beruhenden Methoden, erweitern wir diese Idee hinsichtlich Kontrollierbarkeit mittels impliziten Abgrenzungen (Kapitel 3). WƤhrend die ursprĆ¼ngliche Konstruktion im Raum definiert ist, prƤsentieren wir auch eine oberflƤchenbasierte Version, welche ein genaueres Festlegen der Abgrenzungen und bessere Kontrolle ermƶglicht (Kapitel 4). Wir zeigen, dass vektorfeldbasierte Deformationen auch zur Animation von elastischen Bewegungen benutzt werden kƶnnen, ohne dass komplexe Simulationen nƶtig sind (Kapitel 5). Des weiteren zeigen wir eine alternative Mƶglichkeit, mit der man das Volumen von Dreiecksnetzen erhalten kann, welche mittels Skelett-Animation deformiert werden (Kapitel 6). Dies erreichen wir durch ein Deformationsfeld auf der OberflƤche, das das ursprĆ¼ngliche Volumen wieder hergestellt. Wir zeigen auĆerdem, dass Deformierungen mittels Vektorfeld-Integration auch zur Visualisierung von Rauch in dynamischen FlĆ¼ssen genutzt werden kƶnnen(Kapitel 7)
Realistic simulation and animation of clouds using SkewT-LogP diagrams
Nuvens e clima sĆ£o tĆ³picos importantes em computaĆ§Ć£o grĆ”fica, nomeadamente na simulaĆ§Ć£o e animaĆ§Ć£o de fenĆ³menos naturais. Tal deve-se ao facto de a simulaĆ§Ć£o de fenĆ³menos naturaisāonde as nuvens estĆ£o incluĆdasāencontrar aplicaƧƵes em filmes, jogos e simuladores de voo. Contudo, as tĆ©cnicas existentes em computaĆ§Ć£o grĆ”fica apenas permitem representaƧƵes de nuvens simplificadas, tornadas possĆveis atravĆ©s de dinĆ¢micas fictĆcias que imitam a realidade. O problema que este trabalho pretende abordar prende-se com a simulaĆ§Ć£o de nuvens adequadas para utilizaĆ§Ć£o em ambientes virtuais, isto Ć©, nuvens com dinĆ¢mica baseada em fĆsica que variam ao longo do tempo.
Em meteorologia Ć© comum usar tĆ©cnicas de simulaĆ§Ć£o de nuvens baseadas em leis da fĆsica, contudoossistemasatmosfĆ©ricosdeprediĆ§Ć£onumĆ©ricasĆ£ocomputacionalmente pesados e normalmente possuem maior precisĆ£o numĆ©rica do que o necessĆ”rio em computaĆ§Ć£o grĆ”fica. Neste campo, torna-se necessĆ”rio direcionar e ajustar as caracterĆsticas fĆsicas ou contornar a realidade de modo a atingir os objetivos artĆsticos, sendo um fator fundamental que faz com que a computaĆ§Ć£o grĆ”fica se distinga das ciĆŖncias fĆsicas. Contudo, simulaƧƵes puramente baseadas em fĆsica geram soluƧƵes de acordo com regras predefinidas e tornam-se notoriamente difĆceis de controlar.
De modo a enfrentar esses desafios desenvolvemos um novo mĆ©todo de simulaĆ§Ć£o de nuvens baseado em fĆsica que possui a caracterĆstica de ser computacionalmente leve e simula as propriedades dinĆ¢micas relacionadas com a formaĆ§Ć£o de nuvens. Este novo modelo evita resolver as equaƧƵes fĆsicas, ao apresentar uma soluĆ§Ć£o explĆcita para essas equaƧƵes atravĆ©s de diagramas termodinĆ¢micos SkewT/LogP. O sistema incorpora dados reais de forma a simular os parĆ¢metros necessĆ”rios para a formaĆ§Ć£o de nuvens. Ć especialmente adequado para a simulaĆ§Ć£o de nuvens cumulus que se formam devido ao um processo convectivo. Esta abordagem permite nĆ£o sĆ³ reduzir os custos computacionais de mĆ©todos baseados em fĆsica, mas tambĆ©m fornece a possibilidade de controlar a forma e dinĆ¢mica de nuvens atravĆ©s do controlo dos nĆveis atmosfĆ©ricos existentes no diagrama SkewT/LogP.
Nestatese,abordĆ”mostambĆ©mumoutrodesafio,queestĆ”relacionadocomasimulaĆ§Ć£o de nuvens orogrĆ”ficas. Do nosso conhecimento, esta Ć© a primeira tentativa de simular a formaĆ§Ć£o deste tipo de nuvens. A novidade deste mĆ©todo reside no fato de este tipo de nuvens serem nĆ£o convectivas, oque se traduz nocĆ”lculodeoutrosnĆveis atmosfĆ©ricos. AlĆ©m disso, atendendo a que este tipo de nuvens se forma sobre montanhas, Ć© tambĆ©m apresentadoumalgoritmoparadeterminarainfluĆŖnciadamontanhasobreomovimento da nuvem.
Em resumo, esta dissertaĆ§Ć£o apresenta um conjunto de algoritmos para a modelaĆ§Ć£o e simulaĆ§Ć£o de nuvens cumulus e orogrĆ”ficas, recorrendo a diagramas termodinĆ¢micos SkewT/LogP pela primeira vez no campo da computaĆ§Ć£o grĆ”fica.Clouds and weather are important topics in computer graphics, in particular in the simulation and animation of natural phenomena. This is so because simulation of natural phenomenaāwhere clouds are includedāfind applications in movies, games and flight simulators. However, existing techniques in computer graphics only offer the simplified cloud representations, possibly with fake dynamics that mimic the reality. The problem that this work addresses is how to find realistic simulation of cloud formation and evolution, that are suitable for virtual environments, i.e., clouds with physically-based dynamics over time.
It happens that techniques for cloud simulation are available within the area of meteorology, but numerical weather prediction systems based on physics laws are computationally expensive and provide more numerical accuracy than the required accuracy in computer graphics. In computer graphics, we often need to direct and adjust physical features, or even to bend the reality, to meet artistic goals, which is a key factor that makes computer graphics distinct from physical sciences. However, pure physically-based simulations evolve their solutions according to pre-set physics rules that are notoriously difficult to control.
In order to face these challenges we have developed a new lightweight physically-based cloudsimulationschemethatsimulatesthedynamicpropertiesofcloudformation. This new model avoids solving the physically-based equations typically used to simulate the formation of clouds by explicitly solving these equations using SkewT/LogP thermodynamic diagrams. The system incorporates a weather model that uses real data to simulate parameters related to cloud formation. This is specially suitable to the simulation of cumulus clouds, which result from a convective process. This approach not only reduces the computational costs of previous physically-based methods, but also provides a technique to control the shape and dynamics of clouds by handling the cloud levels in SkewT/LogP diagrams.
In this thesis, we have also tackled a new challenge, which is related to the simulation oforographic clouds. From ourknowledge, this isthefirstattempttosimulatethis type of cloud formation. The novelty in this method relates to the fact that these clouds are non-convective, so that different atmospheric levels have to be determined. Moreover, since orographic clouds form over mountains, we have also to determine the mountain influence in the cloud motion.
In summary, this thesis presents a set of algorithms for the modelling and simulation of cumulus and orographic clouds, taking advantage of the SkewT/LogP diagrams for the first time in the field of computer graphics
Realistic natural atmospheric phenomena and weather effects for interactive virtual environments.
Clouds and the weather are important aspects of any natural outdoor scene, but existing dynamic techniques within computer graphics only offer the simplest of cloud representations. The problem that this work looks to address is how to provide a means of simulating clouds and weather features such as precipitation, that are suitable for virtual environments. Techniques for cloud simulation are available within the area of meteorology, but numerical weather prediction systems are computationally expensive, give more numerical accuracy than we require for graphics and are restricted to the laws of physics. Within computer graphics, we often need to direct and adjust physical features or to bend reality to meet artistic goals, which is a key difference between the subjects of computer graphics and physical science. Pure physicallybased simulations, however, evolve their solutions according to pre-set rules and are notoriously difficult to control. The challenge then is for the solution to be computationally lightweight and able to be directed in some measure while at the same time producing believable results. This work presents a lightweight physically-based cloud simulation scheme that simulates the dynamic properties of cloud formation and weather effects. The system simulates water vapour, cloud water, cloud ice, rain, snow and hail. The water model incorporates control parameters and the cloud model uses an arbitrary vertical temperature profile, with a tool described to allow the user to define this. The result of this work is that clouds can now be simulated in near real-time complete with precipitation. The temperature profile and tool then provide a means of directing the resulting formation
Appearance Modelling and Reconstruction for Navigation in Minimally Invasive Surgery
Minimally invasive surgery is playing an increasingly important role for patient
care. Whilst its direct patient benefit in terms of reduced trauma,
improved recovery and shortened hospitalisation has been well established,
there is a sustained need for improved training of the existing procedures
and the development of new smart instruments to tackle the issue of visualisation,
ergonomic control, haptic and tactile feedback. For endoscopic
intervention, the small field of view in the presence of a complex anatomy
can easily introduce disorientation to the operator as the tortuous access
pathway is not always easy to predict and control with standard endoscopes.
Effective training through simulation devices, based on either virtual reality
or mixed-reality simulators, can help to improve the spatial awareness,
consistency and safety of these procedures.
This thesis examines the use of endoscopic videos for both simulation
and navigation purposes. More specifically, it addresses the challenging
problem of how to build high-fidelity subject-specific simulation environments
for improved training and skills assessment. Issues related to mesh
parameterisation and texture blending are investigated. With the maturity
of computer vision in terms of both 3D shape reconstruction and localisation
and mapping, vision-based techniques have enjoyed significant interest
in recent years for surgical navigation. The thesis also tackles the problem
of how to use vision-based techniques for providing a detailed 3D map and
dynamically expanded field of view to improve spatial awareness and avoid
operator disorientation. The key advantage of this approach is that it does
not require additional hardware, and thus introduces minimal interference
to the existing surgical workflow. The derived 3D map can be effectively
integrated with pre-operative data, allowing both global and local 3D navigation
by taking into account tissue structural and appearance changes.
Both simulation and laboratory-based experiments are conducted throughout
this research to assess the practical value of the method proposed
Efficient data structures for piecewise-smooth video processing
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2011.Cataloged from PDF version of thesis.Includes bibliographical references (p. 95-102).A number of useful image and video processing techniques, ranging from low level operations such as denoising and detail enhancement to higher level methods such as object manipulation and special effects, rely on piecewise-smooth functions computed from the input data. In this thesis, we present two computationally efficient data structures for representing piecewise-smooth visual information and demonstrate how they can dramatically simplify and accelerate a variety of video processing algorithms. We start by introducing the bilateral grid, an image representation that explicitly accounts for intensity edges. By interpreting brightness values as Euclidean coordinates, the bilateral grid enables simple expressions for edge-aware filters. Smooth functions defined on the bilateral grid are piecewise-smooth in image space. Within this framework, we derive efficient reinterpretations of a number of edge-aware filters commonly used in computational photography as operations on the bilateral grid, including the bilateral filter, edgeaware scattered data interpolation, and local histogram equalization. We also show how these techniques can be easily parallelized onto modern graphics hardware for real-time processing of high definition video. The second data structure we introduce is the video mesh, designed as a flexible central data structure for general-purpose video editing. It represents objects in a video sequence as 2.5D "paper cutouts" and allows interactive editing of moving objects and modeling of depth, which enables 3D effects and post-exposure camera control. In our representation, we assume that motion and depth are piecewise-smooth, and encode them sparsely as a set of points tracked over time. The video mesh is a triangulation over this point set and per-pixel information is obtained by interpolation. To handle occlusions and detailed object boundaries, we rely on the user to rotoscope the scene at a sparse set of frames using spline curves. We introduce an algorithm to robustly and automatically cut the mesh into local layers with proper occlusion topology, and propagate the splines to the remaining frames. Object boundaries are refined with per-pixel alpha mattes. At its core, the video mesh is a collection of texture-mapped triangles, which we can edit and render interactively using graphics hardware. We demonstrate the effectiveness of our representation with special effects such as 3D viewpoint changes, object insertion, depthof- field manipulation, and 2D to 3D video conversion.by Jiawen Chen.Ph.D