1889751
Fast simulation of deformable models in contact using dynamic deformation textures
We present an efficient algorithm for simulating contacts between deformable bodies with high-resolution surface geometry using dynamic deformation textures, which reformulate the 3D elastoplastic deformation and collision handling on a 2D parametric atlas to reduce the extremely high number of degrees of freedom in such a computationally demanding simulation. We perform proximity queries for deformable bodies using a two-stage algorithm directly on dynamic deformation textures, resulting in output-sensitive collision detection that is independent of the combinatorial complexity of the deforming meshes. We present a robust, parallelizable formulation for computing constraint forces using implicit methods that exploits the structure of the motion equations to achieve highly stable simulation, while taking large time steps with inhomogeneous materials. The dynamic deformation textures can also be used directly for real-time shading and can easily be implemented using SIMD architecture on commodity hardware. We show that our approach, complementing existing pioneering work, offers significant computational advantages on challenging contact scenarios in dynamic simulation of deformable bodies.
8273317
A video-based rendering acceleration algorithm for interactive walkthroughs
We present a new approach for faster rendering of large synthetic environments using video-based representations. We decompose the large environment into cells and pre-compute video based impostors using MPEG compression to represent sets of objects that are far from each cell. At runtime, we decode the MPEG streams and use rendering algorithms that provide nearly constant-time random access to any frame. The resulting system has been implemented and used for an interactive walkthrough of a model of a house with 260,000 polygons and realistic lighting and textures. It is able to render this model at 16 frames per second (an eightfold improvement over simpler algorithms) on average on a Pentium II PC with an off-the-shelf graphics card.
9041268
Modeling ice dynamics as a thin-film Stefan problem
Large, 3D ice formations such as icicles exhibit a high degree of geometric and optical complexity. Modeling these features by hand can be a daunting task, so we present a novel physically-based algorithm for simulating this phenomenon. Solidification is usually posed as a so-called 'Stefan problem', but the problem in its classic form is inappropriate for simulating the ice typically found in a winter scene. We instead use the 'thin-film' variant of the Stefan problem to derive velocity equations for a level set simulation. However, due to the scales involved in the problem, even an adaptive grid level set solver is still insufficient to track the tip of an icicle. Therefore, we derive an analytical solution for the icicle tip and use it to correct the level set simulation. The results appear to be in agreement with experimental data. We also present a physically-based technique for modeling ripples along the ice surface that alleviates the need to explicitly track small-scale geometry. To our knowledge, our approach is the most complete model available, and produces complex visual phenomena that no previous method has been able to capture.
7169150
A versatile interactive 3D brush model
We present a flexible modeling approach capable of realistically simulating many varieties of brushes commonly used in painting. Our geometric model of brush heads is a combination of subdivision surfaces and hundreds of individual bristles represented by thin polygonal strips. We exploit bristle-to-bristle coherence, simulating only a fraction of the bristles and using interpolation for the remainder. Our dynamic model incorporates realistic physically-based deformation, including anisotropic friction, brush plasticity, and tip spreading. We use an energy minimization framework with a novel geometric representation of the brush head to generate a wider variety of brushes. Finally, we have developed an improved haptic model that provides realistic force feedback, directly related to the results of the brush dynamic simulation. Using this model, we are able to simulate a wide range of brush styles and create an excellent variety of strokes such as the crisp, curvy strokes of Western decorative painting, or rough scratchy strokes like certain Oriental calligraphy. We have also developed an exporter for a popular free 3D modeling package that makes it easier for non-programmers to create any desired style of brush, real or fanciful.
206451107
Sensation-Preserving Haptic Rendering
Most human-computer interactive systems focus primarily on the graphical rendering of visual information and, to a lesser extent, on the display of auditory information. Haptic interfaces have the potential to increase the quality of human-computer interaction by accommodating the sense of touch. They provide an attractive augmentation to visual display and enhance the level of understanding of complex data sets. A haptic rendering system generates contact or restoring forces to prevent penetration into the virtual objects and create a sense of touch. The system computes contact forces by first detecting if a collision or penetration has occurred. Then, the system determines the (projected) contact points on the model surface. Finally, it computes restoring forces based on the amount of penetration. Researchers have recently investigated the problem of rendering the contact forces and torques between 3D virtual objects. This problem is known as six-degrees-of-freedom (6-DOF) haptic rendering, as the computed output includes both 3-DOF forces and 3-DOF torques. This article presents an overview of our work in this area. We suggest different approximation methods based on the principle of preserving the dominant perceptual factors in haptic exploration.
7639620
Stable and responsive six-degree-of-freedom haptic manipulation using implicit integration
In this paper we present a novel approach for simulating the rigid body dynamics of a haptically manipulated object using implicit integration. Our formulation requires the linearization of contact and manipulation forces, and it provides higher stability and responsiveness than previous methods. The linearization of contact forces, coupled with fast, perceptually based collision detection algorithms, enables us to perform highly stable and responsive 6-degree-of-freedom haptic rendering of complex polygonal models.
33339608
Almost Optimal Solutions for Bin Coloring Problems
In this paper we study two interesting bin coloring problems: Minimum Bin Coloring Problem (MinBC) and Online Maximum Bin Coloring Problem (OMaxBC), motivated from several applications in networking. For the MinBC problem, we first show that it is NP-complete, and then present two near linear time approximation algorithms to achieve almost optimal solutions, i.e., no more than OPT+2 and OPT+1 respectively, where OPT is the optimal solution. For the OMaxBC problem, we first introduce a deterministic 2-competitive greedy algorithm, and then give lower bounds for any deterministic and randomized (against adaptive offline adversary) online algorithms. The lower bounds show that our deterministic algorithm achieves the best possible competitive ratio.
5692452
k-server optimal task scheduling problem with convex cost function
We consider a class of k-server optimal task scheduling problems partitioning and scheduling N tasks with various real-time constrains and work loads on k servers with convex task processing cost function so as to minimize the total task processing cost while still guaranteeing satisfaction of all time constraints. This class has broad expressing power for practical scheduling problems in several areas such as real-time multimedia wireless transmission , CPU energy conservation, and warehouse order processing management, et. al. Our formulation is quite general such that most previous works can be readily reduced to a special case of the presented k-server optimal task scheduling problem. We show that, when k = 1, optimal solution can be obtained in computational complexity of O(N) and the corresponding optimal scheduling problem is equivalent to finding the shortest 2D Euclidean distance between two vertices inside a well-defined 2D polygon. However, when k 2, the optimal scheduling problem can be demonstrated to be NP-hard by reducing it to a well-known NP-complete bin-packing problem. Therefore, we conclude no polynomial time algorithm exists for a general k-server optimal task scheduling problem. We then construct approximation algorithms to solve the presented k-server problem in a practical way and illustrate its performance by simulation results and analysis.
890758
On Balanced Graphs
Berge defined a hypergraph to be balanced if its incidence matrix is balanced. We consider this concept applied to graphs, and call a graph to be balanced when its clique matrix is balanced. Characterizations of balanced graphs by forbidden subgraphs and by clique subgraphs are proved in this work. Using properties of domination we define four subclasses of balanced graphs. Two of them are characterized by 0–1 matrices and can be recognized in polynomial time. Furthermore, we propose polynomial time combinatorial algorithms for the problems of stable set, clique-independent set and clique-transversal for one of these subclasses of balanced graphs. Finally, we analyse the behavior of balanced graphs and these four subclasses under the clique graph operator.
760636
Accelerated occlusion culling using shadow frusta
Many applications in computer graphics and virtual environments need to render datasets with large numbers of primitives and high depth complexity at interactive rates. However, standard techniques like view frustum culling and a hardware z-bu er are unable to display datasets composed of hundred of thousands of polygons at interactive frame rates on current high-end graphics systems. We add a \conservative"visibility culling stage to the rendering pipeline, attempting to identify and avoid processing of occluded polygons. Given a moving viewpoint, the algorithm dynamically chooses a set of occluders. Each occluder is used to compute a shadow frustum, and all primitives contained within this frustumare culled. The algorithmhierarchicallytraverses the model, culling out parts not visible from the current viewpoint using e cient, robust, and in some cases specialized interference detection algorithms. The algorithm's performance varies with the location of the viewpoint and the depth complexity of the model. In the worst case it is linear in the input size with a small constant. In this paper, we demonstrate its performance on a city model composed of 500;000 polygons and possessing varying depth complexity. We are able to cull an average of 55% of the polygons that would not be culled by view-frustum culling and obtain a commensurate improvement in frame rate. The overall approach is e ective and scalable, is applicable to all polygonal models, and can be easily implemented on top of view-frustum culling.
50312
The distributed program reliability analysis on ring-type topologies
Abstract Distributed computing system (DCS) has become very popular for its high fault-tolerance, potential for parallel processing, and better reliability performance. One of the important issues in the design of the DCS is the reliability performance. Distributed program reliability (DPR) is addressed to obtain this reliability measure. In this paper, we propose a polynomial-time algorithm for computing the DPR of ring topology and show that solving the DPR problem on a ring of trees topology is NP-hard. Scope and purpose The widespread use of distributed computing system is due to the price–performance revolution in microelectronics, the development of cost-effective and efficient communication subsets, the development of resource sharing software, and the increased user demands for communication, economical sharing of resources, and productivity. This article is concerned with the analysis of distributed program reliability on a ring-distributed computing system. The distributed program reliability is a useful measure for reliability evaluation of distributed computing system. The distributed program reliability analyses also give a good index for designing a high-reliability-performance-distributed computing system.