8956586
Interactive navigation in complex environments using path planning
We present a novel approach for interactive navigation in complex 3D synthetic environments using path planning. Our algorithm precomputes a global roadmap of the environment by using a variant of randomized motion planning algorithm along with a reachability-based analysis. At runtime, our algorithm performs graph searching and automatically computes a collision-free and constrained path between two user specified locations. It also enables local user-steered exploration, subject to motion constraints and integrates these capabilities in the control loop of 3D interaction. Our algorithm only requires the scene geometry, avatar orientation, and parameters relating the avatar size to the model size. The performance of the preprocessing algorithm grows as a linear function of the model size. We demonstrate its performance on two large environments: a power plant and a factory room.
6243696
Geometry-driven physical interaction between avatars and virtual environments
We present an interactive technique on virtual contact handling for avatars in virtual environments using geometry-driven physics. If a contact has occurred between an articulated avatar and a virtual environment, the global penetration depth and contact points are estimated based on a fast local penetration depth computation for decomposed convex pieces. The penetration depth and contact information are then used to resolve overlap between the avatar and the virtual environment. If applicable, joint angles for an articulated body are computed using an inverse kinematics approach based on cyclic coordinate descent. Resulting dynamic response with friction is modeled with impulse-based dynamics under the Coulomb friction law. We demonstrate the algorithm on a modestly complex virtual environment. The resulting system is able to maintain an interactive frame rate of 30–60 Hz. Copyright © 2004 John Wiley & Sons, Ltd.
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.
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.
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.
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.
28156768
A VLSI implementation of the blowfish encryption/decryption algorithm
We propose an efficient hardware architecture for the Blowfish algorithm [1]. The speed is up to 4 bit/clock, which is 9 times faster than a Pentium. By applying operator-rescheduling method, the critical path delay is improved by 21.7%. We have successfully implemented it using Compass cell library targeted at a 0.6 μm TSMC SPTM CMOS process. The die size is 5.7x6.1 mm and the maximum frequency is 50MHz.
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.
205481590
Fast and simple algorithms to count the number of vertex covers in an interval graph
This study provides the following fast and simple algorithms for an interval graph: (1) an algorithm for counting the number of vertex covers, and (2) an algorithm for counting the number of minimal vertex covers.
16920752
Runlength Limited Codes for Single Error-Detection and Single Error-Correction with Mixed Type Errors
Runlength limited (RLL) codes are used in magnetic recording. The error patterns that occur with peak detection magnetic recording systems when using a runlength-limited code consist of both symmetric errors and shift errors. We refer to shift errors and symmetric errors collectively as mixed type errors. A method of providing error control for mixed type errors that occur in a runlength limited code comprised of (d, k) constrained sequences is examined. The coding scheme is to choose parity blocks to insert in the constrained information sequence. The parity blocks are chosen to satisfy the constraints and to provide some error control. The cases of single error-detection and single error-correction are investigated, where the single error is allowed to be a shift error or a symmetric error. Bounds are discussed on the possible lengths for the parity blocks. It is shown that the single error-detection codes are the best possible in terms of the length of the parity blocks.
30294156
Cycle embedding in faulty wrapped butterfly graphs
In this paper, we study the maximal length of cycle embedding in a faulty wrapped butterfly graph BFn with at most two faults in vertices and/or edges. When there is one vertex fault and one edge fault, we prove that the maximum cycle length is n2n − 2 if n is even and n2n − 1 if n is odd. When there are two faulty vertices, the maximum cycle length is n2n − 2 for odd n. All these results are optimal because the wrapped butterfly graph is bipartite if and only if n is even. © 2003 Wiley Periodicals, Inc.