We describe and demonstrate an algorithm that takes as input an unorganized set of points fx1�:::�xng IR 3 on or near an unknown manifold M, and produces as output a simplicial surface that approximates M. Neither the topology, the presence of boundaries, nor the geometry of M are assumed to be known in advance — all are inferred automatically from the data. This problem naturally arises in a variety of practical situations such as range scanning an object from multiple view points, recovery of biological shapes from two-dimensional slices, and interactive surface sketching.

The bottle-neck in most cloth simulation systems is that time steps must be small to avoid numerical instability. This paper describes a cloth simulation system that can stably take large time steps. The simulation system couples a new technique for enforcing constraints on individual cloth particles with an implicit integration method. The simulator models cloth as a triangular mesh, with internal cloth forces derived using a simple continuum formulation that supports modeling operations such as local anisotropic stretch or compression; a unified treatment of damping forces is included as well. The implicit integration method generates a large, unbanded sparse linear system at each time step which is solved using a modified conjugate gradient method that simultaneously enforces particles' constraints. The constraints are always maintained exactly, independent of the number of conjugate gradient iterations, which is typically small. The resulting simulation system is significantly fast...

We present a fast marching level set method for monotonically advancing fronts, which leads to an extremely fast scheme for solving the Eikonal equation. Level set methods are numerical techniques for computing the position of propagating fronts. They rely on an initial value partial dierential equation for a propagating level set function, and use techniques borrowed from hyperbolic conservation laws. Topological changes, corner and cusp development, and accurate determination of geometric properties such as curvature and normal direction are naturally obtained in this setting. In this paper, we describe a particular case of such methods for interfaces whose speed depends only on local position. The technique works by coupling work on entropy conditions for interface motion, the theory of viscosity solutions for Hamilton-Jacobi equations and fast adaptive narrow band level set methods. The technique is applicable to a variety of problems, including shape-from-shading problems, lithog...

We present a method for searching in an image database using a query image that is similar to the intended target. The query image may be a hand-drawn sketch or a (potentially low-quality) scan of the image to be retrieved. Our searching algorithm makes use of multiresolution wavelet decompositions of the query and database images. The coefficients of these decompositions are distilled into small "signatures" for each image. We introduce an "image querying metric" that operates on these signatures. This metric essentially compares how many significant wavelet coefficients the query has in common with potential targets. The metric includes parameters that can be tuned, using a statistical analysis, to accommodate the kinds of image distortions found in different types of image queries. The resulting algorithm is simple, requires very little storage overhead for the database of signatures, and is fast enough to be performed on a database of 20,000 images at interactive rates (on standard...

this paper, we introduce a method for recovery of compact volumetric models for single part objects. To solve the shape recovery problem in isolation from segmentation, we assume that only a single object is present in the scene at a time. Although we made this simplification to break up the problem, this assumption is still valid for some restricted environments [30]. We show that the shape of those objects can be recovered subject to the model's internal constraints. In this work we use a partic- ular example of compact volumetric models--superquad- ric primitives with parametric deformations. We introduce a least-squares minimization method to recover model and deformation parameters using range data as the input. Range data enables us to study shape recovery independent of different passive techniques of obtaining depth data, such as depth from stereo, depth from focus, or depth from motion. The fitting function which we min- imize is a cost or energy function whose value depends on the distance of points from the model's surface and on the overall size of the model. We show that the solution space, which can have more than one "deep" minimum or acceptable solution and many shallow local minima, can be searched efficiently with a gradient descent method. By using a stochastic technique, the procedure can escape from shallow local minima, and a particular solution among several acceptable solutions can be reached by searching in a constrained parameter subspace. The paper is organized as follows. Section II is on parametric models in computer vision, focusing on comparison of generalized cylinders and superquadrics. Section III explains superquadric models in detail. Section IV is about recovery of nondeformed superquadric models, and Section V is on recovery of defo...

This paper gives an overview of the implementation of Nesl, a portable nested data-parallel language. This language and its implementation are the first to fully support nested data structures as well as nested dataparallel function calls. These features allow the concise description of parallel algorithms on irregular data, such as sparse matrices and graphs. In addition, they maintain the advantages of data-parallel languages: a simple programming model and portability. The current Nesl implementation is based on an intermediate language called Vcode and a library of vector routines called Cvl. It runs on the Connection Machine CM-2, the Cray Y-MP C90, and serial machines. We compare initial benchmark results of Nesl with those of machine-specific code on these machines for three algorithms: least-squares line-fitting, median finding, and a sparse-matrix vector product. These results show that Nesl's performance is competitive with that of machine-specific codes for regular dense da...

We describe a multiresolution curve representation, based on wavelets, that conveniently supports a variety of operations: smoothing a curve; editing the overall form of a curve while preserving its details; and approximating a curve within any given error tolerance for scan conversion. We present methods to support continuous levels of smoothing as well as direct manipulation of an arbitrary portion of the curve; the control points, as well as the discrete nature of the underlying hierarchical representation, can be hidden from the user. The multiresolution representation requires no extra storage beyond that of the original control points, and the algorithms using the representation are both simple and fast.

A model for the dynamic simulation of flexible bodies subject to non-penetration constraints is presented. Flexible bodies are described in terms of global deformations of a rest shape. The dynamical behavior of these bodies that most closely matches the behavior of ideal continuum bodies is derived, and subsumes the results of earlier Lagrangian dynamics-based models. The dynamics derived for the flexible-body model allows the unification of previous work on flexible body simulation and previous work on non-penetrating rigid body simulation. The non-penetration constraints for a system of bodies that contact at multiple points are maintained by analytically calculated contact forces. An implementation for first- and second-order polynomially deformable bodies is described. The simulation of second-order or higher deformations currently involves a polyhedral boundary approximation for collision detection purposes.

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Wavelets have been making an appearance in many pure and applied areas of science and engineering. Computer graphics with its many and varied computational problems has been no exception to this rule. In these notes we will attempt to motivate and explain the basic ideas behind wavelets and what makes them so successful in application areas. The main