Brian A. Barsky

Local Control of Bias and Tension in Beta-splines

The Beta-spline introduced recently by Barsky is a generalization of the uniform cubic B-spline: parametric discontinuities are introduced in such a way as to preserve continuity of the unit tangent and curvature vectors at joints ( geometric continuity ) while providing bias and tension parameters, independent of the position of control vertices, by which the shape of a curve or surface can be manipulated. Using a restricted form of quintic Hermite interpolation, it is possible to allow distinct bias and tension parameters at each joint without destroying geometric continuity. This provides a new means of obtaining local control of bias and tension in piecewise polynomial curves and surfaces.

Making them move: mechanics, control, and animation of articulated figures

Making Them Move: Mechanics, Control, and Animation of Articulated Figures Edited by Norman I. Badler, Brian A. Barsky, and David Zeltzer PART ONE -- INTERACTING WITH ARTICULATED FIGURES Chapter 1 Task-level Graphical Simulation: Abstraction, Representation, and Control David Zeltzer Chapter 2 Composition of Realistic Animation Sequences for Multiple Human Figures Tom Calvert Chapter 3 Animation from Instructions Norman I. Badler, Bonnie L. Webber, Jugal Kalita, and Jeffrey Esakov PART TWO -- ARTIFICIAL AND BIOLOGICAL MECHANISMS FOR MOTOR CONTROL ARTIFICIAL MOTOR PROGRAMS Chapter 4 A Robot that Walks: Emergent Behaviors from a Carefully Evolved Network Rodney A. Brooks BIOLOGICAL MOTOR PROGRAMS Chapter 5 Sensory Elements in Pattern-Generating Networks K.G. Pearson Chapter 6 Motor Programs as Units of Movement Control Douglas E. Young and Richard A. Schmidt Chapter 7 Dynamics and Task-specific Coordinations M.T. Turvey, Elliot Saltzman, and R.C. Schmidt Chapter 8 Dynamic Pattern Generation and Recognition J.A.S. Kelso and A.S. Pandya LEARNING MOTOR PROGRAMS Chapter 9 A Computer System for Movement Schemas Peter H. Greene and Dan Solomon PART THREE -- MOTION CONTROL ALGORITHMS Chapter 10 Constrained Optimization of Articulated Animal Movement in Computer Animation Michael Girard Chapter 11 Goal-directed Animation of Tubular Articulated Figures or How Snakes Play Golf Gavin Miller Chapter 12 Human Body Deformations Using Joint-dependent Local Operators and Finite-Element Theory Nadia Magnenat-Thalmann and Daniel Thalmann PART FOUR -- COMPUTING THE DYNAMICS OF MOTION Chapter 13 Dynamic Experiences Jane Wilhelms Chapter 14 Using Dynamics in Computer Animation: Control and Solution Issues Mark Green Chapter 15 Teleological Modeling Alan H. Barr Appendix A: Video Notes Appendix B: About the Authors Index

An adaptive subdivision method for surface-fitting from sampled data

A method is developed for surface-fitting from sampled data. Surface-fitting is the process of constructing a compact representation to model the surface of an object based on a fairly large number of given data points. In our case, the data is obtained from a real object using an automatic three-dimensional digitizing system. The method is based on an adaptive subdivision approach, a technique previously used for the design and display of free-form curved surface objects. Our approach begins with a rough approximating surface and progressively refines it in successive steps in regions where the data is poorly approximated. The method has been implemented using a parametric piecewise bicubic Bernstein-Bézier surface possessing G1 geometric continuity. An advantage of this approach is that the refinement is essentially local reducing the computational requirements which permits the processing of large databases. Furthermore, the method is simple in concept, yet realizes efficient data compression. Some experimental results are given which show that the representation constructed by this method is faithful to the original database.

A New Concept and Method for Line Clipping

A new concept and method for line clipping is developed that describes clipping in an exact and mathematical form. The basic ideas form the foundation for a family of algorithms for two-dimensional, three-dimensional, and four-dimensional (homogeneous coordinates) line clipping. The line segment to be clipped is mapped into a parametric representation. From this, a set of conditions is derived that describes the interior of the clipping region. Observing that these conditions are all of similar form, they are rewritten such that the solution to the clipping problem is reduced to a simple max/min expression. For each dimension, the mathematics are discussed, an example is given, the algorithm is designed, and a performance test is conducted. The new algorithm is compared with the traditional Sutherland-Cohen clipping algorithm. Using randomly generated data, the new algorithm showed a 36 percent, 40 percent, and 79 percent improvement for two-dimensional, three-dimensional, and four- dimensional clipping, respectively. One of the advantages of this algorithm is the quick rejection of line segments that are invisible. In addition, this algorithm can be easily generalized for clipping against any convex viewing volume

Computer graphics and geometric modeling using Beta-splines

Computer graphics and geometric modeling using Beta-splines , Computer graphics and geometric modeling using Beta-splines , مرکز فناوری اطلاعات و اطلاع رسانی کشاورزی

Modeling and rendering waves: wave-tracing using beta-splines and reflective and refractive texture mapping.

The graphical simulation of a certain subset of hydrodynamics phenomena is examined. New algorithms for both modeling and rendering these complex phenomena are presented. The modeling algorithms deal with wave refraction in an ocean. Waves refract in much the same way as light. In both cases, the equation that controls the change in direction is Snells law. Ocean waves are continuous but can be discretely decomposed into wave rays or wave orthogonals. These wave orthogonals are wave-traced in a manner similar to the rendering algorithm of ray-tracing. The refracted wave orthogonals are later traversed and their height contributions to the final surface are calculated using a sinusoidal shape approximation and the principle of wave superposition. The surface is then represented by Beta-splines, using the tension (or β2) shape parameter to easily add more complexity to the surface. The rendering algorithms are based on the use of texture maps and Fresnels law of reflection. In each algorithm, two texture maps are used to simulate reflection and refraction. Based on surface normal orientation and Fresnels law, a weighting is calculated that determines what fractions of reflected color and refracted color are assigned to a point. These algorithms are more efficient, though less accurate, alternatives to standard ray-tracing techniques.

Geometric continuity of parametric curves: three equivalent characterizations

Some of the important basic results on geometric continuity of curves are presented in a self-contained manner. The paper covers parametric representation and smoothness, parametric continuity, reparameterization and equivalent parameterization, beta-constraints, and arc-length parameterization.<<ETX>>

Personalized photograph ranking and selection system

In this paper, we propose a novel personalized ranking system for amateur photographs. Although some of the features used in our system are similar to previous work, new features, such as texture, RGB color, portrait (through face detection), and black-and-white, are included for individual preferences. Our goal of automatically ranking photographs is not intended for award-wining professional photographs but for photographs taken by amateurs, especially when individual preference is taken into account. The performance of our system in terms of precision-recall diagram and binary classification accuracy (93%) is close to the best results to date for both overall system and individual features. Two personalized ranking user interfaces are provided: one is feature-based and the other is example-based. Although both interfaces are effective in providing personalized preferences, our user study showed that example-based was preferred by twice as many people as feature-based.

Geometrically exact dynamic splines

In this paper, we propose a complete model handling the physical simulation of deformable 1D objects. We formulate continuous expressions for stretching, bending and twisting energies. These expressions are mechanically rigorous and geometrically exact. Both elastic and plastic deformations are handled to simulate a wide range of materials. We validate the proposed model in several classical test configurations. The use of geometrical exact energies with dynamic splines provides very accurate results as well as interactive simulation times, which shows the suitability of the proposed model for constrained CAD applications. We illustrate the application potential of the proposed model by describing a virtual system for cable positioning, which can be used to test compatibility between planned fixing clip positions, and mechanical cable properties.

Geometric continuity, shape parameters, and geometric constructions for Catmull-Rom splines

Catmull-Rom splines have local control, can be either approximating or interpolating, and are efficiently computable. Experience with Beta-splines has shown that it is useful to endow a spline with shape parameters, used to modify the shape of the curve or surface independently of the defining control vertices. Thus it is desirable to construct a subclass of the Catmull-Rom splines that has shape parameters. We present such a class, some members of which are interpolating and others approximating. As was done for the Beta-spline, shape parameters are introduced by requiring geometric rather than parametric continuity. Splines in this class are defined by a set of control vertices and a set of shape parameter values. The shape parameters may be applied globally, affecting the entire curve, or they may be modified locally, affecting only a portion of the curve near the corresponding joint. We show that this class results from combining geometrically continuous (Beta-spline) blending functions with a new set of geometrically continuous interpolating functions related to the classical Lagrange curves. We demonstrate the practicality of several members of the class by developing efficient computational algorithms. These algorithms are based on geometric constructions that take as input a control polygon and a set of shape parameter values and produce as output a sequence of Bézier control polygons that exactly describes the original curve. A specific example of shape design using a low-degree member of the class is given.