Richard E. Parent

Layered construction for deformable animated characters

A methodology is proposed for creating and animating computer generated characters which combines recent research advances in robotics, physically based modeling and geometric modeling. The control points of geometric modeling deformations are constrained by an underlying articulated robotics skeleton. These deformations are tailored by the animator and act as a muscle layer to provide automatic squash and stretch behavior of the surface geometry. A hierarchy of composite deformations provides the animator with a multi-layered approach to defining both local and global transition of the characters shape. The muscle deformations determine the resulting geometric surface of the character. This approach provides independent representation of articulation from surface geometry, supports higher level motion control based on various computational models, as well as a consistent, uniform character representation which can be tuned and tweaked by the animator to meet very precise expressive qualities. A prototype system (Critter) currently under development demonstrates research results towards layered construction of deformable animated characters.

Shape transformation for polyhedral objects

Techniques that transform one two-dimensionaf image into another have gained widespread use m recent yeara. Extending these techniques to transform pairs of 3D objects, as opposed to 2D images of the objects, providea several advsntagea, including the ability to snimate the objects independently of the transformation. This paper presents an algorithm for computing such transformations. The algorithm merges the topological structures of a pair of 3D polyhedral models into a common vertex/edgeJface network. This allows trsmsformations from one object to the other to be easily computed by interpolating between corresponding v@ex positions.

Anatomy-based modeling of the human musculature

Artists study anatomy to understand the relationship between exterior form and the structures responsible for creating it. In this paper we follow a similar approach in developing anatomy-based models of muscles. We consider the influence of the musculature on surface form and develop muscle models which react automatically to changes in the posture of an underlying articulated skeleton. The models are implemented in a procedural language that provides convenient facilities for defining and manipulating articulated models. To illustrate their operation, the models are applied to the torso and arm of a human figure. However, they are sufficiently general to be applied in other contexts where articulated skeletons provide the basis of modeling. CR

Rendering and animation of gaseous phenomena by combining fast volume and scanline A-buffer techniques

This paper describes a new technique that efficiently combines volume rendering and scanline a-buffer techniques. This technique is useful for combining all types of volume-rendered objects with scanline rendered objects and is especially useful for rendering scenes containing gaseous phenomena such as clouds, fog, and smoke. The rendering and animation of these phenomena has been a difficult problem in computer graphics.A new algorithm for realistically modeling and animating gaseous phenomena is presented, providing true three-dimensional volumes of gas. The gases are modeled using turbulent flow based solid texturing to define their geometry and are animated based on turbulent flow simulations. A low albedo illumination model is used that takes into consideration self-shadowing of the volumes.

Shape averaging and its applications to industrial design

A computer-assisted technique called shape averaging is presented. Shape averaging produces an abstraction of the typical representation from a set of shapes. Since the averaging is assumed to preserve the characteristics of the original shapes, the result is useful in predicting trends in form or extracting stereotypes from a group of related shapes. The technique can be used to create new forms by blending global features of existing unrelated shapes. The syntactic averaging of shapes consisting of 2-D planar polygons or of 3-D objects represented by planar contours is examined. An algorithm is presented to determine the correspondence between polygons defined by arbitrary numbers of vertices. Algorithms to extract the mean, the median, and the mode from the shapes are also introduced. Potential applications of shape averaging in design are illustrated.<<ETX>>

Coverage optimization to support security monitoring

The placement of sensors to support security monitoring is obviously critical as it will directly impact the efficacy of allocated resources and system performance. It is critical to be able to observe and monitor the greatest total area possible. In addition, it is necessary to be able to spatially track the movement of people and activities in support of security. It is shown that important aspects of the security sensor placement problem can be modeled using the maximal covering location problem (MCLP) and/or the backup coverage location problem (BCLP) combined with visibility analysis. Thus, an approach is detailed for supporting security monitoring. The approach is applied in the context of video sensor placement in an urban area, illustrating the various tradeoffs that can be identified using optimization-based techniques.

Automated generation of control skeletons for use in animation

The animation of an articulated figure is typically accomplished through the use of a corresponding control skeleton. Although the control skeleton is an effective tool, the manual construction of the skeleton can be a laborious process often requiring several hours of work and a fair degree of proficiency with the animation software used. The focus of the research described here is the automatic generation of such control skeletons. To this end, two solutions to the problem are presented, one general and one specific. In both cases, the input is required to be a set of polygonal data that defines the figure, and the output is a description of a control skeleton to be used in animating that figure. The general solution is widely applicable; it makes very few assumptions about the figure given as input or about the type of control skeleton that should be generated. A system is described that divides the problem into a series of steps, each of which is performed automatically. The basic process involves discretizing the figure, approximating its medial surface, and using that surface to construct a control skeleton. The system can produce a reasonably good control skeleton for any of a variety of figures in as little as one or two minutes on a low-end PC. The specific solution builds upon the general one but is geared toward producing more desirable skeletons for the very common case involving human-like and animal-like figures. Certain assumptions are made about the figure and about the type of control skeleton desired. In addition, heuristics based upon human and animal anatomy are invoked to adjust the control skeleton so that it is more anatomically appropriate. The motivation for this solution is the belief that a more anatomically appropriate control skeleton allows for more natural looking movement of a human or animal-like figure. Partly to support that claim, the system can produce geometry for individual bones that might function as the anatomical skeleton of the figure. This skeletal geometry can form the foundation for additional anatomical modeling that might add more realism to the animation of the figure.

Towards an interactive high visual complexity animation system

A computer animation system is discussed which employs interactive techniques and presents a unified approach to the graphical display of complex three dimensional data. The system facilitates the generation, manipulation and display of highly detailed data with the aid of interactive devices and a video interface to a standard color TV monitor. The system enables the animator to create a variety of objects (including texture) and to specify the necessary transformations for animation sequences. A run length processing technique combined with a brute force Z-buffer algorithm has been newly designed and implemented that can handle the intersection of several million faces, lines and points. This makes possible a full range of visual cues to simulate fire, smoke, water and complex 3-D texture such as grass, hair and bark. Basic concepts and approaches are described. The display algorithm and the procedure model to generate texture are presented and the implications of the system for computer animation are discussed. Extensions to the system are outlined which include a unique graphics display processor currently under construction that includes a partial implementation of the display algorithm in hardware.

Computing the arc length of parametric curves

Specifying constraints on motion is simpler if the curve is parameterized by arc length, but many parametric curves of practical interest cannot be parameterized by arc length. An approximate numerical reparameterization technique that improves on a previous algorithm by using a different numerical integration procedure that recursively subdivides the curve and creates a table of the subdivision points is presented. The use of the table greatly reduces the computation required for subsequent arc length calculations. After table construction, the algorithm takes nearly constant time for each arc length calculation. A linear increase in the number of control points can result in a more than linear increase in computation. Examples of this type of behavior are shown.<<ETX>>

The behavioral test-bed: Obtaining complex behavior from simple rules

Behavioral simulation is presented as a means to obtain complex global motion by simulating simple rules of behavior between locally related actors. A test-bed which has been developed to support experimentation with behavioral simulation is described. This test-bed has been used to create a library of physically behaving actors which can realistically reproduce the motion of flexible objects. The application of behavioral simulation to problems of motion specification in animation are described. The extension of this technique to simulate social behaviors is discussed.