Paul G. Kry

FoleyAutomatic: physically-based sound effects for interactive simulation and animation

We describe algorithms for real-time synthesis of realistic sound effects for interactive simulations (e.g., games) and animation. These sound effects are produced automatically, from 3D models using dynamic simulation and user interaction. We develop algorithms that are efficient, physically-based, and can be controlled by users in natural ways. We develop effective techniques for producing high quality continuous contact sounds from dynamic simulations running at video rates which are slow relative to audio synthesis. We accomplish this using modal models driven by contact forces modeled at audio rates, which are much higher than the graphics frame rate. The contact forces can be computed from simulations or can be custom designed. We demonstrate the effectiveness with complex realistic simulations.

EigenSkin: real time large deformation character skinning in hardware

We present a technique which allows subtle nonlinear quasi-static deformations of articulated characters to be compactly approximated by data-dependent eigenbases which are optimized for real time rendering on commodity graphics hardware. The method extends the common Skeletal-Subspace Deformation (SSD) technique to provide efficient approximations of the complex deformation behaviours exhibited in simulated, measured, and artist-drawn characters. Instead of storing displacements for key poses (which may be numerous), we precompute principal components of the deformation influences for individual kinematic joints, and so construct error-optimal eigenbases describing each joints deformation subspace. Pose-dependent deformations are then expressed in terms of these reduced eigenbases, allowing precomputed coefficients of the eigenbasis to be interpolated at run time. Vertex program hardware can then efficiently render nonlinear skin deformations using a small number of eigendisplacements stored in graphics hardware. We refer to the final resulting character skinning construct as the models EigenSkin. Animation results are presented for a very large nonlinear finite element model of a human hand rendered in real time at minimal cost to the main CPU.

Preserving topology and elasticity for embedded deformable models

In this paper we introduce a new approach for the embedding of linear elastic deformable models. Our technique results in significant improvements in the efficient physically based simulation of highly detailed objects. First, our embedding takes into account topological details, that is, disconnected parts that fall into the same coarse element are simulated independently. Second, we account for the varying material properties by computing stiffness and interpolation functions for coarse elements which accurately approximate the behaviour of the embedded material. Finally, we also take into account empty space in the coarse embeddings, which provides a better simulation of the boundary. The result is a straightforward approach to simulating complex deformable models with the ease and speed associated with a coarse regular embedding, and with a quality of detail that would only be possible at much finer resolution.

Interaction capture and synthesis

Modifying motion capture to satisfy the constraints of new animation is difficult when contact is involved, and a critical problem for animation of hands. The compliance with which a character makes contact also reveals important aspects of the movements purpose. We present a new technique called interaction capture, for capturing these contact phenomena. We capture contact forces at the same time as motion, at a high rate, and use both to estimate a nominal reference trajectory and joint compliance. Unlike traditional methods, our method estimates joint compliance without the need for motorized perturbation devices. New interactions can then be synthesized by physically based simulation. We describe a novel position-based linear complementarity problem formulation that includes friction, breaking contact, and the compliant coupling between contacts at different fingers. The technique is validated using data from previous work and our own perturbation-based estimates.

Continuous contact simulation for smooth surfaces

Dynamics simulation of smooth surfaced rigid bodies in contact is a critical problem in physically based animation and interactive virtual environments. We describe a technique that uses reduced coordinates to evolve a single continuous contact between smooth piecewise parametric surfaces. The incorporation of friction into our algorithm is straightforward. The dynamics equations, although slightly more complex due to the reduced coordinate formulation, can be integrated easily using explicit integrators without the need for constraint stabilization. Reduced coordinates confine integration errors to the constraint manifold, thereby permitting a wide choice of step sizes with visually acceptable results. We demonstrate these results using Loop Subdivision surfaces with parametric evaluation.

Modal Locomotion: Animating Virtual Characters with Natural Vibrations

We present a general method to intuitively create a wide range of locomotion controllers for 3D legged characters. The key of our approach is the assumption that efficient locomotion can exploit the natural vibration modes of the body, where these modes are related to morphological parameters such as the shape, size, mass, and joint stiffness. The vibration modes are computed for a mechanical model of any 3D character with rigid bones, elastic joints, and additional constraints as desired. A small number of vibration modes can be selected with respect to their relevance to locomotion patterns and combined into a compact controller driven by very few parameters. We show that these controllers can be used in dynamic simulations of simple creatures, and for kinematic animations of more complex creatures of a variety of shapes and sizes.

The Tango: a tangible tangoreceptive whole-hand human interface

We describe the Tango, a new passive haptic interface for whole-hand interaction with 3D objects. The Tango is shaped like a ball and can be grasped comfortably in one hand. Its pressure sensitive skin measures the contact pressures exerted by the users hand, and accelerometers within the device measure its motion and attitude. This information can be used for novel modes of interaction with three-dimensional objects. We describe the design of the device, and the software for interpreting the sensor data for user interaction. Accompanying this paper, there is a demonstration of the device at the Hands-On Demo session of the conference.

Forward dynamics algorithms for multibody chains and contact

We describe a framework for derivation of several forward dynamics algorithms used in robotics. The framework is based on formulating an augmented system and performing block matrix elimination on this system. Several popular algorithms such as the O(N) articulated body method, and the composite rigid body method can be easily derived. We also derive an algorithm for simulation of contact between smooth bodies of arbitrary shape, in contact coordinates. Finally, we discuss some potential numerical difficulties that could arise and their solution.

HandNavigator: hands-on interaction for desktop virtual reality

This paper presents a novel interaction system, aimed at hands-on manipulation of digital models through natural hand gestures. Our system is composed of a new physical interaction device coupled with a simulated compliant virtual hand model. The physical interface consists of a SpaceNavigator, augmented with pressure sensors to detect directional forces applied by the users fingertips. This information controls the position, orientation, and posture of the virtual hand in the same way that the SpaceNavigator uses measured forces to animate a virtual frame. In this manner, user control does not involve fatigue due to reaching gestures or holding a desired hand shape. During contact, the user has a realistic visual feedback in the form of plausible interactions between the virtual hand and its environment. Our device is well suited to any situation where hand gesture, contact, or manipulation tasks need to be performed in virtual. We demonstrate the device in several simple virtual worlds and evaluate it through a series of user studies.

Embedded thin shells for wrinkle simulation

We present a new technique for simulating high resolution surface wrinkling deformations of composite objects consisting of a soft interior and a harder skin. We combine high resolution thin shells with coarse finite element lattices and define frequency based constraints that allow the formation of wrinkles with properties matching those predicted by the physical parameters of the composite object. Our two-way coupled model produces the expected wrinkling behavior without the computational expense of a large number of volumetric elements to model deformations under the surface. We use C1 quadratic shape functions for the interior deformations, allowing very coarse resolutions to model the overall global deformation efficiently, while avoiding visual artifacts of wrinkling at discretization boundaries. We demonstrate that our model produces wrinkle wavelengths that match both theoretical predictions and high resolution volumetric simulations. We also show example applications in simulating wrinkles on passive objects, such as furniture, and for wrinkles on faces in character animation.