Wayne L. Wooten

Animating human athletics

This paper describes algorithms for the animation of male and female models performing three dynamic athletic behaviors: running, bicycling, and vaulting. We animate these behaviors using control algorithms that cause a physically realistic model to perform the desired maneuver. For example, control algorithms allow the simulated humans to maintain balance while moving their arms, to run or bicycle at a variety of speeds, and to perform two vaults. For each simulation, we compare the computed motion to that of humans performing similar maneuvers. We perform the comparison both qualitatively through real and simulated video images and quantitatively through simulated and biomechanical data.

Simulating leaping, tumbling, landing and balancing humans

This paper describes a technique for generating transitions between simulated behaviors. By parametrizing individual basis behaviors, we can design control systems such that the exit states of one leaves the simulated character in a valid initial state for the next. The parametrization allows one to generate a wide variety of motions from a single basis behavior. The nesting of the input and output states allows easy transitions between behaviors and generation of many behaviors from a small set of basis behaviors. We demonstrate this approach with four basis behaviors: leaping, tumbling, landing, and balancing. We demonstrate transitions by generating a diverse set of gymnastic behaviors, including a standing broad jump, vertical leap, forward somersault, backward somersault, back handspring, and various platform dives.

Ray Differentials and Multiresolution Geometry Caching for Distribution Ray Tracing in Complex Scenes

When rendering only directly visible objects, ray tracing a few levels of specular reflection from large, low‐curvaturesurfaces, and ray tracing shadows from point‐like light sources, the accessed geometry is coherentand a geometry cache performs well. But in many other cases, the accessed geometry is incoherent and a standardgeometry cache performs poorly: ray tracing of specular reflection from highly curved surfaces, tracing rays thatare many reflection levels deep, and distribution ray tracing for wide glossy reflection, global illumination, widesoft shadows, and ambient occlusion. Fortunately, less geometric accuracy is necessary in the incoherent cases.This observation can be formalized by looking at the ray differentials for different types of scattering: coherentrays have small differentials, while incoherent rays have large differentials. We utilize this observation to obtainefficient multiresolution caching of geometry and textures (including displacement maps) for classic and distributionray tracing in complex scenes. We use an existing multiresolution caching scheme (originally developed forscanline rendering) for textures and displacement maps, and introduce a multiresolution geometry caching schemefor tessellated surfaces. The multiresolution geometry caching scheme makes it possible to efficiently render scenesthat, if fully tessellated, would use 100 times more memory than the geometry cache size.

Reducing crosstalk between stereoscopic views

Crosstalk between the left and right eyes consists of the one eyes image seen faintly by the other. Image processing can reduce this. The technique is effective, but there are costs of course, and some surprises.

Animation of Human Diving

The motion of a human platform diver was simulated using a dynamic model and a control system. The dynamic model has 32 actuated degrees of freedom and dynamic parameters within the range of those reported in the literature for humans. The control system uses algorithms for balance, jumping, and twisting to initiate the dive, sequences of desired values for proportional‐derivative servos to perform the aerial portion of the dice, and a state machine to sequence the actions throughout the dice. The motion of the simulated diver closely resembles video footage of dices performed by human athletes. The control and simulation techniques presented in this paper are useful for providing realistic motion for synthetic actors in computer animations and virtual environments and may some day be useful for analysis of sports performance.

GROOP: an object-oriented toolkit for animated 3D graphics

GROOP is an object-oriented toolkit for creating 3D computer graphics applications. It is designed for application developers who are not familiar with computer graphics, but are familiar with object-oriented programming. While application programmers are able to quickly create animated 3D graphical objects, the toolkit is also sophisticated enough for experience programmers. In addition to creating stationary 3D objects, the toolkit is used to construct animated objects. Sophisticated reusable articulated objects have been created for use in a variety of applications, similar to static 2D and 3D clip art available today.

Transitions between dynamically simulated motions: leaping, tumbling, landing, and balancing

Animating characters for video games is a challenge because a good game requires a wide variety of appealing character motion and realistic responses to unpredictable user input. Video game systems usually generate continuous action by selecting an appropriate motion from a library of data and then smoothly interpolating between the current motion and the newly selected motion. We present an alternative, simulation-based approach that computes the desired motion by making smooth transitions between a set of parameterized basis control systems. One potential advantage of dynamic simulation is that a basis control system can be parameterized to produce a variety of motions [1]. We use the term basis controller to describe a control system for a speci c low-level task such as leaping, tumbling, landing, or balancing. Each basis control system provides a set of parameters for modifying the desired behavior. For example, the basis controller for leaping allows the speci cation of the height and the distance of the jump. To produce the equivalent range of behavior using a motion library, a number of jumping sequences would have to be interpolated. By using a sequence of basis controllers, we can create a wider variety of motions for more complex tasks. Control systems can be designed so that the exit state of one control system usually leaves the simulation in a valid initial state for the next control system, making transitions easy to achieve [2]. We demonstrate the basis control systems and transitions between them by generating a diverse set of behaviors for a male and female character, including an inward 2-1/2 somersault pike, standing forward and backward somersaults, a handspring, and vari-

RenderMan: An Advanced Path-Tracing Architecture for Movie Rendering

Pixar’s RenderMan renderer is used to render all of Pixar’s films and by many film studios to render visual effects for live-action movies. RenderMan started as a scanline renderer based on the Reyes algorithm, and it was extended over the years with ray tracing and several global illumination algorithms. This article describes the modern version of RenderMan, a new architecture for an extensible and programmable path tracer with many features that are essential to handle the fiercely complex scenes in movie production. Users can write their own materials using a bxdf interface and their own light transport algorithms using an integrator interface—or they can use the materials and light transport algorithms provided with RenderMan. Complex geometry and textures are handled with efficient multi-resolution representations, with resolution chosen using path differentials. We trace rays and shade ray hit points in medium-sized groups, which provides the benefits of SIMD execution without excessive memory overhead or data streaming. The path-tracing architecture handles surface, subsurface, and volume scattering. We show examples of the use of path tracing, bidirectional path tracing, VCM, and UPBP light transport algorithms. We also describe our progressive rendering for interactive use and our adaptation of denoising techniques.

Synthetic visible imagery for multiattribute target identification

A visible band signature model is under development at the Georgia Tech Research Institute (GTRI) to support research activities ranging from performance studies of human observers to the definition and development of feature extraction algorithms. This model generates visible band imagery based on a solar illumination model coupled with computer graphics rendering algorithms. The solar illunination model employs a modified version of a radiative transfer algorithm originally developed for the Air Force. Selection of an appropriate reflection model followed an evaluation of several techniques. The selection criteria and results of the survey are presented.

Enhanced Atmospheric Models For IR Image Simulation

Several techniques are presented for modeling sky backgrounds in an infrared scene simulation. Each technique provides a part of the overall requirements for an accurate sky background model. A description of each technique is given and examples of each are presented. The main result of these investigations is that it is possible to combine both physically accurate models of atmospheric radiative transfer with computer algorithms for the generation of realistic cloud imagery.