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Object Space EWA Surface Splatting: A Hardware Accelerated Approach to High Quality Point Rendering

Liu Ren, Hanspeter Pfister, and Matthias Zwicker

Abstract

Elliptical weighted average (EWA) surface splatting is a technique for high quality rendering of point-sampled 3D objects. EWA surface splatting renders water-tight surfaces of complex point models with high quality, anisotropic texture filtering. In this paper we introduce a new multi-pass approach to perform EWA surface splatting on modern PC graphics hardware, called object space EWA splatting. We derive an object space formulation of the EWA filter, which is amenable for acceleration by conventional triangle-based graphics hardware. We describe how to implement the object space EWA filter using a two pass rendering algorithm. In the first rendering pass, visibility splatting is performed by shifting opaque surfel polygons backward along the viewing rays, while in the second rendering pass view-dependent EWA prefiltering is performed by deforming texture mapped surfel polygons. We use texture mapping and alpha blending to facilitate the splatting process. We implement our algorithm using programmable vertex and pixel shaders, fully exploiting the capabilities of today's graphics processing units (GPUs).

Citation

Liu Ren, Hanspeter Pfister, and Matthias Zwicker. Object space EWA surface splatting: A hardware accelerated approach to high quality point rendering. In Computer Graphics Forum (Eurographics 2002), volume 21, September 2002. [BiBTeX]

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Creating Models of Truss Structures with Optimization

Jeffrey Smith, Jessica K. Hodgins, Irving Oppenheim, and Andrew Witkin

Abstract

We present a method for designing truss structures, a common and complex category of buildings, using non-linear optimization. Truss structures are ubiquitous in the industrialized world, appearing as bridges, towers, roof supports and building exoskeletons, yet are complex enough that modeling them by hand is time consuming and tedious. We represent trusses as a set of rigid bars connected by pin joints, which may change location during optimization. By including the location of the joints as well as the strength of individual beams in our design variables, we can simultaneously optimize the geometry and the mass of structures. We present the details of our technique together with examples illustrating its use, including comparisons with real structures.

Citation

Jeffrey Smith, Jessica K. Hodgins, Irving Oppenheim, and Andrew Witkin. Creating models of truss structures with optimization. ACM Transactions on Graphics (SIGGRAPH 2002), 21(3):295–301, July 2002. [BiBTeX]

Graphical Modeling and Animation of Ductile Fracture

James F. O'Brien, Adam W. Bargteil, and Jessica K. Hodgins

Abstract

In this paper, we describe a method for realistically animating ductile fracture in common solid materials such as plastics and metals. The effects that characterize ductile fracture occur due to interaction between plastic yielding and the fracture process. By modeling this interaction, our ductile fracture method can generate realistic motion for a much wider range of materials than could be realized with a purely brittle model. This method directly extends our prior work on brittle fracture [O'Brien and Hodgins, SIGGRAPH 99]. We show that adapting that method to ductile as well as brittle materials requires only a simple to implement modification that is computationally inexpensive. This paper describes this modification and presents results demonstrating some of the effects that may be realized with it.

Citation

James F. O'Brien, Adam W. Bargteil, and Jessica K. Hodgins. Graphical modeling and animation of ductile fracture. ACM Transactions on Graphics (SIGGRAPH 2002), 21(3):291–294, July 2002. [BiBTeX]

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Interactive Control of Avatars Animated With Human Motion Data

Jehee Lee, Jinxiang Chai, Paul S. A. Reitsma, Jessica K. Hodgins, and Nancy S. Pollard

Abstract

Real-time control of three-dimensional avatars is an important problem in the context of computer games and virtual environments. Avatar animation and control is difficult, however, because a large repertoire of avatar behaviors must be made available, and the user must be able to select from this set of behaviors, possibly with a low-dimensional input device. One appealing approach to obtaining a rich set of avatar behaviors is to collect an extended, unlabeled sequence of motion data appropriate to the application. In this paper, we show that such a motion database can be preprocessed for flexibility in behavior and efficient search and exploited for real-time avatar control. Flexibility is created by identifying plausible transitions between motion segments, and efficient search through the resulting graph structure is obtained through clustering. Three interface techniques are demonstrated for controlling avatar motion using this data structure: the user selects from a set of available choices, sketches a path through an environment, or acts out a desired motion in front of a video camera. We demonstrate the flexibility of the approach through four different applications and compare the avatar motion to directly recorded human motion.

Citation

Jehee Lee, Jinxiang Chai, Paul S. A. Reitsma, Jessica K. Hodgins, and Nancy S. Pollard. Interactive control of avatars animated with human motion data. ACM Transactions on Graphics (SIGGRAPH 2002), 21(3):491–500, July 2002. [BiBTeX]

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Motion Capture-Driven Simulations that Hit and React

Victor B. Zordan and Jessica K. Hodgins

Abstract

Controllable, reactive human motion is essential in many video games and training environments. Characters in these applications often perform tasks based on modified motion data, but response to unpredicted events is also important in order to maintain realism. We approach the problem of motion synthesis for interactive, humanlike characters by combining dynamic simulation and human motion capture data. Our control systems use trajectory tracking to follow motion capture data and a balance controller to keep the character upright while modifying sequences from a small motion library to accomplish specified tasks, such as throwing punches or swinging a racket. The system reacts to forces computed from a physical collision model by changing stiffness and damping terms. The freestanding, simulated humans respond automatically to impacts and smoothly return to tracking. We compare the resulting motion with video and recorded human data.

Citation

Victor B. Zordan and Jessica K. Hodgins. Motion capture-driven simulations that hit and react. In Proceedings of the 2002 ACM SIGGRAPH / Eurographics Symposium on Computer animation, pages 89–96. ACM Press, 2002. [BiBTeX]

Simulation Level of Detail for Multiagent Control

David C. Brogan and Jessica K. Hodgins

Abstract

Many classes of applications require multiagent navigation control algorithms to specify the movements and actions of heterogeneous groups containing thousands of characters. The scale and complexity of these interacting character groups require navigation control algorithms that are both generalizable and specifically tuned to particular character platforms. We propose a technique called simulation level of detail (LOD) that provides a simulation-based interface between navigation control algorithms and the specific mobile characters on which they operate. A simulation LOD efficiently models a character's ability to move given its dynamic state and provides this simplified version of the character to navigation controllers for use in run-time search algorithms that compute locomotion actions. We develop our simulation LOD algorithms on groups of physically simulated human and alien bicyclists and demonstrate reusable controllers that provide improvements in path following and herding tasks.

Citation

David C. Brogan and Jessica K. Hodgins. Simulation level of detail for multiagent control. In Proceedings of the First International Joint Conference on Autonomous Agents and Multiagent Systems, pages 199–206. ACM Press, 2002. [BiBTeX]

Computing the Physical Parameters of Rigid-Body Motion from Video

Kiran S. Bhat, Steven M. Seitz, Jovan Popović, and P. K. Khosla

Abstract

This paper presents an optimization framework for estimating the motion and underlying physical parameters of a rigid body in free flight from video. The algorithm takes a video clip of a tumbling rigid body of known shape and generates a physical simulation of the object observed in the video clip. This solution is found by optimizing the simulation parameters to best match the motion observed in the video sequence. These simulation parameters include initial positions and velocities, environment parameters like gravity direction and parameters of the camera. A global objective function computes the sum squared difference between the silhouette of the object in simulation and the silhouette obtained from video at each frame. Applications include creating interesting rigid body animations, tracking complex rigid body motions in video and estimating camera parameters from video.

Citation

Kiran S. Bhat, Steven M. Seitz, Jovan Popović, and P. K. Khosla. Computing the physical parameters of rigid-body motion from video. In 7th European Conference on Computer Vision (ECCV 2002) (Part I), pages 551–565, May 2002. [BiBTeX]

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