SCA 07: Eurographics/SIGGRAPH Symposium on Computer Animation
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Browsing SCA 07: Eurographics/SIGGRAPH Symposium on Computer Animation by Subject "Categories and Subject Descriptors (according to ACM CCS): I.3.7 [Computer Graphics]: Three-Dimensional Graphics and Realism"
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Item Guided TimeWarping for Motion Editing(The Eurographics Association, 2007) Hsu, Eugene; Silva, Marco da; Popovic, Jovan; Dimitris Metaxas and Jovan PopovicTime warping allows users to modify timing without affecting poses. It has many applications in animation systems for motion editing, such as refining motions to meet new timing constraints or modifying the acting of animated characters. However, time warping typically requires many manual adjustments to achieve the desired results. We present a technique which simplifies this process by allowing time warps to be guided by a provided reference motion. Given few timing constraints, it computes a warp that both satisfies these constraints and maximizes local timing similarities to the reference. The algorithm is fast enough to incorporate into standard animation workflows. We apply the technique to two common tasks: preserving the natural timing of motions under new time constraints and modifying the timing of motions for stylistic effects.Item Legendre Fluids: A Unified Framework for Analytic Reduced Space Modeling and Rendering of Participating Media(The Eurographics Association, 2007) Gupta, Mohit; Narasimhan, Srinivasa G.; Dimitris Metaxas and Jovan PopovicIn this paper, we present a unified framework for reduced space modeling and rendering of dynamic and non- homogenous participating media, like snow, smoke, dust and fog. The key idea is to represent the 3D spatial variation of the density, velocity and intensity fields of the media using the same analytic basis. In many situa- tions, natural effects such as mist, outdoor smoke and dust are smooth (low frequency) phenomena, and can be compactly represented by a small number of coefficients of a Legendre polynomial basis. We derive analytic ex- pressions for the derivative and integral operators in the Legendre coefficient space, as well as the triple product integrals of Legendre polynomials. These mathematical results allow us to solve both the Navier-Stokes equations for fluid flow and light transport equations for single scattering efficiently in the reduced Legendre space. Since our technique does not depend on volume grid resolution, we can achieve computational speedups as compared to spatial domain methods while having low memory and pre-computation requirements as compared to data- driven approaches. Also, analytic definition of derivatives and integral operators in the Legendre domain avoids the approximation errors inherent in spatial domain finite difference methods. We demonstrate many interesting visual effects resulting from particles immersed in fluids as well as volumetric scattering in non-homogenous and dynamic participating media, such as fog and mist.Item On the Beat! Timing and Tension for Dynamic Characters(The Eurographics Association, 2007) Allen, Brian; Chu, Derek; Shapiro, Ari; Faloutsos, Petros; Dimitris Metaxas and Jovan PopovicDynamic simulation is a promising complement to kinematic motion synthesis, particularly in cases where simulated characters need to respond to unpredictable interactions. Moving beyond simple rag-doll effects, though, requires dynamic control. The main issue with dynamic control is that there are no standardized techniques that allow an animator to precisely specify the timing of the motion while still providing natural response to external disturbances. The few proposed techniques that address this problem are based on heuristically or manually tuning proportional-derivative (PD) control parameters and do not generalize easily. We propose an approach to dynamic character control that is able to honor timing constraints, to provide naturallooking motion and to allow for realistic response to perturbations. Our approach uses traditional PD control to interpolate between key-frames. The key innovation is that the parameters of the PD controllers are computed for each joint analytically. By continuously updating these parameters over time, the controller is able to respond naturally to both external perturbations and changes in the state of the character