Browsing by Author "Kry, Paul G."

Now showing 1 - 6 of 6
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    Adaptive Rigidification of Discrete Shells
    (ACM Association for Computing Machinery, 2023) Mercier-Aubin, Alexandre; Kry, Paul G.; Wang, Huamin; Ye, Yuting; Victor Zordan
    We present a method to improve the computation time of thin shell simulations by using adaptive rigidification to reduce the number of degrees of freedom. Our method uses a discretization independent metric for bending rates, and we derive a membrane strain rate to curvature rate equivalence that permits the use of a common threshold. To improve accuracy, we enhance the elastification oracle by considering both membrane and bending deformation to determine when to rigidify or elastify. Furthermore, we explore different approaches that are compatible with the previous work on adaptive rigidifcation and enhance the accuracy of the elastification on new contacts without increasing the computational overhead. Additionally, we propose a scaling approach that reduces the conditioning issues that arise from mixing rigid and elastic bodies in the same model.
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    Coupling Friction with Visual Appearance
    (ACM, 2021) Andrews, Sheldon; Nassif, Loic; Erleben, Kenny; Kry, Paul G.; Narain, Rahul and Neff, Michael and Zordan, Victor
    We present a novel meso-scale model for computing anisotropic and asymmetric friction for contacts in rigid body simulations that is based on surface facet orientations. The main idea behind our approach is to compute a direction dependent friction coefficient that is determined by an object's roughness. Specifically, where the friction is dependent on asperity interlocking, but at a scale where surface roughness is also a visual characteristic of the surface. A GPU rendering pipeline is employed to rasterize surfaces using a shallow depth orthographic projection at each contact point in order to sample facet normal information from both surfaces, which we then combine to produce direction dependent friction coefficients that can be directly used in typical LCP contact solvers, such as the projected Gauss-Seidel method. We demonstrate our approach with a variety of rough textures, where the roughness is both visible in the rendering and in the motion produced by the physical simulation.
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    Distant Collision Response in Rigid Body Simulations
    (The Eurographics Association and John Wiley & Sons Ltd., 2020) Coevoet, Eulalie; Andrews, Sheldon; Relles, Denali; Kry, Paul G.; Bender, Jan and Popa, Tiberiu
    We use a finite element model to predict the vibration response of objects in a rigid body simulation, such that rigid objects are augmented to provide a plausible elastic collision response between distant objects due to vibration. We start with a generalized eigenvalue decomposition of the elastic model to precompute a response to an impact at any point on an elastic object with fixed boundary conditions. Then, given a collision between objects, we generate an approximate response impulse to distribute to other objects already in contact with the colliding bodies. This can lead to distant impacts causing an object to slip, or a delicate stack of objects to fall. We also use a geodesic distance based spatial attenuation approximation for travelling waves in objects to respond to an impact at one contact with an impulse at other locations. This response ultimately allows a long distance relationship between contacts, both across a single object being struck, but also traversing the contact graph of a larger collection of objects. We qualitatively validate our approach with a ground truth simulation, and demonstrate a number of scenarios where a long distance relationship between contacts is valuable.
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    Global Position Prediction for Interactive Motion Capture
    (ACM, 2021) Schreiner, Paul; Perepichka, Maksym; Lewis, Hayden; Darkner, Sune; Kry, Paul G.; Erleben, Kenny; Zordan, Victor B.; Narain, Rahul and Neff, Michael and Zordan, Victor
    We present a method for reconstructing the global position of motion capture where position sensing is poor or unavailable. Capture systems, such as IMU suits, can provide excellent pose and orientation data of a capture subject, but otherwise need post processing to estimate global position. We propose a solution that trains a neural network to predict, in real-time, the height and body displacement given a short window of pose and orientation data. Our training dataset contains pre-recorded data with global positions from many different capture subjects, performing a wide variety of activities in order to broadly train a network to estimate on like and unseen activities. We compare training on two network architectures, a universal network (u-net) and a traditional convolutional neural network (CNN) - observing better error properties for the u-net in our results. We also evaluate our method for different classes of motion. We observe high quality results for motion examples with good representation in specialized datasets, while general performance appears better in a more broadly sampled dataset when input motions are far from training examples.
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    Inverse Dynamics Filtering for Sampling‐based Motion Control
    (© 2021 Eurographics ‐ The European Association for Computer Graphics and John Wiley & Sons Ltd, 2021) Xie, Kaixiang; Kry, Paul G.; Benes, Bedrich and Hauser, Helwig
    We improve the sampling‐based motion control method proposed by Liu et al. using inverse dynamics. To deal with noise in the motion capture we filter the motion data using a Butterworth filter where we choose the cutoff frequency such that the zero‐moment point falls within the support polygon for the greatest number of frames. We discuss how to detect foot contact for foot and ground optimization and inverse dynamics, and we optimize to increase the area of supporting polygon. Sample simulations receive filtered inverse dynamics torques at frames where the ZMP is sufficiently close to the support polygon, which simplifies the problem of finding the PD targets that produce physically valid control matching the target motion. We test our method on different motions and we demonstrate that our method has lower error, higher success rates, and generally produces smoother results.
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    Too Stiff, Too Strong, Too Smart: Evaluating Fundamental Problems with Motion Control Policies
    (ACM Association for Computing Machinery, 2023) Xie, Kaixiang; Xu, Pei; Andrews, Sheldon; Zordan, Victor B.; Kry, Paul G.; Wang, Huamin; Ye, Yuting; Victor Zordan
    Deep reinforcement learning (DRL) methods have demonstrated impressive results for skilled motion synthesis of physically based characters, and while these methods perform well in terms of tracking reference motions or achieving complex tasks, several concerns arise when evaluating the naturalness of the motion. In this paper, we conduct a preliminary study of specific quantitative metrics for measuring the naturalness of motion produced by DRL control policies beyond their visual appearance. Namely, we propose to study the stiffness of the control policy, in anticipation that it will influence how the character behaves in the presence of external perturbation. Second, we establish two baselines for strength that allow evaluating the use of joint torques in comparison to human performance. Third, we propose the study of variability to reveal the unnatural precision of control policies and how they compare to real human motion. In sum, we aim to establish repeatable measures to assess the naturalness of control policies produced by DRL methods, and we present a set of comparisons from state-of-the-art systems. Finally, we propose simple modifications to improve realism on these axes.