MaterialCloning: Acquiring Elasticity Parameters from Images for Medical Applications

A Visual Approach to Measure Cloth-Body and Cloth-Cloth Friction

Measuring contact friction in soft-bodies usually requires a specialised physics bench and a tedious acquisition protocol. This makes the prospect of a purely non-invasive, video-based measurement technique particularly attractive. Previous works have shown that such a video-based estimation is feasible for material parameters using deep learning, but this has never been applied to the friction estimation problem which results in even more subtle visual variations. Because acquiring a large dataset for this problem is impractical, generating it from simulation is the obvious alternative. However, this requires the use of a frictional contact simulator whose results are not only visually plausible, but physically-correct enough to match observations made at the macroscopic scale. In this paper, which is an extended version of our former work A. H. Rasheed, V. Romero, F. Bertails-Descoubes, S. Wuhrer, J.-S. Franco, and A Lazarus, "Learning to measure the static friction coefficient in cloth contact," in Proc. IEEE/CVF Conf. Comput. Vis. Pattern Recognit., 2020, pp. 9909-9918, we propose to our knowledge the first non-invasive measurement network and adjoining synthetic training dataset for estimating cloth friction at contact, for both cloth-hard body and cloth-cloth contacts. To this end we build a protocol for validating and calibrating a state-of-the-art frictional contact simulator, in order to produce a reliable dataset. We furthermore show that without our careful calibration procedure, the training fails to provide accurate estimation results on real data. We present extensive results on a large acquired test set of several hundred real video sequences of cloth in friction, which validates the proposed protocol and its accuracy.

Learning Physical Parameters and Detail Enhancement for Gaseous Scene Design Based on Data Guidance

This article articulates a novel learning framework for both parameter estimation and detail enhancement for Eulerian gas based on data guidance. The key motivation of this article is to devise a new hybrid, grid-based simulation that could inherit modeling and simulation advantages from both physically-correct simulation methods and powerful data-driven methods, while combating existing difficulties exhibited in both approaches. We first employ a convolutional neural network (CNN) to estimate the physical parameters of gaseous phenomena in Eulerian settings, then we can use the just-learnt parameters to re-simulate (with or without artists' guidance) for specific scenes with flexible coupling effects. Next, a second CNN is adopted to reconstruct the high-resolution velocity field to guide a fast re-simulation on the finer grid, achieving richer and more realistic details with little extra computational expense. From the perspective of physics-based simulation, our trained networks respect temporal coherence and physical constraints. From the perspective of the data-driven machine-learning approaches, our network design aims at extracting a meaningful parameters and reconstructing visually realistic details. Additionally, our implementation based on parallel acceleration could significantly enhance the computational performance of every involved module. Our comprehensive experiments confirm the controllability, effectiveness, and accuracy of our novel approach when producing various gaseous scenes with rich details for widespread graphics applications.

A Novel Nonlinear Parameter Estimation Method of Soft Tissues

The elastic parameters of soft tissues are important for medical diagnosis and virtual surgery simulation. In this study, we propose a novel nonlinear parameter estimation method for soft tissues. Firstly, an in-house data acquisition platform was used to obtain external forces and their corresponding deformation values. To provide highly precise data for estimating nonlinear parameters, the measured forces were corrected using the constructed weighted combination forecasting model based on a support vector machine (WCFM_SVM). Secondly, a tetrahedral finite element parameter estimation model was established to describe the physical characteristics of soft tissues, using the substitution parameters of Young's modulus and Poisson's ratio to avoid solving complicated nonlinear problems. To improve the robustness of our model and avoid poor local minima, the initial parameters solved by a linear finite element model were introduced into the parameter estimation model. Finally, a self-adapting Levenberg-Marquardt (LM) algorithm was presented, which is capable of adaptively adjusting iterative parameters to solve the established parameter estimation model. The maximum absolute error of our WCFM_SVM model was less than 0.03 Newton, resulting in more accurate forces in comparison with other correction models tested. The maximum absolute error between the calculated and measured nodal displacements was less than 1.5 mm, demonstrating that our nonlinear parameters are precise.