<H1>1. Introduction</H1>
      
      Today’s cloth simulators for animation, visual effects, games, and apparel design can mimic real cloth to a high degree of fidelity. But to fully exploit their capabilities, the constitutive models for cloth deformation must be tuned with great care. During this tuning process it is difficult to tell which models and which parameters are giving results more like the real material. This paper aims to solve this problem by introducing new techniques to measure complete cloth behavior under controlled conditions and to estimate cloth deformation models from these measurements. Most methods for testing cloth move the sample into a state of near-uniform strain, exercising one or at most two components of strain at once: pure stretching, pure shearing, or pure bending. One or two forces are measured to quantify the cloth’s resistance to deformation, and the resulting forcedisplacement curves are valuable in studying the differences between materials. However, this approach has certain limitations. The inevitable deviations from uniform strain create modeling error that cannot be quantified without knowing the actual strain variation; and force-displacement curves can be used directly to tune a cloth model, but do not provide any way to validate the resulting fit. The contributions of this paper are, first, a new, general system for observing cloth properties that measures more complete data than previous work in cloth capture or textile testing, and second, a new method for fitting parametric models to this type of data. Finally we show results that illustrate the performance of several widely used cloth models. Our measurement system applies forces to a sample of cloth using actuators and force sensors that let us know the complete applied force, in 3D. The resulting deformation is tracked by a stereo computer vision system that captures the complete deformation, also in 3D. Having deformation and force information makes our data well suited to model validation—the experiment measures the complete answer that should be predicted by a cloth simulator. Also, we do not need uniform strain, and in this paper we illustrate a range of tests, some that mimic traditional tests and some with more complex deformations. Our approach to model estimation is to numerically optimize nonlinear stress-strain curves to minimize errors in force and position compared to the measurement. We have designed a general fitting method, suited for the vast majority of existing cloth models, that leverages equilibrium conditions to guide the iteration. By estimating model parameters under a sequence of deformations of increasing complexity, we alleviate problems with convergence in the presence of abundant local minima. We have used our system to fit three membrane models and two bending models from the graphics literature, each based on a different strain measure, and to evaluate the resulting models against more complex motions.
      3. MIT CSAIL 4. Cornell University
      c 2012 The Author(s) Computer Graphics Forum c 2012 The Eurographics Association and Blackwell Publishing Ltd. Published by Blackwell Publishing, 9600 Garsington Road, Oxford OX4 2DQ, UK and 350 Main Street, Malden, MA 02148, USA.
      Miguel et al. / Data-Driven Estimation of Cloth Simulation Models
      
        