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PublicationPhysics-Based Object Pose and Shape Estimation from Multiple Views(1994-11-01) Metaxas, Dimitris; Metaxas, DimitrisThis paper presents a new algorithm for object pose and shape estimation from multiple views. Using a qualitative shape recovery scheme we first segment the image into parts which belong to a vocabulary of primitives. Based on the additional constraints provided by the qualitative shapes we extend our physics-based framework to allow object pose and shape estimation from stereo images where the two cameras have arbitrary relative orientations. We then generalize our algorithm to integrate measurements from multiple views. To recover more complex objects we generalize the definition for the global bending deformation. We also present an algorithm for model discretization which evenly tessellates the model surface. We demonstrate the usefulness of our technique in experiments involving real images from of a variety of object shapes which may be partially occluded. PublicationPhysics-based Tracking of 3D Objects in 2D Image Sequences(1994-11-01) Metaxas, Dimitris; Metaxas, Dimitris; Dickinson, SvenWe present a new technique for tracking 3D objects in 2D image sequences. We assume that objects are constructed from a class of volumetric part primitives. The models are initially recovered using a qualitative shape recovery process. We subsequently track the objects using local forces computed from image potentials. Therefore, we avoid the expensive computation of image features. By integrating measurements from stereo images, 3D positions(as well as other model parameters) of the objects can be continuously updated using an extended Kalman filter. Our model-based approach can handle occlusions in scenes with multiple moving objects by predicting their occurrences. To handle severe or unexpected occlusion we use a feedback mechanism between the quantitative and qualitative shape estimation systems. We demonstrate our technique in experiments involving image sequences from complex motions of objects. PublicationIntegration of Quantitative and Qualitative Techniques for Deformable Model Fitting from Orthographic, Perspective, and Stereo Projections(1993) Metaxas, Dimitris; Metaxas, Dimitris; Dickinson, Sven JIn this paper, we synthesize a new approach to 3-D object shape recovery by integrating qualitative shape recovery techniques and quantitative physics based shape estimation techniques. Specifically, we first use qualitative shape recovery and recognition techniques to provide strong fitting constraints on physics-based deformable model recovery techniques. Secondly, we extend our previously developed technique of fitting deformable models to occluding image contours to the case of image data captured under general orthographic, perspective, and stereo projections. PublicationActive Part-Decomposition, Shape and Motion Estimation of Articulated Objects: A Physics-based Approach(1994-11-01) Kakadiaris, Ioannis A.; Metaxas, Dimitris; Metaxas, Dimitris; Bajcsy, RuzenaWe present a novel, robust, integrated approach to segmentation shape and motion estimation of articulated objects. Initially, we assume the object consists of a single part, and we fit a deformable model to the given data using our physics-based framework. As the object attains new postures, we decide based on certain criteria if and when to replace the initial model with two new models. These criteria are based on the model’s state and the given data. We then fit the models to the data using a novel algorithm for assigning forces from the data to the two models, which allows partial overlap between them and determination of joint location. This approach is applied iteratively until all the object’s moving parts are identified. Furthermore, we define new global deformations and we demonstrate our technique in a series of experiments, where Kalman filtering is employed to account for noise and occlusion. PublicationCollision Resolutions in Cloth Simulation(2001-11-07) Huh, Suejung; Metaxas, Dimitris; Badler, Norman I; Huh, Suejung; Metaxas, Dimitris; Badler, Norman IWe present a new collision resolution scheme for cloth collisions. Our main concern is to find dynamically convincing resolutions, i.e. positions and velocities of cloth elements, for any kinds of collisions occuring in cloth simulation (cloth-cloth, cloth-rigid, and cloth-cloth-rigid). We define our cloth surface as connected faces of mass particles where each particle is controlled by its internal energy functions. Our collision resolution method finds appropriate next positions and velocities of particles by conserving the particles’ momentums as accurately as possible. Cloth-cloth collision resolution is a special case of deformable N-body collision resolution. So to solve deformable N-body collision resolutions, we propose a new collision resolution method, which groups cloth particles into parts and resolves collisions between parts using the law of momentum conservation. To resolve collisions, we solve a system of linear equations derived from the collision relationships. A system of linear equations is built using a scheme adapted from the simultaneous resolution method for rigid N-body collisions . For the special case where we can find cyclic relationships in collisions, we solve a system of linear inequalities derived from the collision relationships.