Calipso: Physics-based Image and Video Editing through CAD Model Proxies

We present Calipso, an interactive method for editing images and videos in a physically-coherent manner. Our main idea is to realize physics-based manipulations by running a full physics simulation on proxy geometries given by non-rigidly aligned CAD models. Running these simulations allows us to apply new, unseen forces to move or deform selected objects, change physical parameters such as mass or elasticity, or even add entire new objects that interact with the rest of the underlying scene. In Calipso, the user makes edits directly in 3D; these edits are processed by the simulation and then transfered to the target 2D content using shape-to-image correspondences in a photo-realistic rendering process. To align the CAD models, we introduce an efficient CAD-to-image alignment procedure that jointly minimizes for rigid and non-rigid alignment while preserving the high-level structure of the input shape. Moreover, the user can choose to exploit image flow to estimate scene motion, producing coherent physical behavior with ambient dynamics. We demonstrate Calipso's physics-based editing on a wide range of examples producing myriad physical behavior while preserving geometric and visual consistency.Comment: 11 page

La complémentarité « livres – Internet » dans les pratiques documentaires des étudiants en histoire

Actually, a double process gets the university education. The first one concerns the empowerment of universities (Laws relative to the Responsibilities of Universities, LRU). The second shows itself by the dominion of one complex informative paradigm, too often reduce under the notion of "Information society" or confused with "Internet". However, the specifically scriptural requirements of the system of validation of teachings Educations, distributed show themselves essentially through épistémiques, ethical and methodological frames of the disciplinary fields. How could we envisage the impact of this double movement on the capacities of the students to dead new educational and informative imperatives ? We wish to bring some elements of answer by analyzing the documentary practices of historian students, considered in the whole of the general intellectual practices, registered in a particular épistémique, methodological and ethical environment .Un double processus touche actuellement le système d'enseignement universitaire. Le premier concerne l'autonomisation des universités (Lois relatives aux Responsabilités des Universités, LRU). Le second se manifeste par la domination d'un paradigme informationnel complexe trop souvent condenser sous la notion de « Société de l'information » ou réduit à Internet. Or, les exigences spécifiquement scripturales du système de validation des enseignements dispensés au sein même de l'université se manifestent essentiellement au travers de cadres épistémiques, éthiques et méthodologiques propres aux champs disciplinaires. Comment dans ces conditions envisager l'impact de ce double mouvement sur les capacités des étudiants à appréhender de nouveaux impératifs pédagogiques et informationnels ? Nous souhaitons apporter certains éléments de réponse en analysant les pratiques documentaires des étudiants en histoire, considérées dans l'ensemble des pratiques intellectuelles générales, inscrites dans un environnement épistémique, méthodologique et éthique particulier

Real-time Error Control for Surgical Simulation

Objective: To present the first real-time a posteriori error-driven adaptive finite element approach for real-time simulation and to demonstrate the method on a needle insertion problem. Methods: We use corotational elasticity and a frictional needle/tissue interaction model. The problem is solved using finite elements within SOFA. The refinement strategy relies upon a hexahedron-based finite element method, combined with a posteriori error estimation driven local $h$-refinement, for simulating soft tissue deformation. Results: We control the local and global error level in the mechanical fields (e.g. displacement or stresses) during the simulation. We show the convergence of the algorithm on academic examples, and demonstrate its practical usability on a percutaneous procedure involving needle insertion in a liver. For the latter case, we compare the force displacement curves obtained from the proposed adaptive algorithm with that obtained from a uniform refinement approach. Conclusions: Error control guarantees that a tolerable error level is not exceeded during the simulations. Local mesh refinement accelerates simulations. Significance: Our work provides a first step to discriminate between discretization error and modeling error by providing a robust quantification of discretization error during simulations.Comment: 12 pages, 16 figures, change of the title, submitted to IEEE TBM

Efficient parallelization strategy for real-time FE simulations

This paper introduces an efficient and generic framework for finite-element simulations under an implicit time integration scheme. Being compatible with generic constitutive models, a fast matrix assembly method exploits the fact that system matrices are created in a deterministic way as long as the mesh topology remains constant. Using the sparsity pattern of the assembled system brings about significant optimizations on the assembly stage. As a result, developed techniques of GPU-based parallelization can be directly applied with the assembled system. Moreover, an asynchronous Cholesky precondition scheme is used to improve the convergence of the system solver. On this basis, a GPU-based Cholesky preconditioner is developed, significantly reducing the data transfer between the CPU/GPU during the solving stage. We evaluate the performance of our method with different mesh elements and hyperelastic models and compare it with typical approaches on the CPU and the GPU

Internet au coeur des pratiques documentaires des étudiants : dans quelle mesure ?

Intervention aux 7èmes Rencontres FORMIST (ENSSIB, 14 juin 2007). Internet reste pour beaucoup d\u27étudiants un moyen essentiel permettant de répondre à ces multiples exigences. Ainsi, Internet prime désormais autant que le livre, sur les autres supports documentaires, le livre conservant toutefois un impact essentiel de par une certaine caution intellectuelle forte. Il semble donc important de mesurer l\u27impact de cet outil au sein même des pratiques documentaires des étudiants, c\u27est-à-dire, de mettre en perspective non seulement les représentations que ces publics peuvent en avoir mais aussi la place qu\u27ils lui accordent dans le travail intellectuel quotidien qu\u27ils mènent

Implicit FEM and Fluid Coupling on GPU for Interactive Multiphysics Simulation

International audienceWe present a method to implement on the GPU an implicit FEM solver which is fast and stable enough to handle interactions and collisions. We combine this method with GPU-based fluids and collision detection to achieve interactive multiphysics simulations entirely running on the GPU

Controlling the Error on Target Motion through Real-time Mesh Adaptation: Applications to Deep Brain Stimulation

We present an error-controlled mesh refinement procedure for needle insertion simulation and apply it to the simulation of electrode implantation for deep brain stimulation, including brain shift. Our approach enables to control the error in the computation of the displacement and stress fields around the needle tip and needle shaft by suitably refining the mesh, whilst maintaining a coarser mesh in other parts of the domain. We demonstrate through academic and practical examples that our approach increases the accuracy of the displacement and stress fields around the needle without increasing the computational expense. This enables real-time simulations. The proposed methodology has direct implications to increase the accuracy and control the computational expense of the simulation of percutaneous procedures such as biopsy, brachytherapy, regional anesthesia, or cryotherapy and can be essential to the development of robotic guidance.Comment: 21 pages, 14 figure

Asynchronous Preconditioners for Efficient Solving of Non-linear Deformations

International audienceIn this paper, we present a set of methods to improve numerical solvers, as used in real-time non-linear deformable models based on implicit integration schemes. The proposed approach is particularly beneficial to simulate nonhomogeneous objects or ill-conditioned problem at high frequency. The first contribution is to desynchronize the computation of a preconditioner from the simulation loop.We also exploit today's heterogeneous parallel architectures: the graphic processor performs the mechanical computations whereas the CPU produces efficient preconditioners for the simulation. Moreover, we propose to take advantage of a warping method to limit the divergence of the preconditioner over time. Finally, we validate our work with several preconditioners on different deformable models. In typical scenarios, our method improves significantly the performances of the perconditioned version of the conjugate gradient

Haptic Rendering of Hyperelastic Models with Friction

International audience— This paper presents an original method for inter-actions' haptic rendering when treating hyperelastic materials. Such simulations are known to be difficult due to the non-linear behavior of hyperelastic bodies; furthermore, haptic constraints enjoin contact forces to be refreshed at least at 1000 updates per second. To enforce the stability of simulations of generic objects of any range of stiffness, this method relies on implicit time integration. Soft tissues dynamics is simulated in real time (20 to 100 Hz) using the Multiplicative Jacobian Energy Decomposition (MJED) method. An asynchronous preconditioner, updated at low rates (1 to 10 Hz), is used to obtain a close approximation of the mechanical coupling of interactions. Finally, the contact problem is linearized and, using a specific-loop, it is updated at typical haptic rates (around 1000 Hz) allowing this way new simulations of prompt stiff-contacts and providing a continuous haptic feedback as well