This paper addresses the problem of simulating deformations between objects and the hand of a synthetic character during a grasping process. A numerical method based on finite element theory allows us to take into account the active forces of the fingers on the object and the reactive forces of the object on the fingers. The method improves control of synthetic human behavior in a task level animation system because it provides information about the environment of a synthetic human and so can be compared to the sense of touch. Finite element theory currently used in engineering seems one of the best approaches for modeling both elastic and plastic deformation of objects, as well as shocks with or without penetration between deformable objects. We show that intrinsic properties of the method based on composition/decomposition of elements have an impact in computer animation. We also state that the use of the same method for modeling both objects and human bodies improves the modeling both objects and human bodies improves the modeling of the contacts between them. Moreover, it allows a realistic envelope deformation of the human fingers comparable to existing methods. To show what we can expect from the method, we apply it to the grasping and pressing of a ball. Our solution to the grasping problem is based on displacement commands instead of force commands used in robotics and human behavior.

A filling algorithm for irregular polygons is described. This algorithm is oriented towards raster graphics and uses image memories as job areas. The algorithm is based on the encoding of polygon boundaries by contour following so that all topologies are successfully processed. Thus, concave or convex polygons, holed or not, including possibly duplicate points can be filled. It is quite robust and easy to implement. It uses systematic encoding without special cases. Only two bits for encoding are needed and, thereby, it is suitable for hardware implementation. This algorithm can be used in many fields such as image synthesis, 3D objects or mathematical surface displays with hidden parts.

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This work is designed to control the movement of hand structural agents under external action, using the implicit animation driven by explicit animation technique (AI-CAE technique). Starting from the configuration of a hand at rest obtained by a 3D scanner and after meshing of the structural agents, we seek the configuration of the rigid agents under orthopaedic surgeon external action and interacting reliance of deformable and rigid agents. We have developed a model and software tools to answer this interactive application with adaptive execution. The first contribution comes from notations and definition of a versatile multi-body system dedicated to the explicit and implicit animation. The second contribution comes from the implicit animation driven by explicit animation itself, and from its ability to mimic the role of cartilages and ligaments. The resulting technique is applied to the bone structure consistency of a specific human hand in the context of virtual hand orthopaedic surgery. The versatile specific multi-body is made up of hierarchical interacting agents conceivable as a construction set of rigid bones with cartilages-ligaments and underlying links. The explicit animation produces a desired configuration from geometric command parameters of torsion, flexion, pivot and axis shifting, given in a scenario subdivided into temporal sequences. The implicit animation controls the movement by implementing a physicsbased model and fuzzy constraints of position and orientation. It gives better configuration than the explicit animation because it takes into account the interactions between agents, and it gives a neat solution without the problems of complexity due to geometric modelling. A methodology based on the AI-CAE technique is discussed, medical expertise and validation tests are presented.