Search

We introduce an algorithm that consistently and accurately processes arbitrary intersections in tetrahedral meshes in real-time. The intersection surfaces are modeled up to the current cut tool position at every point in time. Tetrahedra are subdivided by using a progressive method, which inserts the required sub-structures step by step. A state machine tracks the topology of each tetrahedron and controls the progressive subdivision. In order to keep the state machine as small and clear as possible, each topological pattern of a tetrahedral intersection appears only once. These topological patterns are mapped onto the actual case of a tetrahedral intersection by some given transformation operations. The state transitions, which contain the specific subdivision operations, are described in a predefined lookup table, which is written in a simple script language. The handling of reverse movements and possible trembling of the users hand, as well as a recursive continuation of the state machine concept, complement the proposed algorithm. In three examples, covering free form modeling, volume visualization, and surgery simulation, we indicate the large field of applications in which our algorithm can be utilized.

We describe a physically based framework for interactive modeling and cutting of 3-dimensional soft tissue that can be used for surgery simulation. Unlike existing approaches which are mostly designed for tensorproduct grids our methods operate on tetrahedral decompositions giving more topological and geometric flexibility for the efficient modeling of complex anatomical structures. We start from an initial tetrahedralization such as being provided by any conventional meshing method. In order to track topological changes tetrahedra intersected by the virtual scalpel are split into substructures whose connectivity follows the trajectory of the cut, which can be arbitrary. For the efficient computation of collisions between the scalpel and individual tetrahedra we devised a local collision detection algorithm. The underlying physics is approximated through masses and springs attached to each tetrahedral vertex and edge. A hierarchical Runge-Kutta iteration computes the relaxation of the system by traversing the designed data structures in a breadth-first order. The framework includes a force-feedback interface and uses real-time texture mapping to enhance the visual realism.

We present IVORY a newly developed, platform-independent framework for physics based visualization. IVORY is especially designed for information visualization applications and multidimensional graph layout. It is fully implemented in Java 1.1 and its architecture features client server setup, which allows us to run the visualization even on thin clients. In addition, VRML 2.0 exports can be viewed by any VRML plugged-in WWW browser. Individual visual metaphors are invoked into IVORY via an advanced plug-in mechanism, where plug-ins can be implemented by any experienced user. The configuration of IVORY is accomplished using a script language, called IVML. Some interactive visualization examples, such as the integration of a haptic interface illustrate the performance and versatility of our system. Our current implementation supports NT 4.0.

Presents a framework for the interactive simulation of surgical cuts, such as those practiced in surgical treatment. Unlike most existing methods, our framework is based on tetrahedral volume meshes providing more topological flexibility. In order to keep the representation consistent, we apply adaptive subdivision schemes dynamically during the simulation. The detection of collisions between the surgical tool and the tissue is accomplished by using an axis-aligned bounding-box hierarchy which was adapted for deformable objects. For haptic rendering and feedback, we devised a mechanical scalpel model which accounts for the most important interaction forces between the scalpel and the tissue. The relaxation is computed using a localized, semi-implicit ODE (ordinary differential equation) solver. The achieved quality and performance of the presented framework is demonstrated using a human soft-tissue model.