David Cazier

Virtual cutting of deformable objects based on efficient topological operations

Virtual cutting of deformable objects is at the core of many applications in interactive simulation and especially in computational medicine. The ability to simulate surgical cuts, dissection, soft tissue tearing or micro-fractures is essential for augmenting the capabilities of existing or future simulation systems. To support such features, we combine a new remeshing algorithm with a fast finite element approach. The proposed method is generic enough to support a large variety of applications. We show the benefits of our approach evaluating the impact of cuts on the number of nodes and the numerical quality of the mesh. These points are crucial to ensure accurate and stable real-time simulations.

CGoGN: N-dimensional Meshes with Combinatorial Maps

Summary. Many data structures are available for the representation and manipulation of meshes. In the context of algorithms that need to traverse local neighborhoods, topological structures are of particular interest. Many such existing structures are specialized for the representation of objects of a given dimension like surface or volume meshes. Many of them find their roots in combinatorial maps, a mathematical model for the representation of the topology of the subdivision of objects, which is consistently defined in any dimension. We present a practical implementation of combinatorial maps that competes with modern state-of-the-art data structures in terms of efficiency, memory footprint and usability. Among other benefits, developers can use a single consistent library to manipulate objects of various dimensions.

Particle-based forecast mechanism for continuous collision detection in deformable environments

Collision detection in geometrically complex scenes is crucial in physical simulations and real time applications. Works based on spatial hierarchical structures have been proposed for years. If correct performances are obtained for static scenes, these approaches show some limitations when the complexity of the scene increases and particularly in case of deformable meshes. The main drawback is the time needed to update the spatial structures - often trees - when global deformations or topological changes occur in the scene. We propose a method to detect collisions in complex and deformable environments with constant time amortized complexity for small displacements. Our method is based on a convex decomposition of the environment coupled with a forecast mechanism exploiting temporal coherence. We use the topological adjacencies and incidence relationships to reduce the number of geometrical tests. Deformations of the scenes are handled with no cost as far as no topological changes occur. Topological transformations, like cuts and sewings, are handled locally, exploiting the spatial coherence and do not imply global updates. We illustrate our method in two experimental frameworks: a particles flow simulation and a meshless animation system both lying in a deformable mesh. We compare our work with classical optimization based on bounding volumes hierarchies to validate its efficiency on large scenes.

n-Dimensional multiresolution representation of subdivision meshes with arbitrary topology

We present a new model for the representation of n-dimensional multiresolution meshes. It provides a robust topological representation of arbitrary meshes that are combined in closely interlinked levels of resolution. The proposed combinatorial model is formalized through the mathematical model of combinatorial maps allowing us to give a general formulation, in any dimensions, of the topological subdivision process that is a key issue to robustly and soundly define mesh hierarchies. It fully supports multiresolution edition what allows the implementation of most mesh processing algorithms - like filtering or compression - for n-dimensional meshes with arbitrary topologies. We illustrate this model, in dimension 3, with an new truly multiresolution representation of subdivision volumes. It allows us to extend classical subdivision schemes to arbitrary polyhedrons and to handle adaptive subdivision with an elegant solution to compliance issues. We propose an implementation of this model as an effective and relatively inexpensive data structure.

A unified structure for crowd simulation

Realistic simulation of crowds is an important issue for the production of virtual worlds for games, entertainment or architectural and urban planning. Difficult issues need to be addressed such as collision avoidance and the handling of dynamic environments. In this paper, we present a unified structure for the simulation of crowds in complex urban environments. We propose a topological multiresolution model supporting different levels of details, allowing efficient proximity querying and compatible with real‐time rendering and hierarchical path planning. A fine exploitation of the multiscale aspect of the underlying model allows to achieve the same efficiency as the fastest existing methods. The generality of the approach allows the simulation to be executed on any two manifold, and the unified approach eases the handling of dynamic environments. Copyright

Fully-automatic Branching Reconstruction Algorithm: Application to Vascular Trees

Reconstructing tubular structures with high-order branching is a difficult task to perform automatically. Medical applications in particular demand accurate models of such objects that fulfill specific topological and geometric criteria. Indeed, the reconstructed object should be a 2-manifold surface with compact, adaptive geometry. We present a generic algorithm for automatically reconstructing n-furcated tubular surfaces. Our approach relies on a strong underlying topological structure and a novel n-furcation reconstruction algorithm using convex entities.

Augmented Reality during Cutting and Tearing of Deformable Objects

Current methods dealing with non-rigid augmented reality only provide an augmented view when the topology of the tracked object is not modified, which is an important limitation. In this paper we solve this shortcoming by introducing a method for physics-based non-rigid augmented reality. Singularities caused by topological changes are detected by analyzing the displacement field of the underlying deformable model. These topological changes are then applied to the physics-based model to approximate the real cut. All these steps, from deformation to cutting simulation, are performed in real-time. This significantly improves the coherence between the actual view and the model, and provides added value.

Edge collision detection in complex deformable environments

We present in this paper a simulation framework that allows a precise and efficient handling of collisions and contacts between deformable moving bodies and their environment. The moving bodies are sampled as meshes whose vertices are followed in a convex subdivision of the surrounding space. Particles are continuously spanned along the edges to detect collisions with cells of this subdivision. Our method supports dynamic subdivision of the moving bodies and contact areas. It allows us to correctly handle geometric and topological changes in the environment, like cuts, tears or breaks and, more generally, additions or removals of material. We report experimental results obtained with mass spring and shape matching based physical simulations and discuss the performance of our method. We compare our approach with classical ones based on hierarchical data structures.

Handling Topological Changes during Elastic Registration: Application to Augmented Reality in Laparoscopic Surgery

PurposeLocating the internal structures of an organ is a critical aspect of many surgical procedures. Minimally invasive surgery, associated with augmented reality techniques, offers the potential to visualize inner structures, allowing for improved analysis, depth perception or for supporting planning and decision systems.MethodsMost of the current methods dealing with rigid or non-rigid augmented reality make the assumption that the topology of the organ is not modified. As surgery relies essentially on cutting and dissection of anatomical structures, such methods are limited to the early stages of the surgery.We solve this shortcoming with the introduction of a method for physics-based elastic registration using a single view from a monocular camera. Singularities caused by topological changes are detected and propagated to the preoperative model. This significantly improves the coherence between the actual laparoscopic view and the model and provides added value in terms of navigation and decision-making, e.g., by overlaying the internal structures of an organ on the laparoscopic view.ResultsOur real-time augmentation method is assessed on several scenarios, using synthetic objects and real organs. In all cases, the impact of our approach is demonstrated, both qualitatively and quantitatively (http://www.open-cas.org/?q=PaulusIJCARS16).ConclusionThe presented approach tackles the challenge of localizing internal structures throughout a complete surgical procedure, even after surgical cuts. This information is crucial for surgeons to improve the outcome for their surgical procedure and avoid complications.

X-maps: An Efficient Model for Non-manifold Modeling

Many representation schemes have been proposed to deal with non-manifold and mixed dimensionalities objects. A majority of those models are based on incidence graphs and although they provide efficient ways to query topological adjacencies, they suffer two major drawbacks: redundancy in the storage of topological entities and relationships, and the lack of a uniform representation of those entities that leads to the development of large sets of intricate topological operators. As regards to manifold meshes -- and specifically triangular ones -- compact and efficient models are known for twenty years. Ordered topological models like combinatorial maps or half edges based data structures are widely studied and used. We propose a new representation scheme -- the extended maps or