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Quadtree representation of two-dimensional objects is performed with a tree that describes the recursive subdivision of the more complex parts of a picture until the desired resolution is reached. At the end, all the leaves of the tree are square cells that lie completely inside or outside the object. There are two great disadvantages in the use of(More)
This paper describes the Visibility Octree, a data structure to accelerate 3D navigation through very complex scenes. A conservative visibility algorithm that computes and hierarchically stores the structure at a preprocessing stage is presented. The Visibility Octree is used during navigation and its main contribution is its ability to provide an eeective(More)
An interactive cerebral blood vessel exploration system is described. It has been designed on the basis of neurosurgeon's requirements in order to assist them in the diagnosis of vas-cular pathologies. The system is based on the construction of a symbolic model of the vascular tree with an automatic identification and labelling of vessel bifurcations,(More)
Occlusion culling and level-of-detail rendering have become two powerful tools for accelerating the handling of very large models in real-time visualization applications. We present a framework that combines both techniques to improve rendering times. Classical occlusion culling algorithms compute potentially visible sets (PVS), which are supersets of the(More)
Volume models often show high depth complexity. This poses difficulties to the observer in judging the spatial relationships accurately. Illustrators usually use certain techniques such as improving the shading through shadows, halos, or edge darkening in order to enhance depth perception of certain structures. Both effects are difficult to generate in(More)
BACKGROUND We previously showed that abdominal distension in patients with functional gut disorders is due to a paradoxical diaphragmatic contraction without major increment in intraabdominal volume. Our aim was to characterize the pattern of gas retention and the abdomino-thoracic mechanics associated with abdominal distension in patients with intestinal(More)
Since the publication of the original Marching Cubes algorithm, numerous variations have been proposed for guaranteeing watertight constructions of triangulated approximations of isosurfaces. Most approaches divide the 3D space into cubes that each occupy the space between eight neighboring samples of a regular lattice. The portion of the isosurface inside(More)
Level-of-detail occlusion culling is a novel approach to the management of occluders that can be easily integrated into most current visibility culling algorithms. The main contribution of this paper is an algorithm that automatically generates sets of densely overlapping boxes with enhanced occlusion properties from non-convex subsets. We call this method(More)