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Although 3D texture-based volume rendering guarantees image quality almost interactively, it is difficult to maintain an interactive rate when the technique has to be exploited on large datasets. In this paper, we propose a new texture memory representation and a management policy that substitute the classical one-texel per voxel approach for a hierarchical(More)
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)
BACKGROUND The precise relation of intestinal gas to symptoms, particularly abdominal bloating and distension remains incompletely elucidated. Our aim was to define the normal values of intestinal gas volume and distribution and to identify abnormalities in relation to functional-type symptoms. METHODS Abdominal computed tomography scans were evaluated in(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)
Medical doctors are often faced with the problem of selecting anchoring points in 3D space. These points are commonly used for measurement tasks, such as lengths of bones, or dimensions of pathological structures (e. g. tumours). Since previous research indicates that measurement tasks can be usually carried out more efficiently in VR environments than in(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)