Marco Attene 
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Characterization of 3D shape parts for semantic annotation Marco Attene, Francesco Robbiano, Michela Spagnuolo and Bianca Falcidieno Computer-Aided Design, Vol. 41, No. 10, pp. 756-763, 2009. Online version. Abstract
3D content stored in big databases or shared on the Internet is a precious resource for several applications,
but unfortunately it risks being underexploited due to the difficulty of retrieving it efficiently.
In this paper we describe a system called the ShapeAnnotator through which it is possible to perform non-trivial
segmentations of 3D surface meshes and annotate the detected parts through concepts expressed by an ontology.
Each part is connected to an instance that can be stored in a knowledge base to ease the retrieval process based on semantics.
Through an intuitive interface, users create such instances by simply selecting proper classes in the ontology; attributes
and relations with other instances can be computed automatically based on a customizable analysis of the underlying topology
and geometry of the parts. We show how our part-based annotation framework can be used in two scenarios, namely for the
creation of avatars in emerging Internet-based virtual worlds, and for product design in e-manufacturing. 
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(c) Elsevier 2009.
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Hierarchical Convex Approximation of 3D Shapes for Fast Region Selection Marco Attene, Michela Mortara, Michela Spagnuolo and Bianca Falcidieno Computer Graphics Forum, Vol. 27, No. 5, pp. 1323-1333, 2008. Abstract
Given a 3D solid model S represented by a tetrahedral mesh, we describe a novel algorithm to compute a hierarchy
of convex polyhedra that tightly enclose S. The hierarchy can be browsed at interactive speed on a modern PC
and it is useful for implementing an intuitive feature selection paradigm for 3D editing environments.Convex parts often coincide with perceptually relevant shape components and, for their identification, existing methods rely on the boundary surface only. In contrast, we show that the notion of part concavity can be expressed and implemented more intuitively and efficiently by exploiting a tetrahedrization of the shape volume. The method proposed is completely automatic, and generates a tree of convex polyhedra in which the root is the convex hull of the whole shape, and the leaves are the tetrahedra of the input mesh. The algorithm proceeds bottomup by hierarchically clustering tetrahedra into nearly convex aggregations, and the whole process is significantly fast. We prove that, in the average case, for a mesh of n tetrahedra O(n log^2 n) operations are sufficient to compute the whole tree.
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Combinatorial 3-manifolds from sets of tetrahedra Marco Attene, Massimo Ferri and Daniela Giorgi IEEE Procs. of Cyberworlds 2007, special session on the NASAGEM workshop, pp. 367-365. 
Abstract
We propose an algorithm to convert a tetrahedral mesh with singularities to a
combinatorial 3-manifold using only local modifications. We outline sufficient
conditions on the mesh to guarantee the feasibility of the approach and we show
how singularities can be both identified and removed according to the configuration
of their link. Furthermore, we demonstrate that the algorithm can be implemented
using a flexible state-of-the-art data structure for manifold tetrahedral meshes
suitable for efficient and general applications.
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(c) IEEE 2007.
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Hierarchical Mesh Segmentation based on Fitting Primitives Marco Attene, Bianca Falcidieno and Michela Spagnuolo The Visual Computer 22(3): 181-193, 2006. Abstract
In this paper we describe a
hierarchical face clustering algorithm for triangle meshes based on
fitting primitives belonging to an arbitrary set. The method proposed is
completely automatic, and generates a binary tree of clusters, each of
which fitted by one of the primitives employed. Initially, each triangle
represents a single cluster; at every iteration, all the pairs of adjacent
clusters are considered, and the one that can be better approximated by
one of the primitives forms a new single cluster. The approximation error
is evaluated using the same metric for all the primitives, so that it
makes sense to choose which is the most suitable primitive to
approximate the set of triangles in a cluster.
Based on this approach, we
implemented a prototype which uses planes, spheres and cylinders, and have
experimented that for meshes made of 100k faces, the whole binary tree of
clusters can be built in about 8 seconds on a standard PC.
The framework here described has
natural application in reverse engineering processes, but it has been also
tested for surface de-nosing, feature recovery and character
skinning.
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(c) Springer 2006.
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Sharpen&Bend: Recovering curved sharp edges in triangle meshes produced by feature-insensitive sampling Marco Attene, Bianca Falcidieno, Jarek Rossignac and Michela Spagnuolo IEEE Transactions on Visualization and Computer Graphics, 11(2): pp. 181-192, 2005. Abstract
Various acquisition, analysis, visualization and compression
approaches sample surfaces of 3D shapes in a uniform fashion, without any
attempt to align the samples with sharp edges or to adapt the sampling
density to the surface curvature. Consequently, triangle meshes that
interpolate these samples usually chamfer sharp features and exhibit a
relatively large error in their vicinity. We present two new filters that
improve the quality of these re-sampled models. EdgeSharpener
restores the sharp edges by splitting the chamfer edges and forcing the
new vertices to lie on intersections of planes extending the smooth
surfaces incident upon these chamfers. Bender refines the resulting
triangle mesh using an interpolating subdivision scheme that preserves the
sharpness of the recovered sharp edges while bending their polyline
approximations into smooth curves. A combined Sharpen&Bend
post-processing significantly reduces the error produced by
feature-insensitive sampling processes. For example, we have observed that
the mean-squared distortion introduced by the SwingWrapper remeshing-based
compressor can often be reduced by 80% executing EdgeSharpener alone after
decompression. For models with curved regions, this error may be further
reduced by an additional 60% if we follow the EdgeSharpening phase by
Bender.
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(c) IEEE 2005.
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SwingWrapper: Retiling Triangle Meshes for Better EdgeBreaker Compression Marco Attene, Bianca Falcidieno, Michela Spagnuolo and Jarek Rossignac ACM Transactions on Graphics, 22(4): pp. 982-996, 2003. Abstract
We focus on
the lossy compression of manifold triangle meshes. Our SwingWrapper
approach partitions the surface of an original mesh M into simply
connected regions, called triangloids. From these, we generate a new mesh
M?. Each triangle of M? is an approximation of a triangloid of M. By
construction, the connectivity of M? is fairly regular and can be
compressed to less than a bit per triangle using EdgeBreaker or one of the
other recently developed schemes. The locations of the vertices of M? are
compactly encoded with our new prediction technique, which uses a single
correction parameter per vertex. SwingWrapper strives to reach a
user-defined output file size rather than to guarantee a given error
bound. For a variety of popular models, a rate of 0.4 bits/triangle yields
an L2 distortion of about 0.01% of the bounding box diagonal. The proposed
solution may also be used to encode crude meshes for adaptive transmission
or for controlling subdivision surfaces.
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(c) ACM 2003.
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A mapping independent primitive for the triangulation of parametric surfaces Marco Attene, Bianca Falcidieno, Michela Spagnuolo and Geoff Wyvill Graphical Models, 65(5): pp. 260-273, 2003 (special issue on Shape Modeling International 2002). Abstract
This
paper describes a new technique for the triangulation of parametric
surfaces. Most earlier methods sample the parameter domain, and the wrong
choice of parameterization can spoil the triangulation or even cause the
algorithm to fail. Conversely, we use a local tessellation primitive to
sample and triangulate the surface. The sampling is almost uniform and the
parameterization becomes irrelevant. If sampling density or triangle shape
has to be adaptive, the resulting uniform mesh can be used either as an
initial coarse mesh for a refinement process, or as a fine mesh to be
reduced.
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(c) Elsevier Science (USA) 2003.
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Shape understanding by contour-driven retiling Marco Attene, Silvia Biasotti and Michela Spagnuolo The Visual Computer, 19(2-3): pp. 127-138, 2003. Abstract
Given a triangle
mesh representing a closed manifold surface of arbitrary genus, a method
is proposed to automatically extract the Reeb graph of the manifold with
respect to the height function. The method is based on a slicing strategy
that traces contours while inserting them directly in the mesh as
constraints. Critical areas, which identify isolated and non-isolated
critical points of the surface, are recognized and coded in the Extended
Reeb Graph (ERG). The remeshing strategy guarantees that topological
features are correctly maintained in the graph, and the tiling of ERG
nodes reproduces the original shape at a minimal, but topologically
correct, geometric level.
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(c) Springer-Verlag 2003.
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Automatic surface reconstruction from point sets in space Marco Attene and Michela Spagnuolo Computer Graphics Forum (Procs. of EUROGRAPHICS '00), 19(3): pp.457-465, 2000. 
AbstractIn this paper an algorithm is proposed that takes as input a generic set of unorganized points, sampled on a real object, and returns a closed interpolating surface. Specifically, this method generates a closed 2-manifold surface made of triangular faces, without limitations on the shape or genus of the original solid. The reconstruction method is based on generation of the Delaunay tetrahedralization of the point set, followed by a sculpturing process constrained to particular criteria. The main applications of this tool are in medical analysis and in reverse engineering areas. It is possible, for example, to reconstruct anatomical parts starting from surveys based on TACs or magnetic resonance.
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(c) The Eurographics Association and Blackwell Publishers Ltd. 2000.
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