Decomposition of branching volume data by tip detection

We present an approach to decomposing branching volume data into sub-branches. First, a metric is proposed for evaluating local convexities in volumetric data, and it is a criterion for global selection of tip points. Second, a multi-path growing strategy is adopted to segment the volumes based on a DFS transformation starting from the tips. Experiments show that this approach is capable of generating desirable components and reasonable segmentation boundaries of a volume.http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcApp=PARTNER_APP&SrcAuth=LinksAMR&KeyUT=WOS:000265921401004&DestLinkType=FullRecord&DestApp=ALL_WOS&UsrCustomerID=8e1609b174ce4e31116a60747a720701Computer Science, Artificial IntelligenceEngineering, Electrical & ElectronicImaging Science & Photographic TechnologyCPCI-S(ISTP)

Atlas-Based Character Skinning with Automatic Mesh Decomposition

Skinning is the most tedious part in the character animation process. Using standard methods, joint weights must be attached to each vertex of the character's mesh, which is often time-consuming if an accurate animation is required. We propose a new modeling of the skinning process, inspired by the notion of atlas of charts. Starting from the character's animation skeleton, we first automatically decompose the mesh into anatomically meaningful overlapping regions. Regions are then blended in their overlapping parts using continuous transition functions. This leads to a simple yet efficient skinning process for which the weights are automatically defined and do not depend on the Euclidean distance but on the distance on the surface.Le skinning est l'étape la plus fastidieuse du processus d'animation d'un personnage. Dans les méthodes classiques, un poids associé à chaque articulation doit être attaché à chaque sommet du maillage du personnage, ce qui est souvent très coûteux en temps lorsqu'une animation précise est exigée. Nous proposons une nouvelle modélisation du processus de skinning, s'inspirant de la notion d'atlas de cartes. A partir du squelette d'animation du personnage, nous décomposons d'abord automatiquement le maillage en régions anatomiquement significatives et qui se chevauchent. Ces régions sont ensuite fusionnées dans leurs zones de chevauchement grˆace à l'utilisation de fonctions de transition continues. Ceci conduit à un processus de skinning simple mais néanmoins efficace, pour lequel les poids sont automatiquement définis et ne dépendent pas de la distance euclidienne entre sommets, mais de la distance sur la surface

Fast Approximate Convex Decomposition

Approximate convex decomposition (ACD) is a technique that partitions an input object into "approximately convex" components. Decomposition into approximately convex pieces is both more efficient to compute than exact convex decomposition and can also generate a more manageable number of components. It can be used as a basis of divide-and-conquer algorithms for applications such as collision detection, skeleton extraction and mesh generation. In this paper, we propose a new method called Fast Approximate Convex Decomposition (FACD) that improves the quality of the decomposition and reduces the cost of computing it for both 2D and 3D models. In particular, we propose a new strategy for evaluating potential cuts that aims to reduce the relative concavity, rather than absolute concavity. As shown in our results, this leads to more natural and smaller decompositions that include components for small but important features such as toes or fingers while not decomposing larger components, such as the torso that may have concavities due to surface texture. Second, instead of decomposing a component into two pieces at each step, as in the original ACD, we propose a new strategy that uses a dynamic programming approach to select a set of n_c non-crossing (independent) cuts that can be simultaneously applied to decompose the component into n_c + 1 components. This reduces the depth of recursion and, together with a more efficient method for computing the concavity measure, leads to significant gains in efficiency. We provide comparative results for 2D and 3D models illustrating the improvements obtained by FACD over ACD and we compare with the segmentation methods given in the Princeton Shape Benchmark

"Studio e implementazione di un algoritmo per lo skinning automatico di mesh poligonali deformabili"

L’animazione tridimensionale è un argomento di grande interesse in svariati ambiti, che vanno dal puro intrattenimento a più serie simulazioni. Esistono numerosissime tecniche di animazione che bilanciano in modo diverso prestazioni, qualità dei risultati, semplicità dell’approccio e possibilità di riutilizzo. In questo scenario trova uno spazio tutto suo l’animazione di figure umanoidi, i cosiddetti Virtual Humans (VHs). Da circa 50 anni la ricerca ha prodotto una gran quantità di metodi per trattare VHs, adatti alle più diverse esigenze e occupandosi di riprodurre le molteplici sfaccettature del movimento umano. Tra i molti campi di applicazione dell’animazione umana, citiamo alcuni esempi: la simulazione per l’addestramento nell’eseguire operazioni pericolose, difficili o comunque che comporterebbero alti costi; l’analisi dell’interazione umana con oggetti ed ambienti; la creazione di attori virtuali per l’entertainment; lo studio di nuovi metodi di interazione uomo-macchina; le ricostruzioni di attività umane a scopo didattico o per riprodurre e studiare le dinamiche di eventi. Tra i metodi per modellare il movimento di figure umane, uno dei paradigmi più diffusi si basa sull’utilizzo di due elementi: il primo è un’approssimazione dello scheletro (skeleton) che viene usato per descrivere le animazioni in modo indipendente dalla figura da animare, così da poter essere riutilizzabile con diversi modelli; il secondo è il modello da animare, che viene visto come una superficie detta pelle (skin), la quale si modifica seguendo lo skeleton. Un approccio per far si che la skin si deformi secondo le ossa (bones) dello skeleton è chiamato skinning. L’algoritmo più diffuso per effettuare lo skinning nel campo delle applicazioni real-time è noto sotto il nome di Linear Blend Skinning (LBS). Tale approccio consiste nell’associare ad ogni vertice della skin un peso che varia tra 0 e 1 per ogni bones, di modo che più il bone ha influenza sul vertice più tale peso è vicino a 1. I pesi vengono poi usati in un blend lineare di trasformazioni rigide per deformare la skin. Il settaggio dei pesi per ogni vertice avviene generalmente in modo manuale tramite l’ausilio di appositi tool, integrati in strumenti di modellazione. Quest’operazione comporta comunque un certo sforzo da parte del modellatore. Inoltre in certi applicativi si preferirebbe che la determinazione dei pesi avvenisse in modo totalmente automatico e con buoni risultati visivi, senza la necessità di intervento da parte di un modellatore esperto. In questa tesi si analizzano i metodi più noti per il calcolo automatico dei pesi da utilizzare assieme all’LBS, di modo da ottenere una distribuzione dei pesi il più realistica possibile

Variational, meaningful shape decomposition

Mesh decomposition into meaningful components has many applications in modeling and CG and has received a lot of attention in the last few years. The accepted notion of meaningful parts relies on human perception, and is based on the observation tha

A Hierarchical Segmentation Of Articulated Bodies

This paper presents a novel segmentation method to assist the rigging of articulated bodies. The method computes a coarse-to-fine hierarchy of segments ordered by the level of detail. The results are invariant to deformations, and numerically robust to noise, irregular tessellations, and topological short-circuits. The segmentation is based on two key ideas. First, it exploits the multiscale properties of the diffusion distance on surfaces, and then it introduces a new definition of medial structures, composing a bijection between medial structures and segments. Our method computes this bijection through a simple and fast iterative approach, and applies it to triangulated meshes. © 2008 The Author(s) Journal compilation © 2008 The Eurographics Association and Blackwell Publishing Ltd.27513491356Attene, M., Katz, S., Mortara, M., Patane, G., Spagnuolo, M., Tal, A., Mesh segmentation - a comparative study (2006) Proc. of the IEEE Intl. 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Graph. and Appl., pp. 129-138Katz, S., Leifman, G., Tal, A., Mesh segmentation using feature point and core extraction (2005) The Visual Computer (Pacific Graph.), 21 (8-10). , 649-658Krayevoy, V., Sheffer, A., Variational, meaningful shape decomposition (2006) SIGGRAPH Technical Sketches, p. 50. , ACMKatz, S., Tal, A., Hierarchical mesh decomposition using fuzzy clustering and cuts (2003) SIGGRAPH, pp. 954-961. , ACMLien, J.-M., Amato, N.M., Approximate convex decomposition of polyhedra (2004) SIGGRAPH Posters, p. 2. , ACMLien, J.-M., Keyser, J., Amato, N.M., Simultaneous shape decomposition and skeletonization (2006) Proc. of the ACM Symp. on solid and physical modeling, pp. 219-228Lee, Y., Lee, S., Shamir, A., Cohen-Or, D., Seidel, H.-P., Mesh scissoring with minima rule and part salience (2005) Comp. Aided Geom. 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Graphics, 5 (4), pp. 308-321Page, D.L., Koschan, A., Abidi, M., Perception-based 3D triangle mesh segmentation using fast marching watersheds (2003) Proc. of the Computer Vision and Pattern Recognition, pp. 27-32Rustamov, R.M., Laplace-beltrami eigenfunctions for deformation invariant shape representation (2007) Proc. of the fifth Eurographics Symp. on Geometry Processing (SGP), pp. 225-233Reuter, M., Wolter, F.-E., Peinecke, N., Laplace-beltrami spectra as "shape-dna", of surfaces and solids (2006) Computer-Aided Design, 38 (4), pp. 342-366Shamir, A., A formulation of boundary mesh segmentation (2004) Proc. of the 2nd Intl. Symp. on 3D Data Proc.Visualization, and Transmission, pp. 82-89Shamir, A., Segmentation and shape extraction of 3D boundary meshes (2006) State-of-art Report: Eurographics, pp. 137-149Shapira, L., Shamir, A., Cohen-Or, D., Consistent mesh partitioning and skeletonisation using the shape diameter function (2008) Visual Comp, 24 (4), pp. 249-259Shlafman, S., Tal, A., Katz, S., Metamorphosis of polyhedral surfaces using decomposition (2002) Computer Graphics Forum, 21 (3), pp. 219-228Schaefer, S., Yuksel, C., Example-based skeleton extraction (2007) Proc. of the fifth Eurographics Symp. on Geometry Processing, pp. 153-162Vallet, B., Levy, B., Spectral geometry processing with manifold harmonics (2008) Computer Graphics Forum (Proc. Eurographics), 27, p. 2Zhang, H., Liu, R., Mesh segmentation via recursive and visually salient spectral cuts (2005) Proc. of Vision.Modeling, and Visualization, pp. 429-436Zhang, E., Mischaikow, K., Turk, G., Feature-based surface parameterization and texture mapping (2005) ACM Trans. on Graph., 24 (1), pp. 1-2