Compression of Dense and Regular Point Clouds

We present a simple technique for single-rate compression of point clouds sampled from a surface, based on a spanning tree of the points. Unlike previous methods, we predict future vertices using both a linear predictor, which uses the previous edge as a predictor for the current edge, and lateral predictors that rotate the previous edge 90 degrees left or right about an estimated normal. By careful construction of the spanning tree and choice of prediction rules, our method improves upon existing compression rates when applied to regularly sampled point sets, such as those produced by laser range scanning or uniform tesselation of higherorder surfaces. For less regular sets of points, the compression rate is still generally within 1.5 bits per point of other compression algorithms

3D Compression: from A to Zip a first complete example

Imagens invadiram a maioria das publicacações e comunicacões contemporâneas. Esta expansão acelerou-se com o desenvolvimento de métodos eficientes de compressão da imagem. Hoje o processo da criação de imagens é baseado nos objetos multidimensionais gerados por CAD, simulações físicas, representações de dados ou soluções de problemas de otimização. Esta variedade das fontes motiva o desenho de esquemas de compressão adaptados a classes específicas de modelos. O lançamento recente do Google Sketch’up com o seu armazém de modelos 3D acelerou a passagem das imagens bidimensionais às tridimensionais. Entretanto, este o tipo de sistemas requer um acesso rápido aos modelos 3D, possivelmente gigantes, que é possível somente usando de esquemas eficientes da compressão. Esse trabalho faz parte de um tutorial ministrado no Sibgrapi 2007.Images invaded most of contemporary publications and communications. This expansion has accelerated with the development of efficient schemes dedicated to image compression. Nowadays, the image creation process relies on multidimensional objects generated from computer aided design, physical simulations, data representation or optimisation problem solutions. This variety of sources motivates the design of compression schemes adapted to specific class of models. The recent launch of Google Sketch’up and its 3D models warehouse has accelerated the shift from two-dimensional images to three-dimensional ones. However, these kind of systems require fast access to eventually huge models, which is possible only through the use of efficient compression schemes. This work is part of a tutorial given at the XXth Brazilian Symposium on Computer Graphics and Image Processing (Sibgrapi 2007)

Transformations compactes de triangulations surfaciques par bascule d'arête

The development of scanning 3D shapes (national heritage conservation, ecommerce, reverse engineering, virtual reality environments) and the growing need for geometric objects in many applications (computer-aided design, simulations, geographic information systems, digital entertainment) have led to a dramatic increase in the volume of data to be processed, and the emergence of many methods of compression of 3D models. This volume of data becomes even more difficult to control when the temporal aspect comes in. Meshes correspond to the pattern typically used to model the scanned forms and some approaches exploit a property of compression that a good estimation of connectivity can be derived from sampling, when it appears sufficiently dense. Compressing the connectivity of a mesh is equivalent to coding the difference between two close connectivities. In this thesis, we focus on the compact coding of this difference for 2-dimensional meshes. Our work is based on the use and study of the properties of the edge flip. Our contributions are the following : - Given two connected triangulations that share the same number of vertices and the same topological genus, we propose a direct and efficient algorithm to generate a sequence of edge flips to change one mesh into the other. We rely on a correspondence between the vertices of the two meshes, which, if not provided, may be chosen randomly. The validity of the algorithm is based on the fact that we intend to work in a triangulation of a different class from those generally used. - We then generalize the edge flips to triangulations in which we identify each edge with a label. We show that a sequence of edge flips can be used to transpose two labels, under certain conditions. From this result, the edge flip can be generalized to meshes whose faces are not necessarily triangular, which allowed us to develop an algorithm for reducing sequences of edge flips. - Finally, we present a compact coding approach for a sequence of edge flips, and determine under what conditions it is better to use this compact transformation between two connectivities instead of coding them independently by a static algorithmLe développement de la numérisation systématique des formes 3D (conservation du patrimoine national, commerce électronique, reverse engineering, intégration d’objets réels dans des environnements de réalité virtuelle) et le besoin toujours croissant de ces objets géométriques dans de nombreuses applications (conception assistée par ordinateur, calcul de simulations par éléments finis, système d’informations géographiques, loisirs numériques) a entrainé une augmentation vertigineuse du volume de données à traiter, avec l’émergence de nombreuses méthodes de compression de modèles 3D. Ce volume de données devient encore plus difficile à maitriser lorsque l’aspect temporel entre en jeu. Les maillages correspondent au modèle classiquement utilisé pour modéliser les formes numérisées et certaines approches de compression exploitent la propriété qu’une bonne estimation de la connectivité peut être déduite de l’échantillonnage, lorsque ce dernier s’avère suffisamment dense. La compression de la connectivité d’un maillage revient alors au codage de l’écart entre deux connectivités proches. Dans ce mémoire, nous nous intéressons au codage compact de cette différence pour des maillages surfaciques. Nos travaux sont fondés sur l’utilisation de la bascule d’arête (edge flip) et l’étude de ses propriétés. Nos contributions sont les suivantes. Etant donné deux triangulations connexes partageant le même nombre de sommets et un même genre topologique, nous proposons un algorithme direct et efficace pour générer une séquence de bascules d’arêtes permettant de passer d’un maillage `a un autre. Nous nous appuyons sur une correspondance entre les sommets des deux maillages, qui, si elle est non fournie, peut être choisie de manière totalement aléatoir

Spatio-Temporal Data Handling for Generic Mobile Geoinformation Systems

Within this thesis, a workflow for an efficient and practical handling of spatio-temporal data is presented. This workflow consists of three layered parts. The first part is the efficient management of spatio-temporal data. The second part focuses on the development of Web services for the dissemination of spatio-temporal data. The third part is a generic mobile GIS for professional users as a typical application for the spatio-temporal data management model and the related Web services

Freelence - coding with free valences

We introduce FreeLence, a novel and simple single-rate compression coder for triangle manifold meshes. Our method uses free valences and exploits geometric information for connectivity encoding. Furthermore, we introduce a novel linear prediction scheme for geometry compression of 3D meshes. Together, these approaches yield a significant entropy reduction for mesh encoding with an average of 20-30 % over leading single-rate regiongrowing coders, both for connectivity and geometry

(Guest Editors) FreeLence- Coding with Free Valences

We introduce FreeLence, a novel and simple single-rate compression coder for triangle manifold meshes. Our method uses free valences and exploits geometric information for connectivity encoding. Furthermore, we introduce a novel linear prediction scheme for geometry compression of 3D meshes. Together, these approaches yield a significant entropy reduction for mesh encoding with an average of 20-30 % over leading single-rate regiongrowing coders, both for connectivity and geometry. Categories and Subject Descriptors (according to ACM CCS): I.3.3 [Computer Graphics]: Surface mesh compression, connectivity coding, geometry coding. 1