Combinatorial models for topology-based geometric modeling

Many combinatorial (topological) models have been proposed in geometric modeling, computational geometry, image processing or analysis, for representing subdivided geometric objects, i.e. partitionned into cells of different dimensions: vertices, edges, faces, volumes, etc. We can distinguish among models according to the type of cells (regular or not regular ones), the type of assembly ("manifold" or "non manifold"), the type of representation (incidence graphs or ordered models), etc

Computing Homology Generators for Volumes Using Minimal Generalized Maps

International audienceIn this paper, we present an algorithm for computing efficiently homology generators of 3D subdivided orientable objects which can contain tunnels and cavities. Starting with an initial subdivision, represented with a generalized map where every cell is a topological ball, the number of cells is reduced using simplification operations (removal of cells), while preserving homology. We obtain a minimal representation which is homologous to the initial object. A set of homology generators is then directly deduced on the simplified 3D object

Formalizing a Discrete Model of the Continuum in Coq from a Discrete Geometry Perspective

International audienceThis work presents a formalization of the discrete model of the continuum introduced by Harthong and Reeb, the Harthong-Reeb line. This model was at the origin of important developments in the Discrete Geometry field. The formalization is based on previous work by Chollet, Fuchs et al. where it was shown that the Harthong-Reeb line satisfies the axioms for constructive real numbers introduced by Bridges. Laugwitz-Schmieden numbers are then introduced and their limitations with respect to being a model of the Harthong-Reeb line is investigated. In this paper, we transpose all these definitions and properties into a formal description using the Coq proof assistant. We also show that Laugwitz-Schmieden numbers can be used to actually compute continuous functions. We hope that this work could improve techniques for both implementing numeric computations and reasoning about them in geometric systems

A Framework for n-dimension Visibility Calculation

4 pagesVisibility computation is a fundamental task in computer graphics, as in many other scientific domains. While it is well understood in two dimensions, this does not remain true in high dimensional spaces. Using Grassmann Algebra, we propose a framework for solving visibility problems in any n-dimensional spaces, for n ≥ 2. Our presentation recalls the problem statement, in two and three dimensions. Then, we formalize the space of n-dimensional lines. Finally, we show how this leads to a global framework for visibility computations, giving an example of use with exact soft shadows

Incremental Computation of the Homology of Generalized Maps: An Application of Effective Homology Results

This paper deals with the incremental computation of the homology of " cellular " combinatorial structures, namely combinatorial maps and incidence graphs. " Incremental " is related to the operations which are applied to construct such structures: basic operations, i.e. the creation of cells and the identification of cells, are considered in the paper. Such incremental computation is done by applying results of effective homology [RS06]: a correspondence between the chain complex associated with a given combinatorial structure is maintained with a " smaller " chain complex , from which the homology groups and homology generators can be more efficiently computed

Decomposition of nD-rotations: Classification, properties and algorithm

International audienceIn this paper, the decomposition of nD-rotations is studied. Using this decomposition, nD-rotations are classified and properties are underlined. A generalization of the algorithm previously presented by the authors to decompose nD-rotation into planar rotations is proposed. Since our framework includes experimental applications, we designed a method that is somewhat robust to noise. An alternate algorithm based on the Schur decomposition is investigated. A comparison between both methods is finally provided

Three-dimensional quadrics in extended conformal geometric algebras of higher dimensions from control points, implicit equations and axis alignment

International audienceWe introduce the quadric conformal geometric algebra (QCGA) inside the algebra of R 9,6. In particular, this paper presents how three-dimensional quadratic surfaces can be defined by the outer product of conformal geometric algebra points in higher dimensions, or alternatively by a linear combination of basis vectors with coefficients straight from the implicit quadratic equation. These multivector expressions code all types of quadratic surfaces in arbitrary scale, location, and orientation. Furthermore, we investigate two types of definitions of axis aligned quadric surfaces, from contact points and dually from linear combinations of R 9,6 basis vectors

Foundational aspects of multiscale digitization

International audienceIn this article, we describe the theoretical foundations of the Ω-arithmetization. This method provides a multi-scale discretization of a continuous function that is a solution of a differential equation. This discretization process is based on the Harthong-Reeb line HRω. The Harthong-Reeb line is a linear space that is both discrete and continuous. This strange line HRω stems from a nonstandard point of view on arithmetic based, in this paper, on the concept of Ω-numbers introduced by Laugwitz and Schmieden. After a full description of this nonstandard background and of the first properties of HRω, we introduce the Ω-arithmetization and we apply it to some significant examples. An important point is that the constructive properties of our approach leads to algorithms which can be exactly translated into functional computer programs without uncontrolled numerical error. Afterwards, we investigate to what extent HRω fits Bridges's axioms of the constructive continuum. Finally, we give an overview of a formalization of the Harthong-Reeb line with the Coq proof assistant

Characterization of elemental content & green house gases fluxes from different zones in the Lena Delta River

Permafrost science remains limited in data. Observations at isolated spaces and times are insufficient to evaluate the long term climatic and environmental responses over large regions. Permafrost models may be used to establish links between the geographical scales from local to large regional, continental, and hemispheric scales. This poster aims to show some examples for measuring C/N quantities and CO2/CH4 fluxes and to offer comparison of their contribution in C-cycle in different areas of Lena Delta River (2-core comparison and a global one on 12 core samples from the KoPf Expedition in 2018