Pierre Alliez Senior Researcher Inria Sophia-Antipolis - Mediterranee Contact information Pierre Alliez Inria Sophia-Antipolis BP 93 06902 Sophia-Antipolis cedex FRANCE Office: Y313 (Byron building) Phone: (33) 4 92 38 76 77 Fax: (33) 4 97 15 53 95 Email:

My main research interests are on topics commonly referred to as Geometry Processing: geometry compression, surface approximation, mesh parameterization, surface remeshing and mesh generation. Initially considered as a subfield of Computer Graphics and Computational Geometry, Geometry Processing has developed over the last years into a whole research community seeking automatic, computerized processing of complex shapes. My overall research goal is to design methods which are both theoretically founded and computationally tractable to render them robust to unprocessed inputs, reliable, and, above all, with real impact on technological applications. Targeting these properties requires a complete rethinking of the geometry pipeline and of its foundational algorithms so that bottlenecks (i.e., parts of the pipeline which are too labor–intensive or too brittle for practitioners) are removed.

I received the Eurographics Young Researcher Award 2005. I was co-chair of the EUROGRAPHICS Symposium on Geometry Processing 2008 and program co-chair of Pacific Graphics 2010. I have defended my habilitation in 2009, and I have been nominated as associate editor of the ACM Transactions on Graphics in 2010.
I have been awarded in 2011 a Starting Grant from the European Research Council. My proposal is entitled IRON, which stands for "Robust Geometry Processing".

Publications and presentations
- you find here a list of my main publications as well as some presentations.
- click here if you look for a more complete list.

Recent publications and Courses:

	Integer-Grid Maps for Reliable Quad Meshing David Bommes, Marcel Campen, Hans-Christian Ebke, Pierre Alliez, Leif Kobbelt To appear at SIGGRAPH 2013. Abstract: Quadrilateral remeshing approaches based on global parametrization enable many desirable mesh properties. Two of the most important ones are (1) high regularity due to explicit control over irregular vertices and (2) smooth distribution of distortion achieved by convex variational formulations. Apart from these strengths, state-of-the-art techniques suffer from limited reliability on real-world input data, i.e. the determined map might have degeneracies like (local) non-injectivities and consequently often cannot be used directly to generate a quadrilateral mesh. In this paper we propose a novel convex Mixed-Integer Quadratic Programming (MIQP) formulation which ensures by construction that the resulting map is within the class of so called Integer-Grid Maps that are guaranteed to imply a quad mesh. In order to overcome the NP-hardness of MIQP and to be able to remesh typical input geometries in acceptable time we propose two additional problem specific optimizations: a complexity reduction algorithm and singularity separating conditions. While the former decouples the dimension of the MIQP search space from the input complexity of the triangle mesh and thus is able to dramatically speed up the computation without inducing inaccuracies, the latter improves the continuous relaxation, which is crucial for the success of modern MIQP optimizers. Our experiments show that the reliability of the resulting algorithm does not only annihilate the main drawback of parametrization based quad-remeshing but moreover enables the global search for high-quality coarse quad layouts - a difficult task solely tackled by greedy methodologies before.
	On the Equilibrium of Simplicial Masonry Structures Fernando de Goes, Pierre Alliez, Houman Owhadi and Mathieu Desbrun. To appear at SIGGRAPH 2013. Abstract: We present a novel approach for the analysis and design of selfsupporting simplicial masonry structures. A finite-dimensional formulation of their compressive stress field is derived, offering a new interpretation of thrust networks through numerical homogenization theory. We further leverage geometric properties of the resulting force diagram to identify a set of reduced coordinates characterizing the equilibrium of simplicial masonry. We finally derive computational form-finding tools that improve over previous work in efficiency, accuracy, and scalability.
	Surface Reconstruction through Point Set Structuring Florent Lafarge and Pierre Alliez. To appear at EUROGRAPHICS 2013. Abstract: We present a method for reconstructing surfaces from point sets. The main novelty lies in a structure-preserving approach where the input point set is first consolidated by structuring and resampling the planar components, before reconstructing the surface from both the consolidated components and the unstructured points. The final surface is obtained through solving a graph-cut problem formulated on the 3D Delaunay triangulation of the structured point set where the tetrahedra are labeled as inside or outside cells. Structuring facilitates the surface reconstruction as the point set is substantially reduced and the points are enriched with structural meaning related to adjacency between primitives. Our approach departs from the common dichotomy between smooth/piecewisesmooth and primitive-based representations by gracefully combining canonical parts from detected primitives and free-form parts of the inferred shape. Our experiments on a variety of inputs illustrate the potential of our approach in terms of robustness, flexibility and efficiency.
	Anisotropic Rectangular Metric for Polygonal Surface Remeshing Bertrand Pellenard, Jean-Marie Morvan and Pierre Alliez. International Meshing Roundtable 2012 Abstract: We propose a new method for anisotropic polygonal surface remeshing. Our algorithm takes as input a surface triangle mesh. An anisotropic rectangular metric, defined at each triangle facet of the input mesh, is derived from both a user-specified normal-based tolerance error and the requirement to favor rectangle-shaped polygons. Our algorithm uses a greedy optimization procedure that adds, deletes and relocates generators so as to match two criteria related to partitioning and conformity.
	Feature-Preserving Surface Reconstruction and Simplification from Defect-Laden Point Sets. Julie Digne, David Cohen-Steiner, Pierre Alliez, Mathieu Desbrun, Fernando de Goes. To appear in Journal of Mathematical Imaging and Vision Special issue for Mathematics and Image Analysis 2012 Abstract: We introduce a robust and feature-capturing surface reconstruction and simplification method that turns an input point set into a low triangle-count simplicial complex. Our approach starts with a (possibly non-manifold) simplicial complex filtered from a 3D Delaunay triangulation of the input points. This initial approximation is iteratively simplified based on an error metric that measures, through optimal transport, the distance between the input points and the current simplicial complex, both seen as mass distributions. Our approach is shown to exhibit both robustness to noise and outliers, as well as preservation of sharp features and boundaries. Our new feature-sensitive metric between point sets and triangle meshes can also be used as a post-processing tool that, from the smooth output of a reconstruction method, recovers sharp features and boundaries present in the initial point set.
	Progressive Compression of Manifold Polygon Meshes Adrien Maglo, Clément Courbet, Pierre Alliez and Céline Hudelot. Proceedings of Shape Modeling International 2012. Source code Abstract: We present a new algorithm for the progressive compression of surface polygon meshes. The input surface is decimated by several traversals that generate successive levels of detail through a specific patch decimation operator which combines vertex removal and local remeshing. This operator encodes the mesh connectivity through a transformation that generates two lists of Boolean symbols during face and edge removals. The geometry is encoded with a barycentric error prediction of the removed vertex coordinates. In order to further reduce the size of the geometry and connectivity data, we propose a curvature prediction method and a connectivity prediction scheme based on the mesh geometry. We also include two methods that improve the rate-distortion performance: a wavelet formulation with a lifting scheme and an adaptive quantization technique. Experimental results demonstrate the effectiveness of our approach in terms of compression rates and rate-distortion performance. Our approach compares favorably to compression schemes specialized to triangle meshes.
	Isotropic 2D Quadrangle Meshing with Size and Orientation Control Bertrand Pellenard, Pierre Alliez and Jean-Marie Morvan. International Meshing Roundtable 2011 Abstract: We propose an approach for automatically generating isotropic 2D quadrangle meshes from arbitrary domains with a fine control over sizing and orientation of the elements. At the heart of our algorithm is an optimization procedure that, from a coarse initial tiling of the 2D domain, enforces each of the desirable mesh quality criteria (size, shape, orientation, degree, regularity) one at a time, in an order designed not to undo previous enhancements. Our experiments demonstrate how well our resulting quadrangle meshes conform to a wide range of input sizing and orientation fields.
	An Optimal Transport Approach to Robust Reconstruction and Simplification of 2D Shapes Fernando de Goes, David Cohen-Steiner, Pierre Alliez, and Mathieu Desbrun. Symposium on Geometry Processing, 2011. Abstract: We propose a robust 2D shape reconstruction and simplification algorithm which takes as input a defect- laden point set with noise and outliers. We introduce an optimal-transport driven approach where the input point set, considered as a sum of Dirac measures, is approximated by a simplicial complex considered as a sum of uniform measures on 0- and 1-simplices. A fine-to-coarse scheme is devised to construct the resulting simplicial complex through greedy decimation of a Delaunay triangulation of the input point set. Our method performs well on a variety of examples ranging from line drawings to grayscale images, with or without noise, features, and boundaries.
	Polygon Mesh Processing (see also from amazon) See also slides Mario Botsch, Leif Kobbelt, Mark Pauly, Pierre Alliez and Bruno Levy. AK Peters, ISBN 978-1-56881-426-1, 2010. Abstract: Geometry processing, or mesh processing, is a fast-growing area of research that uses concepts from applied mathematics, computer science, and engineering to design efficient algorithms for the acquisition, reconstruction, analysis, manipulation, simulation, and transmission of complex 3D models. Applications of geometry processing algorithms already cover a wide range of areas from multimedia, entertainment, and classical computer-aided design, to biomedical computing, reverse engineering, and scientific computing. Over the last several years, triangle meshes have become increasingly popular, as irregular triangle meshes have developed into a valuable alternative to traditional spline surfaces. This book discusses the whole geometry processing pipeline based on triangle meshes. The pipeline starts with data input, for example, a model acquired by 3D scanning techniques. This data can then go through processes of error removal, mesh creation, smoothing, conversion, morphing, and more. The authors detail techniques for those processes using triangle meshes.

Students and post-docs
- 2012: Kaimo Hu (post-doc on Robust surface remeshing)
- 2012: Thijs van Lankveld (Surface reconstruction for cultural heritage data)
- 2012: Yiyi Wei (Well-centered triangulations, co-advised with Mariette Yvinec)
- 2012: Manish Mandad (PhD on robust shape approximation with guarantees)
- 2012: Sven Oesau (Indoor scene reconstruction, co-advised with Florent Lafarge)
- 2012: David Bommes (Surface tiling)
- 2011: Xavier Rolland-Neviere (Watermarking of surface meshes, at Technicolor, co-advised with Gwenael Doerr)
- 2011: Simon Giraudot (Robust reconstruction of surfaces)
- 2011: Paul Seron (Reconstruction of urban scenes)
- 2011: Renata Nascimento (visiting PhD student on quadrangle surface tiling)
- 2011: Julie Digne (post-doc on robust shape reconstruction, now researcher at CNRS in Lyon)
- 2011: Sagar Chordia (shape approximation)
- 2010: Alain Tayeb (Meshing NURBS surfaces)
- 2010: Boris Dalstein (quadrangle surface tiling)
- 2009-present: Bertrand Pellenard (PhD on surface and domain tiling, defended Dec 18th 2012)
- 2009: Hugo Feree (ENS Lyon: probing implicit surfaces, now PhD student at Inria Nancy)
- 2009: Rahul Srinivasan (IIT Bombay: accelerating ODT mesh optimization and sliver removal)
- 2008: Amit Gupta (IIT Bombay: Poisson reconstruction for polygon soups)
- 2008: Saurabh Chakradeo (IIT Bombay: Fast intersections and projections for polyhedral surfaces)
- 2007: Ankit Gupta (IIT Bombay: PCA in CGAL and application to normal estimation), now at Stanford
- 2006-2009: Jane Tournois (PhD on mesh optimization), now at Geometry Factory.
- 2006: Lakulish Antani (IIT Bombay: mesh sizing using additively weighted Voronoi diagrams), now at UNC
- 2004: Abdelkrim Mebarki (master: placement of streamlines)
- 2004: Jérôme Gahide (progressive triangle mesh compression)
- 2003-2007: Marie Samozino (Ph.D.: reconstruction of surfaces from noisy point sets, co-advised with Mariette Yvinec), now Professor in Mathematics
- 2002: Mathieu Monnier (compression of 2D vectorial data)

Teaching
- Ecole des Ponts ParisTech
- EFREI
- MASTER EPU IFI-VIM

Software
I am an avid user of the CGAL library. I am a CGAL editor and developer as well, implementing or participating to various projects: placement of streamlines from 2D vector fields, planar parameterization of triangle surface meshes, Principal Component Analysis, Surface reconstruction, Point Set Processing and 3D Isotropic Tetrahedron Mesh Generation and Optimization.

Demos for windows running with the CGAL library:
- 2D Voronoi diagram and Lloyd iteration
- A tutorial for CGAL Polyhedron
- Estimating curvature tensors on triangle meshes
- Placement of streamlines

3D models
I contributed to coordinate the AIM@SHAPE repository



Current Projects
EU ERC Starting grant IRON (Robust Geometry Processing)
ANR GIGA (national project about geometric inference and analysis)
Grand emprunt Investissements d’avenir: Culture 3D clouds

Past Projects
ANR GYROVIZ (national project for reconstructing urban scenes from localized photos and videos)
Focus K3D (EU FP7 Coordination Action)
AIM@SHAPE (EU Network of Excellence)


Activities

2014
- European paper co-chair, Geometric Modeling and Processing (around May, Singapore)

2013
- thesis committee: Noura Faraj (Telecom ParisTech)
- joined board of Computer Aided Geometric Design
- paper committee, Shape Modeling International 2013
- paper committee, Eurographics Symposium on Geometry Processing (Genova, Italy)
- habilitation thesis reviewer: Guillaume Lavoue (Universite de Lyon)

2012
- thesis reviewer, Nicolas Mellado, (Inria Bordeaux)
- thesis reviewer, David Bommes (RWTCH Aachen)
- invited speaker, MICCAI workshop on Mesh Processing in Medical Image Analysis (Nice).
- invited speaker, 3DIMPVT: 3D Imaging, Modeling, Processing, Visualization and Transmission (Zurich).
- paper committee, EUROGRAPHICS conference (Cagliari, Italy)
- paper committee, Eurographics Symposium on Geometry Processing (Talinn, Estonia)
- program committee, International Workshop on Point Cloud Processing (in conjunction with CVPR)
- invited speaker, Advances in Architectural Geometry (Paris).

2011
- thesis reviewer: Vincent Vidal (Universite de Lyon)
- habilitation thesis reviewer: Raphaelle Chaine (Universite de Lyon)
- thesis committee: Patrick Mullen (Caltech)
- programme committee, VAST International Symposium on Virtual Reality, Archaeology and Cultural Heritage
- programme committee, Sibgrapi 2011
- paper committee, Eurographics Symposium on Geometry Processing
- programme committee, Shape Modeling International
- thesis reviewer: Clement Courbet (Ecole Centrale Paris)
- thesis committee: Marcio Cabral (INRIA Sophia)
- thesis reviewer: Sahar Hassan (University of Grenoble)

2010
- joined board of Elsevier Graphical Models
- thesis reviewer: Julie Digne (ENS Cachan)
- paper co-chair, Pacific Graphics 2010
- programme committee, Shape Modeling International
- programme committee, ACM Symposium on Solid and Physical Modeling
- paper committee, Eurographics Symposium on Geometry Processing
- scientific committee: Advances in Architectural Geometry
- thesis committee: Mathieu Bredif (Telecom ParisTech and IGN, France)
- thesis reviewer: Thierry Stein (INRIA Rhone Alpes)

2009
- associate editor of the ACM Transactions on Graphics
- short paper co-chair, Eurographics
- programme committee, IMA Mathematics of Surfaces XIII conference.
- programme committee, SIAM/ACM Joint Conference on Geometric and Physical Modeling
- paper committee, Eurographics Symposium on Geometry Processing
- paper committee, Pacific Graphics
- thesis reviewer: Patrick Labatut (ENS Paris)
- thesis committee: Jean-Marie Favreau (University of Clermont-Ferrand)
- thesis committee: Jane Tournois (INRIA Sophia)


2008
- paper co-chair, Eurographics Symposium on Geometry Processing
- paper committee, EUROGRAPHICS
- paper committee, Pacific Graphics
- paper committee, Shape Modeling International
- paper committee, ACm Symposium on Solid and Physical Modeling
- paper committee, Symposium on 3D Data Processing, Visualization and Transmission
- thesis reviewer: Christopher Dyken (University of Oslo)
- thesis reviewer: Johan Seland (University of Oslo)


2007
- paper committee, SIGGRAPH
- paper committee, CAD/Graphics
- paper committee, Pacific Graphics
- paper committee, Shape Modeling International
- paper committee, ACM Symposium on Solid and Physical Modeling
- paper committee, Eurographics Symposium on Geometry Processing

2006
- paper committee, Pacific Graphics
- associate editor of the Visual Computer
- associate editor of Computers & Graphics
- part of the french ANR project GEOTOPAL
- thesis reviewer: Martin Marinov (RWTH Aachen)
- paper committee, ACM Symposium on Solid and Physical Modeling
- paper committee, Eurographics Symposium on Geometry Processing
- paper committee, IEEE International Conference on Shape Modeling and Applications

2005
- Video and Multimedia presentation program committee, SOCG 2005
- paper committee, EUROGRAPHICS Symposium on Geometry Processing 2005
- paper committee, EUROGRAPHICS 2005
- paper committee, Pacific Graphics 2005
- thesis reviewer: Christian Rossl (MPII Saarbruck), Raphaele Balter (University of Rennes)
- member of thesis committee:Marie-Claude Frasson (University of Nice), Guillaume Lavoue (University of Lyon), Gabriel Peyre (Ecole Polytechnique)

2004-2006
- ACI GeoComp 2004-2007
- AIM@SHAPE EU Network of Excellence (workpackage leader)

2004
- organizing co-chair, Second Eurographics Symposium on Geometry Processing 2004
- paper committee, Eurographics Symposium on Geometry Processing 2004
- paper committee, Eurographics 2004
- paper committee, Pacific Graphics 2004
- paper committee, Shape Modeling International 2004
- member of thesis committee: Frederic Payan