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Eric Galin

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Cristina Rebollo Santamaría

Universitat Jaume I de Castelló

Delft University of Technology

Gregory B Pasternack

University of California, Davis

Bartłomiej Szypuła

University of Silesia in Katowice

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Papers by Eric Galin

Large-scale Terrain Authoring through Interactive Erosion Simulation

ACM Transactions on Graphics

Large-scale terrains are essential in the definition of virtual worlds. Given the diversity of la... more Large-scale terrains are essential in the definition of virtual worlds. Given the diversity of landforms and the geomorphological complexity, there is a need for authoring techniques offering hydrological consistency without sacrificing user control. In this article, we bridge the gap between large-scale erosion simulation and authoring into an efficient framework. We set aside modeling in the elevation domain in favour of the uplift domain and compute emerging reliefs by simulating the stream power erosion. Our simulation relies on a fast yet accurate approximation of drainage area and flow routing to compute the erosion interactively, which allows for incremental authoring. Our model provides landscape artists with tools for shaping mountain ranges and valleys, such as copy-and-paste operations; warping for imitating folds and faults; and point and curve elevation constraints to precisely sculpt ridges or carve river networks. It also lends itself to inverse procedural modeling by...

Volume 19, (2000), Number yyy pp. Morphing

Implicit surfaces have proved to be a particularly well suited and efficient model for animating ... more Implicit surfaces have proved to be a particularly well suited and efficient model for animating and morphing shapes of arbitrary topologies. The BlobTree model is characterized as a hierarchical combination of skeletal primitives organized in a tree. The nodes hold blending, boolean and warping operators, which allows the design of complex objects. In this paper, we address the metamorphosis of the BlobTree. This appears a difficult task as the tree datastructures of the initial and final shapes are completely different in the general case, and consequently cannot be matched easily. We propose an original technique that solves the correspondence process and creates an intermediate generic BlobTree model whose instances interpolate the initial and final shapes. The animator may control the correspondence between features and can specify both the speed of transformation and the trajectory of the nodes and the leaves of the generic BlobTree model. This provides the end user with a tig...

Volumetric Spot Noise for Procedural 3D Shell Texture Synthesis

In this paper, we present an extension of the Locally Controlled Spot Noise and a visualization p... more In this paper, we present an extension of the Locally Controlled Spot Noise and a visualization pipeline for volumetric fuzzy details synthesis. We extend the noise model to author volumetric fuzzy details using filtered 3D quadratic kernel functions convolved with a projective non-uniform 2D distribution of impulses. We propose a new method based on order independent splatting to compute a fast view dependent approximation of shell noise at interactive rates. Our method outperforms ray marching techniques and avoids aliasing artifacts, thus improving interactive content authoring feedback. Moreover, generated surface details share the same properties as procedural noise: they extend on potentially infinite surfaces, are defined in an extremely compact way, are non-repetitive, continuous (no discrete voxel-artifacts when zooming) and independent of the definition of the underlying surface (no surface parameterization is required).

Métamorphose et visualisation de blobs à squelettes

Bien que la modelisation, l'animation et la visualisation d'objets definis a partir de su... more Bien que la modelisation, l'animation et la visualisation d'objets definis a partir de surfaces implicites aient ete largement etudiees au cours de la derniere decennie, la metamorphose a fait l'objet de peu d'attention et les techniques proposees jusqu'ici se sont averees limitees, soit par le type meme de blobs pouvant etre animes, soit par le manque de controle sur la transformation. Dans cette these, nous nous sommes interesses a la metamorphose et a la visualisation de blobs a squelettes polyedriques. Nous avons propose une approche originale et generale caracterisant les formes intermediaires a partir d'un modele de blob generique. Notre methode presente differents niveaux d'abstraction et de controle, depuis l'ebauche d'une metamorphose grossiere jusqu'a la realisation d'une transformation complexe ou l'animateur peut controler toute une gamme d'effets speciaux. Enfin, nous avons ete amenes a developper des methodes de lance...

N-Adic Subdivision Schemes for Local Mesh Deformation

This paper presents an interpolating subdivision scheme based on an N-adic decomposition of the p... more This paper presents an interpolating subdivision scheme based on an N-adic decomposition of the parameter space. This approach enables us to locally deform the surface according to a modification of the normals at the vertices of the control mesh. Experiments show that the N-adic decomposition provides a better control over the deformations, whereas a dyadic decomposition method often produces smoother surfaces.

Data-driven authoring of large-scale ecosystems

ACM Transactions on Graphics, 2020

In computer graphics populating a large-scale natural scene with plants in a fashion that both re... more In computer graphics populating a large-scale natural scene with plants in a fashion that both reflects the complex interrelationships and diversity present in real ecosystems and is computationally efficient enough to support iterative authoring remains an open problem. Ecosystem simulations embody many of the botanical influences, such as sunlight, temperature, and moisture, but require hours to complete, while synthesis from statistical distributions tends not to capture fine-scale variety and complexity. Instead, we leverage real-world data and machine learning to derive a canopy height model (CHM) for unseen terrain provided by the user. Trees in the canopy layer are then fitted to the resulting CHM through a constrained iterative process that optimizes for a given distribution of species, and, finally, an understorey layer is synthesised using distributions derived from biome-specific undergrowth simulations. Such a hybrid data-driven approach has the advantage that it incorpo...

M etamorphose du Blob {Tree

Modélisation et placement de champignons

Metamorphose d'objets polyedriques. Polygonal objects metamorphosis

Métamorphose d'objets polyédriques: Quelques méthodes d'accélération

Cet article traite de la metamorphose d'objets polyedriques par les sommes de Minkowski. Lors... more Cet article traite de la metamorphose d'objets polyedriques par les sommes de Minkowski. Lorsque les polyedres arguments sont convexes, la transformation peut etre caracterisee par un polyedre generique convexe dont la topologie est invariante au cours du temps. Nous proposons des algorithmes acceleres tirant parti des informations topologiques pour la construction de la somme de Minkowski de deux polyedres convexes. Les polyedres de Bezier sont presentes comme une extension a plusieurs polyedres. Nous montrons que la conservation de la topologie permet d'ajouter et de retirer iterativement des polyedres de controle sans avoir a reconstruire l'ensemble de la topologie. Enfin, nous montrons comment la distributivite de la somme de Minkowski par rapport a l'union permet de traiter efficacement certains objets complexes definis comme union de sous elements convexes.

The HybridTree: A Hybrid Constructive Shape Representation for Free-Form Modeling

Lecture Notes in Computer Science

In this paper, we describe a hybrid modeling framework for creating complex 3D objects incrementa... more In this paper, we describe a hybrid modeling framework for creating complex 3D objects incrementally. Our system relies on an extended CSG tree that assembles skeletal implicit primitives, triangle meshes and point set models in a coherent fashion: we call this structure the HybridTree. Editing operations are performed by exploiting the complementary abilities of implicit and polygonal mesh surface representations

Fast processing of triangle meshes using triangle fans

International Conference on Shape Modeling and Applications 2005 (SMI' 05)

... Samir Akkouche LIRIS - CNRS Université Claude Bernard Lyon 1 [email protected]. fr Ab... more

Landscape specification resizing

2014 XL Latin American Computing Conference (CLEI), 2014

In this work, we introduce a method for resizing a landscape specification, i.e., a vector model ... more In this work, we introduce a method for resizing a landscape specification, i.e., a vector model containing a set of objects present in a virtual environment. Our goal is to change the landscape dimensions while keeping its overall appearance. Our method is based on the insertion and removal of objects in the specification, followed by some adjustments of the scene adapting the initial model to these changes. Besides the proposed approach for the positioning the objects, this method can be easily extended to use techniques of the state of the art for spreading objects in the landscape. The adjustment of the scene components consists in performing vertical or horizontal translations onto the position of the objects. It is based on a removal or insertion of paths in the grid created over the scene space using dynamic programming. In spite of dealing with a vector model, all proposed operations are performed in the pixel space. This technique is an adaptation of the Seam Carving for the context of vector landscapes specification. This model is simpler than common images, and thus, we can achieve results as good as those obtained in the image context, using simpler metrics.

Modélisation de détails dans les scènes naturelles

Cet article présente un système pour modéliser et distribuer des détails dans une scène virtuelle... more Cet article présente un système pour modéliser et distribuer des détails dans une scène virtuelle. Ces deux aspects jouent un rôle fondamental sur le réalisme des scènes de synthèse. L'architecture que nous proposons repose sur deux éléments clés : un atlas de formes complexes représentant des fragments de détails et des algorithmes de dispersion et de propagation dépendant des caractéristiques

Simulating How Salt Decay Ages Buildings

IEEE Computer Graphics and Applications, 2012

A ging affects all real surfaces. 1,2 It particularly visibly affects urban scenes with construct... more A ging affects all real surfaces. 1,2 It particularly visibly affects urban scenes with construction materials. So, simulating such materials' decay is an important research topic with many applications, from designing buildings to conserving cultural heritage. Construction materials' alterations depend on a range of parameters from chemical composition to surface characteristics. Moreover, the alterations can vary according to the specific location, even on a single wall. The underlying aging processes vary from biological colonization to atmospheric pollution effects, thus requiring us to handle them with specific models. In particular, salt decay effects have an important visual influence. As Figure 1 shows, salt decay can produce different patterns and behaviors, depending on external conditions, such as ■ exposure (for instance, to rain or sunlight), ■ height (capillary rise from the ground), or ■ architectural features (such as sculptures, facades, or windows).

Blob Metamorphosis based on Minkowski Sums

Computer Graphics Forum, 1996

This paper addresses the metamorphosis of soft objects built from skeletons. We propose a new app... more This paper addresses the metamorphosis of soft objects built from skeletons. We propose a new approach that may be split into three steps. The first step consists in an original splitting of the initial and the final shapes with a view to creating a bijective graph of correspondence. In the second step, we assume that the skeletons are convex polygonal shapes, and thus take advantage of the properties of Minkowski sums to characterize the skeletons of intermediate shapes. Eventually, we characterize the intermediate distance and field functions; we describe a set of interpolation methods and propose to use a restricted class of parametrized distance and field functions so as to preserve coherence and speed-up computations. We show that we can easily extend those results to achieve a Bézier like metamorphosis where control points are replaced by control soft objects; in this scope, we have adapted existing accelerated techniques that build a Bézier transformation from a set of convex polyhedra to any kind of convex polygonal shapes. Eventually, we point out that matching all components of the initial and the final shapes generates amorphous intermediate shapes based on an overwhelming number of intermediate sub-components. Thus, we propose heuristics with a view to preserving coherence during the transformation and accelerating computations. We have implemented and tested our techniques in an experimental ray-tracer.

Shape constrained blob metamorphosis

Proceedings of Implicit Surfaces' 96, 1996

Page 1. Shape Constrained Blob Metamorphosis E. Galin, S. Akkouche Ecole Centrale de Lyon BP 163,... more

Fast surface reconstruction from contours using implicit surfaces

Implicit Surfaces, 1998

Page 1. Fast Surface Reconstruction from Contours using Implicit Surfaces Eric Galin &amp;amp... more

Procedural Cloudscapes

Computer Graphics Forum, 2018

We present a phenomenological approach for modeling and animating cloudscapes. We propose a compa... more We present a phenomenological approach for modeling and animating cloudscapes. We propose a compact procedural model for representing the different types of cloud over a range of altitudes. We define primitive-based field functions that allow the user to control and author the cloud cover over large distances easily. Our approach allows us to animate cloudscapes by morphing: instead of simulating the evolution of clouds using a physically-based simulation, we compute the movement of clouds using key-frame interpolation and tackle the morphing problem as an Optimal Transport problem. The trajectories of the cloud cover primitives are generated by solving an Anisotropic Shortest Path problem with a cost function that takes into account the elevation of the terrain and the parameters of the wind field.

EUROGRAPHICS 2004 / M. Alexa and E. Galin Short Presentations Interactive Modeling of Mushrooms

HAL is a multi-disciplinary open access archive for the deposit and dissemination of sci-entific ... more HAL is a multi-disciplinary open access archive for the deposit and dissemination of sci-entific research documents, whether they are pub-lished or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et a ̀ la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Large-scale Terrain Authoring through Interactive Erosion Simulation

ACM Transactions on Graphics

Large-scale terrains are essential in the definition of virtual worlds. Given the diversity of la... more Large-scale terrains are essential in the definition of virtual worlds. Given the diversity of landforms and the geomorphological complexity, there is a need for authoring techniques offering hydrological consistency without sacrificing user control. In this article, we bridge the gap between large-scale erosion simulation and authoring into an efficient framework. We set aside modeling in the elevation domain in favour of the uplift domain and compute emerging reliefs by simulating the stream power erosion. Our simulation relies on a fast yet accurate approximation of drainage area and flow routing to compute the erosion interactively, which allows for incremental authoring. Our model provides landscape artists with tools for shaping mountain ranges and valleys, such as copy-and-paste operations; warping for imitating folds and faults; and point and curve elevation constraints to precisely sculpt ridges or carve river networks. It also lends itself to inverse procedural modeling by...

Volume 19, (2000), Number yyy pp. Morphing

Implicit surfaces have proved to be a particularly well suited and efficient model for animating ... more Implicit surfaces have proved to be a particularly well suited and efficient model for animating and morphing shapes of arbitrary topologies. The BlobTree model is characterized as a hierarchical combination of skeletal primitives organized in a tree. The nodes hold blending, boolean and warping operators, which allows the design of complex objects. In this paper, we address the metamorphosis of the BlobTree. This appears a difficult task as the tree datastructures of the initial and final shapes are completely different in the general case, and consequently cannot be matched easily. We propose an original technique that solves the correspondence process and creates an intermediate generic BlobTree model whose instances interpolate the initial and final shapes. The animator may control the correspondence between features and can specify both the speed of transformation and the trajectory of the nodes and the leaves of the generic BlobTree model. This provides the end user with a tig...

Volumetric Spot Noise for Procedural 3D Shell Texture Synthesis

In this paper, we present an extension of the Locally Controlled Spot Noise and a visualization p... more In this paper, we present an extension of the Locally Controlled Spot Noise and a visualization pipeline for volumetric fuzzy details synthesis. We extend the noise model to author volumetric fuzzy details using filtered 3D quadratic kernel functions convolved with a projective non-uniform 2D distribution of impulses. We propose a new method based on order independent splatting to compute a fast view dependent approximation of shell noise at interactive rates. Our method outperforms ray marching techniques and avoids aliasing artifacts, thus improving interactive content authoring feedback. Moreover, generated surface details share the same properties as procedural noise: they extend on potentially infinite surfaces, are defined in an extremely compact way, are non-repetitive, continuous (no discrete voxel-artifacts when zooming) and independent of the definition of the underlying surface (no surface parameterization is required).

Métamorphose et visualisation de blobs à squelettes

Bien que la modelisation, l'animation et la visualisation d'objets definis a partir de su... more Bien que la modelisation, l'animation et la visualisation d'objets definis a partir de surfaces implicites aient ete largement etudiees au cours de la derniere decennie, la metamorphose a fait l'objet de peu d'attention et les techniques proposees jusqu'ici se sont averees limitees, soit par le type meme de blobs pouvant etre animes, soit par le manque de controle sur la transformation. Dans cette these, nous nous sommes interesses a la metamorphose et a la visualisation de blobs a squelettes polyedriques. Nous avons propose une approche originale et generale caracterisant les formes intermediaires a partir d'un modele de blob generique. Notre methode presente differents niveaux d'abstraction et de controle, depuis l'ebauche d'une metamorphose grossiere jusqu'a la realisation d'une transformation complexe ou l'animateur peut controler toute une gamme d'effets speciaux. Enfin, nous avons ete amenes a developper des methodes de lance...

N-Adic Subdivision Schemes for Local Mesh Deformation

This paper presents an interpolating subdivision scheme based on an N-adic decomposition of the p... more This paper presents an interpolating subdivision scheme based on an N-adic decomposition of the parameter space. This approach enables us to locally deform the surface according to a modification of the normals at the vertices of the control mesh. Experiments show that the N-adic decomposition provides a better control over the deformations, whereas a dyadic decomposition method often produces smoother surfaces.

Data-driven authoring of large-scale ecosystems

ACM Transactions on Graphics, 2020

In computer graphics populating a large-scale natural scene with plants in a fashion that both re... more In computer graphics populating a large-scale natural scene with plants in a fashion that both reflects the complex interrelationships and diversity present in real ecosystems and is computationally efficient enough to support iterative authoring remains an open problem. Ecosystem simulations embody many of the botanical influences, such as sunlight, temperature, and moisture, but require hours to complete, while synthesis from statistical distributions tends not to capture fine-scale variety and complexity. Instead, we leverage real-world data and machine learning to derive a canopy height model (CHM) for unseen terrain provided by the user. Trees in the canopy layer are then fitted to the resulting CHM through a constrained iterative process that optimizes for a given distribution of species, and, finally, an understorey layer is synthesised using distributions derived from biome-specific undergrowth simulations. Such a hybrid data-driven approach has the advantage that it incorpo...

M etamorphose du Blob {Tree

Modélisation et placement de champignons

Metamorphose d'objets polyedriques. Polygonal objects metamorphosis

Métamorphose d'objets polyédriques: Quelques méthodes d'accélération

Cet article traite de la metamorphose d'objets polyedriques par les sommes de Minkowski. Lors... more Cet article traite de la metamorphose d'objets polyedriques par les sommes de Minkowski. Lorsque les polyedres arguments sont convexes, la transformation peut etre caracterisee par un polyedre generique convexe dont la topologie est invariante au cours du temps. Nous proposons des algorithmes acceleres tirant parti des informations topologiques pour la construction de la somme de Minkowski de deux polyedres convexes. Les polyedres de Bezier sont presentes comme une extension a plusieurs polyedres. Nous montrons que la conservation de la topologie permet d'ajouter et de retirer iterativement des polyedres de controle sans avoir a reconstruire l'ensemble de la topologie. Enfin, nous montrons comment la distributivite de la somme de Minkowski par rapport a l'union permet de traiter efficacement certains objets complexes definis comme union de sous elements convexes.

The HybridTree: A Hybrid Constructive Shape Representation for Free-Form Modeling

Lecture Notes in Computer Science

In this paper, we describe a hybrid modeling framework for creating complex 3D objects incrementa... more In this paper, we describe a hybrid modeling framework for creating complex 3D objects incrementally. Our system relies on an extended CSG tree that assembles skeletal implicit primitives, triangle meshes and point set models in a coherent fashion: we call this structure the HybridTree. Editing operations are performed by exploiting the complementary abilities of implicit and polygonal mesh surface representations

Fast processing of triangle meshes using triangle fans

International Conference on Shape Modeling and Applications 2005 (SMI' 05)

... Samir Akkouche LIRIS - CNRS Université Claude Bernard Lyon 1 [email protected]. fr Ab... more

Landscape specification resizing

2014 XL Latin American Computing Conference (CLEI), 2014

In this work, we introduce a method for resizing a landscape specification, i.e., a vector model ... more In this work, we introduce a method for resizing a landscape specification, i.e., a vector model containing a set of objects present in a virtual environment. Our goal is to change the landscape dimensions while keeping its overall appearance. Our method is based on the insertion and removal of objects in the specification, followed by some adjustments of the scene adapting the initial model to these changes. Besides the proposed approach for the positioning the objects, this method can be easily extended to use techniques of the state of the art for spreading objects in the landscape. The adjustment of the scene components consists in performing vertical or horizontal translations onto the position of the objects. It is based on a removal or insertion of paths in the grid created over the scene space using dynamic programming. In spite of dealing with a vector model, all proposed operations are performed in the pixel space. This technique is an adaptation of the Seam Carving for the context of vector landscapes specification. This model is simpler than common images, and thus, we can achieve results as good as those obtained in the image context, using simpler metrics.

Modélisation de détails dans les scènes naturelles

Cet article présente un système pour modéliser et distribuer des détails dans une scène virtuelle... more Cet article présente un système pour modéliser et distribuer des détails dans une scène virtuelle. Ces deux aspects jouent un rôle fondamental sur le réalisme des scènes de synthèse. L'architecture que nous proposons repose sur deux éléments clés : un atlas de formes complexes représentant des fragments de détails et des algorithmes de dispersion et de propagation dépendant des caractéristiques

Simulating How Salt Decay Ages Buildings

IEEE Computer Graphics and Applications, 2012

A ging affects all real surfaces. 1,2 It particularly visibly affects urban scenes with construct... more A ging affects all real surfaces. 1,2 It particularly visibly affects urban scenes with construction materials. So, simulating such materials' decay is an important research topic with many applications, from designing buildings to conserving cultural heritage. Construction materials' alterations depend on a range of parameters from chemical composition to surface characteristics. Moreover, the alterations can vary according to the specific location, even on a single wall. The underlying aging processes vary from biological colonization to atmospheric pollution effects, thus requiring us to handle them with specific models. In particular, salt decay effects have an important visual influence. As Figure 1 shows, salt decay can produce different patterns and behaviors, depending on external conditions, such as ■ exposure (for instance, to rain or sunlight), ■ height (capillary rise from the ground), or ■ architectural features (such as sculptures, facades, or windows).

Blob Metamorphosis based on Minkowski Sums

Computer Graphics Forum, 1996

This paper addresses the metamorphosis of soft objects built from skeletons. We propose a new app... more This paper addresses the metamorphosis of soft objects built from skeletons. We propose a new approach that may be split into three steps. The first step consists in an original splitting of the initial and the final shapes with a view to creating a bijective graph of correspondence. In the second step, we assume that the skeletons are convex polygonal shapes, and thus take advantage of the properties of Minkowski sums to characterize the skeletons of intermediate shapes. Eventually, we characterize the intermediate distance and field functions; we describe a set of interpolation methods and propose to use a restricted class of parametrized distance and field functions so as to preserve coherence and speed-up computations. We show that we can easily extend those results to achieve a Bézier like metamorphosis where control points are replaced by control soft objects; in this scope, we have adapted existing accelerated techniques that build a Bézier transformation from a set of convex polyhedra to any kind of convex polygonal shapes. Eventually, we point out that matching all components of the initial and the final shapes generates amorphous intermediate shapes based on an overwhelming number of intermediate sub-components. Thus, we propose heuristics with a view to preserving coherence during the transformation and accelerating computations. We have implemented and tested our techniques in an experimental ray-tracer.

Shape constrained blob metamorphosis

Proceedings of Implicit Surfaces' 96, 1996

Page 1. Shape Constrained Blob Metamorphosis E. Galin, S. Akkouche Ecole Centrale de Lyon BP 163,... more

Fast surface reconstruction from contours using implicit surfaces

Implicit Surfaces, 1998

Page 1. Fast Surface Reconstruction from Contours using Implicit Surfaces Eric Galin &amp;amp... more

Procedural Cloudscapes

Computer Graphics Forum, 2018

We present a phenomenological approach for modeling and animating cloudscapes. We propose a compa... more We present a phenomenological approach for modeling and animating cloudscapes. We propose a compact procedural model for representing the different types of cloud over a range of altitudes. We define primitive-based field functions that allow the user to control and author the cloud cover over large distances easily. Our approach allows us to animate cloudscapes by morphing: instead of simulating the evolution of clouds using a physically-based simulation, we compute the movement of clouds using key-frame interpolation and tackle the morphing problem as an Optimal Transport problem. The trajectories of the cloud cover primitives are generated by solving an Anisotropic Shortest Path problem with a cost function that takes into account the elevation of the terrain and the parameters of the wind field.

EUROGRAPHICS 2004 / M. Alexa and E. Galin Short Presentations Interactive Modeling of Mushrooms

HAL is a multi-disciplinary open access archive for the deposit and dissemination of sci-entific ... more HAL is a multi-disciplinary open access archive for the deposit and dissemination of sci-entific research documents, whether they are pub-lished or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et a ̀ la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.