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Remi Ronfard

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University of Kent

University of Michigan

The University of Auckland

California Institute of Integral Studies

gregory sholette

Queens College of the City University of New York

Kunsthochschule Berlin-Weißensee

University of London, Central School of Speech and Drama

Ethnology Institute of National Academy of Sciences of Ukraine

Kaiti Diamantakou

National & Kapodistrian University of Athens

Cesário Augusto Pimentel de Alencar

UFPA - Federal University of Pará

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Papers by Remi Ronfard

Making Movies from Make-Believe Games

HAL (Le Centre pour la Communication Scientifique Directe), Apr 24, 2017

HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific r... more HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published 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 à 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.

Which prosodic features contribute to the recognition of dramatic attitudes?

Speech Communication, Dec 1, 2017

In this work we explore the capability of audiovisual prosodic features (such as fundamental freq... more In this work we explore the capability of audiovisual prosodic features (such as fundamental frequency, head motion or facial expressions) to discriminate among different dramatic attitudes. We extract the audiovisual parameters from an acted corpus of attitudes and structure them as frame, syllable and sentence-level features. Using Linear Discriminant Analysis classifiers, we show that prosodic features present a higher discriminating rate at sentence-level. This finding is confirmed by the perceptual evaluation results of audio and/or visual stimuli obtained from the recorded attitudes.

Spatial Motion Doodles: Sketching Animation in VR Using Hand Gestures and Laban Motion Analysis

Figure 1: Left: A user drawing a spatial motion doodle (SMD) which is the six-dimensional traject... more Figure 1: Left: A user drawing a spatial motion doodle (SMD) which is the six-dimensional trajectory of a moving frame (position and orientation), here attached to the HTC Vive controller. Right: The SMD is parsed into a string of motion tokens, allowing to recognize actions and extract the associated motion qualities. This information is transferred to an articulated character to generate an expressive 3D animation sequence.

Automatic generation of geological stories from a single sketch

Proceedings of the Joint Symposium on Computational Aesthetics and Sketch-Based Interfaces and Modeling and Non-Photorealistic Animation and Rendering, 2018

Describing the history of a terrain from a vertical geological crosssection is an important probl... more Describing the history of a terrain from a vertical geological crosssection is an important problem in geology, called geological restoration. Designing the sequential evolution of the geometry is usually done manually, involving many trials and errors. In this work, we recast this problem as a storyboarding problem, where the di erent stages in the restoration are automatically generated as storyboard panels and displayed as geological stories. Our system allows geologists to interactively explore multiple scenarios by selecting plausible geological event sequences and backward simulating them at interactive rate, causing the terrain layers to be progressively un-deposited, un-eroded, un-compacted, unfolded and un-faulted. Storyboard sketches are generated along the way. When a restoration is complete, the storyboard panels can be used for automatically generating a forward animation of the terrain history, enabling quick visualization and validation of hypotheses. As a proof-of-concept, we describe how our system was used by geologists to restore and animate cross-sections in real examples at various spatial and temporal scales and with di erent levels of complexity, including the Chartreuse region in the French Alps.

Figurines, a multimodal framework for tangible storytelling

6th Workshop on Child Computer Interaction (WOCCI 2017), 2017

This paper presents Figurines, an offline framework for narrative creation with tangible objects,... more This paper presents Figurines, an offline framework for narrative creation with tangible objects, designed to record storytelling sessions with children, teenagers or adults. This framework uses tangible diegetic objects to record a free narrative from up to two storytellers and construct a fully annotated representation of the story. This representation is composed of the 3D position and orientation of the figurines, the position of decor elements and interpretation of the storytellers' actions (facial expression, gestures and voice). While maintaining the playful dimension of the storytelling session, the system must tackle the challenge of recovering the free-form motion of the figurines and the storytellers in uncontrolled environments. To do so, we record the storytelling session using a hybrid setup with two RGB-D sensors and figurines augmented with IMU sensors. The first RGB-D sensor completes IMU information in order to identify figurines and tracks them as well as decor elements. It also tracks the storytellers jointly with the second RGB-D sensor. The framework has been used to record preliminary experiments to validate interest of our approach. These experiments evaluate figurine following and combination of motion and storyteller's voice, gesture and facial expressions. In a make-believe game, this story representation was re-targeted on virtual characters to produce an animated version of the story. The final goal of the Figurines framework is to enhance our understanding of the creative processes at work during immersive storytelling.

Implementing Hitchcock - the Role of Focalization and Viewpoint

Focalization and viewpoint are important aspects of narrative movie-making that need to be taken ... more Focalization and viewpoint are important aspects of narrative movie-making that need to be taken into account by cinematography and editing. In this paper, we argue that viewpoint can be determined from the first principles of focalization in the screenplay and adherence to a slightly modified version of Hitchcock's rule in cinematography and editing. With minor changes to previous work in automatic cinematography and editing, we show that this strategy makes it possible to easily control the viewpoint in the movie by rewriting and annotating the screenplay. We illustrate our claim with four versions of a moderately complex movie scene obtained by focalizing on its four main characters, with dramatically different camera choices.

R.: Audio-Visual Speaker Conversion Using Prosody Features

The article presents a joint audio-video approach towards speaker identity conversion, based on s... more The article presents a joint audio-video approach towards speaker identity conversion, based on statistical meth-ods originally introduced for voice conversion. Using the experimental data from the 3D BIWI Audiovisual corpus of Affective Communication, mapping functions are built between each two speakers in order to con-vert speaker-specific features: speech signal and 3D fa-cial expressions. The results obtained by combining au-dio and visual features are compared to corresponding results from earlier approaches, while outlining the im-provements brought by introducing dynamic features and exploiting prosodic features. Index Terms: speaker identity conversion, gaussian mix-ture model, dynamic features, prosodic features

CLAVIS - Un systeme de raisonnement temporel pour la classification de sequences audiovisuelles

L'analyse des images et des sons

L'apparition de nouveaux moyens de stockage et de traitement des longues sequences de video n... more L'apparition de nouveaux moyens de stockage et de traitement des longues sequences de video numerique conduit les chercheurs en analyse d'image des nouveaux sytemes de description. Ceux-ci forment la base d'une discipline nouvelle, l'analyse de scene, dont il existe une version sonore et une version visuelle. Toutes deux visent a extraire du flux d'images et des sons quelques elements caracteristiques, permettant leur manipulation a un niveau symbolique

Audiovisual speaker conversion using prosodic features

The article presents a joint audio-video approach towards speaker identity conversion, based on s... more The article presents a joint audio-video approach towards speaker identity conversion, based on statistical methods originally introduced for voice conversion. Using the experimental data from the 3D BIWI Audiovisual corpus of Affective Communication, mapping functions are built between each two speakers in order to convert speaker-specific features: speech signal and 3D facial expressions. The results obtained by combining audio and visual features are compared to corresponding results from earlier approaches, while outlining the improvements brought by introducing dynamic features and exploiting prosodic features

2014 - How Do We Evaluate the Quality of Computational Editing Systems

Captation vidéo et analyse génétique du théâtre: l'informatique au service de la recherche théâtrale

Ma communication porte sur deux projets de recherche en cours sur la captation vidéo de spectacle... more Ma communication porte sur deux projets de recherche en cours sur la captation vidéo de spectacles de théâtre et leur exploitation informatique. Le projet Scénoptique est une investigation des nouvelles techniques de captation en ultra haute définition qui permettent le recadrage et le montage en post-production. Le projet Spectacle En Ligne(s) poursuit l'objectif de constituer pour les chercheurs, les enseignants et le public un corpus original de captations de répétitions de théâtre et d'opéra afin d'aborder un champ de recherche encore peu exploré faute de corpus adapté : celui de l'analyse génétique des oeuvres. Les captations matérialisent la forme visuelle et sonore de l'évolution génétique du spectacle, qui devient un objet d'étude scientifique en même temps qu'un objet d'appréciation esthétique. Ce type de recherche nécessite une méthodologie de captation, un dispositif audiovisuel industriel à bas coût et des méthodes d'indexation adaptées à la constitution d'un corpus audiovisuel très interopérable, ouvert à des publications scientifiques, pédagogiques et grand public dans un contexte contributif où le public amateur aspire à de nouvelles situations de confrontation aux oeuvres.

Audio-visual speaker conversion using prosody features

The article presents a joint audio-video approach towards speaker identity conversion, based on s... more The article presents a joint audio-video approach towards speaker identity conversion, based on statistical methods originally introduced for voice conversion. Using the experimental data from the 3D BIWI Audiovisual corpus of Affective Communication, mapping functions are built between each two speakers in order to convert speaker-specific features: speech signal and 3D facial expressions. The results obtained by combining audio and visual features are compared to corresponding results from earlier approaches, while outlining the improvements brought by introducing dynamic features and exploiting prosodic features.

Detail-preserving variational surface design with multiresolution constraints

Proceedings Shape Modeling Applications, 2004.

We present a variational framework for rapid shape prototyping. The modeled shape is represented ... more We present a variational framework for rapid shape prototyping. The modeled shape is represented as a Catmull-Clark multiresolution subdivision surface which is interactively deformed by direct user input. Free-form design goals are formulated as constraints on the shape and the modeling problem is cast into a constrained optimization one. The focus of this paper is on handling multiresolution constraints of different kinds and on preserving surface details throughout the deformation process. Our approach eliminates the need for an explicit decomposition of the input model into frequency bands and the overhead associated with saving and restoring high-frequency detail after global shape fairing. Instead, we define a deformation vector field over the model and we optimize its energy. Surface details are considered as part of the rest shape and are preserved during free-form model editing. We explore approximating the solution of the optimization problem to various degrees to balance trade-offs between interactivity and accuracy of the results.

Vector graphics complexes

ACM Transactions on Graphics, 2014

Basic topological modeling, such as the ability to have several faces share a common edge, has be... more Basic topological modeling, such as the ability to have several faces share a common edge, has been largely absent from vector graphics. We introduce the vector graphics complex (VGC) as a simple data structure to support fundamental topological modeling operations for vector graphics illustrations. The VGC can represent any arbitrary non-manifold topology as an immersion in the plane, unlike planar maps which can only represent embeddings. This allows for the direct representation of incidence relationships between objects and can therefore more faithfully capture the intended semantics of many illustrations, while at the same time keeping the geometric flexibility of stacking-based systems. We describe and implement a set of topological editing operations for the VGC, including glue, unglue, cut, and uncut. Our system maintains a global stacking order for all faces, edges, and vertices without requiring that components of an object reside together on a single layer. This allows fo...

Tracking with the kinematics of extremal contours

This paper addresses the problem of articulated motion tracking from image sequences. We describe... more This paper addresses the problem of articulated motion tracking from image sequences. We describe a method that relies on an explicit parameterization of the extremal contours in terms of the joint parameters of an associated kinematic model. The latter allows us to predict the extremal contours from the body-part primitives of an articulated model and to compare them with observed image contours. The error function that measures the discrepancy between observed contours and predicted contours is minimized using an analytical expression of the Jacobian that maps joint velocities onto contour velocities. In practice we model people both by their geometry (truncated elliptical cones) and with their articulated structure-a kinematic model with 40 rotational degrees of freedom. We observe image data gathered with several synchronized cameras. The tracker has been successfully applied to image sequences gathered at 30 frames/second.

Implicit simplicial models for adaptive curve reconstruction

IEEE Transactions on Pattern Analysis and Machine Intelligence, 1996

Modeling people: Vision-based understanding of a person’s shape, appearance, movement, and behaviour

Computer Vision and Image Understanding, 2006

Triangulating multiply‐connected polygons: A simple, yet efficient algorithm

Computer Graphics Forum, 1994

We present a new, simple, yet efficient algorithm for triangulating multiply‐connected polygons. ... more We present a new, simple, yet efficient algorithm for triangulating multiply‐connected polygons. The algorithm requires sorting only local concave minima (sags). The order in which triangles are created mimics a flooding process of the interior of the polygon. At each stage, the algorithm analyses the positions and neighborhoods of two vertices only, and possibly checks for active sags, so as to determine which of five possible actions to take. Actions are based on a local decomposition of the polygon into monotonic regions, or gorges (raise the water level in the current gorge, spill into an adjacent gorge, jump to the other bank of a filled gorge, divide a gorge into two, and fill a gorge to its top). The implementation is extremely simple and numerically robust for a large class of polygons. It has been tested on millions of cases as a preprocessing step of a walkthrough and inspection program for complex mechanical and architectural scenes. Extensive experimental results indicat...

Full‐range approximation of triangulated polyhedra

Computer Graphics Forum, 1996

We propose a new algorithm for automatically computing approximations of a given polyhedral objec... more We propose a new algorithm for automatically computing approximations of a given polyhedral object at different levels of details. The application for this algorithm is the display of very complex scenes. where many objects are seen with a range of varying levels of detail. Our approach is similar to the region‐merging method used for image segmentation. We iteratively collapse edges, based on a measure of the geometric deviation from the initial shape. When edges are merged in the right order, this strategy produces a continuum of valid approximations of the original object, which can be used for faster rendering at vastly different scales.

Making Movies from Make-Believe Games

HAL (Le Centre pour la Communication Scientifique Directe), Apr 24, 2017

HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific r... more HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published 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 à 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.

Which prosodic features contribute to the recognition of dramatic attitudes?

Speech Communication, Dec 1, 2017

In this work we explore the capability of audiovisual prosodic features (such as fundamental freq... more In this work we explore the capability of audiovisual prosodic features (such as fundamental frequency, head motion or facial expressions) to discriminate among different dramatic attitudes. We extract the audiovisual parameters from an acted corpus of attitudes and structure them as frame, syllable and sentence-level features. Using Linear Discriminant Analysis classifiers, we show that prosodic features present a higher discriminating rate at sentence-level. This finding is confirmed by the perceptual evaluation results of audio and/or visual stimuli obtained from the recorded attitudes.

Spatial Motion Doodles: Sketching Animation in VR Using Hand Gestures and Laban Motion Analysis

Figure 1: Left: A user drawing a spatial motion doodle (SMD) which is the six-dimensional traject... more Figure 1: Left: A user drawing a spatial motion doodle (SMD) which is the six-dimensional trajectory of a moving frame (position and orientation), here attached to the HTC Vive controller. Right: The SMD is parsed into a string of motion tokens, allowing to recognize actions and extract the associated motion qualities. This information is transferred to an articulated character to generate an expressive 3D animation sequence.

Automatic generation of geological stories from a single sketch

Proceedings of the Joint Symposium on Computational Aesthetics and Sketch-Based Interfaces and Modeling and Non-Photorealistic Animation and Rendering, 2018

Describing the history of a terrain from a vertical geological crosssection is an important probl... more Describing the history of a terrain from a vertical geological crosssection is an important problem in geology, called geological restoration. Designing the sequential evolution of the geometry is usually done manually, involving many trials and errors. In this work, we recast this problem as a storyboarding problem, where the di erent stages in the restoration are automatically generated as storyboard panels and displayed as geological stories. Our system allows geologists to interactively explore multiple scenarios by selecting plausible geological event sequences and backward simulating them at interactive rate, causing the terrain layers to be progressively un-deposited, un-eroded, un-compacted, unfolded and un-faulted. Storyboard sketches are generated along the way. When a restoration is complete, the storyboard panels can be used for automatically generating a forward animation of the terrain history, enabling quick visualization and validation of hypotheses. As a proof-of-concept, we describe how our system was used by geologists to restore and animate cross-sections in real examples at various spatial and temporal scales and with di erent levels of complexity, including the Chartreuse region in the French Alps.

Figurines, a multimodal framework for tangible storytelling

6th Workshop on Child Computer Interaction (WOCCI 2017), 2017

This paper presents Figurines, an offline framework for narrative creation with tangible objects,... more This paper presents Figurines, an offline framework for narrative creation with tangible objects, designed to record storytelling sessions with children, teenagers or adults. This framework uses tangible diegetic objects to record a free narrative from up to two storytellers and construct a fully annotated representation of the story. This representation is composed of the 3D position and orientation of the figurines, the position of decor elements and interpretation of the storytellers' actions (facial expression, gestures and voice). While maintaining the playful dimension of the storytelling session, the system must tackle the challenge of recovering the free-form motion of the figurines and the storytellers in uncontrolled environments. To do so, we record the storytelling session using a hybrid setup with two RGB-D sensors and figurines augmented with IMU sensors. The first RGB-D sensor completes IMU information in order to identify figurines and tracks them as well as decor elements. It also tracks the storytellers jointly with the second RGB-D sensor. The framework has been used to record preliminary experiments to validate interest of our approach. These experiments evaluate figurine following and combination of motion and storyteller's voice, gesture and facial expressions. In a make-believe game, this story representation was re-targeted on virtual characters to produce an animated version of the story. The final goal of the Figurines framework is to enhance our understanding of the creative processes at work during immersive storytelling.

Implementing Hitchcock - the Role of Focalization and Viewpoint

Focalization and viewpoint are important aspects of narrative movie-making that need to be taken ... more Focalization and viewpoint are important aspects of narrative movie-making that need to be taken into account by cinematography and editing. In this paper, we argue that viewpoint can be determined from the first principles of focalization in the screenplay and adherence to a slightly modified version of Hitchcock's rule in cinematography and editing. With minor changes to previous work in automatic cinematography and editing, we show that this strategy makes it possible to easily control the viewpoint in the movie by rewriting and annotating the screenplay. We illustrate our claim with four versions of a moderately complex movie scene obtained by focalizing on its four main characters, with dramatically different camera choices.

R.: Audio-Visual Speaker Conversion Using Prosody Features

The article presents a joint audio-video approach towards speaker identity conversion, based on s... more The article presents a joint audio-video approach towards speaker identity conversion, based on statistical meth-ods originally introduced for voice conversion. Using the experimental data from the 3D BIWI Audiovisual corpus of Affective Communication, mapping functions are built between each two speakers in order to con-vert speaker-specific features: speech signal and 3D fa-cial expressions. The results obtained by combining au-dio and visual features are compared to corresponding results from earlier approaches, while outlining the im-provements brought by introducing dynamic features and exploiting prosodic features. Index Terms: speaker identity conversion, gaussian mix-ture model, dynamic features, prosodic features

CLAVIS - Un systeme de raisonnement temporel pour la classification de sequences audiovisuelles

L'analyse des images et des sons

L'apparition de nouveaux moyens de stockage et de traitement des longues sequences de video n... more L'apparition de nouveaux moyens de stockage et de traitement des longues sequences de video numerique conduit les chercheurs en analyse d'image des nouveaux sytemes de description. Ceux-ci forment la base d'une discipline nouvelle, l'analyse de scene, dont il existe une version sonore et une version visuelle. Toutes deux visent a extraire du flux d'images et des sons quelques elements caracteristiques, permettant leur manipulation a un niveau symbolique

Audiovisual speaker conversion using prosodic features

The article presents a joint audio-video approach towards speaker identity conversion, based on s... more The article presents a joint audio-video approach towards speaker identity conversion, based on statistical methods originally introduced for voice conversion. Using the experimental data from the 3D BIWI Audiovisual corpus of Affective Communication, mapping functions are built between each two speakers in order to convert speaker-specific features: speech signal and 3D facial expressions. The results obtained by combining audio and visual features are compared to corresponding results from earlier approaches, while outlining the improvements brought by introducing dynamic features and exploiting prosodic features

2014 - How Do We Evaluate the Quality of Computational Editing Systems

Captation vidéo et analyse génétique du théâtre: l'informatique au service de la recherche théâtrale

Ma communication porte sur deux projets de recherche en cours sur la captation vidéo de spectacle... more Ma communication porte sur deux projets de recherche en cours sur la captation vidéo de spectacles de théâtre et leur exploitation informatique. Le projet Scénoptique est une investigation des nouvelles techniques de captation en ultra haute définition qui permettent le recadrage et le montage en post-production. Le projet Spectacle En Ligne(s) poursuit l'objectif de constituer pour les chercheurs, les enseignants et le public un corpus original de captations de répétitions de théâtre et d'opéra afin d'aborder un champ de recherche encore peu exploré faute de corpus adapté : celui de l'analyse génétique des oeuvres. Les captations matérialisent la forme visuelle et sonore de l'évolution génétique du spectacle, qui devient un objet d'étude scientifique en même temps qu'un objet d'appréciation esthétique. Ce type de recherche nécessite une méthodologie de captation, un dispositif audiovisuel industriel à bas coût et des méthodes d'indexation adaptées à la constitution d'un corpus audiovisuel très interopérable, ouvert à des publications scientifiques, pédagogiques et grand public dans un contexte contributif où le public amateur aspire à de nouvelles situations de confrontation aux oeuvres.

Audio-visual speaker conversion using prosody features

The article presents a joint audio-video approach towards speaker identity conversion, based on s... more The article presents a joint audio-video approach towards speaker identity conversion, based on statistical methods originally introduced for voice conversion. Using the experimental data from the 3D BIWI Audiovisual corpus of Affective Communication, mapping functions are built between each two speakers in order to convert speaker-specific features: speech signal and 3D facial expressions. The results obtained by combining audio and visual features are compared to corresponding results from earlier approaches, while outlining the improvements brought by introducing dynamic features and exploiting prosodic features.

Detail-preserving variational surface design with multiresolution constraints

Proceedings Shape Modeling Applications, 2004.

We present a variational framework for rapid shape prototyping. The modeled shape is represented ... more We present a variational framework for rapid shape prototyping. The modeled shape is represented as a Catmull-Clark multiresolution subdivision surface which is interactively deformed by direct user input. Free-form design goals are formulated as constraints on the shape and the modeling problem is cast into a constrained optimization one. The focus of this paper is on handling multiresolution constraints of different kinds and on preserving surface details throughout the deformation process. Our approach eliminates the need for an explicit decomposition of the input model into frequency bands and the overhead associated with saving and restoring high-frequency detail after global shape fairing. Instead, we define a deformation vector field over the model and we optimize its energy. Surface details are considered as part of the rest shape and are preserved during free-form model editing. We explore approximating the solution of the optimization problem to various degrees to balance trade-offs between interactivity and accuracy of the results.

Vector graphics complexes

ACM Transactions on Graphics, 2014

Basic topological modeling, such as the ability to have several faces share a common edge, has be... more Basic topological modeling, such as the ability to have several faces share a common edge, has been largely absent from vector graphics. We introduce the vector graphics complex (VGC) as a simple data structure to support fundamental topological modeling operations for vector graphics illustrations. The VGC can represent any arbitrary non-manifold topology as an immersion in the plane, unlike planar maps which can only represent embeddings. This allows for the direct representation of incidence relationships between objects and can therefore more faithfully capture the intended semantics of many illustrations, while at the same time keeping the geometric flexibility of stacking-based systems. We describe and implement a set of topological editing operations for the VGC, including glue, unglue, cut, and uncut. Our system maintains a global stacking order for all faces, edges, and vertices without requiring that components of an object reside together on a single layer. This allows fo...

Tracking with the kinematics of extremal contours

This paper addresses the problem of articulated motion tracking from image sequences. We describe... more This paper addresses the problem of articulated motion tracking from image sequences. We describe a method that relies on an explicit parameterization of the extremal contours in terms of the joint parameters of an associated kinematic model. The latter allows us to predict the extremal contours from the body-part primitives of an articulated model and to compare them with observed image contours. The error function that measures the discrepancy between observed contours and predicted contours is minimized using an analytical expression of the Jacobian that maps joint velocities onto contour velocities. In practice we model people both by their geometry (truncated elliptical cones) and with their articulated structure-a kinematic model with 40 rotational degrees of freedom. We observe image data gathered with several synchronized cameras. The tracker has been successfully applied to image sequences gathered at 30 frames/second.

Implicit simplicial models for adaptive curve reconstruction

IEEE Transactions on Pattern Analysis and Machine Intelligence, 1996

Modeling people: Vision-based understanding of a person’s shape, appearance, movement, and behaviour

Computer Vision and Image Understanding, 2006

Triangulating multiply‐connected polygons: A simple, yet efficient algorithm

Computer Graphics Forum, 1994

We present a new, simple, yet efficient algorithm for triangulating multiply‐connected polygons. ... more We present a new, simple, yet efficient algorithm for triangulating multiply‐connected polygons. The algorithm requires sorting only local concave minima (sags). The order in which triangles are created mimics a flooding process of the interior of the polygon. At each stage, the algorithm analyses the positions and neighborhoods of two vertices only, and possibly checks for active sags, so as to determine which of five possible actions to take. Actions are based on a local decomposition of the polygon into monotonic regions, or gorges (raise the water level in the current gorge, spill into an adjacent gorge, jump to the other bank of a filled gorge, divide a gorge into two, and fill a gorge to its top). The implementation is extremely simple and numerically robust for a large class of polygons. It has been tested on millions of cases as a preprocessing step of a walkthrough and inspection program for complex mechanical and architectural scenes. Extensive experimental results indicat...

Full‐range approximation of triangulated polyhedra

Computer Graphics Forum, 1996

We propose a new algorithm for automatically computing approximations of a given polyhedral objec... more We propose a new algorithm for automatically computing approximations of a given polyhedral object at different levels of details. The application for this algorithm is the display of very complex scenes. where many objects are seen with a range of varying levels of detail. Our approach is similar to the region‐merging method used for image segmentation. We iteratively collapse edges, based on a measure of the geometric deviation from the initial shape. When edges are merged in the right order, this strategy produces a continuum of valid approximations of the original object, which can be used for faster rendering at vastly different scales.