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Item Large Scale Terrain Generation from Tectonic Uplift and Fluvial Erosion(The Eurographics Association and John Wiley & Sons Ltd., 2016) Cordonnier, Guillaume; Braun, Jean; Cani, Marie-Paule; Benes, Bedrich; Galin, Éric; Peytavie, Adrien; Guérin, Éric; Joaquim Jorge and Ming LinAt large scale, landscapes result from the combination of two major processes: tectonics which generate the main relief through crust uplift, and weather which accounts for erosion. This paper presents the first method in computer graphics that combines uplift and hydraulic erosion to generate visually plausible terrains. Given a user-painted uplift map, we generate a stream graph over the entire domain embedding elevation information and stream flow. Our approach relies on the stream power equation introduced in geology for hydraulic erosion. By combining crust uplift and stream power erosion we generate large realistic terrains at a low computational cost. Finally, we convert this graph into a digital elevation model by blending landform feature kernels whose parameters are derived from the information in the graph. Our method gives high-level control over the large scale dendritic structures of the resulting river networks, watersheds, and mountains ridges.Item A Review of Digital Terrain Modeling(The Eurographics Association and John Wiley & Sons Ltd., 2019) Galin, Eric; Guérin, Eric; Peytavie, Adrien; Cordonnier, Guillaume; Cani, Marie-Paule; Benes, Bedrich; Gain, James; Giachetti, Andrea and Rushmeyer, HollyTerrains are a crucial component of three-dimensional scenes and are present in many Computer Graphics applications. Terrain modeling methods focus on capturing landforms in all their intricate detail, including eroded valleys arising from the interplay of varied phenomena, dendritic mountain ranges, and complex river networks. Set against this visual complexity is the need for user control over terrain features, without which designers are unable to adequately express their artistic intent. This article provides an overview of current terrain modeling and authoring techniques, organized according to three categories: procedural modeling, physically-based simulation of erosion and land formation processes, and example-based methods driven by scanned terrain data. We compare and contrast these techniques according to several criteria, specifically: the variety of achievable landforms; realism from both a perceptual and geomorphological perspective; issues of scale in terms of terrain extent and sampling precision; the different interaction metaphors and attendant forms of user-control, and computation and memory performance. We conclude with an in-depth discussion of possible research directions and outstanding technical and scientific challenges.Item Mutable Elastic Models for Sculpting Structured Shapes(The Eurographics Association and Blackwell Publishing Ltd., 2013) Milliez, Antoine; Wand, Michael; Cani, Marie-Paule; Seidel, Hans-Peter; I. Navazo, P. PoulinIn this paper, we propose a new paradigm for free-form shape deformation. Standard deformable models minimize an energy measuring the distance to a single target shape. We propose a new, ''mutable'' elastic model. It represents complex geometry by a collection of parts and measures the distance of each part measures to a larger set of alternative rest configurations. By detecting and reacting to local switches between best-matching rest states, we build a 3D sculpting system: It takes a structured shape consisting of parts and replacement rules as input. The shape can subsequently be elongated, compressed, bent, cut, and merged within a constraints-based free-form editing interface, where alternative rest-states model to such changes. In practical experiments, we show that the approach yields a surprisingly intuitive and easy to implement interface for interactively designing objects described by such discrete shape grammars, for which direct shape control mechanisms were typically lacking.Item Crowd Sculpting: A Space-time Sculpting Method for Populating Virtual Environments(The Eurographics Association and John Wiley and Sons Ltd., 2014) Jordao, Kevin; Pettré, Julien; Christie, Marc; Cani, Marie-Paule; B. Levy and J. KautzWe introduce "Crowd Sculpting": a method to interactively design populated environments by using intuitive deformation gestures to drive both the spatial coverage and the temporal sequencing of a crowd motion. Our approach assembles large environments from sets of spatial elements which contain inter-connectible, periodic crowd animations. Such a Crowd Patches approach allows us to avoid expensive and difficult-to-control simulations. It also overcomes the limitations of motion editing, that would result into animations delimited in space and time. Our novel methods allows the user to control the crowd patches layout in ways inspired by elastic shape sculpting: the user creates and tunes the desired populated environment through stretching, bending, cutting and merging gestures, applied either in space or time. Our examples demonstrate that our method allows the space-time editing of very large populations and results into endless animation, while offering real-time, intuitive control and maintaining animation quality.Item Generation of Folded Terrains from Simple Vector Maps(The Eurographics Association, 2015) Michel, Elie; Emilien, Arnaud; Cani, Marie-Paule; B. Bickel and T. RitschelWhile several terrain generation methods focused on plausible watersheds, the fact that most mountains should not be isolated but rather be part of wider scale mountain ranges was seldom considered. In this work, we present the first procedural method that generates folded terrains from simple user input, in the form of some sparse peak distribution on a vector map. The key idea is to infer possible continental plates from this distribution and to use simplified plate tectonics to generate relevant terrain folds. The resulting terrain with large-scale folds, computed in real-time, can be further refined using standard erosion simulation. This leads to detailed terrains with plausible mountain ranges that match the peak distributions and main rivers specified on simple vector maps.Item Geometric Details on Skeleton-based Implicit Surfaces(The Eurographics Association, 2012) Zanni, Cedric; Bares, P.; Lagae, Ares; Quiblier, M.; Cani, Marie-Paule; Carlos Andujar and Enrico PuppoWe present a modeling technique to enhance implicit surfaces with procedural geometric details. The details are based on Gabor noise, which enables us to seamlessly handle anisotropy. The orientation of details can be defined with respect to the orientation of the main shape features, which reduces the amount of user input. The method extends to complex details that are tilted with respect to the normal of the input surface. Lastly, our method allows the blending of the resulting enhanced implicit primitives without causing the details to blur.Item Implicit Blending Revisited(The Eurographics Association and Blackwell Publishing Ltd, 2010) Bernhardt, Adrien; Barthe, Loic; Cani, Marie-Paule; Wyvill, BrianBlending is both the strength and the weakness of functionally based implicit surfaces (such as F-reps or soft-objects). While it gives them the unique ability to smoothly merge into a single, arbitrary shape, it makes implicit modelling hard to control since implicit surfaces blend at a distance, in a way that heavily depends on the slope of the field functions that define them. This paper presents a novel, generic solution to blending of functionally-based implicit surfaces: the insight is that to be intuitive and easy to control, blends should be located where two objects overlap, while enabling other parts of the objects to come as close to each other as desired without being deformed. Our solution relies on automatically defined blending regions around the intersection curves between two objects. Outside of these volumes, a clean union of the objects is computed thanks to a new operator that guarantees the smoothness of the resulting field function; meanwhile, a smooth blend is generated inside the blending regions. Parameters can automatically be tuned in order to prevent small objects from blurring out when blended into larger ones, and to generate a progressive blend when two animated objects come in contact.Item Folded Paper Geometry from 2D Pattern and 3D Contour(The Eurographics Association, 2011) Rohmer, Damien; Cani, Marie-Paule; Hahmann, Stefanie; Thibert, Boris; N. Avis and S. LefebvreFolded paper exhibits very characteristic shapes, due to the presence of sharp folds and to exact isometry with a given planar pattern. Therefore, none of the physically-based simulators developed so far can handle paper-like material. We propose a purely geometric solution to generate static folded paper geometry from a 2D pattern and a 3D placement of its contour curve. Fold lines are explicitly identified and used to control a recursive, local sub- division process, leading to an efficient procedural modeling of the surface through a fold-aligned mesh. Contrary to previous work, our method generates paper-like surfaces with sharp creases while maintaining approximate isometry with the input pattern.Item Sketch-based Modeling(The Eurographics Association, 2016) Cordier, Frederic; Singh, Karan; Etem, Even; Cani, Marie-Paule; Gingold, Yotam; Augusto Sousa and Kadi BouatouchSketching is one of the most natural ways to exchange ideas. It has been used by human beings since prehistory. Research has shown that human beings have an inherent ability to understand sketches. This is why sketch-based interfaces for 3D modeling are so appealing; creating and animating 3D shapes could become as simple as drawing with a tablet and a digital pen. The purpose of this tutorial is to explore the most important aspects of sketch-based modeling, from the preprocessing of sketch strokes to the problem of 3D reconstruction. We will first explain some aspects of how humans interpret sketches. The second part of the tutorial will be dedicated to the problem of filtering and processing strokes. Other parts of the tutorial will focus on the sketch-based modeling of curves and surfaces using multi-view and single-view sketches. Sketch-based modeling using prior-knowledge will be also discussed; this class of methods is particularly well adapted to the 3D reconstruction of complex shapes. The last part of the tutorial addresses sketch-based interfaces for editing 3D shapes.Item Towards Developable Products from a Sketch(The Eurographics Association, 2017) Fondevilla, Amélie; Bousseau, Adrien; Rohmer, Damien; Hahmann, Stefanie; Cani, Marie-Paule; Pierre Benard and Daniel SykoraDevelopable surfaces are surfaces that can be unfolded onto a plane, without distortion, and are widely used in industry. We propose an end-to-end system for the interactive modeling of developable objects from a single annotated photo, restricted to the case of symmetrical objects made by assemblies of planes and generalized cylinders.