We present a new set of algorithms for line-art rendering of smooth surfaces. We introduce an efficient, deterministic algorithm for finding silhouettes based on geometric duality, and an algorithm for segmenting the silhouette curves into smooth parts with constant visibility. These methods can be used to find all silhouettes in real time in software. We present an automatic method for generating hatch marks in order to convey surface shape. We demonstrate these algorithms with a drawing style inspired by A Topological Picturebook by G. Francis.

Illustrating smooth surfaces

We present a new globally smooth parameterization method for the triangulated surfaces of arbitrary topology. Given two orthogonal piecewise linear vector fields defined over the input mesh (typically the estimated principal curvature directions), our method computes two piecewise linear periodic functions, aligned with the input vector fields, by minimizing an objective function. The bivariate function they define is a smooth parameterization almost everywhere on the surface, except in the vicinity of singular vertices, edges, and triangles, where the derivatives of the parameterization vanish. We extract a quadrilateral chart layout from the parameterization function and propose an automatic procedure to detect the singularities, and fix them by splitting and reparameterizing the containing charts. Our method can construct both quasiconformal (angle preserving) and quasi-isometric (angle and area preserving) parameterizations. The more restrictive class of quasi-isometric parameterizations is constructed at the expense of introducing more singularities. The constructed parameterizations can be used for a variety of geometry processing applications. Since we can align the parameterization with the principal curvature directions, our result is particularly suitable for surface fitting and remeshing.

/pdf/periodic-global-parameterization-nenh5affvs.pdf

Periodic global parameterization

We present a new adaptive model for real-time fluid simulation based on Smoothed Particle Hydrodynamics (SPH) framework. Unlike traditional time-consuming SPH methods, our model can simulate fluid at a considerably faster speed without losing realism. In our model, we first introduce the non-uniform particle system and propose a generalized distance field function which considers not only geometrical complexity but also physical complexity of fluid body. And the new sampling rules for splitting and merging of particles are also presented. This can greatly reduce the computation time of the dynamic fluid simulation. Then, a new pressure state equation and an adaptive surface tension model are proposed to enhance the stability of the system and to make the free surface more realistic. To further accelerate the computation, a special fluid solver is designed and implemented using GPU. Various fluid phenomena like breaking wave and flood are simulated at real-time. Experiments demonstrate that our new adaptive model can greatly enhance the computation efficiency of fluid simulation compared with previous adaptive methods. Copyright © 2009 John Wiley & Sons, Ltd.

We present a new adaptive sampling model based on SPH framework for real-time fluid simulation by introducing a generalized distance field function in non-uniform particle system and building the splitting and merging rules for particles. To make the simulation more stable and visually continuous, we introduce a modified pressure state equation and a new surface tension model. Various fluid scenes including breaking wave and flood are simulated in real-time with realism.

Real-time fluid simulation with adaptive SPH

In this paper, we propose a novel polygonal remeshing technique that exploits a key aspect of surfaces: the intrinsic anisotropy of natural or man-made geometry. In particular, we use curvature dir...

/pdf/anisotropic-polygonal-remeshing-4yu9rk0m0v.pdf

Anisotropic polygonal remeshing

This tutorial describes several stroke-based rendering (SBR) algorithms. SBR is an automatic approach to creating nonphotorealistic imagery by placing discrete elements such as paint strokes or stipples.

/pdf/a-survey-of-stroke-based-rendering-3mdqbfueig.pdf

A survey of stroke-based rendering

This paper presents a new evenly-spaced streamlines placement algorithm to visualize 2D steady flows. The main technical contribution of this work is to propose a single method to compute a wide variety of flow field images, ranging from texture-like to hand-drawing styles. Indeed the control of the density of the field is very easy since the user only needs to set the separating distance between adjacent streamlines, which is related to the overall density of the image. We show that our method produces images of a quality at least as good as other methods but that it is computationally less expensive and offers a better control on the rendering process.

Creating Evenly-Spaced Streamlines of Arbitrary Density

The paper presents a new approach for animating 2D steady flow fields. It is based on an original data structure called the motion map. The motion map contains not only a dense representation of the flow field but also all the motion information required to animate the flow. An important feature of this method is that it allows, in a natural way, cyclical variable-speed animations. As far as efficiency is concerned, the advantage of this method is that computing the motion map does not take more time than computing a single still image of the flow and the motion map has to be computed only once. Another advantage is that the memory requirements for a cyclical animation of an arbitrary number of frames amounts to the memory cost of a single still image.

/pdf/the-motion-map-efficient-computation-of-steady-flow-17oowmnq62.pdf

The motion map: efficient computation of steady flow animations

Simulators for dynamic systems are now widely used in various application areas and raise the need for effective and accurate flow visualization techniques. Animation allows us to depict direction, orientation, and velocity of a vector field accurately. We extend a former proposal for a new approach to produce perfectly cyclic and variable-speed animations for 2D steady vector fields [B. Jobard, et al., (1997)] and [C. Chedot, et al., (1998)]. A complete animation of an arbitrary number of frames is encoded in a single image. The animation can be played using the color table animation technique, which is very effective even on low-end workstations. A cyclic set of textures can be produced as well and then encoded in a common animation format or used for texture mapping on 3D objects. As compared to other approaches, the method presented produces smoother animations and is more effective, both in memory requirements to store the animation, and in computation time.

High-quality animation of 2D steady vector fields

La simulation d’evacuation de bâtiment en proie au feu a pour objectif de diagnostiquer, des les premieres phases de la conception d’un bâtiment, sa capacite a etre evacue par des individus dans differents scenarios d’incendie. De telles simulations peuvent servir de base de decision pour l’implantation de dispositifs de securite, telles que des systemes d’extraction de fumee, la signalisation des issues ou encore des extincteurs, la revision de la conception des bâtiments ou le developpement de procedures d’evacuation propres a ces derniers. La prise en compte du facteur humain est essentielle afin d’esperer des resultats realistes. Dans cet article nous decrivons une architecture logicielle et un ensemble de concepts permettant de controler l’adaptation des comportements humains dans le cadre d’un scenario d’evacuation de bâtiment en feu.

Modélisation du comportement humain pour la simulation d’évacuation de bâtiment en feu

We propose to segment two-dimensional CT scans traumatic brain injuries with various methods. These methods are hybrid, feature extraction, level sets, region growing, and watershed which are analysed based upon their parametric and nonparametric arguments. The pixel intensities, gradient magnitude, affinity map, and catchment basins of these methods are validated based upon various constraints evaluations. In this article, we also develop a new methodology for a computational pipeline that uses bilateral filtering, diffusion properties, watershed, and filtering with mathematical morphology operators for the contour extraction of the lesion in the feature available based mainly on the gradient function. The evaluations of the classification of these lesions are very briefly outlined in this context and are being undertaken by pattern recognition in another paper work.

/pdf/semi-automatic-integrated-segmentation-approaches-and-ln3nm2aklj.pdf

Semi-automatic integrated segmentation approaches and contour extraction applied to computed tomography scan images

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