Short Presentations 2005

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https://diglib.eg.org/handle/10.2312/250

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Constriction Computation using Surface Curvature
(The Eurographics Association, 2005) Hétroy, F.; John Dingliana and Fabio Ganovelli
This paper provides a curvature-based algorithm to compute locally shortest geodesics on closed triangulated surfaces. These curves, which are called "constrictions", are useful for shape segmentation. The key idea of the algorithm is that constrictions are almost plane curves; it first finds well-located simple, plane, closed curves, and then slides them along the surface until a shortest geodesic is reached. An initial curve is defined as a connected component of the intersection between the surface and a plane going through an initial vertex. Initial vertices and planes are determined using approximations of surface curvature.
Efficient, Physically Plausible Finite Elements
(The Eurographics Association, 2005) Nesme, Matthieu; Payan, Yohan; Faure, François; John Dingliana and Fabio Ganovelli
This paper discusses FEM-based simulations of soft bodies in terms of speed and robustness. To be physically plausible, three fundamental laws must be respected: rotational invariance, Newton's law and Euler's law. We show that precomputed strain-displacement matrices generate nonphysical torques which can lead to visual artifacts. We then derive the fastest FEM-based method meeting our criteria of plausibility and robustness and discuss their limitations.
Real-Time Marching Cubes on the Vertex Shader
(The Eurographics Association, 2005) Goetz, Frank; Junklewitz, Theodor; Domik, Gitta; John Dingliana and Fabio Ganovelli
In this paper we propose a new approach for visualizing volumetric datasets by their isosurfaces. For an interactive isosurface reconstruction an optimized version of the well-known marching cubes algorithm is used. We extend the original algorithm by an additional vertex shader program. Contrary to other hardware-accelerated solutions our program is not based on a tetrahedral algorithm and thus the implementation for structured grids is more effective. Furthermore, surfaces of time-varying datasets at distinguished threshold values can be extracted in real-time.
Preface
(The Eurographics Association, 2005) -; John Dingliana and Fabio Ganovelli
Preface and Table of Contents
Carving, Painting, and Printing with a Pen Tablet
(The Eurographics Association, 2005) Mizuno, Shinji; Kobayashi, Daigo; Okada, Minoru; Toriwaki, Junichiro; Yamamoto, Shinji; John Dingliana and Fabio Ganovelli
We discuss on an interactive CG system with a pressure sensitive pen tablet. This system is based on the virtual sculpting and printing method which are simulations of real sculpting and woodblock printing. In the sculpting process, the user operates virtual chisels with a pen to carve a virtual wooden object which has a 3D shape. The user can control the carving depth and the carving angle to the surface of the object with the pressure applied to the pen. In the painting process, the user paints ink with a pen on a 3D virtual sculpture created in the sculpting process. The painting result is determined by the surface shape of the sculpture and the pressure to the pen. In the printing process, a pen is used to operate a Japanese printing squeegee, Baren. The user can control the thickness of the print by changing the thickness of ink on the virtual woodblock and the pressure of printing operation.
Proactive Steering Toward Oriented Targets
(The Eurographics Association, 2005) Boulic, Ronan; John Dingliana and Fabio Ganovelli
In this paper we introduce a real-time steering controller ensuring the reach of a (possible mobile) target position and orientation, without requiring to build/update the full trajectory to that target. We name it the funnelling control. The final orientation is achieved through the continuous adjustment of the heading direction. This control mode is proactive in the sense that it anticipates the success/failure of the reach and adjusts the desired speed accordingly. Both features rely on an heterogeneously sampled table of radial-tangential seek angles obtained when the controller reaches a desired position target without prescribed orientation. By construction, the control update has a constant computing cost, even with variable target characteristics. Its low update cost makes it particularly suited for controlling a large number of mobile entities in real-time. The present exposition is made for an obstacle-free context.
Walking with Pens
(The Eurographics Association, 2005) Kolhoff, Philipp; Preuß, Jacqueline; Loviscach, Jörn; John Dingliana and Fabio Ganovelli
Believable 3D animation of walking or running characters still requires complex motion capture technology or extensive skills in manual keyframing. We present an inexpensive, yet natural input method: The user walks on a digital graphics tablet, striding over the surface with two pens in his or her hands, where each pen represents one leg. This technique leverages the popular graphics tablets that can track two drawing tools at the same time. We implemented recording software and a plug-in to use the data in off-the-shelf 3D animation software.
Leaf Cluster Impostors for Tree Rendering with Parallax
(The Eurographics Association, 2005) Garcia, Ismael; Sbert, Mateu; Szirmay-Kalos, László; John Dingliana and Fabio Ganovelli
This paper presents a simple method to render complex trees on high frame rates while maintaining parallax effects. Based on the recognition that a planar impostor is accurate if the represented polygon is in its plane, we find an impostor for each of those groups of tree leaves that lie approximately in the same plane. The groups are built automatically by a clustering algorithm. Unlike billboards, these impostors are not rotated when the camera moves, thus the expected parallax effects are provided. On the other hand, clustering allows the replacement of a large number of leaves by a single semi-transparent quadrilateral, which improves rendering time considerably. Our impostors well represent the tree from any direction and provide accurate depth values, thus the method is also good for shadow computation.
Fast Body-Cloth simulation with moving humanoids
(The Eurographics Association, 2005) Rodriguez-Navarro, Javier; Sainz, Miguel; Susin, Antonio; John Dingliana and Fabio Ganovelli
In this paper we present a very fast method for body-cloth animation. The usual bottle-neck in cloth simulation performance is collision detection, which becomes more difficult to solve when a complex geometry, like a human body, is involved. Recent image based methods, that use depth images to detect collisions, usually relays on CPU for collision correction. In our work we implement a GPU based simulation that takes care both of cloth simulation and body-cloth collisions when the humanoid is moving. Our solution is based on a hierarchic depth map structure. A high frame rate is obtained with both structured and unstructured cloth meshes with thousands of particles.
A Scalable Hardware and Software System for the Holographic Display of Interactive Graphics Applications
(The Eurographics Association, 2005) Balogh, Tibor; Forgács, Tamás; Agács, Tibor; Balet, Olivier; Bouvier, Eric; Bettio, Fabio; Gobbetti, Enrico; Zanetti, Gianluigi; John Dingliana and Fabio Ganovelli
We present a scalable holographic system design targeting multi-user interactive computer graphics applications. The display uses a specially arranged array of micro-displays and a holographic screen. Each point of the holographic screen emits light beams of different color and intensity to the various directions, in a controlled manner. The light beams are generated through a light modulation system arranged in a specific geometry and the holographic screen makes the necessary optical transformation to compose these beams into a perfectly continuous 3D view. With proper software control, the light beams leaving the various pixels can be made to propagate in multiple directions, as if they were emitted from physical objects at fixed spatial locations. The display is driven by DVI streams generated by multiple consumer level graphics boards and decoded in real-time by image processing units that feed the optical modules at high refresh rates. An OpenGL compliant library running on a client PC redefines the OpenGL behavior to multicast graphics commands to server PCs, where they are re-interpreted for implementing holographic rendering. The feasibility of the approach has been successfully evaluated with a working hardware and software 7.4M pixel prototype driven at 10-15Hz by three DVI streams.
Rendering Realistic Trees and Forests in Real Time
(The Eurographics Association, 2005) Candussi, Alberto; Canduss, Nicola; Höllerer, Tobias; John Dingliana and Fabio Ganovelli
Real-Time rendering of realistic trees on common graphics hardware represents a big challenge due to their inherent geometric complexity. In most cases, trees are composed of hundreds of thousands of leaves and branches with complex lighting interrelations. We present novel techniques to render and animate photorealistic trees in real-time. The described techniques are easily implemented with commonly available graphics cards, making them suitable to applications such as visual simulations and video games. Polygon counts are significantly reduced by the use of simplified textured geometry for minor branches and billboarded leaf textures. Fast and realistic lighting and shadowing of the leaves and surroundings enhances realism. We animate the tree branches and leaf textures using simple vertex shaders, creating a realistic effect of the tree swaying in the wind. Discrete levels of detail allow rendering of a large number of trees, making it possible to represent realistic forest scenes made of 1000-1500 trees.
A 3D Perceptual Metric using Just-Noticeable-Difference
(The Eurographics Association, 2005) Cheng, Irene; Boulanger, Pierre; John Dingliana and Fabio Ganovelli
In multimedia applications, it is essential to distribute resources efficiently among different types of data in order to optimize overall quality. We propose a perceptual metric using Just-Noticeable-Difference (JND) to identify redundant mesh data so that available bandwidth can be allocated to improve texture resolution. Evaluation of perceptual impact during runtime is based on statistics in a lookup table generated during preprocessing. If the impact is less than the JND, no mesh refinement is performed. We apply Weber s fraction to compute the JND threshold, which is verified by perceptual evaluations. Experimental result shows that our JND model can accurately predict perceptual impact based on the human visual system.
Improving the Experience of Scenes with a Large Field of View using Shift Lens Perspective
(The Eurographics Association, 2005) Hoeben, Aldo; Stappers, Pieter Jan; John Dingliana and Fabio Ganovelli
In interactive computer graphics such as games and interactive panoramic photos, users are often presented a view with a larger field of view than would correspond to the distance to and size of the screen on which the graphics are viewed. This makes looking at the scene a less claustrophobic experience, showing more of the environment than that which is strictly ahead. In many applications however, where the goal is to get a sense of presence and ambiance of the depicted scene, the large field of view distracts the observer with extreme converging lines when looking up or down. Even though these converging lines are perspectively correct, the resulting image does not match the way we normally perceive the world around us. In this paper we discuss modifying the perspective to reduce the distortions caused by the large field of view, to enhance the experience of these scenes.
Image Reconstruction Invariant to Relighting
(The Eurographics Association, 2005) Georgiev, Todor; John Dingliana and Fabio Ganovelli
This paper describes an improvement to the Poisson image editing method for seamless cloning. Our approach is based on minimizing an energy expression invariant to relighting. The improved method reconstructs seamlessly the selected region, matching both pixel values and texture contrast of the surrounding area, while previous algorithms matched pixel values only. Our algorithm solves a deeper problem: It performs reconstruction in terms of the internal working mechanisms of human visual system. Retinex-type effects of adaptation are built into the structure of the mathematical model, producing results that change covariantly with lighting.
Estimating Mobile Memory Requirements and Rendering Time for Remote Execution of the Graphics Pipeline
(The Eurographics Association, 2005) Banerjee, Kutty; Wu, Fan; Agu, Emmanuel; John Dingliana and Fabio Ganovelli
Mobile devices have limited processing power, memory and battery power. Remote execution, wherein part or entire graphics pipeline is offloaded to a powerful surrogate server, is an attractive solution for low end mobile devices such as PDAs and cell phones that lack floating point units or GPUs. We have found that remote execution of floating-point-intensive pipeline stages such as transform and geometry operations can produce speedups of up to 10 times for a low-end mobile device. We introduce generalized pipeline-splitting, a paradigm whereby 15 sub-stages of the graphics pipeline are instrumented with networking code such that they can run either on a mobile client or a surrogate server. To validate our concepts, we create Remote Mesa (RMesa). As a foundation for deciding which stages of the pipeline would benefit from remote execution, this paper presents analytical models for the overall rendering time, memory requirements and roundtrip network delay incurred by RMesa.
Sculpting in Augmented Reality
(The Eurographics Association, 2005) Mackie, Jayson; John Dingliana and Fabio Ganovelli
We present an Augmented Reality (AR) application which allows a user to manipulate a piece of virtual clay using a marker-free unencumbered hand. By removing the need to wear a glove or place markers on the hand the application is made more accessible, allowing users to interact with the environment without special preparation.
Scalar Tagged PN Triangles
(The Eurographics Association, 2005) Boubekeur, Tamy; Reuter, Patrick; Schlick, Christophe; John Dingliana and Fabio Ganovelli
This paper presents a new technique to convert a coarse polygonal geometric model into a smooth surface interpolating the mesh vertices, by improving the principle proposed by Vlachos et al. in their "Curved PN-Triangles". The key idea is to assign to each mesh vertex, a set of three scalar tags that act as shape controllers. These scalar tags (called sharpness, bias, and tension) are used to compute a procedural displacement map that enriches the geometry, and a procedural normal map that enriches the shading. The resulting technique offers two majors features: First, it can be applied on meshes of arbitrary topology while always generating surfaces with consistent behaviors across edge and vertex boundaries, second, it only involves operations that are purely local to each polygon, which means that it is very well suited for hardware implementations.
Spherical Harmonic Lighting of Wavelength-Dependent Phenomena
(The Eurographics Association, 2005) Lindsay, Clifford; Agu, Emmanuel; John Dingliana and Fabio Ganovelli
Rendering of objects that exhibit iridescence has previously been limited to simple lighting conditions generated from a few point or directional lights. We extend this idea by modeling light interference as a Bidirectional Re- flectance Distribution Function (BRDF) and precomputing the physically based surface response to hemisphere lighting in terms of a low order spherical harmonic basis. Parameterizing by view direction, we can store the light interference effect in a 2D texture map, where each entry contains a vector of spherical harmonic basis function coefficients. Our technique achieves a full spectral representation of interference color by maintaining the spherical harmonic basis in terms of Spectral Power Distribution (SPD) instead of a color-based format such as RGB. In addition, we demonstrate that our approach is amenable to current graphics hardware and can render at real-time frame rates.
Photon Map Gathering on the GPU
(The Eurographics Association, 2005) Czuczor, Szabolcs; Szirmay-Kalos, László; Szécsi, László; Neumann, László; John Dingliana and Fabio Ganovelli
Photon mapping methods obtain the indirect illumination of a point by finding those photon hits that arrived at the neighborhood of the point on the object surface. This paper proposes a method that stores the photon hits in a texture of the graphics hardware and replaces the traditional kd-tree based neighborhood searches by the filtering of this texture. This step finds the irradiance of all points (i.e. all texels) simultaneously in a single step, thus the average irradiance of a point can be obtained by a single texture lookup. Using this approach we can port the final gathering step of photon mapping to the graphics hardware (GPU). The CPU is only responsible for generating new light paths and updating the unfiltered photon map. Thanks to the optimal subdivision of the computation work between the the CPU and the GPU, the proposed algorithm can render globally illuminated scenes interactively.
Differential Photon Mapping - Consistent Augmentation of Photographs with Correction of all Light Paths
(The Eurographics Association, 2005) Grosch, Thorsten; John Dingliana and Fabio Ganovelli
Augmenting images with consistent lighting is possible with differential rendering. This composition technique requires two lighting simulations, one simulation with only real geometry and another one with additional virtual objects. The difference of the two simulations can be used to modify the original pixel colors. The main drawback of differential rendering is that not all modified light paths can be displayed: The result of the lighting simulation is visible in a reflective object instead of the real environment, augmented with virtual objects. Moreover, many regions in the photograph remain unchanged and the same work is done twice without any visual effect. In this paper we present a new approach for augmenting a photograph with only a single photon mapping simulation. The changes in lighting introduced by a virtual object are directly simulated using a differential photon map. All light paths intersecting the virtual object are corrected. To demonstrate the correctness of our approach, we compare our simulation results with real photographs.

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