EG 2015 - Short Papers

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https://diglib7.eg.org/handle/10.2312/12087

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3D Architectural Modeling: Efficient RANSAC for n-gonal Primitive Fitting
(The Eurographics Association, 2015) Abdullah, Ahsan; Bajwa, Reema; Gilani, Syed Rizwan; Agha, Zuha; Boor, Saeed Boor; Taj, Murtaza; Khan, Sohaib Ahmed; B. Bickel and T. Ritschel
We present a modeling approach to automatically fit 3D primitives to point clouds in order to generate a CAD like model. For detailed modeling we propose a new n-gonal 3D primitive and a novel RANSAC based fitting approach. Non-planar surfaces are modeled through surface of revolution with B-spline profiles. We first reduce the dimension by projecting the 3D data onto a 2D plane. Primitive fitting algorithm is then applied in this 2D space. Our approach compares favorably both with manually and automatically generated models. Not only is it much more time efficient than manual modeling, but it also gives significantly better output than state-of-the-art automatic methods. Since the focal technique of our approach is the fitting of detailed primitives, our results are ideal in the domain of architecture and preservation of heritage.
4D Mesh Reconstruction from Time-Varying Voxelized Geometry through ARAP Tracking
(The Eurographics Association, 2015) Blache, Ludovic; Desbrun, Mathieu; Loscos, Celine; Lucas, Laurent; B. Bickel and T. Ritschel
We present a method to derive a time-evolving triangle mesh representation from a sequence of binary volumetric data representing an arbitrary motion. Multi-view reconstruction studios use a multiple camera set to turn an actor's performance into a time series of visual hulls. However, the reconstructed sequence lacks temporal coherence as each frame is generated independently, preventing easy post-production editing with off-the-shelf modeling tools. We propose an automated tracking approach to convert the raw input sequence into a single, animated mesh. An initial mesh is globally deformed via as-rigid-as-possible, detail-preserving transformations guided by a motion flow estimated from consecutive frames. Local optimization is added to better match the mesh surface to the current visual hull, leading to a robust 4D mesh reconstruction.
Adaptive LightSlice for Virtual Ray Lights
(The Eurographics Association, 2015) Frederickx, Roald; Bartels, Pieterjan; Dutré, Philip; B. Bickel and T. Ritschel
We speed up the rendering of participating media with Virtual Ray Lights (VRLs) by clustering them in a preprocessing step. A subset of representative VRLs is then sampled from the clustering, which is used for the final rendering. By performing a full variance analysis, we can explicitly estimate the convergence rate of the rendering process and automatically find the locally ideal number of clusters to maximize efficiency. Overall, we report speed-up factors ranging from 13 to 16 compared to unclustered rendering.
Content-Aware Projection for Tiny Planets
(The Eurographics Association, 2015) Brown, Matthew; B. Bickel and T. Ritschel
Tiny Planets visualise the world looking down at the ground, with physically unrealisable projections that curve the ground plane to look like small worlds. Whilst certain geometries, such as Stereographic, are known to give good Tiny Planet visualisations, the best projection to use depends on the image content. In this work we define a family of Tiny Planet projections that includes several commonly used projection types, but allows for datadependent adaptation to best present the image content to the viewer.We show how to select optimal content-aware projections from this set, minimising distortions from conformality whilst closing gaps and emphasising salient areas in the scene.
EUROGRAPHICS 2015: Short Papers Frontmatter
(Eurographics Association, 2015) Bernd Bickel; Tobias Ritschel;
Eye-tracktive: Measuring Attention to Body Parts when Judging Human Motions
(The Eurographics Association, 2015) Ennis, Cathy; Hoyet, Ludovic; O'Sullivan, Carol; B. Bickel and T. Ritschel
Virtual humans are often endowed with human-like characteristics to make them more appealing and engaging. Motion capture is a reliable way to represent natural motion on such characters, thereby allowing a wide range of animations to be automatically created and replicated. However, interpersonal differences in actors' performances can be subtle and complex, yet have a strong effect on the human observer. Such effects can be very difficult to express quantitatively or indeed even qualitatively. We investigate two subjective human motion characteristics: attractiveness and distinctiveness. We conduct a perceptual experiment, where participants' eye movements are tracked while they rate the motions of a range of actors. We found that participants fixate mostly on the torso, regardless of gait and actor sex, and very little on the limbs. However, they self-reported that they used hands, elbows and feet in their judgments, indicating a holistic approach to the problem.
Fast Edge-based Geodesic Poisson Disk Remeshing
(The Eurographics Association, 2015) Uhlmann, Tom; Váša, Libor; Brunnett, Guido; B. Bickel and T. Ritschel
Triangular meshes of high complexity are common when created by a 3D scanner device and must be reduced for further processing. The geodesic Poisson disk remeshing [FZ08] is a method that generates a simplified mesh with highly regular triangles at the cost of exorbitant computation time. In this paper we will outline a new approach to this technique that makes it applicable for highly complex models. Our approach operates directly on the surface of the mesh, therefore works for meshes of arbitrary topology. Meshes consisting of millions of triangles can be reduced to an arbitrary complexity in just a few minutes while the original approach processes meshes with thousands of triangles in the same time. Our easy to implement remeshing technique also provides several options to preserve features.
Fractured Object Reassembly via Robust Surface Registration
(The Eurographics Association, 2015) Mavridis, Pavlos; Andreadis, Anthousis; Papaioannou, Georgios; B. Bickel and T. Ritschel
The reassembly of fractured 3D objects from their parts is an important problem in cultural heritage and other domains.We approach reassembly from a geometric matching perspective and propose a pipeline for the automatic solution of the problem, where an efficient and generic three-level coarse-to-fine search strategy is used for the underlying global optimization. Key to the efficiency of our approach is the use of a discretized approximation of the surfaces' distance field, which significantly reduces the cost of distance queries and allows our method to systematically search the global parameter space with minimal cost. The resulting reassembly pipeline provides highly reliable alignment, as demonstrated through the reassembly of fractured objects from their fragments and the reconstruction of 3D objects from partial scans, showcasing the wide applicability of our methodology.
Generation of Folded Terrains from Simple Vector Maps
(The Eurographics Association, 2015) Michel, Elie; Emilien, Arnaud; Cani, Marie-Paule; B. Bickel and T. Ritschel
While 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.
High-Quality Shadows for Streaming Terrain Rendering
(The Eurographics Association, 2015) Chajdas, Matthäus G.; Reichl, Florian; Dick, Christian; Westermann, Rüdiger; B. Bickel and T. Ritschel
Rendering of large, detailed 3D terrains on commodity hardware has become possible through the use of raycasting, data caching and prefetching. Adding dynamic shadows as they appear during a day-night cycle remais a challenge however, because shadow rendering requires access to the entire terrain, invalidating data streaming strategies. In this work we present a novel, practicable shadow rendering approach which distinguishes between near- and precomputed far-shadows to significantly reduce data access and runtime costs. While near-shadows are raytraced using the current cache content, far-shadows are precomputed and stored in a very compact format requiring approximately 3 bit per height-map sample for an entire day-night cycle.
Improving k-buffer Methods via Occupancy Maps
(The Eurographics Association, 2015) Vasilakis, Andreas A.; Papaioannou, Georgios; B. Bickel and T. Ritschel
In this work, we investigate an efficient approach to treat fragment racing when computing k-nearest fragments. Based on the observation that knowing the depth position of the k-th fragment we can optimally find the k-closest fragments, we introduce a novel fragment culling component by employing occupancy maps.Without any softwareredesign, the proposed scheme can easily be attached at any k-buffer pipeline to efficiently perform early-z culling. Finally, we report on the efficiency, memory space, and robustness of the upgraded k-buffer alternatives providing comprehensive comparison results.
Individual Time Stepping for SPH Fluids
(The Eurographics Association, 2015) He, Liangliang; Ban, Xiaojuan; Liu, Xu; Wang, Xiaokun; B. Bickel and T. Ritschel
We present a novel adaptive stepping scheme for SPH fluids, in which particles have their own time-steps determined from local conditions, e.g. Courant condition. These individual time-steps are constrained for global convergence and stability. Fluid particles are then updated asynchronously. The approach naturally allocates computing resources to visually complex regions, e.g. regions with intense collisions, thereby reducing the overall computational time. The experiments show that our approach is more efficient than the standard method and the method with globally adaptive time steps, especially in highly dynamic scenes.
An Interactive Editing System for Visual Appearances of Fire and Explosions
(The Eurographics Association, 2015) Dobashi, Yoshinori; Shibukawa, Yuhei; Tada, Munehiro; Sato, Syuhei; Iwasaki, Kei; Yamamoto, Tsuyoshi; B. Bickel and T. Ritschel
Synthetic volumetric fire and explosions are important visual effects used in many applications such as computer games and movies. For these applications, artists are often requested to achieve the desired visual appearance by adjusting some parameters for rendering them. However, this is extremely difficult and tedious, due to the complexity of these phenomena and the expensive computational cost for the rendering. This paper presents an interactive system that assists this adjustment process. Our method allows the user to interactively change the ratio of smoke and flame regions, the emissivity of the flame, and the optical thicknesses of the smoke and flame separately. The image is updated in real-time while the user modifies these parameters, taking into account the multiple scattering of light. We demonstrate the usefulness of our method by applying our method to editing of the visual appearances of fire and explosions
Interactive HDR Environment Map Capturing on Mobile Devices
(The Eurographics Association, 2015) Kán, Peter; B. Bickel and T. Ritschel
Real world illumination, captured by digitizing devices, is beneficial to solve many problems in computer graphics. Therefore, practical methods for capturing this illumination are of high interest. In this paper, we present a novel method for capturing environmental illumination by a mobile device. Our method is highly practical as it requires only a consumer mobile phone and the result can be instantly used for rendering or material estimation.We capture the real light in high dynamic range (HDR) to preserve its high contrast. Our method utilizes the moving camera of a mobile phone in auto-exposure mode to reconstruct HDR values. The projection of the image to the spherical environment map is based on the orientation of the mobile device. Both HDR reconstruction and projection run on the mobile GPU to enable interactivity. Moreover, an additional image alignment step is performed. Our results show that the presented method faithfully captures the real environment and that the rendering with our reconstructed environment maps achieves high quality, comparable to reality.
Interactive Pixel-Accurate Rendering of LR-Splines and T-Splines
(The Eurographics Association, 2015) Hjelmervik, Jon M.; Fuchs, Franz G.; B. Bickel and T. Ritschel
Flexible surface types on irregular grids, such as T-splines and LR-splines, are gaining popularity in science and industry due to the possibility for local grid refinement. We present a novel rendering algorithm for those surface types that guarantees pixel-accurate geometry and water-tight tessellation (no drop-outs). Before rendering, we extract the Bézier coefficients. The resulting irregular grids of Bézier patches are then rendered using a multistage algorithm, that decouples the tesselator and the patch geometry. The implementation using OpenGL utilizes compute shaders and hardware tessellation functionality. We showcase interactive rendering achieved by our approach on three representative use cases.
Isogeometric Analysis for Modelling and Design
(The Eurographics Association, 2015) Riffnaller-Schiefer, Andreas; Augsdörfer, Ursula H.; Fellner, Dieter W.; B. Bickel and T. Ritschel
We present an isogeometric design and analysis approach based on NURBS-compatible subdivision surfaces. The approach enables the description of watertight free-form surfaces of arbitrary degree, including conic sections and an accurate simulation and analysis based directly on the designed surface. To explore the seamless integration of design and analysis provided by the isogeometric approach, we built a prototype software which combines free-form modelling tools with thin shell simulation tools to offer the designer a wide range of design and analysis instruments.
Pixel Merge Unit
(The Eurographics Association, 2015) Sathe, Rahul; Akenine-Möller, Tomas; B. Bickel and T. Ritschel
Multi-sample anti-aliasing is a popular technique for reducing geometric aliasing (jagged edges) and is supported in all modern graphics processors. With multi-sampling anti-aliasing, visibility and depth are sampled more than once per pixel, while shading is done only once per pixel per primitive. Although this significantly reduces the appearance of jagged edges around object boundaries, the image quality improvement in non-silhouette regions is hardly noticeable. We propose a hardware unit, called the pixel merge unit, which is located just after the early depth test unit but before the pixel shader. Our unit attempts to reduce the shading rate to once per pixel per group of connected primitives covering a pixel using a novel merging strategy. We demonstrate up to 15% reduction in pixel shader executions. Given the simple implementation that we propose, this is a substantial reduction.
Quadratic Encoding for Hand Pose Reconstruction from Multi-Touch Input
(The Eurographics Association, 2015) Chung, Se-Joon; Kim, Junggon; Han, Shangchen; Pollard, Nancy S.; B. Bickel and T. Ritschel
One of the most compelling challenges in virtual reality today is to allow users to carry out virtual manipulation tasks using their hands. Multi-touch devices are an interesting interface for this task, as they are widely available, they provide users with some haptic sensation of their motions, and they give very precise locations of the fingertips. We introduce a quadratic encoding technique to provide plausible and smooth hand reconstructions from multi-touch input at real-time rates suitable for virtual reality applications. Another nice feature of our datadriven approach is that it does not require explicit identification or registration of fingers. We show that quadratic encoding outperforms linear encoding, cubic encoding, and a PCA based inverse kinematics approach, and is well suited for performing real-time virtual manipulation using a multi-touch device.
Separation of Manga Line Drawings and Screentones
(The Eurographics Association, 2015) Ito, Kota; Matsui, Yusuke; Yamasaki, Toshihiko; Aizawa, Kiyoharu; B. Bickel and T. Ritschel
Screentones are unique expressions of Japanese comics (manga), which enrich their visual expression. However, such screentones have a very different visual nature from that of line drawing areas; this prevents us from applying various kinds of image processing techniques to manga. We propose a method for extracting line drawings and removing screentones. We employ Laplacians of Gaussian filters and flow-based differences of Gaussian filters, one for removing screentones and the other for preserving lines, and make a binary mask for separating line drawings from manga by merging the results of the two filters. We show that the proposed method successfully separates line drawings and is better than existing methods in comparative studies.
Sketch-Based Controllers for Blendshape Facial Animation
(The Eurographics Association, 2015) Cetinaslan, Ozan; Orvalho, Verónica; Lewis, John; B. Bickel and T. Ritschel
The blendshape approach is a widely used technique to generate realistic facial animation. However, creating blendshape facial animations using traditional weight editing tools requires either memorizing the function of a large number of parameters, or a trial-and-error search in a high-dimensional space. Direct manipulation interfaces address this problem, allowing the artist to directly move and pin manipulators placed on the surface of the face. Placing manipulators is an open-ended and slightly unnatural task for artists however. In this paper we present a sketch-based approach to this problem, inspired by artists' brush painting on canvas. In this approach the artist simply sketches directly onto the 3D model the positions of the manipulators that they feel are needed to produce particular facial expression. The manipulators activate the blendshapes in the model and allow the user to interactively create the desired facial poses by a dragging operation in screen coordinates. Our hybrid method can be used with any blendshape facial model and allows producing expeditious manipulation in an intuitive way.

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