EG2015

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https://diglib.eg.org/handle/10.2312/12086

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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.
3D Fabrication of 2D Mechanisms
(The Eurographics Association and John Wiley & Sons Ltd., 2015) Hergel, Jean; Lefebvre, Sylvain; Olga Sorkine-Hornung and Michael Wimmer
The success of physics sandbox applications and physics-based puzzle games is a strong indication that casual users and hobbyists enjoy designing mechanisms, for educational or entertainment purposes. In these applications, a variety of mechanisms are designed by assembling two-dimensional shapes, creating gears, cranks, cams, and racks. The experience is made enjoyable by the fact that the user does not need to worry about the intricate geometric details that would be necessary to produce a real mechanism. In this paper, we propose to start from such casual designs of mechanisms and turn them into a 3D model that can be printed onto widely available, inexpensive filament based 3D printers. Our intent is to empower the users of such tools with the ability to physically realize their mechanisms and see them operate in the real world. To achieve this goal we tackle several challenges. The input 2D mechanism allows for some parts to overlap during simulation. These overlapping parts have to be resolved into non-intersecting 3D parts in the real mechanism. We introduce a novel scheme based on the idea of including moving parts into one another whenever possible. This reduces bending stresses on axles compared to previous methods. Our approach supports sliding parts and arbitrarily shaped mechanical parts in the 2D input. The exact 3D shape of the parts is inferred from the 2D input and the simulation of the mechanism, using boolean operations between shapes. The input mechanism is often simply attached to the background. We automatically synthesize a chassis by formulating a topology optimization problem, taking into account the stresses exerted by the mechanism on the chassis through time.
3D Video: from Capture to Interactive Display
(The Eurographics Association, 2015) Loscos, Céline; Rémion, Yannick; Lucas, Laurent; Guillemot, Romain; Battin, Benjamin; M. Zwicker and C. Soler
While 3D vision and 3D/4D imaging has existed for many years, the use of 3D cameras and video-based modeling by the film industry and recent access to cheap contactless control devices has induced an explosion of interest for 3D acquisition technology, 3D content, 3D displays and 3D interaction. As such, 3D video has become one of the new technology trends of this century. This tutorial aims at introducing theoretical, technological and practical concepts associated to multiview systems and the possible interactions with the 3D/4D content. It covers acquisition, manipulation, and rendering. Stepping away from traditional 3D vision, the authors, all currently involved in these areas, provide the necessary elements for understanding the underlying computer-based science of these technologies.
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.
Adaptable Anatomical Models for Realistic Bone Motion Reconstruction
(The Eurographics Association and John Wiley & Sons Ltd., 2015) Zhu, Lifeng; Hu, Xiaoyan; Kavan, Ladislav; Olga Sorkine-Hornung and Michael Wimmer
We present a system to reconstruct subject-specific anatomy models while relying only on exterior measurements represented by point clouds. Our model combines geometry, kinematics, and skin deformations (skinning). This joint model can be adapted to different individuals without breaking its functionality, i.e., the bones and the skin remain well-articulated after the adaptation.We propose an optimization algorithm which learns the subject-specific (anthropometric) parameters from input point clouds captured using commodity depth cameras. The resulting personalized models can be used to reconstruct motion of human subjects. We validate our approach for upper and lower limbs, using both synthetic data and recordings of three different human subjects. Our reconstructed bone motion is comparable to results obtained by optical motion capture (Vicon) combined with anatomically-based inverse kinematics (OpenSIM). We demonstrate that our adapted models better preserve the joint structure than previous methods such as OpenSIM or Anatomy Transfer.
Adapting the Twelve Principles of Classic Animation to Lectures
(The Eurographics Association, 2015) Gilardi, Marco; Holroyd, Patrick; Newbury, Paul; Watten, Phil L.; M. Bronstein and M. Teschner
This paper borrows from the fields of classic animation and 3D animation and adapts the fundamental principles of these subjects to the lecturing context. An analogy is drawn between an animator and a lecturer due to their shared objective: to communicate in an engaging way. If the fundamental principles of animation are read under the point of view of how they communicate a message, it is not difficult to see that they summarise some of the key concepts in the fields of education and educational psychology. Once adapted the principles can be used as a guideline by novice lecturers to increase students' engagement both in traditional lectures and in e-learning environments. The principles have been applied successfully in teaching the Programming for 3D module and a number of modules at the University of Sussex obtaining good feedback from students.
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.
Approximating Free-form Geometry with Height Fields for Manufacturing
(The Eurographics Association and John Wiley & Sons Ltd., 2015) Herholz, Philipp; Matusik, Wojciech; Alexa, Marc; Olga Sorkine-Hornung and Michael Wimmer
We consider the problem of manufacturing free-form geometry with classical manufacturing techniques, such as mold casting or 3-axis milling. We determine a set of constraints that are necessary for manufacturability and then decompose and, if necessary, deform the shape to satisfy the constraints per segment. We show that many objects can be generated from a small number of (mold-)pieces if slight deformations are acceptable. We provide examples of actual molds and the resulting manufactured objects.
Approximating the Generalized Voronoi Diagram of Closely Spaced Objects
(The Eurographics Association and John Wiley & Sons Ltd., 2015) Edwards, John; Daniel, Eric; Pascucci, Valerio; Bajaj, Chandrajit; Olga Sorkine-Hornung and Michael Wimmer
We present an algorithm to compute an approximation of the generalized Voronoi diagram (GVD) on arbitrary collections of 2D or 3D geometric objects. In particular, we focus on datasets with closely spaced objects; GVD approximation is expensive and sometimes intractable on these datasets using previous algorithms. With our approach, the GVD can be computed using commodity hardware even on datasets with many, extremely tightly packed objects. Our approach is to subdivide the space with an octree that is represented with an adjacency structure. We then use a novel adaptive distance transform to compute the distance function on octree vertices. The computed distance field is sampled more densely in areas of close object spacing, enabling robust and parallelizable GVD surface generation. We demonstrate our method on a variety of data and show example applications of the GVD in 2D and 3D.
Augmented Reality as a Tool to Deliver e-Learning based Blended Content in and out of the Class-room
(The Eurographics Association, 2015) Erdt, Marius; Maroothynaden, Jason; Peng, Junming; Müller-Wittig, Wolfgang; Gagnon, Paul; M. Bronstein and M. Teschner
In this paper, we present a mobile Augmented Reality application that can be used for undergraduate anatomical education. It can be used in and out of the classroom. In the classroom, the application can track and augment 3D objects such as a cadaveric solid organ (e.g. heart) specimens as well as 3D plastic anatomical models without the use of observable markers. Out-side the classroom, virtual representations of the hearts were computed and added as an offline version to the application allowing students to self-learn. To allow students to ''sense-make'' concepts and add additional educational value to offline content, the application can also track 2D content like printed posters. Augmentation in 2D and 3D views via various digital content modalities supports students in learning and ''sense-making'' anatomical terms and concepts.
Augmenting Design Curriculum with Location-Aware Technologies
(The Eurographics Association, 2015) Zarzycki, Andrzej; M. Bronstein and M. Teschner
This paper discusses ways in which emerging interactive augmented reality (AR) technologies are being adopted by designers and extended into areas of tourism, education, entertainment and commerce. It discusses, in detail, project development stages and methodologies used to engage design focused students into, often complex, technological issues. The discussion is contextualized through a number of case studies of mobile and marker-based AR applications developed within the university curriculum.
Big City 3D Visual Analysis
(The Eurographics Association, 2015) Lv, Zhihan; Li, Xiaoming; Zhang, Baoyun; Wang, Weixi; Feng, Shengzhong; Hu, Jinxing; B. Solenthaler and E. Puppo
A big city visual analysis platform based on Web Virtual Reality Geographical Information System (WEBVRGIS) is presented. Extensive model editing functions and spatial analysis functions are available, including terrain analysis, spatial analysis, sunlight analysis, traffic analysis, population analysis and community analysis.
Biologically-Inspired Visual Simulation of Insect Swarms
(The Eurographics Association and John Wiley & Sons Ltd., 2015) Li, Weizi; Wolinski, David; Pettré, Julien; Lin, Ming C.; Olga Sorkine-Hornung and Michael Wimmer
Representing the majority of living animals, insects are the most ubiquitous biological organisms on Earth. Being able to simulate insect swarms could enhance visual realism of various graphical applications. However, the very complex nature of insect behaviors makes its simulation a challenging computational problem. To address this, we present a general biologically-inspired framework for visual simulation of insect swarms. Our approach is inspired by the observation that insects exhibit emergent behaviors at various scales in nature. At the low level, our framework automatically selects and configures the most suitable steering algorithm for the local collision avoidance task. At the intermediate level, it processes insect trajectories into piecewise-linear segments and constructs probability distribution functions for sampling waypoints. These waypoints are then evaluated by the Metropolis- Hastings algorithm to preserve global structures of insect swarms at the high level. With this biologically inspired, data-driven approach, we are able to simulate insect behaviors at different scales and we evaluate our simulation using both qualitative and quantitative metrics. Furthermore, as insect data could be difficult to acquire, our framework can be adopted as a computer-assisted animation tool to interpret sketch-like input as user control and generate simulations of complex insect swarming phenomena.
A Biophysically-Based Model of the Optical Properties of Skin Aging
(The Eurographics Association and John Wiley & Sons Ltd., 2015) Iglesias-Guitian, Jose A.; Aliaga, Carlos; Jarabo, Adrian; Gutierrez, Diego; Olga Sorkine-Hornung and Michael Wimmer
This paper presents a time-varying, multi-layered biophysically-based model of the optical properties of human skin, suitable for simulating appearance changes due to aging. We have identified the key aspects that cause such changes, both in terms of the structure of skin and its chromophore concentrations, and rely on the extensive medical and optical tissue literature for accurate data. Our model can be expressed in terms of biophysical parameters, optical parameters commonly used in graphics and rendering (such as spectral absorption and scattering coefficients), or more intuitively with higher-level parameters such as age, gender, skin care or skin type. It can be used with any rendering algorithm that uses diffusion profiles, and it allows to automatically simulate different types of skin at different stages of aging, avoiding the need for artistic input or costly capture processes. While the presented skin model is inspired on tissue optics studies, we also provided a simplified version valid for non-diagnostic applications.
CHC+RT: Coherent Hierarchical Culling for Ray Tracing
(The Eurographics Association and John Wiley & Sons Ltd., 2015) Mattausch, Oliver; Bittner, Jirí; Jaspe, Alberto; Gobbetti, Enrico; Wimmer, Michael; Pajarola, Renato; Olga Sorkine-Hornung and Michael Wimmer
We propose a new technique for in-core and out-of-core GPU ray tracing using a generalization of hierarchical occlusion culling in the style of the CHC++ method. Our method exploits the rasterization pipeline and hardware occlusion queries in order to create coherent batches of work for localized shader-based ray tracing kernels. By combining hierarchies in both ray space and object space, the method is able to share intermediate traversal results among multiple rays. We exploit temporal coherence among similar ray sets between frames and also within the given frame. A suitable management of the current visibility state makes it possible to benefit from occlusion culling for less coherent ray types like diffuse reflections. Since large scenes are still a challenge for modern GPU ray tracers, our method is most useful for scenes with medium to high complexity, especially since our method inherently supports ray tracing highly complex scenes that do not fit in GPU memory. For in-core scenes our method is comparable to CUDA ray tracing and performs up to 5:94 better than pure shader-based ray tracing.
Color Sequence Preserving Decolorization
(The Eurographics Association and John Wiley & Sons Ltd., 2015) Yoo, Min-Joon; Lee, In-Kwon; Lee, Seungyong; Olga Sorkine-Hornung and Michael Wimmer
Many visualization techniques use images containing meaningful color sequences. If such images are converted to grayscale, the sequence is often distorted, compromising the information in the image.We preserve the significance of a color sequence during decolorization by mapping the colors from a source image to a grid in the CIELAB color space. We then identify the most significant hues, and thin the corresponding cells of the grid to approximate a curve in the color space, eliminating outliers using a weighted Laplacian eigenmap. This curve is then mapped to a monotonic sequence of gray levels. The saturation values of the resulting image are combined with the original intensity channels to restore details such as text. Our approach can also be used to recolor images containing color sequences, for instance for viewers with color-deficient vision, or to interpolate between two images that use the same geometry and color sequence to present different data.
Combining Human Visual System Models for Geographic Gaze Contingent Displays
(The Eurographics Association, 2015) Bektas, Kenan; Çöltekin, Arzu; Krüger, Jens; Duchowski, Andrew T.; B. Solenthaler and E. Puppo
We present a gaze-contingent display (GCD) in which we combine multiple models of the human visual system (HVS) to manage the visual level of detail (LOD). GCDs respond to the viewer's gaze in real time, rendering a space-variant visualization. We aim to measure the computational and perceptual benefits of the proposed HVS models in terms of data reduction and user experience. Specifically, we combine models of contrast sensitivity, color perception and depth of field; and customize our implementation for geographic imagery. We believe this research is relevant in all domains that use image interpretation.
Composition-Aware Scene Optimization for Product Images
(The Eurographics Association and John Wiley & Sons Ltd., 2015) Liu, Tianqiang; McCann, Jim; Li, Wilmot; Funkhouser, Thomas; Olga Sorkine-Hornung and Michael Wimmer
Increasingly, companies are creating product advertisements and catalog images using computer renderings of 3D scenes. A common goal for these companies is to create aesthetically appealing compositions that highlight objects of interest within the context of a scene. Unfortunately, this goal is challenging, not only due to the need to balance the trade-off among aesthetic principles and design constraints, but also because of the huge search space induced by possible camera parameters, object placement, material choices, etc. Previous methods have investigated only optimization of camera parameters. In this paper, we develop a tool that starts from an initial scene description and a set of high-level constraints provided by a stylist and then automatically generates an optimized scene whose 2D composition is improved. It does so by locally adjusting the 3D object transformations, surface materials, and camera parameters. The value of this tool is demonstrated in a variety of applications motivated by product catalogs, including rough layout refinement, detail image creation, home planning, cultural customization, and text inlay placement. Results of a perceptual study indicate that our system produces images preferable for product advertisement compared to a more traditional camera-only optimization.
Comprehensible Video Thumbnails
(The Eurographics Association and John Wiley & Sons Ltd., 2015) Kim, Jongdae; Gray, Charles; Asente, Paul; Collomosse, John; Olga Sorkine-Hornung and Michael Wimmer
We present the Comprehensible Video Thumbnail; an automatically generated visual précis that summarizes salient objects and their dynamics within a video clip. Salient moving objects are detected within clips using a novel stochastic sampling technique that identifies, clusters and then tracks regions exhibiting affine motion coherence within the clip. Tracks are analyzed to determine salient instants at which motion and/or appearance changes significantly, and the resulting objects arranged in a stylized composition optimized to reduce visual clutter and enhance understanding of scene content through classification and depiction of motion type and trajectory. The result is an object-level visual gist of the clip, obtained with full automation and depicting content and motion with greater descriptive power that prior approaches. We demonstrate these benefits through a user study in which the comprehension of our video thumbnails is compared to the state of the art over a wide variety of sports footage.
Compressive Image Reconstruction in Reduced Union of Subspaces
(The Eurographics Association and John Wiley & Sons Ltd., 2015) Miandji, Ehsan; Kronander, Joel; Unger, Jonas; Olga Sorkine-Hornung and Michael Wimmer
We present a new compressed sensing framework for reconstruction of incomplete and possibly noisy images and their higher dimensional variants, e.g. animations and light-fields. The algorithm relies on a learning-based basis representation. We train an ensemble of intrinsically two-dimensional (2D) dictionaries that operate locally on a set of 2D patches extracted from the input data. We show that one can convert the problem of 2D sparse signal recovery to an equivalent 1D form, enabling us to utilize a large family of sparse solvers. The proposed framework represents the input signals in a reduced union of subspaces model, while allowing sparsity in each subspace. Such a model leads to a much more sparse representation than widely used methods such as K-SVD. To evaluate our method, we apply it to three different scenarios where the signal dimensionality varies from 2D (images) to 3D (animations) and 4D (light-fields). We show that our method outperforms state-of-the-art algorithms in computer graphics and image processing literature.

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