EG2013

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https://diglib.eg.org/handle/10.2312/298

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Position-based Methods for the Simulation of Solid Objects in Computer Graphics
(The Eurographics Association, 2013) Bender, Jan; Müller, Matthias; Otaduy, Miguel A.; Teschner, Matthias; M. Sbert and L. Szirmay-Kalos
The dynamic simulation of solids has a long history in computer graphics. The classical methods in this field are based on the use of forces or impulses to simulate joints between rigid bodies as well as the stretching, shearing and bending stiffness of deformable objects. In the last years the class of position-based methods has become popular in the graphics community. These kinds of methods are fast, unconditionally stable and controllable which make them well-suited for the use in interactive environments. Position-based methods are not as accurate as force based methods in general but they provide visual plausibility. Therefore, the main application areas of these approaches are virtual reality, computer games and special effects in movies. This state of the art report covers the large variety of position-based methods that were developed in the field of deformable solids. We will introduce the concept of position-based dynamics, present dynamic simulation based on shape matching and discuss data-driven approaches. Furthermore, we will present several applications for these methods.
CIIG: Granada Graphics Group, Granada, Spain
(The Eurographics Association, 2013) Martin, D.; Torres, J. C.; J. C. Torres and A. Lecuyer
The Granada Graphics Group is one of the research groups of the Software System Department. It covers education and research activities on Comouter Graphics at the University of Granada.
Rendering Gigaray Light Fields
(The Eurographics Association and Blackwell Publishing Ltd., 2013) Birklbauer, Clemens; Opelt, Simon; Bimber, Oliver; I. Navazo, P. Poulin
We present a caching framework with a novel probability-based prefetching and eviction strategy applied to atomic cache units that enables interactive rendering of gigaray light fields. Further, we describe two new use cases that are supported by our framework: panoramic light fields, including a robust imaging technique and an appropriate parameterization scheme for real-time rendering and caching; and light-field-cached volume rendering, which supports interactive exploration of large volumetric datasets using light-field rendering. We consider applications such as light-field photography and the visualization of large image stacks from modern scanning microscopes.
Extraction and Visual Analysis of Seismic Horizon Ensembles
(The Eurographics Association, 2013) Höllt, Thomas; Chen, Guoning; Hansen, Charles D.; Hadwiger, Markus; M.- A. Otaduy and O. Sorkine
Seismic interpretation is an important step in building subsurface models, which are needed to efficiently exploit fossil fuel reservoirs. However, seismic features are seldom unambiguous, resulting in a high degree of uncertainty in the extracted model. In this paper we present a novel system for the extraction, analysis, and visualization of ensemble data of seismic horizons. By parameterizing the cost function of a global optimization technique for seismic horizon extraction, we can create ensembles of surfaces describing each horizon, instead of just a single surface. Our system also provides the tools for a complete statistical analysis of these data. Additionally, we allow an interactive exploration of the parameter space to help finding optimal parameter settings for a given dataset.
Capturing Relightable Human Performances under General Uncontrolled Illumination
(The Eurographics Association and Blackwell Publishing Ltd., 2013) Li, Guannan; Wu, Chenglei; Stoll, Carsten; Liu, Yebin; Varanasi, Kiran; Dai, Qionghai; Theobalt, Christian; I. Navazo, P. Poulin
We present a novel approach to create relightable free-viewpoint human performances from multi-view video recorded under general uncontrolled and uncalibated illumination.We first capture a multi-view sequence of an actor wearing arbitrary apparel and reconstruct a spatio-temporal coherent coarse 3D model of the performance using a marker-less tracking approach. Using these coarse reconstructions, we estimate the low-frequency component of the illumination in a spherical harmonics (SH) basis as well as the diffuse reflectance, and then utilize them to estimate the dynamic geometry detail of human actors based on shading cues. Given the high-quality time-varying geometry, the estimated illumination is extended to the all-frequency domain by re-estimating it in the wavelet basis. Finally, the high-quality all-frequency illumination is utilized to reconstruct the spatially-varying BRDF of the surface. The recovered time-varying surface geometry and spatially-varying non-Lambertian reflectance allow us to generate high-quality model-based free view-point videos of the actor under novel illumination conditions. Our method enables plausible reconstruction of relightable dynamic scene models without a complex controlled lighting apparatus, and opens up a path towards relightable performance capture in less constrained environments and using less complex acquisition setups.
Centers of Approximate Spherical Symmetry and Radial Symmetry Graphs
(The Eurographics Association, 2013) Giachetti, Andrea; Lovato, Christian; M.- A. Otaduy and O. Sorkine
In this paper we propose the possible use of a new type of salient points we call CASS (Centers of Approximate Spherical Symmetry) that are extracted from the Multiscale Area Projection transform described in [GL12]. In particular, we show that it is possible to build graphs joining these points following maximal values of the MAPT (Radial Symmetry Graphs) and that these graphs can be used to extract relevant shape properties (e.g. intrin- sic symmetries) or to establish point correspondences on models robustly against holes, topological noise and articulated deformations.
Pose Space Image Based Rendering
(The Eurographics Association and Blackwell Publishing Ltd., 2013) Hilsmann, Anna; Fechteler, Philipp; Eisert, Peter; I. Navazo, P. Poulin
This paper introduces a new image-based rendering approach for articulated objects with complex pose-dependent appearance, such as clothes. Our approach combines body-pose-dependent appearance and geometry to synthesize images of new poses from a database of examples. A geometric model allows animation and view interpolation, while small details as well as complex shading and reflection properties are modeled by pose-dependent appearance examples in a database. Correspondences between the images are represented as mesh-based warps, both in the spatial and intensity domain. For rendering, these warps are interpolated in pose space, i.e. the space of body poses, using scattered data interpolation methods. Warp estimation as well as geometry reconstruction is performed in an offline procedure, thus shifting computational complexity to an a-priori training phase.
Sifted Disks
(The Eurographics Association and Blackwell Publishing Ltd., 2013) Ebeida, Mohamed S.; Mahmoud, Ahmed H.; Awad, Muhammad A.; Mohammed, Mohammed A.; Mitchell, Scott A.; Rand, Alexander; Owens, John D.; I. Navazo, P. Poulin
We introduce the Sifted Disk technique for locally resampling a point cloud in order to reduce the number of points. Two neighboring points are removed and we attempt to find a single random point that is sufficient to replace them both. The resampling respects the original sizing function; In that sense it is not a coarsening. The angle and edge length guarantees of a Delaunay triangulation of the points are preserved. The sifted point cloud is still suitable for texture synthesis because the Fourier spectrum is largely unchanged. We provide an efficient algorithm, and demonstrate that sifting uniform Maximal Poisson-disk Sampling (MPS) and Delaunay Refinement (DR) points reduces the number of points by about 25 percent, and achieves a density about 1/3 more than the theoretical minimum. We show two-dimensional stippling and meshing applications to demonstrate the significance of the concept.
Feature-preserving Direct Blue Noise Sampling for Surface Meshes
(The Eurographics Association, 2013) Peyrot, Jean-Luc; Payan, Frédéric; Antonini, Marc; M.- A. Otaduy and O. Sorkine
We present a new direct Poisson disk sampling for surface meshes. Our objective is to sample triangular meshes, while satisfying good blue noise properties, but also preserving features. Our method combines a feature detection technique based on vertex curvature, and geodesic-based dart throwing. Our method is fast, automatic, and experimental results prove that our method is well-suited to CAD models, since it handles sharp features and high genus meshes, while having good blue noise properties.
Projective Geometry, Duality and Precision of Computation in Computer Graphics, Visualization and Games
(The Eurographics Association, 2013) Skala, Vaclav; Diego Gutierrez and Karol Myszkowski
Homogeneous coordinates and projective geometry are mostly connected with geometric transformations only. However the projective extension of the Euclidean system allows reformulation of geometrical problems which can be easily solved. In many cases quite complicated formulae are becoming simple from the geometrical and computational point of view. In addition they lead to simple parallelization and to matrix-vector operations which are convenient for matrix-vector hardwarearchitecture like GPU. In this short tutorial we will introduce "practical theory" of the projective space and homogeneous coordinates. We will show that a solution of linear system of equations is equivalent to generalized cross product and how this influences basic geometrical algorithms. The projective formulation is also convenient for computation of barycentric coordinates, as it is actually one crossproduct implemented as one clock instruction on GPU. Additional speed up can be expected, too.Moreover use of projective representation enables to postpone division operations in many geometrical problems, which increases robustness and stability of algorithms. There is no need to convert coordinates of points from the homogeneous coordinates to the Euclidean ones as the projective formulation supports homogeneous coordinates natively. The presented approach can be applied in computational problems, games and visualization applications as well.
Locally Adaptive Products for All-Frequency Relighting
(The Eurographics Association and Blackwell Publishing Ltd., 2013) Inger, Yaron; Farbman, Zeev; Lischinski, Dani; I. Navazo, P. Poulin
Triple product integrals evaluate the shading at a point by factoring the reflection equation into incident illumination, visibility, and BRDF. By densely sampling the space of incident directions, this approach is capable of highly accurate rendering scenes lit by high-frequency environment lighting, containing complex materials and featuring intricate shadows. Efficient evaluation of triple product integrals using Haar wavelets enables near-interactive rendering of such scenes, while dynamically changing the lighting and the view. Although faster methods have been proposed in the recent real-time rendering literature, the approximations employed in these methods typically limit them to lower frequency phenomena. In this paper, we present a new approach for high-frequency scene relighting within the triple product framework. Our approach breaks the computation to smaller solid angles (blocks) over most of which the triple product degenerates to a dot product. We introduce a lossless, yet compact, differential representation of the visibility function over each block, and sample the BRDF on the fly, eliminating the need to store multiple rotated copies of each BRDF. By combining these ideas, we are able to achieve true interactive performance even when running on a CPU, while supporting high frequency effects in scenes with high vertex counts.
Path Space Regularization for Holistic and Robust Light Transport
(The Eurographics Association and Blackwell Publishing Ltd., 2013) Kaplanyan, Anton S.; Dachsbacher, Carsten; I. Navazo, P. Poulin
We propose a simple yet powerful regularization framework for robust light transport simulation. It builds on top of existing unbiased methods and resorts to a consistent estimation using regularization only for paths which cannot be sampled in an unbiased way. To introduce as little bias as possible, we selectively regularize individual interactions along paths, and also derive the regularization consistency conditions. Our approach is compatible with the majority of unbiased methods, e.g. (bidirectional) path tracing and Metropolis light transport (MLT), and only a simple modification is required to adapt existing renderers. We compare to recent unbiased and consistent methods and show examples of scenes with difficult light paths, where regularization is required to account for all illumination features. When coupled with MLT we are able to sample all phenomena, like recent consistent methods, while achieving superior convergence.
Gaze-driven Object Tracking for Real Time Rendering
(The Eurographics Association and Blackwell Publishing Ltd., 2013) Mantiuk, Radoslaw; Bazyluk, Bartosz; Mantiuk, Rafal K.; I. Navazo, P. Poulin
To efficiently deploy eye-tracking within 3D graphics applications, we present a new probabilistic method that predicts the patterns of user's eye fixations in animated 3D scenes from noisy eye-tracker data. The proposed method utilises both the eye-tracker data and the known information about the 3D scene to improve the accuracy, robustness and stability. Eye-tracking can thus be used, for example, to induce focal cues via gaze-contingent depth-of-field rendering, add intuitive controls to a video game, and create a highly reliable scene-aware saliency model. The computed probabilities rely on the consistency of the gaze scan-paths to the position and velocity of a moving or stationary target. The temporal characteristic of eye fixations is imposed by a Hidden Markov model, which steers the solution towards the most probable fixation patterns. The derivation of the algorithm is driven by the data from two eye-tracking experiments: the first experiment provides actual eye-tracker readings and the position of the target to be tracked. The second experiment is used to derive a JND-scaled (Just Noticeable Difference) quality metric that quantifies the perceived loss of quality due to the errors of the tracking algorithm. Data from both experiments are used to justify design choices, and to calibrate and validate the tracking algorithms. This novel method outperforms commonly used fixation algorithms and is able to track objects smaller then the nominal error of an eye-tracker.
A Correlated Parts Model for Object Detection in Large 3D Scans
(The Eurographics Association and Blackwell Publishing Ltd., 2013) Sunkel, Martin; Jansen, Silke; Wand, Michael; Seidel, Hans-Peter; I. Navazo, P. Poulin
This paper addresses the problem of detecting objects in 3D scans according to object classes learned from sparse user annotation. We model objects belonging to a class by a set of fully correlated parts, encoding dependencies between local shapes of different parts as well as their relative spatial arrangement. For an efficient and comprehensive retrieval of instances belonging to a class of interest, we introduce a new approximate inference scheme and a corresponding planning procedure. We extend our technique to hierarchical composite structures, reducing training effort and modeling spatial relations between detected instances. We evaluate our method on a number of real-world 3D scans and demonstrate its benefits as well as the performance of the new inference algorithm.
Automatic Modeling of Planar-Hinged Buildings
(The Eurographics Association, 2013) Garcia-Dorado, Ignacio; Aliaga, Daniel G.; M.- A. Otaduy and O. Sorkine
We present a framework to automatically model and reconstruct buildings in a dense urban area. Our method is robust to noise and recovers planar features and sharp edges, producing a water-tight triangulation suitable for texture mapping and interactive rendering. Building and architectural priors, such as the Manhattan world and Atlanta world assumptions, have been used to improve the quality of reconstructions. We extend the framework to include buildings consisting of arbitrary planar faces interconnected by hinges. Given millions of initial 3D points and normals (i.e., via an image-based reconstruction), we estimate the location and properties of the building model hinges and planar segments. Then, starting with a closed Poisson triangulation, we use an energy-based metric to iteratively refine the initial model so as to attempt to recover the planar-hinged model and maintain building details where possible. Our results include automatically reconstructing a variety of buildings spanning a large and dense urban area, comparisons, and analysis of our method. The end product is an automatic method to produce watertight models that are very suitable for 3D city modeling and computer graphics applications.
Project-Based Learning of Advanced Computer Graphics and Interaction
(The Eurographics Association, 2013) Romero, Mario; Jean-Jacques Bourdin and Eva Cerezo and Steve Cunningham
This paper presents an educational case study and its pedagogical lessons. It is a project-based course in advanced computer graphics and interaction, DH2413, conducted in the fall of 2012 at the Royal Institute of Technology (KTH), Stockholm, Sweden. The students and the teacher, the author, learned through a constructivist approach. The students defined and researched the material covered in class through their theme selection of original research projects which consisted of interactive graphics systems. The students demonstrated, taught, and discussed with each other what they had learned. Finally, the students openly presented their work to hundreds of people in large public venues. The teacher s role was to design the learning environment, guide the research, provide indepth lectures on the research material chosen by the students, and organize and motivate the students to produce accountable results. In synthesis, the pedagogical lessons are: 1) learning means building with self-motivation, guidance, and accountability; 2) self-motivation means trust and independence; 3) guidance means asking for less, not more; and 4) accountability means public presentations of working systems.
Landmark-Guided Elastic Shape Analysis of Spherically-Parameterized Surfaces
(The Eurographics Association and Blackwell Publishing Ltd., 2013) Kurtek, Sebastian; Srivastava, Anuj; Klassen, Eric; Laga, Hamid; I. Navazo, P. Poulin
We argue that full surface correspondence (registration) and optimal deformations (geodesics) are two related problems and propose a framework that solves them simultaneously. We build on the Riemannian shape analysis of anatomical and star-shaped surfaces of Kurtek et al. and focus on articulated complex shapes that undergo elastic deformations and that may contain missing parts. Our core contribution is the re-formulation of Kurtek et al.'s approach as a constrained optimization over all possible re-parameterizations of the surfaces, using a sparse set of corresponding landmarks. We introduce a landmark-constrained basis, which we use to numerically solve this optimization and therefore establish full surface registration and geodesic deformation between two surfaces. The length of the geodesic provides a measure of dissimilarity between surfaces. The advantages of this approach are: (1) simultaneous computation of full correspondence and geodesic between two surfaces, given a sparse set of matching landmarks (2) ability to handle more comprehensive deformations than nearly isometric, and (3) the geodesics and the geodesic lengths can be further used for symmetrizing 3D shapes and for computing their statistical averages. We validate the framework on challenging cases of large isometric and elastic deformations, and on surfaces with missing parts. We also provide multiple examples of averaging and symmetrizing 3D models.
Accelerating kd-tree Searches for all k-nearest Neighbours
(The Eurographics Association, 2013) Merry, Bruce; Gain, James; Marais, Patrick; M.- A. Otaduy and O. Sorkine
Finding the k nearest neighbours of each point in a point cloud forms an integral part of many point-cloud processing tasks. One common approach is to build a kd-tree over the points and then iteratively query the k nearest neighbors of each point. We introduce a simple modification to these queries to exploit the coherence between successive points; no changes are required to the kd-tree data structure. The path from the root to the appropriate leaf is updated incrementally, and backtracking is done bottom-up. We show that this can reduce the time to compute the neighbourhood graph of a 3D point cloud by over 10%, and by up to 24% when k
Accurate Binary Image Selection from Inaccurate User Input
(The Eurographics Association and Blackwell Publishing Ltd., 2013) Subr, Kartic; Paris, Sylvain; Soler, Cyril; Kautz, Jan; I. Navazo, P. Poulin
Selections are central to image editing, e.g., they are the starting point of common operations such as copy-pasting and local edits. Creating them by hand is particularly tedious and scribble-based techniques have been introduced to assist the process. By interpolating a few strokes specified by users, these methods generate precise selections. However, most of the algorithms assume a 100 percent accurate input, and even small inaccuracies in the scribbles often degrade the selection quality, which imposes an additional burden on users. In this paper, we propose a selection technique tolerant to input inaccuracies. We use a dense conditional random field (CRF) to robustly infer a selection from possibly inaccurate input. Further, we show that patch-based pixel similarity functions yield more precise selection than simple point-wise metrics. However, efficiently solving a dense CRF is only possible in low-dimensional Euclidean spaces, and the metrics that we use are high-dimensional and often non-Euclidean.We address this challenge by embedding pixels in a low-dimensional Euclidean space with a metric that approximates the desired similarity function. The results show that our approach performs better than previous techniques and that two options are sufficient to cover a variety of images depending on whether the objects are textured.
Global Selection of Stream Surfaces
(The Eurographics Association and Blackwell Publishing Ltd., 2013) Esturo, Janick Martinez; Schulze, Maik; Rössl, Christian; Theisel, Holger; I. Navazo, P. Poulin
Stream surfaces are well-known and widely-used structures for 3D flow visualization. A single surface can be sufficient to represent important global flow characteristics. Unfortunately, due to the huge space of possible stream surfaces, finding the globally most representative stream surface turns out to be a hard task that is usually performed by time-consuming manual trial and error exploration using slight modifications of seed geometries. To assist users we propose a new stream surface selection method that acts as an automatic preprocessing step before data analysis. We measure stream surface relevance by a novel surface-based quality measure that prefers surfaces where the flow is aligned with principal curvature directions. The problem of seed structure selection can then be reduced to the computation of simple minimal paths in a weighted graph spanning the domain. We apply a simulated annealing-based optimization method to find smooth seed curves of globally near-optimal stream surfaces. We illustrate the effectiveness of our method on a series of synthetic and real-world data sets.

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