EG 2013 - Short Papers

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https://diglib.eg.org/handle/10.2312/300

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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
Adaptive Remeshing for Real-Time Mesh Deformation
(The Eurographics Association, 2013) Dunyach, Marion; Vanderhaeghe, David; Barthe, Loïc; Botsch, Mario; M.- A. Otaduy and O. Sorkine
We present an adaptive isotropic remeshing technique that is fast enough to be used in interactive applications, such as mesh deformation or mesh sculpting. Previous real-time remeshing techniques are either not adaptive, hence requiring too many triangles, or make compromises in terms of triangle quality. High quality adaptive remeshing techniques are too slow for interactive applications. In this short paper we present a simple extension of a uniform remeshing approach that results in an efficient, yet high quality, curvature-adaptive remeshing.
Automatic Generation of Constructable Brick Sculptures
(The Eurographics Association, 2013) Testuz, Romain; Schwartzburg, Yuliy; Pauly, Mark; M.- A. Otaduy and O. Sorkine
Fabrication of LEGO R models in large scale requires careful pre-planning to produce constructable and stable models. We propose a system that, starting with a voxelization of a 3D mesh, merges voxels to form larger bricks, and then analyzes and repairs structural problems, finally outputting a set of building instructions. We also present extensions such as producing hollow models, fulfilling limits on the number of bricks of each size, and including colors. Results (both real and virtual) and timings show significant improvements over previous work.
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.
Automatic Parameter Control for Metropolis Light Transport
(The Eurographics Association, 2013) Zsolnai, Károly; Szirmay-Kalos, László; M.- A. Otaduy and O. Sorkine
Sophisticated global illumination algorithms usually have several control parameters that need to be set appropriately in order to obtain high performance and accuracy. Unfortunately, the optimal values of these parameters are scene dependent, thus their setting is a cumbersome process that requires significant care and is usually based on trial and error. To address this problem, this paper presents a method to automatically control the large step probability parameter of Primary Sample Space Metropolis Light Transport (PSSMLT). The method does not require extra computation time or pre-processing, and runs in parallel with the initial phase of the rendering method. During this phase, it gathers statistics from the process and computes the parameters for the remaining part of the sample generation. We show that the theoretically proposed values are close to the manually found optimum for several complex scenes.
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.
Direct Contouring of Implicit Closest Point Surfaces
(The Eurographics Association, 2013) Auer, Stefan; Westermann, Rüdiger; M.- A. Otaduy and O. Sorkine
Constructing a (signed) distance field and contouring its zero level set are two important steps in many surface reconstruction methods. While most high-quality distance transforms compute the distance to the surface as well as the closest point on it, the contouring step typically uses only the distance and omits the closest point information. Our novel closest point contouring algorithm (CPC) uses the full closest point field, and, thus, allows improving existing methods for high-quality triangle mesh reconstruction based on implicit function models: Since we select the vertex positions directly from the set of closest points, all triangle vertices are guaranteed to lie exactly on the zero-contour and no approximations are necessary. By employing recent findings in the context of so-called embedding techniques, we derive a formulation of the mean curvature vector on the closest point representation and use this formulation to properly select the vertices to be triangulated. In combination with a new table-based triangulation scheme this allows us to detect and preserve sharp features, and to avoid small degenerated triangles in smooth areas. CPC can handle open and non-orientable surfaces, and its data-parallel nature makes it well suited for GPUs.
Enhanced Lattice Boltzmann Shallow Waters for Real-time Fluid Simulations
(The Eurographics Association, 2013) Ojeda, Jesus; Susín, Anton; M.- A. Otaduy and O. Sorkine
We present a novel approach at simulating fluids in real-time by coupling the Lattice Boltzmann Method for Shallow Waters (LBMSW) with particle systems. The LBM can handle arbitrary underlying terrain and arbitrary fluid depth, which, in turn, allows us to extend it to track dry regions. The LBM is also two-way coupled with rigid bodies. The particle system adds more detail to the LBM; breaking waves are detected from the surface simulation and particles are generated to provide the effect, taking effectively certain amounts of fluid and reintegrating it back once they fall over again. Both the LBM and the particle simulation are implemented in CUDA, although rigid bodies are simulated in CPU. Finally, we show the effectiveness of the method on commodity hardware.
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.
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.
Generating Pseudo-3D Painting Based on Visual Saliency and Composition Rules
(The Eurographics Association, 2013) Zheng, Zhibin; Zhang, Yan; Sun, Zhengxing; M.- A. Otaduy and O. Sorkine
Pseudo-3D painting shows stereoscopic artistic effect in the 2D plane and displays artistic conception as the known verse "Far, near, high, low-no two parts alike", it brings a true feeling of stereo space to observers. This paper proposes a cropping method based on visual saliency and composition rules to get pseudo-3D painting from a 2D given image. On the basis of segmenting the given image into foreground and background, we utilize visual saliency to determine the highlighted region and combine existing composition rules to automatically crop the image using PSO optimization algorithm. Additionally, we add the border and pseudo-perspective transformation to enhance stereoscopic effect of our results. Experimental results demonstrate our method could turn a reference image into a pseudo-3D painting effectively, bringing a stereoscopic feeling to observers.
GPU Roof Grammars
(The Eurographics Association, 2013) Buron, Cyprien; Marvie, Jean-Eudes; Gautron, Pascal; M.- A. Otaduy and O. Sorkine
We extend GPU shape grammars [MBG12] to model highly detailed roofs. Starting from a consistent roof structure such as a straight skeleton computed from the building footprints, we decompose this information into local roof parameters per input segments compliant with GPU shape grammars. We also introduce Join and Project rules for a consistent description of roofs using grammars, bringing the massive parallelism of GPU shape grammars to the benefit of coherent generation of global structures.
Graph Abstraction for Simplified Proofreading of Slice-based Volume Segmentation
(The Eurographics Association, 2013) Sicat, Ronell B.; Hadwiger, Markus; Mitra, Niloy J.; M.- A. Otaduy and O. Sorkine
Volume segmentation is an integral data analysis tool in experimental science. For example, in neuroscience, analysis of 3D volumes of neural structures from electron microscopy data is a key analysis step. Despite advances in computational methods, experts still prefer to manually proofread and correct the automatic segmentation outputs. Such corrections are often annotated at the level of data slices in order to minimize distortion artifacts and effectively handle the massive data volumes. In absence of crucial global context in 3D, such a workflow remains tedious, time consuming, and error prone. In this paper, we present a simple graph-based abstraction for segmentation volumes leading to an interactive proofreading tool making the process simpler, faster, and intuitive. Starting from an initial volume segmentation, we first construct a graph abstraction and then use it to identify potential problematic regions for the user to investigate and correct spurious segmentations, if identified. We also use the graph to suggest automatic corrections, thus drastically simplifying the proofreading effort. We implemented the proofreading tool as an Avizo c plugin and evaluated the method on complex real-world use cases.
Guided Capturing of Multi-view Stereo Datasets
(The Eurographics Association, 2013) Langguth, Fabian; Goesele, Michael; M.- A. Otaduy and O. Sorkine
We present an application for mobile devices, that allows any user, even without background in computer vision, to capture a complete set of images, that is suitable for a multi-view stereo reconstruction. Compared to related tasks, such as panorama capture, this setting is much harder, as the camera needs to move unrestricted in 3D space. Our system uses structure from motion to register captured images and generates a sparse reconstruction of the scene. The dataset is built in an incremental procedure, where the next best view is computed with a novel view planning strategy, that aims for a good coverage of the scene. The user is then guided towards the new view, and the image is captured automatically at the right position. The next iteration starts after the reconstruction has been updated. The quality of the resulting dataset is on par with datasets captured by an expert user.
Perceptually Motivated Real-Time Compression of Motion Data Enhanced by Incremental Encoding and Parameter Tuning
(The Eurographics Association, 2013) Firouzmanesh, Amirhossein; Cheng, Irene; Basu, Anup; M.- A. Otaduy and O. Sorkine
We address the problem of efficient real-time motion data compression considering human perception. Using incremental encoding plus a database of motion primitives for each key point, our method achieves a higher or competitive compression rate with less online overhead. Trade-off between visual quality and bandwidth usage can be tuned by varying a single threshold value. A user study was performed to measure the sensitivity of human subjects to reconstruction errors in key rotation angles. Based on these evaluations we are able to perform lossy compression on the motion data without noticeable degradation in rendered qualities. While achieving real-time performance, our technique outperforms other methods in our experiments by achieving a compression ratio exceeding 50 : 1 on regular sequences.
Real-time Collision Detection for Dynamic Hardware Tessellated Objects
(The Eurographics Association, 2013) Nießner, Matthias; Siegl, Christian; Schäfer, Henry; Loop, Charles; M.- A. Otaduy and O. Sorkine
We present a novel method for real-time collision detection of patch based, displacement mapped objects using hardware tessellation. Our method supports fully animated, dynamically tessellated objects and runs entirely on the GPU. In order to determine a collision between two objects, we first find the intersecting volume of the corresponding object oriented bounding boxes. Next, patches of both objects are tested for inclusion within this volume. All possibly colliding patches are then voxelized into a uniform grid of single bit voxels. Finally, the resulting voxelization is used to detect collisions. Testing two moderately complex models containing thousands of patches can be done in less than a millisecond making our approach ideally suited for real-time games.
Real-Time High Fidelity Inverse Tone Mapping for Low Dynamic Range Content
(The Eurographics Association, 2013) Banterle, Francesco; Chalmers, Alan; Scopigno, Roberto; M.- A. Otaduy and O. Sorkine
In this paper, we present a novel parallel implementation of a high fidelity inverse tone mapping operator. Our method makes use of point based graphics to accelerate density estimation, and multi-core CPUs for extracting light sources. We show that our method can achieve real-time performance on a lower-end graphics card, with minimum loss of quality.
Real-Time Image-Based Volume Lighting
(The Eurographics Association, 2013) Delalandre, Cyril; Gautron, Pascal; Marvie, Jean-Eudes; M.- A. Otaduy and O. Sorkine
The interaction of translucent objects with light creates complex effects such as scattering, absorption and volumetric shadows. While most accurate rendering approaches resort to heavy computations, recent needs in interactive applications have led to new types of algorithms, trading quality or genericity for speed.
Real-Time Importance Sampling of Dynamic Environment Maps
(The Eurographics Association, 2013) Lu, Heqi; Pacanowski, Romain; Granier, Xavier; M.- A. Otaduy and O. Sorkine
We introduce a simple and effective technique for light-based importance sampling of dynamic environment maps based on the formalism of Multiple Importance Sampling (MIS). The core idea is to balance per pixel the number of samples selected on each cube map face according to a quick and conservative evaluation of the lighting contribution: this increases the number of effective samples. In order to be suitable for dynamically generated or captured HDR environment maps, everything is computed on-line for each frame without any global preprocessing. Our results illustrate that the low number of required samples combined with a full-GPU implementation lead to real-time performance with improved visual quality. Finally, we illustrate that our MIS formalism can be easily extended to other strategies such as BRDF importance sampling.
Seam-Driven Image Stitching
(The Eurographics Association, 2013) Gao, Junhong; Li, Yu; Chin, Tat-Jun; Brown, Michael S.; M.- A. Otaduy and O. Sorkine
Image stitching computes geometric transforms to align images based on the best fit of feature correspondences between overlapping images. Seam-cutting is used afterwards to to hide misalignment artifacts. Interestingly it is often the seam-cutting step that is the most crucial for obtaining a perceptually seamless result. This motivates us to propose a seam-driven image stitching strategy where instead of estimating a geometric transform based on the best fit of feature correspondences, we evaluate the goodness of a transform based on the resulting visual quality of the seam-cut. We show that this new image stitching strategy can often produce better perceptual results than existing methods especially for challenging scenes.

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