Volume 20, number 3 (2012)
Permanent URI for this collection
Browse
Recent Submissions
Item Elastically Deformable Models based on the Finite Element Method Accelerated on Graphics Hardware using CUDA(Václav Skala - UNION Agency, 2012) Verschoor, Mickeal; Jalba, Andrei C.; Skala, VáclavElastically deformable models have found applications in various areas ranging from mechanical sciences and engineering to computer graphics. The method of Finite Elements has been the tool of choice for solving the underlying PDE, when accuracy and stability of the computations are more important than, e.g., computation time. In this paper we show that the computations involved can be performed very efficiently on modern programmable GPUs, regarded as massively parallel co-processors through Nvidia’s CUDA compute paradigm. The resulting global linear system is solved using a highly optimized Conjugate Gradient method. Since the structure of the global sparse matrix does not change during the simulation, its values are updated at each step using the efficient update method proposed in this paper. This allows our fully-fledged FEM-based simulator for elastically deformable models to run at interactive rates. Due to the efficient sparse-matrix update and Conjugate Gradient method, we show that its performance is on par with other state-of-the-art methods, based on e.g. multigrid methods.
Item A layered depth-of-field method for solving partial occlusion(Václav Skala - UNION Agency, 2012) Schedl, David C.; Wimmer, Michael; Skala, VáclavDepth of field (DoF) represents a distance range around a focal plane, where objects on an image are crisp. DoF is one of the effects which significantly contributes to the photorealism of images and therefore is often simulated in rendered images. Various methods for simulating DoF have been proposed so far, but little tackle the issue of partial occlusion: Blurry objects near the camera are semi-transparent and result in partially visible background objects. This effect is strongly apparent in miniature and macro photography. In this work a DoF method is presented which simulates partial occlusion. The contribution of this work is a layered method where the scene is rendered into layers. Blurring is done efficiently with recursive Gaussian filters. Due to the usage of Gaussian filters big artifact-free blurring radii can be simulated at reasonable costs.Item Reconstructing power cables from LIDAR data using eigenvector streamlines of the point distribution tensor field(Václav Skala - UNION Agency, 2012) Ritter, Marcel; Benger, Werner; Skala, VáclavStarting from the computation of a covariance matrix of neighborhoods in a point cloud, streamlines are utilized to reconstruct lines of linearly distributed points following the major Eigenvector of the matrix. This technique is similar to fiber tracking in diffusion tensor imaging (DTI), but in contrast is done mesh-free. Different weighting functions for the computation of the matrix and for the interpolation of the vector in the point cloud have been implemented and compared on artificial test cases. A dataset stemming from light detect and ranging (LIDAR) surveying served as a testbed for parameter studies where, finally, a power cable was reconstructed.Item Hybrid SURF-golay marker detection method for augmented reality applications(Václav Skala - UNION Agency, 2012) Procházka, David; Popelka, Ondřej; Koubek, Tomáš; Landa, Jaromír; Kolomazník, Jan; Skala, VáclavAugmented reality is a visualization technique widely used in many applications including different design tools. These tools are frequently based on tracking artificial objects such as square markers. The markers allow users to add a 3D model into the scene and adjust its position and orientation. Nevertheless, there are significant problems with marker occlusions caused by users or objects within the scene. The occlusions usually cause a disappearance of the 3D model. Such behavior has substantial negative impact on the application usability. In this article we present a hybrid marker detection approach. With this approach, markers are detected using the well-known SURF method. This method is able to recognize complex natural objects and deal with partial occlusions. Further, we overcome the problem of distinguishing similar markers by using the Golay error correction code patterns. The described approach represents a robust method that is able to identify even significantly occluded markers, differentiate similar markers, and it works in a constant time regardless of the amount of used markers.Item A survey of cloud lighting and rendering techniques(Václav Skala - UNION Agency, 2012) Hufnagel, Roland; Held, Martin; Skala, VáclavThe rendering of participating media still forms a big challenge for computer graphics. This remark is particularly true for real-world clouds with their inhomogeneous density distributions, large range of spatial scales and different forms of appearance. We survey techniques for cloud visualization and classify them relative to the type of volume representation, lighting and rendering technique used. We also discuss global illumination techniques applicable to the generation of the optical effects observed in real-world cloud scenes.Item Subpixel reconstruction antialiasing for ray tracing(Václav Skala - UNION Agency, 2012) Chiu, Y. F.; Chen, Y. C.; Chang, C. F.; Lee, R. R.; Skala, VáclavWe introduce a practical antialiasing approach for interactive ray tracing and path tracing. Our method is inspired by the Subpixel Reconstruction Antialiasing (SRAA) method which separates the shading from visibility and geometry sampling to produce antialiased images at reduced cost. While SRAA is designed for GPU-based deferred shading renderer, we extend the concept to ray-tracing based applications. We take a hybrid rendering approach in which we add a GPU rasterization step to produce the depth and normal buffers with subpixel resolution. By utilizing those extra buffers, we are able to produce antialiased ray traced images without incurring performance penalty of tracing additional primary rays. Furthermore, we go beyond the primary rays and achieve antialiasing for shadow rays and reflective rays as well.Item A survey of cloud lighting and rendering techniques(Václav Skala - UNION Agency, 2012) Kanzok, Thomas; Linsen, Lars; Rosenthal, Paul; Skala, VáclavScanning 3D objects has become a valuable asset to many applications. For larger objects such as buildings or bridges, a scanner is positioned at several locations and the scans are merged to one representation. Nowadays, such scanners provide, beside geometry, also color information. The different lighting conditions present when taking the various scans lead to severe luminance artifacts, where scans come together. We present an approach to remove such luminance inconsistencies during rendering. Our approach is based on image-space operations for both luminance correction and point-cloud rendering. It produces smooth-looking surface renderings at interactive rates without any preprocessing steps. The quality of our results is similar to the results obtained with an object-space luminance correction. In contrast to such an object-space technique the presented image-space approach allows for instantaneous rendering of scans, e.g. for immediate on-site checks of scanning quality.Item Interactive segmentation of volume data using watershed hierarchies(Václav Skala - UNION Agency, 2012) Hučko, Michal; Šrámek, Miloš; Skala, VáclavThe available methods for volume data segmentation and/or classification differ in the amount of the required user input on the one side and precision and ability to tweak the obtained results on the other. Automation of the task is more difficult when a general case is considered. In this paper we present an interactive segmentation and classification tool for arbitrary volumetric data, which is based on pre-segmentation of the volume in a hierarchy of homogeneous regions. The hierarchical subdivision allows for interactive adaptation of scale and precision according to the user requirements. The data is processed in three dimensions which minimises the amount of the needed interaction and gives instant overview of the resulting segmentation.Item Visualisation of flow fields in the web platform(Václav Skala - UNION Agency, 2012) Aristizabal, Mauricio; Congote, John; Segura, Alvaro; Moreno, Aior; Arregui, Harbil; Ruiz, Oscar E.; Skala, VáclavVisualization of vector fields plays an important role in research activities nowadays. Web applications allow a fast, multi-platform and multi-device access to data, which results in the need of optimized applications to be implemented in both high and low-performance devices. The computation of trajectories usually repeats calculations due to the fact that several points might lie over the same trajectory. This paper presents a new methodology to calculate point trajectories over a highly-dense and uniformly-distributed grid of points in which the trajectories are forced to lie over the points in the grid. Its advantages rely on a highly parallel computing implementation and in the reduction of the computational effort to calculate the stream paths since unnecessary calculations are avoided by reusing data through iterations. As case study, the visualization of oceanic streams in the web platform is presented and analyzed, using WebGL as the parallel computing architecture and the rendering engine.Item Real-time mesh extraction of dynamic volume data using GPU(Václav Skala - UNION Agency, 2012) Engel, Szymon; Alda, Witold; Boryczko, Krzysztof; Skala, VáclavIn the paper an algorithm of triangle mesh generation for a full three-dimensional volumetric data is presented. Calculations are performed in real time using graphics processors. The method is very well suited for the visu- alization of dynamic data, as the calculations use only the current frame data (not including data from previous frames). Due to high performance of the algorithm, it can be practically applied in programs for digital sculpting, simulators and games which require editable geometries.
