Search Results

Now showing 1 - 9 of 9
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    Heightfield and spatially varying BRDF Reconstruction for Materials with Interreflections
    (The Eurographics Association and Blackwell Publishing Ltd, 2009) Ruiters, Roland; Klein, Reinhard
    Photo-realistic reproduction of material appearance from images has widespread use in applications ranging from movies over advertising to virtual prototyping. A common approach to this task is to reconstruct the small scale geometry of the sample and to capture the reflectance properties using spatially varying BRDFs. For this, multi-view and photometric stereo reconstruction can be used, both of which are limited regarding the amount of either view or light directions and suffer from either low- or high-frequency artifacts, respectively. In this paper, we propose a new algorithm combining both techniques to recover heightfields and spatially varying BRDFs while at the same time overcoming the above mentioned drawbacks. Our main contribution is a novel objective function which allows for the reconstruction of a heightfield and high quality SVBRDF including view dependent effects. Thereby, our method also avoids both low and high frequency artifacts. Additionally, our algorithm takes inter-reflections into account allowing for the reconstruction of undisturbed representations of the underlying material. In our experiments, including synthetic and real-world data, we show that our approach is superior to state-of-the-art methods regarding reconstruction error as well as visual impression. Both the reconstructed geometry and the recovered SVBRDF are highly accurate, resulting in a faithful reproduction of the materials characteristic appearance, which is of paramount importance in the context of material rendering.
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    Visualization Framework for the Integration and Exploration of Heterogeneous Geospatial Data
    (The Eurographics Association, 2009) Greß, Alexander; Klein, Reinhard; D. Ebert and J. Krüger
    This paper presents an interactive visualization framework for heterogeneous geospatial data developed in context of an interdisciplinary research project that aims at the risk analysis of sea-dumped chemical weapons in the Baltic Sea. In the focus of the analysis are geophysical, hydrographical, geochemical, and biological data acquired on research cruises as well as data produced by toxic compound migration and bioaccumulation modeling. These different types of data to be visualized are represented as height fields, 2D vector maps, seismic profiles, and time-dependent scalar and vector fields. In general, these datasets are given at largely varying resolutions and geospatial extents, which makes their integration into one visualization especially challenging and requires efficient level-of-detail techniques. Furthermore, special care is taken on the appropriate integration and efficient 3D visualization of all different types of data at the same time. Several examples demonstrate the effectiveness of the resulting visualizations for collaborative analysis of the data.
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    Markerless Visual Human Movement Tracking for HCI: What Frequency?
    (The Eurographics Association, 2009) Kahlesz, Ferenc; Klein, Reinhard; Wen Tang and John Collomosse
    This paper tries to establish a minimal tracking frequency limit for visual human movement tracking algorithms that intend to be useful for the realization of some kind Human-Computer-Interaction (HCI) metaphor. More specifically, we examine the question of this minimal frequency for Augmented/Virtual Reality (AR/VR) navigation and 3D object manipulation. We approach the question from three different perspectives: shortly reviewing non-visual and visual marker-based solutions integrated regularly into AR/VR systems, spectral analysis of human movement and latency implications for AR/VR settings. Finally, we conclude the paper by combining and discussing the results from these different areas. We find that tracking with update rates as low as 12.5Hz can provide a usable basis for interaction. The most important message of the paper is that stable and working (even if slow, when compared to other techniques) markerless tracking algorithms are desperately needed because only working online with and based on such systems can the pros and cons of markerless tracking be evaluated.
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    Completion and Reconstruction with Primitive Shapes
    (The Eurographics Association and Blackwell Publishing Ltd, 2009) Schnabel, Ruwen; Degener, Patrick; Klein, Reinhard
    We consider the problem of reconstruction from incomplete point-clouds. To find a closed mesh the reconstruction is guided by a set of primitive shapes which has been detected on the input point-cloud (e.g. planes, cylinders etc.). With this guidance we not only continue the surrounding structure into the holes but also synthesize plausible edges and corners from the primitives intersections. To this end we give a surface energy functional that incorporates the primitive shapes in a guiding vector field. The discretized functional can be minimized with an efficient graph-cut algorithm. A novel greedy optimization strategy is proposed to minimize the functional under the constraint that surface parts corresponding to a given primitive must be connected. From the primitive shapes our method can also reconstruct an idealized model that is suitable for use in a CAD system.
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    A 3D Shape Benchmark for Retrieval and Automatic Classification of Architectural Data
    (The Eurographics Association, 2009) Wessel, Raoul; Blümel, Ina; Klein, Reinhard; Michela Spagnuolo and Ioannis Pratikakis and Remco Veltkamp and Theoharis Theoharis
    When drafting new buildings, architects make intensive use of existing 3D models including building elements, furnishing, and environment elements. These models are either directly included into the draft or serve as a source for inspiration. To allow efficient reuse of existing 3D models, shape retrieval methods considering the specific requirements of architects must be developed. Unfortunately, common 3D shape benchmarks which are used to evaluate the performance of retrieval algorithms are not well suited for architectural data. First, they incorporate models which are not related to this domain, and second and even more important, the provided classification schemes usually do not match an architect's intuition regarding their notion of design and function. To overcome these drawbacks, we present a freely downloadable shape benchmark especially designed for architectural 3D models. It currently contains 2257 objects from various content providers, including companies specialized on 3D CAD applications. All models are classified according to a scheme developed in close cooperation with architects taking into account their specific requirements regarding design and function. Additionally, we show retrieval results for this benchmark using unsupervised and supervised shape retrieval methods and discuss the specific problems regarding retrieval of architectural 3D models.
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    BTF-CIELab: A Perceptual Difference Measure for Quality Assessment and Compression of BTFs
    (The Eurographics Association and Blackwell Publishing Ltd, 2009) Guthe, Michael; Mueller, Gero; Schneider, Martin; Klein, Reinhard
    Driven by the advances in lossy compression of bidirectional texture functions (BTFs), there is a growing need for reliable methods to numerically measure the visual quality of the various compressed representations. Based on the CIE "E00 colour difference equation and concepts of its spatio-temporal extension ST-CIELab for video quality assessment, this paper presents a numerical quality measure for compressed BTF representations. By analysing the BTF in its full six-dimensional (6D) space, light and view transition effects are integrated into the measure. In addition to the compressed representation, the method only requires the source BTF images as input and thus aids the objective evaluation of different compression techniques by means of a simple numerical comparison. By separating the spatial and angular components of the difference measure and linearizing each of them, the measure can be incorporated into any linear or multi-linear compression technique. Using a per-colour-channel principal component analysis (PCA), compression rates of about 500:1 can be achieved at excellent visual quality.
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    Variational Surface Approximation and Model Selection
    (The Eurographics Association and Blackwell Publishing Ltd, 2009) Li, Bao; Schnabel, Ruwen; Jin, Shiyao; Klein, Reinhard
    We consider the problem of approximating an arbitrary generic surface with a given set of simple surface primitives. In contrast to previous approaches based on variational surface approximation, which are primarily concerned with finding an optimal partitioning of the input geometry, we propose to integrate a model selection step into the algorithm in order to also optimize the type of primitive for each proxy. Our method is a joint global optimization of both the partitioning of the input surface as well as the types and number of used shape proxies. Thus, our method performs an automatic trade-off between representation complexity and approximation error without relying on a user supplied predetermined number of shape proxies. This way concise surface representations are found that better exploit the full approximative power of the employed primitive types.
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    BTF Compression via Sparse Tensor Decomposition
    (The Eurographics Association and Blackwell Publishing Ltd, 2009) Ruiters, Roland; Klein, Reinhard
    In this paper, we present a novel compression technique for Bidirectional Texture Functions based on a sparse tensor decomposition. We apply the K-SVD algorithm along two different modes of a tensor to decompose it into a small dictionary and two sparse tensors. This representation is very compact, allowing for considerably better compression ratios at the same RMS error than possible with current compression techniques like PCA, N-mode SVD and Per Cluster Factorization. In contrast to other tensor decomposition based techniques, the use of a sparse representation achieves a rendering performance that is at high compression ratios similar to PCA based methods.
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    Parallelized Matrix Factorization for fast BTF Compression
    (The Eurographics Association, 2009) Ruiters, Roland; Rump, Martin; Klein, Reinhard; Kurt Debattista and Daniel Weiskopf and Joao Comba
    Dimensionality reduction methods like Principal Component Analysis (PCA) have become commonplace for the compression of large datasets in computer graphics. One important application is the compression of Bidirectional Texture Functions (BTF). However, the use of such techniques has still many limitations that arise from the large size of the input data which results in impractically high compression times. In this paper, we address these shortcomings and present a method which allows for efficient parallelized computation of the PCA of a large BTF matrix. The matrix is first split into several blocks for which the PCA can be performed independently and thus in parallel. We scale the single subproblems in such a way, that they can be solved in-core using the EM-PCA algorithm. This allows us to perform the calculation on current GPUs exploiting their massive parallel computing power. The eigenspaces determined for the individual blocks are then merged to obtain the PCA of the whole dataset. This way nearly arbitrarily sized matrices can be processed considerably faster than by serial algorithms. Thus, BTFs with much higher spatial and angular resolution can be compressed in reasonable time.