Search Results

Now showing 1 - 10 of 102
  • Item
    Sketch-based Image-independent Editing of 3D Tumor Segmentations using Variational Interpolation
    (The Eurographics Association, 2012) Heckel, Frank; Braunewell, Stefan; Soza, Grzegorz; Tietjen, Christian; Hahn, Horst K.; Timo Ropinski and Anders Ynnerman and Charl Botha and Jos Roerdink
    In the past years sophisticated automatic segmentation algorithms for various medical image segmentation problems have been developed. However, there are always cases where automatic algorithms fail to provide an acceptable segmentation. In these cases the user needs efficient segmentation correction tools, a problem which has not received much attention in research. Cases to be manually corrected are often particularly difficult and the image does often not provide enough information for segmentation, so we present an image-independent method for intuitive sketch-based editing of 3D tumor segmentations. It is based on an object reconstruction using variational interpolation and can be used in any 3D modality, such as CT or MRI. We also discuss sketch-based editing in 2D as well as a hole-correction approach for variational interpolation. Our manual correction algorithm has been evaluated on 89 segmentations of tumors in CT by 2 technical experts with 6+ years of experience in tumor segmentation and assessment. The experts rated the quality of our correction tool as acceptable or better in 92.1% of the cases. They needed a median number of 4 correction steps with one step taking 0.4s on average.
  • Item
    Rib-reinforced Shell Structure
    (The Eurographics Association and John Wiley & Sons Ltd., 2016) Li, Wei; Zheng, Anzong; You, Lihua; Yang, Xiaosong; Zhang, Jianjun; Liu, Ligang; Jernej Barbic and Wen-Chieh Lin and Olga Sorkine-Hornung
    Shell structures are extensively used in engineering due to their efficient load-carrying capacity relative to material volume. However, large-span shells require additional supporting structures to strengthen fragile regions. The problem of designing optimal stiffeners is therefore becoming a major challenge for shell applications. To address it, we propose a computational framework to design and optimize rib layout on arbitrary shell to improve the overall structural stiffness and mechanical performance. The essential of our method is to place ribs along the principal stress lines which reflect paths of material continuity and indicates trajectories of internal forces. Given a surface and user-specified external loads, we perform a Finite Element Analysis. Using the resulting principal stress field, we generate a quad-mesh whose edges align with this cross field. Then we extract an initial rib network from the quad-mesh. After simplifying rib network by removing ribs with little contribution, we perform a rib flow optimization which allows ribs to swing on surface to further adjust rib distribution. Finally, we optimize rib cross-section to maximally reduce material usage while achieving certain structural stiffness requirements. We demonstrate that our rib-reinforced shell structures achieve good static performances. And experimental results by 3D printed objects show the effectiveness of our method.
  • Item
    Non-rigid 3D Shape Retrieval via Sparse Representation
    (The Eurographics Association, 2013) Wan, Lili; Li, Shuai; Miao, Zhenjiang J.; Cen, Yigang G.; Bruno Levy and Xin Tong and KangKang Yin
    Shape descriptor design is an important but challenging problem for non-rigid 3D shape retrieval. Recently, bagof- words based methods are widely used to integrate a model's local shape descriptors into a global histogram. In this paper, we present a new method to pool the local shape descriptors into a global shape descriptor by means of sparse representation. Firstly, we employ heat kernel signature (HKS) to depict the multi-scale local shape. Then, for each model in the training dataset, we take the HKSs corresponding to its mesh vertices to serve as training signals, and thus an over-complete dictionary can be learned from them. Finally, the HKSs of each 3D model are sparsely coded based on the learned dictionary, and such sparse representations can be further integrated to form an object-level shape descriptor. Moreover, we conduct extensive experiments on the state-of-the-art benchmarks, wherein comprehensive evaluations state our method can achieve better performance than other bag-of-words based approaches.
  • Item
    Modelling of Clouds from a Hemispherical Image
    (The Eurographics Association, 2014) Alldieck, Thiemo; Lundtoft, Dennis H.; Montanari, Niels; Nikolov, Ivan; Vlaykov, Iskren G.; Madsen, Claus B.; Rita Borgo and Wen Tang
    This paper presents an image-based method for modelling clouds. Unlike previous image-based approaches, a hemispherical photograph is used as input, enabling to consider an entire sky instead of merely a portion. Our method computes the intensity and opacity of the clouds from the photograph. For this purpose, beforehand, the sun illumination is filtered, the pixels are classified between cloud and sky pixels, and the sky behind the clouds is reconstructed. After having been smoothed, the intensity of the clouds is used to create vertices on a hemisphere, and their radius coordinate is modulated by the intensity value of the corresponding pixel. Finally, the mesh is generated by triangulation of the vertices. Additionally, the use of the opacity of the clouds to simulate their transparency and render them is proposed. The results show that our method can be used to produce a realistic full sky populated with clouds in a very straightforward way for the user.
  • Item
    Euler Operators for Stratified Objects with Incomplete Boundaries
    (The Eurographics Association, 2004) Gomes, A. J. P.; Gershon Elber and Nicholas Patrikalakis and Pere Brunet
    Stratified objects such as those found in geometry-based systems (e.g. CAD systems and animation systems) can be stepwise constructed and manipulated through Euler operators. The operators proposed in this paper extend prior operators (e.g. the Euler-Masuda operators) provided that they can process n-dimensional stratified subanalytic objects with incomplete boundaries. The subanalytic objects form the biggest closed family of geometric objects defined by analytic functions. Basically, such operators are attachment, detachment, subdivision, and coaslescence operations without a prescribed order, providing the user with significant freedom in the design and programming of geometric applications.
  • Item
    An Edit Distance for Reeb Graphs
    (The Eurographics Association, 2016) Bauer, Ulrich; Fabio, Barbara Di; Landi, Claudia; A. Ferreira and A. Giachetti and D. Giorgi
    We consider the problem of assessing the similarity of 3D shapes using Reeb graphs from the standpoint of robustness under perturbations. For this purpose, 3D objects are viewed as spaces endowed with real-valued functions, while the similarity between the resulting Reeb graphs is addressed through a graph edit distance. The cases of smooth functions on manifolds and piecewise linear functions on polyhedra stand out as the most interesting ones. The main contribution of this paper is the introduction of a general edit distance suitable for comparing Reeb graphs in these settings. This edit distance promises to be useful for applications in 3D object retrieval because of its stability properties in the presence of noise.
  • Item
    Effective Characterization of Relief Patterns
    (The Eurographics Association and John Wiley & Sons Ltd., 2018) Giachetti, Andrea; Ju, Tao and Vaxman, Amir
    In this paper, we address the problem of characterizing relief patterns over surface meshes independently on the underlying shape. We propose to tackle the problem by estimating local invariant features and encoding them using the Improved Fisher Vector technique, testing both features estimated on 3D meshes and local descriptors estimated on raster images created by encoding local surface properties (e.g. mean curvature) over a surface parametrization. We compare the robustness of the obtained descriptors against noise and surface bending and evaluate retrieval performances on a specific benchmark proposed in a track of the Eurographics Shape REtrieval Contest 2017. Results show that, with the proposed framework, it is possible to obtain retrieval results largely improving the state of the art and that the image-based approach is still effective when the underlying surface is heavily deformed.
  • Item
    Object Completion using k-Sparse Optimization
    (The Eurographics Association and John Wiley & Sons Ltd., 2015) Mavridis, Pavlos; Sipiran, Ivan; Andreadis, Anthousis; Papaioannou, Georgios; Stam, Jos and Mitra, Niloy J. and Xu, Kun
    We present a new method for the completion of partial globally-symmetric 3D objects, based on the detection of partial and approximate symmetries in the incomplete input dataset. In our approach, symmetry detection is formulated as a constrained sparsity maximization problem, which is solved efficiently using a robust RANSACbased optimizer. The detected partial symmetries are then reused iteratively, in order to complete the missing parts of the object. A global error relaxation method minimizes the accumulated alignment errors and a nonrigid registration approach applies local deformations in order to properly handle approximate symmetry. Unlike previous approaches, our method does not rely on the computation of features, it uniformly handles translational, rotational and reflectional symmetries and can provide plausible object completion results, even on challenging cases, where more than half of the target object is missing. We demonstrate our algorithm in the completion of 3D scans with varying levels of partiality and we show the applicability of our approach in the repair and completion of heavily eroded or incomplete cultural heritage objects.
  • Item
    Evaluating the Curvature Analysis as a Key Feature for the Semantic Description of Architectural Elements
    (The Eurographics Association, 2014) Adrian, Julie; Buglio, David Lo; Luca, Livio De; Reinhard Klein and Pedro Santos
    The recent developments in the fields of photogrammetry and laser scanning, have made possible mass acquisitions of heritage artifacts with a particularly high level of geometric accuracy. A processing of the digital model will be necessary to isolate some characteristics in order to carry on an analysis of the architectural object. In this poster, the potentialities of the curvature maps, extracted from digital acquisitions, are defined to conduct the study on the morphology of architectural elements. The current work focuses on the technical and theoretical issues that will ultimately result in an average surface signature. This will allow to identify the degree of remoteness of each attribute.
  • Item
    Visually Guided Mesh Smoothing for Medical Applications
    (The Eurographics Association, 2012) Moench, Tobias; Kubisch, Christoph; Lawonn, Kai; Westermann, Ruediger; Preim, Bernhard; Timo Ropinski and Anders Ynnerman and Charl Botha and Jos Roerdink
    Surface models derived from medical image data often exhibit artifacts, such as noise and staircases, which can be reduced by applying mesh smoothing filters. Usually, an iterative adaption of smoothing parameters to the specific data and continuous re-evaluation of accuracy and curvature is required. Depending on the number of vertices and the filter algorithm, computation time may vary strongly and interfere with an interactive mesh generation procedure. In this paper, we present an approach to improve the handling of mesh smoothing filters. Based on a GPU mesh smoothing implementation, model quality is evaluated in real-time and provided to the user as quality graphs to support the mental optimization of input parameters. Moreover, this framework is used to find optimal smoothing parameters automatically and to provide data-specific parameter suggestions.