WSCG 2013: Communication Papers Proceedings
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Item Generation of Parameterized Models for Vessels Design(Václav Skala - UNION Agency, 2013) Diaz, Ruben G.; Dreux, Marcelo; Coelho, Luiz Cristovão G.; Skala, VáclavThis work proposes an integrated environment for modeling, and static and dynamic analysis of vessels. The main advantage of the proposed environment is that it is possible to automatically obtain variants of a specific model in order to achieve a desired configuration, not only in relation to geometry but also concerning the static stability aspect. This environment uses the Lua programming language and it is possible to define global variables to be used as parameters which retrieve or modify modeling values such as length, width, height, and so on. Any model can be parameterized, as a function of user chosen variables, which allows an automatic modeling with the variation of those parameters.
Item Real-time visualization of Moebius transformations in space using Quaternionic-Bezier approach(Václav Skala - UNION Agency, 2013) Karpavicius, Vytautas; Krasauskas, Rimvydas; Skala, VáclavMoebius transformations in space are much more sophisticated than the classical case on the plane, which has been well studied. We present a WebGL approach for visualization of Moebius transformations in 3-space by animating deformations of geometric objects composed of patches parametrized by Quaternionic-Bezier formulas. The idea is to represent Moebius transformations in a quaternionic form as well, and to use GPU shaders for transforming control points, weights, and normals, then seamlessly stitching patches with different levels of detail, and computing points on every patch. Finally, we demonstrate the main classes of Moebius transformations in space on several 3D objects including primitive shapes, Dupin cyclide patchworks, and Utah Teapot.Item Similarity Detection for Free-Form Parametric Models(Václav Skala - UNION Agency, 2013) Dang, Quoc-Viet; Mouysset, Sandrine; Morin, Géraldine; Skala, VáclavIn this article, we propose a framework for detecting local similarities in free-form parametric models, in particular on B-Splines or NURBS based B-reps: patches similar up to an approximated isometry are identified. Many recent articles have tackled similarity detection on 3D objects, in particular on 3D meshes. The parametric B-splines, or NURBS models are standard in the CAD (Computer Aided Design) industry, and similarity detection opens the door to interesting applications in this domain, such as model editing, objects comparison or efficient coding. Our contributions are twofold: we adapt the current technique called votes transformation space for parametric surfaces and we improve the identification of isometries. First, an orientation technique independent of the parameterization permits to identify direct versus indirect transformations. Second, the validation step is generalized to extend to the whole B-rep. Then, by classifying the isometries according to their fixed points, we simplify the clustering step. We also apply an unsupervised spectral clustering method which improves the results but also automatically estimates the number of clusters.Item Improved Interactive Reshaping of Humans in Images(Václav Skala - UNION Agency, 2013) Nidhi, Arora; Kumar, Harsh; Dhaliwal, Jagjeet S.; Kalra, Prem; Chaudhuri, Parag; Skala, VáclavIn this paper, we present an interactive and flexible approach for realistic reshaping of human bodies in a single image. For reshaping, a user specifies a set of semantic attributes like weight and height. Then we use a 3Dmorphable model based image retouching technique for global reshaping of the human bodies in the image such that they satisfy the semantic constraints specified by the user. We address the problem of deformation of the environment surrounding the human body being reshaped, which produces visible artifacts, especially noticeable at regions with structural features, in prior work. We are able to separate the human figure from the background. This allows us to reshape the figure, while preserving the background. Missing regions in the background are inpainted in a manner that maintains structural details. We also provide a quantitative measure for distortion and compare our results with the prior work.Item A framework for detection of linear gradient filled regions and their reconstruction for vector graphics(Václav Skala - UNION Agency, 2013) Kansal, Ruchin; Kumar, Subodh; Skala, VáclavLinear gradients are commonly applied in non-photographic art-work for shading and other artistic effects. It is sometimes necessary to generate a vector graphics form of raster images comprising such art-work with the expectation to obtain a simple output that is further editable, say, using any popular vector editing software. Further, this vectorization process should be automatic with minimal user intervention. We present a simple image vectorization algorithm that meets these requirements by detecting linear gradient filled regions and reconstructing the vector definition using that information. It uses a novel interval gradient optimization scheme to derive large regions of uniform gradient. We also demonstrate the technique on noisy images.Item Part-based Construction of digitized 3D objects(Václav Skala - UNION Agency, 2013) Borges, Daniela; Ferreira, Alfredo; Skala, VáclavNowadays, a few 3D acquisition devices are available at low-cost. While 3D capture is a commonplace, decompose the object into its components is not an easy task. Segmentation can help address this problem by suppling data which may be used to identify object components. However, it might not give complete and accurate information about components. In a context where a digital repository with every component that can belong to physical objects is available, retrieval algorithms can be used to construct a composed 3D model. We propose a four phase solution to construct 3D digitized objects. We use Microsoft Kinect® to acquire 3D physical objects. A segmentation algorithm based on color information decomposes the object into a set of sub-parts. The component repository is queried using a shape-based retrieval algorithm, in order to identify which sub-part corresponds to each virtual component. Then, a 3D model of the physical object is constructed by assembling the retrieved components. The work presented in this paper has a wide application domain, ranging from entertainment to health or mechanical industry. To validate our proposal, we implemented a toy-problem and evaluated its precision and efficiency. We used LEGO® blocks, which can provide challenges similar to real-world applications. The results were encouraging and we believe that our approach may even work better with greater object components, geometrically less similar to each other.Item An Optimization of Square Parameterization(Václav Skala - UNION Agency, 2013) Dechvijankit, Anuwat; Nagahashi, Hiroshi; Aoki, Kota; Skala, VáclavIn order to parameterize a three-dimensional surface into a two-dimensional planar domain, we need to convert its polygonal mesh into a disk topology surface. For quality of texturing or re-meshing that uses a parameterization technique, it is more effective if the distortion of two-dimensional manifold planar domain map is as small as possible. Since square planar domain is easily understandable to human or very simple as a computer image file, it has been frequently used in real world applications. We introduce a series of experiments focusing on how to deliver an optimized square parameterization with low-cost calculation and stable result. The result of these experiments shows that our method is a suitable method for optimizing square parameterization.Item The Retrieval of NURBS-surface by Genetic Algorithm on the Basis of Point Cloud(Václav Skala - UNION Agency, 2013) Popov, Eugene Vladimirovich; Rotkov, Sergej Igorevich; Skala, VáclavThe approach to the geometrical modeling problem solution is described in this report. The approach is dedicated to the approximation of the cloud of points by a NURBS-curve or NURBS-surface and is based on the inheritance mechanism or on the so-called Genetic Algorithm. Genetic Algorithm is the heuristic search and optimization technique that mimics the process of natural evolution. The mechanisms of evolution seem well suited for some of the most pressing scientific problems in many fields. Therefore, the concept of evolution can be applied to solve different computational problems and NURBS-surface retrieval including. The efficiency of the approach is demonstrated by the retrieval of a human face and ship hull surface.Item PoolLiveAid: Augmented reality pool table to assist inexperienced players(Václav Skala - UNION Agency, 2013) Alves, Ricardo; Sousa, Luís; Rodrigues, J. M. F.; Skala, VáclavPoolLiveAid is an augmented reality tool designed to assist unskilled or amateur pool, or snooker or billiards players in predicting trajectories. A camera placed above the table acquires and processes the game on-the-fly. The system detects the table border, the ball’s position and the pool cue direction in order to compute the predictable trajectory of the white ball, and the ball directly in its trajectory. The output result is then forwarded to a projector, placed above the table, which then projects onto the snooker playable field. A skilled player can also save a specific layout of a move and load it later in order to achieve the best shot and practising.Item Straight Skeleton for Automatic Generation of 3-D Building Models with General Shaped Roofs(Václav Skala - UNION Agency, 2013) Sugihara, Kenichi; Skala, Václav3D urban models are important in several fields, such as urban planning and gaming industries. However, enormous time and labor has to be consumed to create these 3D models, using a 3D modeling software such as 3ds Max or SketchUp. In order to automate laborious steps, a GIS and CG integrated system is proposed for automatically generating 3D building models, based on building polygons (building footprints) on digital maps. Digital maps shows most building polygons' edges meet at right angles (orthogonal polygon). In the digital map, however, not all building polygons are orthogonal. In either orthogonal or non-orthogonal polygons, the new system is proposed for automatically generating 3D building models with general shaped roofs by straight skeleton computation. In this paper, the algorithm for shrinking a polygon and forming a straight skeleton are clarified and, the new methodology is proposed for constructing roof models by assuming ‘the third event’ and, at the end of the shrinking process, the shrinking polygon is converged to ‘a line of convergence’.Item Generic Fitted Primitives (GFP): Towards Full Object Volumetric Reconstruction for Service Robotics(Václav Skala - UNION Agency, 2013) Cocias, Tiberiu T.; Moldoveanu, Florin; Grigorescu, Sorin M.; Skala, VáclavService robotics applications, such as mobile manipulation in domestic environments, require 3D representations of the objects of interest to be grasped. Simple object recognition or segmentation cannot provide structural shape information mandatory for obtaining reliable grasp configurations. In this paper, the Generic Fitted Primitives (GFP) technique for volumetric reconstruction is introduced. The goal of the method is to build full 3D object shapes from a single camera perspective. In order to obtain the shape of the 3D primitive, we propose an energyminimization algorithm based on the concept of Active Contours applied directly on 3D visual data. Our modeling approach produces compact closed surfaces (volumes) describing the objects of interest which can be further used for service robotics tasks, such as grasping or manipulation. The performance of the proposed technique has been evaluated against two different methods, i.e. generalized active contours and superquadric approximations.Item MCM-CBIR: Multi Clustering Method for Content Based Image Retrieval(Václav Skala - UNION Agency, 2013) Lacheheb, Hadjer; Aouat, Saliha; Hamouchene, Izem; Skala, VáclavImage retrieval systems are designed to provide the ability of searching and retrieving images in huge image databases. A content based image retrieval system (CBIR) is used to offer such tasks based on the content of the image. In this paper we propose a new method of CBIR system based on a learning technique. Our method uses k-means clustering to reduce data and to improve the system performance. The specificity of our approach is the use of each feature vector separately in the clustering process in order to obtain different clustering on the same database, differently to other approaches that combine features vectors to cluster the database. For this reason we call it multi-clustering approach. The advantage of this approach consists in keeping the performance of the features and getting several views of the database due to the separation of features. The experimental results show the efficiency of our approach.Item The 3-Point Method: A Fast, Accurate and Robust Solution to Vanishing Point Estimation(Václav Skala - UNION Agency, 2013) Saini, Vinod; Gade, Shripad; Prasad, Mritunjay; Chatterjee, Saurabh; Skala, VáclavVanishing points can provide information about the 3D world and hence are of great interest for machine vision applications. In this paper, we present a single point perspectivity based method for robust and accurate estimation of Vanishing Points (VPs). It utilizes location of 3 collinear points in image space and their distance ratio in the world frame for VP estimation. We present an algebraic derivation for the proposed 3-Point (3-P) method. It provides us a non-iterative, closed-form solution. The 3-P results are compared with ground truth of VP and it is shown to be accurate. Its robustness to point selection and image noise is proved through extensive simulations. Computational time requirement for 3-P method is shown to be much less than least squares based method. The 3-P method is extremely useful for accurate VP estimation in structured and well-defined environments.Item (Semi) regular tetrahedral tilings(Václav Skala - UNION Agency, 2013) Kolcun, Alexej; Skala, VáclavTriangulation 2D and 3D methods represent an important part of numerical modeling process (e.g. FEM). In many applications it is suitable to use triangulations with a regular structure. Moreover, decomposition with a limited number of different types of tetrahedra enables to reduce the storage and computational demands in the whole modeling process. The submitted contribution presents an overview of possible 3D decompositions using one tetrahedron (regular tilings). These decompositions are confronted with decompositions using six different types of tetrahedra (orthogonal structured tilings). Considering the shape expressivity of particular methods, the paper presents a structure of possible decompositions and comparison of storage demands of the used decompositions.Item A facial motion tracking and transfer method based on a key point detection(Václav Skala - UNION Agency, 2013) Akagi, Yasuhiro; Furukawa, Ryo; Sagawa, Ryusuke; Ogawara, Koichi; Kawasaki, Hiroshi; Skala, VáclavFacial animation is one of the most important contents in 3D CG animations. By the development of scanning and tracking methods of a facial motion, a face model which consists of more than 100,000 points can be used for the animations. To edit the facial animations, key point based approaches such as "face rigging" are still useful ways. Even if a facial tracking method gives us all point-to-point correspondences, a detection method of a suitable set of key points is needed for content creators. Then, we propose a method to detect the key points which efficiently represent motions of a face. We optimize the key points for a Radial Basis Function (RBF) based 3D deformation technique. The RBF based deformation is a common technique to represent a movement of 3D objects in CG animations. Since the key point based approaches usually deform objects by interpolating movements of the key points, these approaches cause errors between the deformed shapes and the original ones. To minimize the errors, we propose a method which automatically inserts additional key points by detecting the area where the error is larger than the surrounding area. Finally, by utilizing the suitable set of key points, the proposed method creates a motion of a face which are transferred form another motion of a face.Item Identification of Abnormal Cervical Regions from Colposcopy Image Sequences(Václav Skala - UNION Agency, 2013) Liang, Mingpei; Zheng, Gaopin; Huang, Xinyu; Milledge, Gaolin; Tokuta, Alade; Skala, VáclavCervical cancer is the third most common cancer in women worldwide and the leading cause of cancer death in women of the developing countries. Cancer death rate can be greatly reduced by regular screening. One of the steps during a screening program is the detection of the abnormal cells that could evolve into cancer. In this paper, we propose an algorithm that automatically identifies the abnormal cervical regions from colposcopy image sequence. Firstly, based on the segmentation of three different image regions, a set of low-level features is extracted to model the temporal changes in the cervix before and after applying acetic acid. Second, a support vector machine (SVM) classifier is trained and used to make predictions on new input feature vectors. As the low-level features are very insensitive to accurate image registration, only a rough normalization step is needed to sample image patches. Our preliminary results show that our algorithm is accurate and effective. Furthermore, our algorithm only needs to sample patches from six image frames within a five-minute time period. Hence, the proposed algorithm also could be applied to improve the accuracy of the mobile telemedicine for cervical cancer screening in low-resource settings.Item Efficient Removal of Inconsistencies in Large Multi-Scan Point Clouds(Václav Skala - UNION Agency, 2013) Kanzok, Thomas; Süß, Falk; Linsen, Lars; Rosenthal, Paul; Skala, VáclavWhen large scale structures are to be digitized using laser scanning, usually multiple scans have to be registered and merged to cover the whole scene. During the scanning process movement in the scene and equipment standing around – which is not always avoidable – may induce artifacts. Since the scans often overlap considerably another scan of the same area might be artifact-free. In this paper we describe an approach to find these "temporal" artifacts (so-called, because they only appear during one single scan) based on shadow mapping, which makes it implementable as a shader program and therefore very fast. The effectiveness of the approach is demonstrated with the help of large-scale real-world data.Item High-velocity optical flow(Václav Skala - UNION Agency, 2013) Vergeest, Joris; Skala, VáclavOptical flow is widely used to estimate the velocity of objects relative to a digital camera. Most commonly, two images taken with the same camera at small time difference are compared in order to detect the displacement of structures in 2D image space. Such displacement could be a measure of displacement, or motion, of objects in the scene relative to the camera. At high velocities, the displacement in image space is relatively large and the correlation of image structures gets more difficult. The displacement can be reduced by reducing the time difference, or increasing the number of frames taken per second. However, due to the reduced exposure time, the quality of the individual images gets poorer. In some practical situations, it appears technically very difficult to achieve reliable speed measurement at high velocities, even when using high-speed cameras. One example is the measurement of self-speed from images of the road surface taken with a camera from a driving car. In view of this purpose we explore the potential of the method and its limitations.Item A Comparative Analysis of Spatial Partitioning Methods for Large-scale, Real-time Crowd Simulation(Václav Skala - UNION Agency, 2013) Li, Bo; Mukundan, Ramakrishnan; Skala, VáclavAcceleration algorithms involving spatial partitioning methods are extensively used in crowd simulation for realtime collision avoidance. Memory and update costs become increasingly important as the crowd size becomes large. The paper presents a detailed analysis of the effectiveness of spatial subdivision data structures, specifically for large-scale crowd simulation. The results demonstrate that a regular grid data structure combined with an extended oriented bounding volume for crowd members can facilitate efficient updates necessary for real-time performance.Item Practical Augmented Visualization on Handheld Devices for Cultural Heritage(Václav Skala - UNION Agency, 2013) Murru, Giovanni; Fratarcangeli, Marco; Empler, Tommaso; Skala, VáclavIn this paper, we present a framework for the interactive 3D visualization of archaeological sites on handheld devices using fast augmented reality techniques. The user interface allows for the ubiquitous, personalized and context-aware browsing of complex digital contents, such like 3D models and videos. The framework is very general and entirely devised and built by the means of free, cross-platform components. We demonstrate the flexibility of our system in a real case scenario, namely the augmented visualization of a historically reliable model of the Ancient Forum of Nerva located in Rome, Italy.
