WSCG '2009: Full Papers Proceedings
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Item Efficient Medial Voxel Extraction for Large Volumetric Models(Václav Skala - UNION Agency, 2009) Michikawa, Takashi; Nakazaki, Shun; Suzuki, Hiromasa; Chen, Min; Skala, VáclavHere we propose a method for medial voxel extraction from large volumetric models based on an out-of-core framework. The method improves upon geodesic-based approaches to enable the handling of large objects. First, distance fields are constructed from input volumes using an out-of-core algorithm. Second, medial voxels are extracted from these distance fields through multi-phase evaluation processes. Trivial medial or non-medial voxels are evaluated by the low-cost pseudo-geodesic distance method first, and the more expensive geodesic distance computation is run last. Using this strategy allows most of the voxels to be extracted in the low-cost process. This paper outlines a number of results regarding the extraction of medial voxels from large volumetric models. Our method also works in parallel, and we demonstrate that computation time becomes even shorter in multi-core environments.
Item Flocking Boids with Geometric Vision, Perception and Recognition(Václav Skala - UNION Agency, 2009) Holland, James; Semwal, Sudhanshu Kumar; Chen, Min; Skala, VáclavIn the natural world, we see endless examples of the behavior known as flocking. From the perspective of graphics simulation, the mechanics of flocking has been reduced down to a few basic behavioral rules. Reynolds coined the term Boid to refer to any simulated flocking, and simulated flocks by collision avoidance, velocity matching, and flock centering. Though these rules have been given other names by various researchers, implementing them into a simulation generally yields good flocking behavior. Most implementations of flocking use a forward looking visual model in which the boids sees everything around it. Our work creates a more realistic model of avian vision by including the possibility of a variety of geometric vision ranges and simple visual recognition based on what boids can see. In addition, a perception algorithm has been implemented which can determine similarity between any two boids. This makes it possible to simulate different boids simultaneously. Results of our simulations are summarized.Item GPU-Based Adaptive-Subdivision for View-Dependent Rendering(Václav Skala - UNION Agency, 2009) Bauman, Gilad; Livny, Yotam; El-Sana, Jihad; Chen, Min; Skala, VáclavIn this paper, we present a novel view-dependent rendering approach for large polygonal models. In an offline stage, the input model is simplified to reach a light coarse representation. Each simplified face is then assigned a displacement map, which resembles the geometry of the corresponding patch on the input model. At runtime, the coarse representation is transmitted to the graphics hardware at each frame. Within the graphics hardware, the GPU subdivides each face with respect to the viewparameters, and adds fine details using the assigned displacement map. Initial results show that our implementation achieves quality images at high frame rates.Item Feature-supported Multi-hypothesis Framework for Multi-object Tracking using Kalman Filter(Václav Skala - UNION Agency, 2009) Pathan, Saira Saleem; Al-Hamadi, Ayoub; Elmezain, Mahmoud; Michaelis, Bernd; Chen, Min; Skala, VáclavA Kalman filter is a recursive estimator and has widely been used for tracking objects. However, unsatisfying tracking of moving objects is observed under complex situations (i.e. inter-object merge and split) which are challenging for classical Kalman filter. This paper describes a multi-hypothesis framework based on multiple features for tracking the moving objects under complex situations using Kalman Tracker. In this framework, a hypothesis (i.e. merge, split, new) is generated on the basis of contextual association probability which identifies the status of the moving objects in the respective occurrences. The association among the moving objects is computed by multi-featured similarity criteria which include spatial size, color and trajectory. Color similarity probability is computed by the correlation-weighted histogram intersection (CWHI). The similarity probabilities of the size and the trajectory are computed and combined with the fused color correlation. The accumulated association probability results in online hypothesis generation. This hypothesis assists Kalman tracker when complex situations appear in real-time tracking (i.e. traffic surveillance, pedestrian tracking). Our algorithm achieves robust tracking with 97.3% accuracy, and 0.07% covariance error in different real-time scenarios.Item The Elucidation of Planar Aesthetic Curves(Václav Skala - UNION Agency, 2009) Gobithaasan, R. U.; Ali, Jamaludin Md.; Miura, Kenjiro T.; Chen, Min; Skala, VáclavA compact formula for Logarithmic Curvature Histogram (LCH) and its gradient for planar curves have been proposed. Using these entities and the analysis of Generalized Cornu Spiral (GCS), the mathematical definition for a curve to be aesthetic has been introduced to overcome the ambiguity that occurs in measuring the beauty of a curve. In the last section, detailed examples are shown on how LCH and its gradient represented as a straight line equation can be used to measure the aesthetic value of planar curves.Item 3D Skeleton Extraction from Volume Data Based on Normalized Gradient Vector Flow(Václav Skala - UNION Agency, 2009) Yoon, Sang Min; Malerczyk, Cornelius; Graf, Holger; Chen, Min; Skala, VáclavSkeleton extraction and visualization of 3D reconstructed target objects from multiple views continues to be a major challenge in terms of providing intuitive and uncluttered images that allow the users to understand their data. This paper presents a three-dimensional skeleton extraction technique of deformable objects based on a normalized gradient vector flow in order to analyze and visualize its characteristics. 3D deformable objects are reconstructed by an image based visual hull technique from known extrinsic and intrinsic camera parameters and silhouettes which are extracted from each camera. Our 3D skeleton extraction methodology employs the normalized gradient vector flow which is a vector diffusion approach based on partial differential equations. The euclidean distance of the magnitude of a normalized gradient vector flow is used to extract the medial axis of volume data. A markerless 3D skeletonization of reconstructed objects from multiple images might be applied to retrieve the 3D model or correct the 3D motion of the target objects.Item Development and evaluation of a virtual reality patient simulation(Václav Skala - UNION Agency, 2009) Nestler, Simon; Huber, Manuel; Echtler, Florian; Dollinger, Andreas; Klinker, Gudrun; Chen, Min; Skala, VáclavIn disasters and mass casualty incidents (MCIs) paramedics initially determine the severeness of all patients' injuries during the so-called triage. In order to enhance disaster preparedness continuous training of all paramedics is indispensable. Due to the fact that large disaster control exercises are laborious and expensive, additional training on a small scale makes sense. Therefore we designed and developed a virtual reality patient simulation (VRPS) to train paramedics in this disaster triage. The presented approach includes gesture based interactions with the virtual patients in order to simulate the triage process as realistically as possible. The evaluated approach focuses on the training of paramedics in disaster triage according to the mSTaRT (modified Simple Triage and Rapid Treatment) triage algorithm on a multi-touch table top device. At the Munich fire department fully-qualified paramedics performed 160 triage processes with the triage simulation. The accuracy of the triage processes was compared to previous disaster control exercises with real mimes. The presented results of this explorative evaluation will be the basis for future, larger evaluations.Item GPU-only Terrain Rendering for Walk-through(Václav Skala - UNION Agency, 2009) Park, Sunyong; Oh, Kyoungsu; Chen, Min; Skala, VáclavAccurate terrain representation takes a very significant role in making a scene more realistic. In this paper, we present a full GPU-based real-time terrain rendering algorithm by ray-casting. Since it requires no geometrical structure like a polygonal mesh, it doesn't need any LOD (Level-Of-Detail) policies. Most of them are processed on CPU and may give much burden on the CPU. As a result, it enhances the whole performance of the system. Our method grants a complete freedom to the view point and its direction, so objects can move around so freely in the air or on the surface that it can be directly applied to any computer games and VR (Virtual Reality) system. To better the rendering quality, we applied curved patches to the height field. On the way, we suggest a simplification for evaluating a ray-patch intersection. We implemented all the processes on GPU, and obtained tens to hundreds of frame rates with a variety of resolutions of height maps: 256ⅹ256~8192ⅹ8192 (texel2).Item CUDA based Level Set Method for 3D Reconstruction of Fishes from Large Acoustic Data(Václav Skala - UNION Agency, 2009) Sharma, Ojaswa; Anton, François; Chen, Min; Skala, VáclavAcoustic images present views of underwater dynamics, even in high depths. With multi-beam echo sounders (SONARs), it is possible to capture series of 2D high resolution acoustic images. 3D reconstruction of the water column and subsequent estimation of fish abundance and fish species identification is highly desirable for planning sustainable fisheries. Main hurdles in analysing acoustic images are the presence of speckle noise and the vast amount of acoustic data. This paper presents a level set formulation for simultaneous fish reconstruction and noise suppression from raw acoustic images. Despite the presence of speckle noise blobs, actual fish intensity values can be distinguished by extremely high values, varying exponentially from the background. Edge detection generally gives excessive false edges that are not reliable. Our approach to reconstruction is based on level set evolution using Mumford-Shah segmentation functional that does not depend on edges in an image. We use the implicit function in conjunction with the image to robustly estimate a threshold for suppressing noise in the image by solving a second differential equation. We provide details of our estimation of suppressing threshold and show its convergence as the evolution proceeds. We also present a GPU based streaming computation of the method using NVIDIA’s CUDA framework to handle large volume data-sets. Our implementation is optimised for memory usage to handle large volumes.Item Integrating Tensile Parameters in Hexahedral Mass-Spring System for Simulation(Václav Skala - UNION Agency, 2009) Baudet, V.; Beuve, M.; Jaillet, F.; Shariat, B.; Zara, F.; Chen, Min; Skala, VáclavBesides finite element method, mass-spring systems are widely used in Computer Graphics. It is indubitably the simplest and most intuitive deformable model. This discrete model allows to perform interactive deformations with ease and to handle complex interactions. Thus, it is perfectly adapted to generate visually plausible animations. However, a drawback of this simple formulation is the relative difficulty to control efficiently physically realistic behaviors. Indeed, none of the existing models has succeeded in dealing with this satisfyingly. We demonstrate that this restriction cannot be over-passed with the classical mass-spring model, and we propose a new general 3D formulation that reconstructs the geometrical model as an assembly of elementary hexahedral "bricks". Each brick (or element) is then transformed into a mass-spring system. Edges are replaced by springs that connect masses representing the vertices. The key point of our approach is the determination of the stiffness springs to reproduce the correct mechanical properties (Young’s modulus and Poisson’s ratio) of the reconstructed object. We validate our methodology by performing some numerical experiments. Finally, we evaluate the accuracy of our approach, by comparing our results with the deformation obtained by finite element method.Item Extracting CAD features from point cloud cross-sections(Václav Skala - UNION Agency, 2009) Kyriazis, Ioannis; Fudos, Ioannis; Palios, Leonidas; Chen, Min; Skala, VáclavWe present a new method for extracting features of a 3D object targeted to CAD modeling directly from the point cloud of its surface scan. The objective is to obtain an editable CAD model that is manufacturable and describes accurately the structure and topology of the point cloud. The entire process is carried out with the least human intervention possible. First, the point cloud is sliced interactively in cross sections. Each cross section consists of a 2D point cloud. Then, a collection of segments represented by a set of feature points is derived for each slice, describing the cross section accurately, and providing the basis for an editable feature-based CAD model. For the extraction of the feature points, we exploit properties of the convex hull and the Voronoi diagram of the point cloud.Item 3D Interaction Techniques for 6 DOF Markerless Hand-Tracking(Václav Skala - UNION Agency, 2009) Schlattmann, Markus; Na Nakorn, Tanin; Klein, Reinhard; Chen, Min; Skala, VáclavRecently, stable markerless 6 DOF video based hand-tracking devices became available. These devices track the position and orientation of the user’s hand in different postures with at least 25 frames per second. Such hand-tracking allows for using the human hand as a natural input device. However, the absence of physical buttons for performing click actions and state changes poses severe challenges in designing an efficient and easy to use 3D interface on top of such a device. In particular, solutions have to be found for clicking menu items, selecting objects and coupling and decoupling the object’s movements to the user’s hand (i.e. grabbing and releasing). In this paper, we introduce a novel technique for grabbing and releasing objects, an efficient clicking operation for selection purposes and last but not least a novel visual feedback in order to support the ease of using this device. All techniques are integrated in a novel 3D interface for virtual manipulations. Several user experiments were performed, which show the superior applicability of this new 3D interface.Item View-Dependent Multiresolution Modeling on the GPU(Václav Skala - UNION Agency, 2009) Ripolles, Oscar; Gumbau, Jesus; Chover, Miguel; Ramos, Francisco; Puig-Centelles, Anna; Chen, Min; Skala, VáclavFor more than a decade, researchers working on level-of-detail techniques have oriented their efforts toward developing better frameworks and adapting their solutions to new hardware. Nevertheless, we believe there is still a gap for efficient yet simple multiresolution models that fully exploit the potential of current GPUs. In this paper we present a level-of-detail framework based on moving the extraction process from updating indices to updating vertices. This feature enables us to perform culling and geomorphing on a vertex basis. Furthermore, it simplifies the update of indices to eliminate degenerate information. The model is capable of offering both uniform and variable resolution and to achieve the latter, a silhouette-based criterion has been included. Finally, we would like to highlight that the model is completely integrated in the GPU and no CPU/GPU communication is necessary once all the information is correctly loaded in hardware memory.Item Geometric Diversity for Crowds on the GPU(Václav Skala - UNION Agency, 2009) Lister, W.; Laycock, R. G.; Day, A. M.; Chen, Min; Skala, VáclavPure geometric techniques have emerged as viable real-time alternatives to those traditionally used for rendering crowds. However, although capable of drawing many thousands of individually animated characters, the potential for injecting intra-crowd diversity within this framework remains to be fully explored. For urban crowds, a prominent source of diversity is that of clothing and this work presents a technique to render a crowd of clothed, virtual humans whilst minimising redundant vertex processing, overdraw and memory consumption. By adopting a piecewise representation, given an assigned outfit and pre-computed visibility metadata, characters can be constructed dynamically from a set of sub-meshes and rendered using skinned instancing. Using this technique, many thousands of independently clothed, animated and textured characters can be rendered at 40 fps.Item Real-Time Dense and Accurate Parallel Optical Flow using CUDA(Václav Skala - UNION Agency, 2009) Marzat, Julien; Dumortier, Yann; Ducrot, Andre; Chen, Min; Skala, VáclavA large number of processes in computer vision are based on the image motion measurement, which is the projection of the real displacement on the focal plane. Such a motion is currently approximated by the visual displacement field, called optical flow. Nowadays, a lot of different methods are commonly used to estimate it, but a good trade-off between execution time and accuracy is hard to achieve with standard integrations. This paper tackles the problem by proposing a parallel implementation of the well-known pyramidal algorithm of Lucas & Kanade, in a Graphics Processing Unit (GPU). It is programmed using the Compute Unified Device Architecture from NVIDIA corporation, to compute a dense and accurate velocity field at about 15 Hz with a 640 480 image definition.Item Quadrilateral mesh generation from point clouds by a Monte Carlo method(Václav Skala - UNION Agency, 2009) Róth, Ágoston; Juhász, Imre; Chen, Min; Skala, VáclavWe present a Monte Carlo method that generates a quadrilateral mesh from a point cloud. The proposed algorithm evolves an initial quadrilateral mesh towards the point cloud which mesh is constructed by means of the skeleton of the input points. The proposed technique proves to be useful in case of relatively complex point clouds that describe smooth and non-self-intersecting surfaces with junctions/branches and loops. The resulted quadrilateral mesh may be used to reconstruct the surfaces by means of tensor product patches such as B-spline or NURBS.Item Repairing Heavy Damaged CAD-models(Václav Skala - UNION Agency, 2009) Emelyanov, Alexander; Astakhov, Yuri; Chen, Min; Skala, VáclavThe presented work is related to the problem of repairing incomplete reconstructed (damaged) CAD-models. To solute this problem, a general concept of the repairing that uses various types of mathematical fields is proposed. One method developed within the framework of this concept is described in details. As the base this method uses interpolation of a given successfully reconstructed surface to estimate the behavior of the corresponding missing one. Ability of the method to repair heavy damaged CAD-models has been proved. This method has a big potential for further development, because the main advantage of the presented concept is that its framework is open to adding various methods of missing surface estimation to supplement each other in the repairing process.Item Low cost finger tracking for a virtual blackboard(Václav Skala - UNION Agency, 2009) Rustico, Eugenio; Chen, Min; Skala, VáclavThis paper presents a complete and inexpensive system to track the movements of a physical pointer on a flat surface. Any opaque object can be used as a pointer (fingers, pens, etc.) and it is possible to discriminate whether the surface is being touched or just pointed at. The system relies on two entry-level webcams and it uses a fast scanline-based algorithm. An automatic wizard helps the user during the initial setup of the two webcams. No markers, gloves or other hand-held devices are required. Since the system is independent from the nature of the pointing surface, it is possible to use a screen or a projected wall as a virtual touchscreen. The complexity of the algorithms used by the system grows less than linearly with resolution, making the software layer very lightweight and suitable also for low-powered devices like embedded controllers.Item Interactive Editing of Upholstered Furniture(Václav Skala - UNION Agency, 2009) Schwartz, Christopher; Degener, Patrick; Klein, Reinhard; Chen, Min; Skala, VáclavFast visualization of industrial parts for rapid prototyping is nowadays eased by the fact that CAD construction data is readily available in most cases. Upholstery constitutes an important exception as its shape is not given a priori but the result of complex physical interactions between hard bodies, soft cushioning and elastic sheets. In this paper we propose an interactive visualization and editing method for upholstery that infers physically plausible surfaces from a sewing pattern. Our method supports fast design decisions by allowing easy and intuitive modifications of the inferred surface at any time. We also propose a reconstruction method for point clouds that is specifically targeted at upholstery. We argue that the sewing pattern encodes important information about shape and material deformations of the final surface and consequently use it as a prior in our reconstruction algorithm. The practicability of our method is demonstrated on two real world data sets.Item Pick-by-Vision: An Augmented Reality supported Picking System(Václav Skala - UNION Agency, 2009) Reif, Rupert; Günthner, Willibald A.; Chen, Min; Skala, VáclavOrder picking is one of the most important process steps in logistics. Because of their flexibility human beings cannot be replaced by machines. But if workers in order picking systems are equipped with a head-mounted display, Augmented Reality can improve the information visualization. In this paper the development of such a system – called Pick-by-Vision - is presented. The system is evaluated in a user study performed in a real storage environment. Important logistics figures as well as subjective figures were measured. The results show that Pick-by-Vision can improve considerably order picking processes.
