Short Papers
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Item Automatic Line Handles for Freeform Deformation(The Eurographics Association, 2012) Schemali, Leïla; Thiery, Jean-Marc; Boubekeur, Tamy; Carlos Andujar and Enrico PuppoInteractive freeform surface deformation methods allow to explore the space of possible shapes using simple control structures. While recent advances in variational editing provide high quality deformations, designing control structures remains a time-consuming manual process. We propose a new automatic control structure generation based on the observation that the most salient visual structures of a surface, such as the one exploited in Line Drawing methods, are tightly linked to the potential deformations it may undergo. Our basic idea is to build control structures from those lines in order to provide users with an automatic set of deformation handles to grab and manipulate, avoiding the tedious task of region selection and handle positioning. The resulting interface inherits view-dependency and adaptivity from line definitions, reduces significantly the modeling session time in a number of scenarii, and remains fully compatible with classical handle-based deformations.Item Automatic Multi-view Surface Matching(The Eurographics Association, 2012) Fantoni, Simone; Castellani, Umberto; Fusiello, Andrea; Carlos Andujar and Enrico PuppoIn this paper we tackle the problem of automatically aligning an unordered set of range views. We propose a full pipeline that goes from the scans to the complete 3D model. The emphasis is on the automation no manual intervention is require and on the fact that no knowledge on the acquisition sequence is assumed. The contribution is twofold: in the pre-alignment phase a voting scheme is proposed that discovers the overlapping relationship among views; in the final refinement step we extend the Levenberg Marquardt-ICP to work with multiple views, in order to solve for the absolute pose of all images simultaneously.Item Efficient Evaluation of Semi-Smooth Creases in Catmull-Clark Subdivision Surfaces(The Eurographics Association, 2012) Nießner, Matthias; Loop, Charles; Greiner, Günther; Carlos Andujar and Enrico PuppoWe present a novel method to evaluate semi-smooth creases in Catmull-Clark subdivision surfaces. Our algorithm supports both integer and fractional crease tags corresponding to the RenderMan (Pixar) specification. In order to perform fast and efficient surface evaluations, we obtain a polynomial surface representation given by the semismooth subdivision rules. While direct surface evaluation is applied for regular patches, we perform adaptive subdivision around extraordinary vertices. In the end, we are able to efficently handle high-order sharpness tags at very low cost. Compared to the state-of-the art, both render time and memory consumption are reduced from exponential to linear complexity. Furthermore, we integrate our algorithm in the hardware tessellation pipeline of modern GPUs. Our method is ideally suited to real-time applications such as games or authoring tools.Item Example-based Road Network Synthesis(The Eurographics Association, 2012) Yu, Qizhi; Steed, Anthony; Carlos Andujar and Enrico PuppoWe present a novel method for automatically synthesizing road networks that are perceptually similar to given example road networks. Our algorithm can grow a new road network from an initial node or expand an existing network. For an unfinished node in the network, we search a set of candidate nodes in the example road networks that have similar node topology, and then find a best one by neighborhood edge matching. Rather than simply copy edges incident to the best matched node, we consider the local constraints including obstacle avoidance and relationships to existing roads. Our results demonstrate that the method produces good results for various typical street patterns. Furthermore, we can blend styles of road networks in an intuitive and easy to control manner.Item Fast Response and Quick Progressive Transitions using Body Part Motion Graphs(The Eurographics Association, 2012) Fernández-Baena, Adso; Miralles, David; Carlos Andujar and Enrico PuppoInteractive applications where 3D character animation plays an important role need avatars ready to perform different activities. This objective has been accomplished in different works [LCR*02] [ZS09] that look for transition points in motion capture clips to allow transitions between them. These works ensure realism and smoothness but their responses and transition durations depend on transition points. Working with partial motions, such as body part motions, allows finding specific transition points for each part in order to optimize whole body transitions in a progressive way. This can be achieved with body part motion graphs (BPMG’s) [FBM11]. In this work we want to show that progressive transitions generated by BPMG’s have fast response and quick execution. In order to demonstrate this we have compared BPMG’s transitions against standard motion graphs (SMG) transitions. The results we have obtained show that our method allows more reaction velocity and execution. Moreover BPMG’s transitions are smoother than SMG transitions.Item Forward+: Bringing Deferred Lighting to the Next Level(The Eurographics Association, 2012) Harada, Takahiro; McKee, Jay; Yang, Jason C.; Carlos Andujar and Enrico PuppoThis paper presents Forward+, a method of rendering many lights by culling and storing only lights that contribute to the pixel. Forward+ is an extension to traditional forward rendering. Light culling, implemented using the compute capability of the GPU, is added to the pipeline to create lists of lights; that list is passed to the final rendering shader, which can access all information about the lights. Although Forward+ increases workload to the final shader, it theoretically requires less memory traffic compared to compute-based deferred lighting. Furthermore, it removes the major drawback of deferred techniques, which is a restriction of materials and lighting models. Experiments are performed to compare the performance of Forward+ and deferred lighting.Item FTLE Computation Beyond First-Order Approximation(The Eurographics Association, 2012) Üffinger, Markus; Sadlo, Filip; Kirby, Mike; Hansen, Charles; Ertl, Thomas; Carlos Andujar and Enrico PuppoWe present a framework for different approaches to finite-time Lyapunov exponent (FTLE) computation for 2D vector fields, based on the advection of seeding circles. On the one hand it unifies the popular flow map approach with techniques based on the evaluation of distinguished trajectories, such as renormalization. On the other hand it allows for the exploration of their order of approximation (first-order approximation representing the flow map gradient). Using this framework, we derive a measure for nonlinearity of the flow map, that brings us to the definition of a new FTLE approach. We also show how the nonlinearity measure can be used as a criterion for flow map refinement for more accurate FTLE computation, and we demonstrate that ridge extraction in supersampled FTLE leads to superior ridge quality.Item Geometric Details on Skeleton-based Implicit Surfaces(The Eurographics Association, 2012) Zanni, Cedric; Bares, P.; Lagae, Ares; Quiblier, M.; Cani, Marie-Paule; Carlos Andujar and Enrico PuppoWe present a modeling technique to enhance implicit surfaces with procedural geometric details. The details are based on Gabor noise, which enables us to seamlessly handle anisotropy. The orientation of details can be defined with respect to the orientation of the main shape features, which reduces the amount of user input. The method extends to complex details that are tilted with respect to the normal of the input surface. Lastly, our method allows the blending of the resulting enhanced implicit primitives without causing the details to blur.Item GPU based ARAP Deformation using Volumetric Lattices(The Eurographics Association, 2012) Zollhöfer, Michael; Sert, Ezgi; Greiner, Günther; Süßmuth, Jochen; Carlos Andujar and Enrico PuppoWe present a novel lattice based direct manipulation paradigm (LARAP) for mesh editing that decouples the runtime complexity from the mesh’s geometric complexity. Since our non-linear optimization is based on the ARAP paradigm, it is very fast and can be easily implemented. Our proxy geometry automatically introduces volumeawareness into the optimization problem, leading to more natural deformations. Since we compute how the space surrounding an object has to be deformed to satisfy a set of user-constraints, we can even handle models with disconnected parts. We analyze the bottlenecks of the presented approach and propose a data-parallel multiresolution implementation on the GPU, which allows to pose even high-quality meshes consisting of millions of triangles in real-time.Item Growing Cell Structures Learning a Progressive Mesh During Surface Reconstruction - A Top-Down Approach(The Eurographics Association, 2012) Vierjahn, Tom; Lorenz, Guido; Mostafawy, Sina; Hinrichs, Klaus; Carlos Andujar and Enrico PuppoGrowing Cell Structures (GCS) have been proven to be suitable for surface reconstruction from unstructured point clouds. The reconstructed triangle mesh can be represented compactly as a progressive mesh with integrated level of detail by storing only vertex split operations. However, half-edge collapse operations are used for GCS. In this paper, we present an improvement to a GCS-based surface reconstruction technique by converting a halfedge collapse to a more general vertex removal to create a progressive mesh. We have evaluated the new technique with respect to running time overhead and mesh quality. Results indicate that this technique can be used for efficient surface reconstruction. We will use the presented findings as basis for future research.Item Hybrid CPU/GPU KD-Tree Construction for Versatile Ray Tracing(The Eurographics Association, 2012) Roccia, Jean-Patrick; Paulin, Mathias; Coustet, Christophe; Carlos Andujar and Enrico PuppoWe propose an hybrid CPU-GPU ray-tracing implementation based on an optimal Kd-Tree as acceleration structure. The construction and traversal of this KD-tree takes benefit from both the CPU and the GPU to achieve high-performance ray-tracing on mainstream hardware. Our approach, flexible enough to use only a single computing unit (CPU or GPU), is able to efficiently distribute workload between CPUs and GPUs for fast KD-tree construction and traversal.Item Hyperplane Culling for Stochastic Rasterization(The Eurographics Association, 2012) Munkberg, Jacob; Akenine-Möller, Tomas; Carlos Andujar and Enrico PuppoWe present two novel culling tests for rasterization of simultaneous depth of field and motion blur. These tests efficiently reduce the set of xyuvt samples that need to be coverage tested within a screen space tile. The first test finds linear bounds in ut- and vt-space using a separating line algorithm. We also derive a hyperplane in xyuvtspace for each triangle edge, and all samples outside of these planes are culled in our second test. Based on these tests, we present an efficient stochastic rasterizer, which has substantially higher sample test efficiency and lower arithmetic cost than previous tile-based stochastic rasterizers.Item Image-based Animation of Clothes(The Eurographics Association, 2012) Hilsmann, Anna; Eisert, Peter; Carlos Andujar and Enrico PuppoWe propose a pose-dependent image-based rendering approach for the visualization of clothes with very high rendering quality. Our representation combines body-pose-dependent geometry and appearance. A geometric model accounts for low-resolution shape adaptation, e.g. animation and view interpolation, while small details as well as complex shading/reflection properties are accounted for through numerous images. Information on shading, texture distortion and silhouette at fine wrinkles are extracted from the images to allow later texture replacement. The image-based representations are estimated in advance from real samples of clothes captured in an offline process, thus shifting computational complexity into the training phase. For rendering, pose dependent geometry and appearance are interpolated and merged from the stored representations.Item Improved Obstacle Relevancy, Distance, and Angle for Crowds Constrained to Arbitrary Manifolds in 3D Space(The Eurographics Association, 2012) Ricks, Brian C.; Egbert, Parris K.; Carlos Andujar and Enrico PuppoRecent work has proposed crowd simulation algorithms on arbitrary manifolds in 3D space. These algorithms simulate crowds on far more realistic surfaces than previously possible, including multi-story structures, science fiction scenarios, and habitats for insects and other animals that can walk on walls. However, current implementations can have distinct artifacts, including collision false positives and false negatives. Also, current implementations fail to account for the cylindrical shape of the characters being simulated. The resulting crowds move unnaturally and have obvious collisions. After identifying the cause of these artifacts, we propose an algorithm that does not struggle from these false positives or false negatives and correctly accounts for the non-spherical shape of agents. The resulting crowds move on large surfaces (over 100k triangles) running with a thousand agents in real-time.Item Incoherent Ray Tracing without Acceleration Structures(The Eurographics Association, 2012) Áfra, Attila T.; Carlos Andujar and Enrico PuppoRecently, a new family of dynamic ray tracing algorithms, called divide-and-conquer ray tracing, has been introduced. This approach partitions the primitives on-the-fly during ray traversal, which eliminates the need for an acceleration structure. We present a new ray traversal method based on this principle, which efficiently handles incoherent rays, and takes advantage of the SSE and AVX instruction sets of the CPU. Our algorithm offers notable performance improvements over similar existing solutions, and it is competitive with powerful static ray tracers.Item Perceptually Based Afterimage Synthesis(The Eurographics Association, 2012) Mikamo, Michihiro; Slomp, Marcos; Raytchev, Bisser; Tamaki, Toru; Kaneda, Kazufumi; Carlos Andujar and Enrico PuppoAfterimages comprise a common, recurring perceptual phenomenon experienced in a daily-basis. Afterimages are best realized when staring at some high intensity light source (i.e., a light bulb) and then shifting the ocular focus to other less luminous portions of the scene: a temporary “ghost” image of that strong intensity remains imprinted on the retina. During the time the afterimage stays active, several exquisite color gradations appear and fade. Although research on the topic has been moderately active in ophthalmology and vision domains, no definitive model has been devised. Furthermore, no afterimage simulation seems to have yet been investigated in computer graphics. In this paper we attempt to introduce the topic to the field and therefore widen the research spectrum of computer graphics. The proposed technique is based on psychophysical and physiological evidence, addressing the color transitions and the duration of the effect. The method is also fast and suitable for real-time applications. Our stance towards afterimages is more than just curiosity on this peculiar effect: we believe that its understanding and proper simulation can assist on relevant tasks such as urban and road engineering for safer pedestrian and vehicle mobility at adverse lighting conditions.Item Physically-Based Depth of Field in Augmented Reality(The Eurographics Association, 2012) Kán, Peter; Kaufmann, Hannes; Carlos Andujar and Enrico PuppoWe present a novel method for rendering and compositing video in augmented reality. We focus on calculating the physically correct result of the depth of field caused by a lens with finite sized aperture. In order to correctly simulate light transport, ray-tracing is used and in a single pass combined with differential rendering to compose the final augmented video. The image is fully rendered on GPUs, therefore an augmented video can be produced at interactive frame rates in high quality. Our method runs on the fly, no video postprocessing is needed. In addition we evaluated the user experiences with our rendering system with the hypothesis that a depth of field effect in augmented reality increases the realistic look of composited video. Results with 30 users show that 90% perceive videos with a depth of field considerably more realistic.Item Real-Time Metaball Ray Casting with Fragment Lists(The Eurographics Association, 2012) Szécsi, László; Illés, Dávid; Carlos Andujar and Enrico PuppoIn this paper we describe a method for rendering particle-based medium representations. The algorithm builds per-pixel lists of relevant metaballs, then incrementally constructs a piecewise polynomial approximation of summed metaball densities along rays, and finds intersections with the isosurface using those. This new approach scales well for a high number of particles, it can handle local extremities of depth complexity robustly, and it does not suffer from the inaccuracies and limitations of screen-space filtering approximation methods.Item Reflective Shadow Map Clustering for Real-Time Global Illumination(The Eurographics Association, 2012) Prutkin, Roman; Kaplanyan, Anton; Dachsbacher, Carsten; Carlos Andujar and Enrico PuppoWe present a method for real-time clustering of VPLs obtained from Reflective Shadow Maps (RSM). The clusters are treated as area light sources and used to approximate indirect illumination. The spatial extent of a cluster is used to deduce the shape and size of the respective area light source. Our method is fully GPU-based and avoids flickering by temporally coherent reinitialization of the clustering. It also incorporates importance sampling for view-dependent clustering. We show visually indistinguishable results of indirect illumination with only a fraction of secondary light sources.Item Robust Outlier Removal from Point Clouds Acquired with Structured Light(The Eurographics Association, 2012) Köhler, Johannes; Nöll, Tobias; Reis, Gerd; Stricker, Didier; Carlos Andujar and Enrico PuppoWe present a method for automatic, robust identification of outliers in point clouds acquired with structured light. In contrast to most state of the art methods, we consider available 2D information instead of operating on the points only. Our method performs robust even for complex, glossy surfaces, where illumination artifacts introduce ghost geometry or outliers that seamlessly blend into the correct surface. The key idea of our algorithm is to only use cameras for reconstruction and the projector for a separate consistency check. We use encoding by phase shifting to obtain per pixel correspondences for the cameras and subpixel accuracy for the projector. The method requires at least 2 cameras, a projector and a precise calibration of all devices.