33-Issue 6

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https://diglib.eg.org/handle/10.2312/11788

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State-of-the-Art in Compressed GPU-Based Direct Volume Rendering
(The Eurographics Association and John Wiley and Sons Ltd., 2014) Rodríguez, M. Balsa; Gobbetti, E.; Guitián, J.A. Iglesias; Makhinya, M.; Marton, F.; Pajarola, R.; Suter, S.K.; Oliver Deussen and Hao (Richard) Zhang
Great advancements in commodity graphics hardware have favoured graphics processing unit (GPU)-based volume rendering as the main adopted solution for interactive exploration of rectilinear scalar volumes on commodity platforms. Nevertheless, long data transfer times and GPU memory size limitations are often the main limiting factors, especially for massive, time-varying or multi-volume visualization, as well as for networked visualization on the emerging mobile devices. To address this issue, a variety of level-of-detail (LOD) data representations and compression techniques have been introduced. In order to improve capabilities and performance over the entire storage, distribution and rendering pipeline, the encoding/decoding process is typically highly asymmetric, and systems should ideally compress at data production time and decompress on demand at rendering time. Compression and LOD pre-computation does not have to adhere to real-time constraints and can be performed off-line for high-quality results. In contrast, adaptive real-time rendering from compressed representations requires fast, transient and spatially independent decompression. In this report, we review the existing compressed GPU volume rendering approaches, covering sampling grid layouts, compact representation models, compression techniques, GPU rendering architectures and fast decoding techniques.GPU-based volume rendering is the major currently adopted solution for interactive exploration of rectilinear scalar volumes on commodity platforms. Nevertheless, long data transfer times and GPU memory size limitations are often the main limiting factors, especially for massive, time-varying or multi-volume visualization, as well as for networked visualization on the emerging mobile devices. This article reviews the existing compressed GPU volume rendering approaches, covering sampling grid layouts, compact representation models, compression techniques, GPU rendering architectures and fast decoding techniques.
A Survey on Procedural Modelling for Virtual Worlds
(The Eurographics Association and John Wiley and Sons Ltd., 2014) Smelik, Ruben M.; Tutenel, Tim; Bidarra, Rafael; Benes, Bedrich; Oliver Deussen and Hao (Richard) Zhang
Procedural modelling deals with (semi-)automatic content generation by means of a program or procedure. Among other advantages, its data compression and the potential to generate a large variety of detailed content with reduced human intervention, have made procedural modelling attractive for creating virtual environments increasingly used in movies, games and simulations. We survey procedural methods that are useful to generate features of virtual worlds, including terrains, vegetation, rivers, roads, buildings and entire cities. In this survey, we focus particularly on the degree of intuitive control and of interactivity offered by each procedural method, because these properties are instrumental for their typical users: designers and artists. We identify the most promising research results that have been recently achieved, but we also realize that there is far from widespread acceptance of procedural methods among non‐technical, creative professionals. We conclude by discussing some of the most important challenges of procedural modelling.Procedural modeling deals with (semi‐)automatic content generation by means of a procedure. This article surveys procedural methods that generate features of virtual worlds, including terrain, vegetation and cities. Promising results are identified, and the most salient challenges are discussed. A special focus is put on their degree of control and interactivity, essential for a more widespread use by creative professionals.
A Survey on Position-Based Simulation Methods in Computer Graphics
(The Eurographics Association and John Wiley and Sons Ltd., 2014) Bender, Jan; Müller, Matthias; Otaduy, Miguel A.; Teschner, Matthias; Macklin, Miles; Oliver Deussen and Hao (Richard) Zhang
The dynamic simulation of mechanical effects has a long history in computer graphics. The classical methods in this field discretize Newton's second law in a variety of Lagrangian or Eulerian ways, and formulate forces appropriate for each mechanical effect: joints for rigid bodies; stretching, shearing or bending for deformable bodies and pressure, or viscosity for fluids, to mention just a few. In the last years, the class of position-based methods has become popular in the graphics community. These kinds of methods are fast, stable and controllable which make them well-suited for use in interactive environments. Position-based methods are not as accurate as force-based methods in general but they provide visual plausibility. Therefore, the main application areas of these approaches are virtual reality, computer games and special effects in movies. This state-of-the-art report covers the large variety of position-based methods that were developed in the field of physically based simulation. We will introduce the concept of position-based dynamics, present dynamic simulation based on shape matching and discuss data-driven upsampling approaches. Furthermore, we will present several applications for these methods.The dynamic simulation of mechanical effects has a long history in computer graphics. The classical methods in this field discretize Newton's second law in a variety of Lagrangian or Eulerian ways, and formulate forces appropriate for each mechanical effect: joints for rigid bodies; stretching, shearing, or bending for deformable bodies; and pressure, or viscosity for fluids, to mention just a few. In the last years the class of position-based methods has become popular in the graphics community. These kinds of methods are fast, stable and controllable which make them well-suited for use in interactive environments. Position-based methods are not as accurate as force-based methods in general but they provide visual plausibility. This state-of-the-art report covers the large variety of position-based methods that were developed in the field of physically based simulation. This state-of-the-art report covers the large variety of position-based methods that were developed in the field of physically based simulation.
Editorial
(The Eurographics Association and Blackwell Publishing Ltd., 2014) Holly Rushmeier and Oliver Deussen
Procedural Modelling of Urban Road Networks
(The Eurographics Association and John Wiley and Sons Ltd., 2014) Bene , Jan; Wilkie, Alexander; Krivánek, Jaroslav; Oliver Deussen and Hao (Richard) Zhang
We present a model for growing procedural road networks in and close to cities. The main idea of our paper is that a city cannot be meaningfully simulated without taking its neighbourhood into account. A simple traffic simulation that considers this neighbourhood is then used to grow new major roads and to influence the locations of minor road growth. Waterways are introduced and used to help position the city nuclei on the map. The resulting cities are formed by allowing several smaller settlements to grow together and to form a rich road structure, much like in real world, and require only minimal per-city input, allowing for batch generation.We present a model for growing procedural road networks in and close to cities. The main idea of our paper is that a city cannot be meaningfully simulated without taking its neighbourhood into account. A simple traffic simulation that considers this neighbourhood is then used to grow new major roads and to influence the locations of minor road growth. Waterways are introduced and used to help position the city nuclei on the map. The resulting cities are formed by allowing several smaller settlements to grow together and to form a rich road structure, much like in real world, and require only minimal per-city input, allowing for batch generation.
Visual Analysis of Trajectories in Multi-Dimensional State Spaces
(The Eurographics Association and John Wiley and Sons Ltd., 2014) Grottel, S.; Heinrich, J.; Weiskopf, D.; Gumhold, S.; Oliver Deussen and Hao (Richard) Zhang
Multi-dimensional data originate from many different sources and are relevant for many applications. One specific sub-type of such data is continuous trajectory data in multi-dimensional state spaces of complex systems. We adapt the concept of spatially continuous scatterplots and spatially continuous parallel coordinate plots to such trajectory data, leading to continuous-time scatterplots and continuous-time parallel coordinates. Together with a temporal heat map representation, we design coordinated views for visual analysis and interactive exploration. We demonstrate the usefulness of our visualization approach for three case studies that cover examples of complex dynamic systems: cyber-physical systems consisting of heterogeneous sensors and actuators networks (the collection of time-dependent sensor network data of an exemplary smart home environment), the dynamics of robot arm movement and motion characteristics of humanoids.Multi-dimensional data originate from many different sources and are relevant for many applications. One specific sub-type of such data is continuous trajectory data in multi-dimensional state spaces of complex systems. We adapt the concept of spatially continuous scatterplots and spatially continuous parallel coordinate plots to such trajectory data, leading to continuous-time scatterplots and continuous-time parallel coordinates. Together with a temporal heat map representation, we design coordinated views for visual analysis and interactive exploration.
Continuous Self-Collision Detection for Deformable Surfaces Interacting with Solid Models
(The Eurographics Association and John Wiley and Sons Ltd., 2014) Wong, Sai-Keung; Cheng, Yu-Chun; Oliver Deussen and Hao (Richard) Zhang
In this paper, we propose a new continuous self-collision detection (CSCD) method for a deformable surface that interacts with a simple solid model. The method is developed based on the radial-view-based culling method. Our method is suitable for the deformable surface that has large contact region with the solid model. The deformable surface may consist of small round-shaped holes. At the pre-processing stage, the holes of the deformable surface are filled with ghost triangles so as to make the mesh of the deformable surface watertight. An observer primitive (i.e. a point or a line segment) is computed so that it lies inside the solid model. At the runtime stage, the orientations of triangles with respect to the observer primitive are evaluated. The collision status of the deformable surface is then determined. We evaluated our method for several animations including virtual garments. Experimental results show that our method improves the process of CSCD.In this paper, we propose a new Q4 continuous self-collision detection (CSCD) method for a deformable surface that interacts with a simple solid model. The method is developed based on the radial-view-based culling method. Our method is suitable for the deformable surface that has large contact region with the solid model. The deformable surface may consist of small round-shaped holes. At the pre-processing stage, the holes of the deformable surface are filled with ghost triangles so as to make the mesh of the deformable surface watertight. An observer primitive (i.e. a point or a line segment) is computed so that it lies inside the solid model.
Robust Detection and Segmentation for Diagnosis of Vertebral Diseases Using Routine MR Images
(The Eurographics Association and John Wiley and Sons Ltd., 2014) Zukic, D enan; Vlasák, Ale; Egger, Jan; Horínek, Daniel; Nimsky, Christopher; Kolb, Andreas; Oliver Deussen and Hao (Richard) Zhang
The diagnosis of certain spine pathologies, such as scoliosis, spondylolisthesis and vertebral fractures, is part of the daily clinical routine. Very frequently, magnetic resonance image data are used to diagnose these kinds of pathologies in order to avoid exposing patients to harmful radiation, like X-ray. We present a method which detects and segments all acquired vertebral bodies, with minimal user intervention. This allows an automatic diagnosis to detect scoliosis, spondylolisthesis and crushed vertebrae. Our approach consists of three major steps. First, vertebral centres are detected using a Viola Jones like method, and then the vertebrae are segmented in a parallel manner, and finally, geometric diagnostic features are deduced in order to diagnose the three diseases. Our method was evaluated on 26 lumbar datasets containing 234 reference vertebrae. Vertebra detection has 7.1% false negatives and 1.3% false positives. The average Dice coefficient to manual reference is 79.3% and mean distance error is 1.76 mm. No severe case of the three illnesses was missed, and false alarms occurred rarely 0% for scoliosis, 3.9% for spondylolisthesis and 2.6% for vertebral fractures. The main advantages of our method are high speed, robust handling of a large variety of routine clinical images, and simple and minimal user interaction.The diagnosis of certain spine pathologies, such as scoliosis, spondylolisthesis and vertebral fractures, are part of the daily clinical routine. Very frequently, MRI data are used to diagnose these kinds of pathologies in order to avoid exposing patients to harmful radiation, like X-ray. We present a method which detects and segments all acquired vertebral bodies, with minimal user intervention. This allows an automatic diagnosis to detect scoliosis, spondylolisthesis and crushed vertebrae.
GEARS: A General and Efficient Algorithm for Rendering Shadows
(The Eurographics Association and John Wiley and Sons Ltd., 2014) Wang, Lili; Zhou, Shiheng; Ke, Wei; Popescu, Voicu; Oliver Deussen and Hao (Richard) Zhang
We present a soft shadow rendering algorithm that is general, efficient and accurate. The algorithm supports fully dynamic scenes, with moving and deforming blockers and receivers, and with changing area light source parameters. For each output image pixel, the algorithm computes a tight but conservative approximation of the set of triangles that block the light source as seen from the pixel sample. The set of potentially blocking triangles allows estimating visibility between light points and pixel samples accurately and efficiently. As the light source size decreases to a point, our algorithm converges to rendering pixel accurate hard shadows.We present a soft shadow rendering algorithm that is general, efficient and accurate. The algorithm supports fully dynamic scenes, with moving and deforming blockers and receivers, and with changing area light source parameters. For each output image pixel, the algorithm computes a tight but conservative approximation of the set of triangles that block the light source as seen from the pixel sample. The set of potentially blocking triangles allows estimating visibility between light points and pixel samples accurately and efficiently. As the light source size decreases to a point, our algorithm converges to rendering pixel accurate hard shadows.
Inherent Noise-Aware Insect Swarm Simulation
(The Eurographics Association and John Wiley and Sons Ltd., 2014) Wang, Xinjie; Jin, Xiaogang; Deng, Zhigang; Zhou, Linling; Oliver Deussen and Hao (Richard) Zhang
Collective behaviour of winged insects is a wondrous and familiar phenomenon in the real world. In this paper, we introduce a highly efficient field-based approach to simulate various insect swarms. Its core idea is to construct a smooth yet noise-aware governing velocity field that can be further decomposed into two sub-fields: (i) a divergence-free curl-noise field to model noise-induced movements of individual insects in a swarm, and (ii) an enhanced global velocity field to control navigational paths in a complex environment along which all the insects in a swarm fly. Through simulation experiments and comparisons with existing crowd simulation approaches, we demonstrate that our approach is effective to simulate various insect swarm behaviours including aggregation, positive phototaxis, sedation, mass-migrating, and so on. Besides its high efficiency, our approach is very friendly to parallel implementation on GPUs (e.g. the speedup achieved through GPU acceleration is higher than 50 if the number of simulated insects is more than 10 000 on an off-the-shelf computer). Our approach is the first multi-agent modelling system that introduces curl-noise into agents' velocity field and uses its non-scattering nature to maintain non-colliding movements in 3D crowd simulation.Collective behavior of winged insects is a wondrous and familiar phenomenon in the real world. In this paper, we introduce a highly efficient field-based approach to simulate various insect swarms. Its core idea is to construct a smooth yet noise-aware governing velocity field that can be further decomposed into two sub-fields: (i) a divergence-free curl noise field to model noise-induced movements of individual insects in a swarm, and (ii) an enhanced global velocity field to control navigational paths in a complex environment along which all the insects in a swarm fly.
PackMerger: A 3D Print Volume Optimizer
(The Eurographics Association and John Wiley and Sons Ltd., 2014) Vanek, J.; Galicia, J. A. Garcia; Benes, B.; Mech, R.; Carr, N.; Stava, O.; Miller, G. S.; Oliver Deussen and Hao (Richard) Zhang
We propose an optimization framework for 3D printing that seeks to save printing time and the support material required to print 3D shapes. Three-dimensional printing technology is rapidly maturing and may revolutionize how we manufacture objects. The total cost of printing, however, is governed by numerous factors which include not only the price of the printer but also the amount of material and time to fabricate the shape. Our PackMerger framework converts the input 3D watertight mesh into a shell by hollowing its inner parts. The shell is then divided into segments. The location of splits is controlled based on several parameters, including the size of the connection areas or volume of each segment. The pieces are then tightly packed using optimization. The optimization attempts to minimize the amount of support material and the bounding box volume of the packed segments while keeping the number of segments minimal. The final packed configuration can be printed with substantial time and material savings, while also allowing printing of objects that would not fit into the printer volume. We have tested our system on three different printers and it shows a reduction of 5 30% of the printing time while simultaneously saving 15 65% of the support material. The optimization time was approximately 1 min. Once the segments are printed, they need to be assembled.We propose an optimization framework for 3D printing that seeks to save printing time and the support material required to print 3D shapes. 3D printing technology is rapidly maturing and may revolutionize how we manufacture objects. The total cost of printing, however, is governed by numerous factors which include not only the price of the printer but also the amount of material and time to fabricate the shape. Our PackMerger framework converts the input 3D watertight mesh into a shell by hollowing its inner parts. The shell is then divided into segments. The pieces are then tightly packed using optimization. The optimization attempts to minimize the amount of support material and the bounding box volume of the packed segments.
Out-of-Core Construction of Sparse Voxel Octrees
(The Eurographics Association and John Wiley and Sons Ltd., 2014) Baert, J.; Lagae, A.; Dutré, Ph.; Oliver Deussen and Hao (Richard) Zhang
Voxel-based rendering has recently received significant attention due to its potential in the context of efficiently rendering massively large and highly detailed scenes. Unfortunately, few scenes are available in the form of sparse voxel octrees. In this paper, we present an out-of-core algorithm for constructing a sparse voxel octree from a triangle mesh. Our algorithm allows the input triangle mesh, the output sparse voxel octree and, most importantly, the intermediate high-resolution 3D voxel grid, to be larger than available memory. We demonstrate that our out-of-core algorithm can construct sparse voxel octrees from triangle meshes using only a fraction of the memory required by an in-core algorithm in roughly the same time, and that our out-of-core algorithm can also handle extremely large triangle meshes.We present an out-of-core algorithm for constructing a sparse voxel octree from a triangle mesh. Our out-of-core algorithm can construct sparse voxel octrees from triangle meshes using only a fraction of the memory required by an in-core algorithm in roughly the same time, and our out-of-core algorithm can also handle extremely large triangle meshes
Distributed Out-of-Core Stochastic Progressive Photon Mapping
(The Eurographics Association and John Wiley and Sons Ltd., 2014) Günther, Tobias; Grosch, Thorsten; Oliver Deussen and Hao (Richard) Zhang
At present, stochastic progressive photon mapping (SPPM) is one of the most comprehensive methods for a consistent global illumination computation. Even though the number of photons is unlimited due to their progressive nature, the scene size is still bound by the available main memory. In this paper, we present the first consistent out-of-core SPPM algorithm. In order to cope with large scenes, we automatically subdivide the geometry and parallelly trace photons and eye rays in a portal-based system, distributed across multiple machines in a commodity cluster. Moreover, modifications of the original SPPM method are introduced that keep both the utilization of tracer machines high and the network traffic low. Therefore, compared to a portal-based single machine setup, our distributed approach achieves a significant speedup. We compare a GPU-based with a CPU-based implementation and demonstrate our system in multiple large test scenes of up to 90 million triangles.At present, stochastic progressive Q21 photon mapping (SPPM) is one of the most comprehensive methods for a consistent global illumination computation. Even though the number of photons is unlimited due to its progressive nature, the scene size is still bound by the available main memory. In this paper, we present the first consistent out-of-core SPPM algorithm. In order to cope with large scenes, we automatically subdivide the geometry and parallelly trace photons and eye rays in a portal-based system, distributed across multiple machines in a commodity cluster. Moreover, modifications of the original SPPM method are introduced that keep both the utilization of tracer machines high and the network traffic low.
Photon Differential Splatting for Rendering Caustics
(The Eurographics Association and John Wiley and Sons Ltd., 2014) Frisvad, Jeppe Revall; Schjøth, Lars; Erleben, Kenny; Sporring, Jon; Oliver Deussen and Hao (Richard) Zhang
We present a photon splatting technique which reduces noise and blur in the rendering of caustics. Blurring of illumination edges is an inherent problem in photon splatting, as each photon is unaware of its neighbours when being splatted. This means that the splat size is usually based on heuristics rather than knowledge of the local flux density. We use photon differentials to determine the size and shape of the splats such that we achieve adaptive anisotropic flux density estimation in photon splatting. As compared to previous work that uses photon differentials, we present the first method where no photons or beams or differentials need to be stored in a map. We also present improvements in the theory of photon differentials, which give more accurate results and a faster implementation. Our technique has good potential for GPU acceleration, and we limit the number of parameters requiring user adjustment to an overall smoothing parameter and the number of photons to be traced.Technique for anisotropic flux density estimation in photon splatting when rendering caustics. The attached graphics compare renderings obtained in equal time when using existing splatting techniques (left and middle) and when using our technique (right). The visual improvement is sharper edges and smoother soft illumination.
Flux-Limited Diffusion for Multiple Scattering in Participating Media
(The Eurographics Association and John Wiley and Sons Ltd., 2014) Koerner, D.; Portsmouth, J.; Sadlo, F.; Ertl, T.; Eberhardt, B.; Oliver Deussen and Hao (Richard) Zhang
For the rendering of multiple scattering effects in participating media, methods based on the diffusion approximation are an extremely efficient alternative to Monte Carlo path tracing. However, in sufficiently transparent regions, classical diffusion approximation suffers from non-physical radiative fluxes which leads to a poor match to correct light transport. In particular, this prevents the application of classical diffusion approximation to heterogeneous media, where opaque material is embedded within transparent regions. To address this limitation, we introduce flux-limited diffusion, a technique from the astrophysics domain. This method provides a better approximation to light transport than classical diffusion approximation, particularly when applied to heterogeneous media, and hence broadens the applicability of diffusion-based techniques. We provide an algorithm for flux-limited diffusion, which is validated using the transport theory for a point light source in an infinite homogeneous medium. We further demonstrate that our implementation of flux-limited diffusion produces more accurate renderings of multiple scattering in various heterogeneous datasets than classical diffusion approximation, by comparing both methods to ground truth renderings obtained via volumetric path tracing.For the rendering of multiple scattering effects in participating media, methods based on the diffusion approximation are an extremely efficient alternative to Monte Carlo path tracing. However, in sufficiently transparent regions, classical diffusion approximation suffers from non-physical radiative fluxes which leads to a poor match to correct light transport. In particular, this prevents the application of classical diffusion approximation to heterogeneous media, where opaque material is embedded within transparent regions. To address this limitation, we introduce flux-limited diffusion, a technique from the astrophysics domain. This method provides a better approximation to light transport than classical diffusion approximation, particularly when applied to heterogeneous media, and hence broadens the applicability of diffusion-based techniques.
SATO: Surface Area Traversal Order for Shadow Ray Tracing
(The Eurographics Association and John Wiley and Sons Ltd., 2014) Nah, Jae-Ho; Manocha, Dinesh; Oliver Deussen and Hao (Richard) Zhang
We present the surface area traversal order (SATO) metric to accelerate shadow ray traversal. Our formulation uses the surface area of each child node to compute the TO. In this metric, we give a traversal priority to the child node with the larger surface area to quickly find occluders. Our algorithm reduces the pre-processing overhead significantly, and is much faster than other metrics. Overall, the SATO is useful for ray tracing large and complex dynamic scenes (e.g. a few million triangles) with shadows.We present the surface-area traversal order (SATO) metric to accelerate shadow ray traversal. Our formulation uses the surface area of each child node to compute the traversal order. Our algorithm reduces the preprocessing overhead significantly, and is much faster than other metrics.
Symmetry-Aware Template Deformation and Fitting
(The Eurographics Association and John Wiley and Sons Ltd., 2014) Kurz, C.; Wu, X.; Wand, M.; Thormählen, T.; Kohli, P.; Seidel, H.-P.; Oliver Deussen and Hao (Richard) Zhang
In this paper, we propose a new method for reconstructing 3D models from a noisy and incomplete 3D scan and a coarse template model. The main idea is to maintain characteristic high-level features of the template that remain unchanged for different variants of the same type of object. As invariants, we chose the partial symmetry structure of the template model under Euclidian transformations, i.e. we maintain the algebraic structure of all reflections, rotations and translations that map the object partially to itself. We propose an optimization scheme that maintains continuous and discrete symmetry properties of this kind while registering a template against scan data using a deformable iterative closest points (ICP) framework with thin-plate-spline regularization. We apply our new deformation approach to a large number of example data sets and demonstrate that symmetry-guided template matching often yields much more plausible reconstructions than previous variants of ICP.In this paper, we propose a new method for reconstructing 3D models from a noisy and incomplete 3D scan and a coarse template model. The main idea is to maintain characteristic high-level features of the template that remain unchanged for different variants of the same type of object. As invariants, we chose the partial symmetry structure of the template model under Euclidean transformations, i.e., we maintain the algebraic structure of all reflections, rotations, and translations that map the object partially to itself.
Robust Treatment of Degenerate Elements in Interactive Corotational FEM Simulations
(The Eurographics Association and John Wiley and Sons Ltd., 2014) Civit-Flores, O.; Susín, A.; Oliver Deussen and Hao (Richard) Zhang
We address the problem of robust and efficient treatment of element collapse and inversion in corotational FEM simulations of deformable objects in two and three dimensions, and show that existing degeneration treatment methods have previously unreported flaws that seriously threaten robustness and physical plausibility in interactive applications. We propose a new method that avoids such flaws, yields faster and smoother degeneration recovery and extends the range of well-behaved degenerate configurations without adding significant complexity or computational cost to standard explicit and quasi-implicit solvers.We address the problem of robust and efficient treatment of element collapse and inversion in Corotational FEM simulations of deformable objects in 2D and 3D, and show that existing degeneration treatment methods have previously unreported flaws that seriously threaten robustness and physical plausibility in interactive applications. We propose a new method that avoids such flaws, yields faster and smoother degeneration recovery and extends the range of well-behaved degenerate configurations without adding significant complexity or computational cost to standard explicit and quasi-implicit solvers.
Partial 3-D Correspondence from Shape Extremities
(The Eurographics Association and John Wiley and Sons Ltd., 2014) Sahillioglu, Y.; Yemez, Y.; Oliver Deussen and Hao (Richard) Zhang
We present a 3-D correspondence method to match the geometric extremities of two shapes which are partially isometric. We consider the most general setting of the isometric partial shape correspondence problem, in which shapes to be matched may have multiple common parts at arbitrary scales as well as parts that are not similar. Our rank-and-vote-and-combine algorithm identifies and ranks potentially correct matches by exploring the space of all possible partial maps between coarsely sampled extremities. The qualified top-ranked matchings are then subjected to a more detailed analysis at a denser resolution and assigned with confidence values that accumulate into a vote matrix. A minimum weight perfect matching algorithm is finally iterated to combine the accumulated votes into an optimal (partial) mapping between shape extremities, which can further be extended to a denser map. We test the performance of our method on several data sets and benchmarks in comparison with state of the art.We present a 3D correspondence method to match the geometric extremities of two shapes which are partially isometric. We consider the most general setting of the isometric partial shape correspondence problem, in which shapes to be matched may have multiple common parts at arbitrary scales as well as parts that are not similar. Our rank-and-voteand-combine (RAVAC) algorithm identifies and ranks potentially correct matches by exploring the space of all possible partial maps between coarsely sampled extremities. The qualified top-ranked matchings are then subjected to a more detailed analysis at a denser resolution and assigned with confidence values that accumulate into a vote matrix.
Inverse Procedural Modelling of Trees
(The Eurographics Association and John Wiley and Sons Ltd., 2014) Stava, O.; Pirk, S.; Kratt, J.; Chen, B.; Mech, R.; Deussen, O.; Benes, B.; Oliver Deussen and Hao (Richard) Zhang
Procedural tree models have been popular in computer graphics for their ability to generate a variety of output trees from a set of input parameters and to simulate plant interaction with the environment for a realistic placement of trees in virtual scenes. However, defining such models and their parameters is a difficult task. We propose an inverse modelling approach for stochastic trees that takes polygonal tree models as input and estimates the parameters of a procedural model so that it produces trees similar to the input. Our framework is based on a novel parametric model for tree generation and uses Monte Carlo Markov Chains to find the optimal set of parameters. We demonstrate our approach on a variety of input models obtained from different sources, such as interactive modelling systems, reconstructed scans of real trees and developmental models.Procedural tree models have been popular in computer graphics for their ability to generate a variety of output trees from a set of input parameters and to simulate plant interaction with the environment for a realistic placement of trees in virtual scenes. However, defining such models and their parameters is a difficult task. We propose an inverse modeling approach for stochastic trees that takes polygonal tree models as input and estimates the parameters of a procedural model so that it produces trees similar to the input.

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