EG2021

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https://diglib.eg.org/handle/10.2312/2633001

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A Survey on Bounding Volume Hierarchies for Ray Tracing
(The Eurographics Association and John Wiley & Sons Ltd., 2021) Meister, Daniel; Ogaki, Shinji; Benthin, Carsten; Doyle, Michael J.; Guthe, Michael; Bittner, Jirí; Bühler, Katja and Rushmeier, Holly
Ray tracing is an inherent part of photorealistic image synthesis algorithms. The problem of ray tracing is to find the nearest intersection with a given ray and scene. Although this geometric operation is relatively simple, in practice, we have to evaluate billions of such operations as the scene consists of millions of primitives, and the image synthesis algorithms require a high number of samples to provide a plausible result. Thus, scene primitives are commonly arranged in spatial data structures to accelerate the search. In the last two decades, the bounding volume hierarchy (BVH) has become the de facto standard acceleration data structure for ray tracing-based rendering algorithms in offline and recently also in real-time applications. In this report, we review the basic principles of bounding volume hierarchies as well as advanced state of the art methods with a focus on the construction and traversal. Furthermore, we discuss industrial frameworks, specialized hardware architectures, other applications of bounding volume hierarchies, best practices, and related open problems.
Visualization and Graphics in Mixed Reality
(The Eurographics Association, 2021) Kalkofen, Denis; Mori, Shohei; Tatzgern, Markus; O'Sullivan, Carol and Schmalstieg, Dieter
This tutorial will present the challenges and unique aspects of mixed reality visualization applications such as organization of data for visualization, real-world data sources for visualization, real time photo-realistic rendering techniques, diminished reality rendering techniques and cognitive and perceptual issues. We are also interested in ways that the existing body of research in the graphics and visualization community can be applied in this research area. We expect the tutorial to be a working event with both presentation of state-of- the-art followed by lively discussion about the key issues and challenges in this research area. Our tutorial is open both for academia and industry, and expected to be a community hub for both areas that are interested in an introduction to the unique challenges of mixed reality visualization. We welcome a diverse audience consisting of students, researchers and developers that have a basic understanding of computer graphics and computer vision.
Teaching Computer Graphics During Pandemic using Observable Notebook
(The Eurographics Association, 2021) Pattanaik, Sumanta N.; Benamira, Alexis; Sousa Santos, Beatriz and Domik, Gitta
Most schools and colleges around the world have resorted to remote teaching during this Covid-19 pandemic. Faced with this challenge we experimented with a novel supplement to standard video lecturing to teach our normal face-to-face large undergraduate graphics class (close to 150 students). This supplement involved using Observable notebook, and turned out to be very effective for remote teaching. We wish to continue its use even after college life turns normal, and would like to share our experience with the community and encourage such use for teaching introductory computer graphics courses.
Interactive Finite Element Model of Needle Insertion and Laceration
(The Eurographics Association, 2021) Perrusi, Pedro Henrique Suruagy; Baksic, Paul; Courtecuisse, Hadrien; Theisel, Holger and Wimmer, Michael
This paper introduces an interactive model of needle insertion, including the possibility to simulate lacerations of tissue around the needle. The method relies on complementary constraints to couple the Finite Element models of the needle and tissue. The cutting path is generated from mechanical criteria (i.e. cutting force) at arbitrary resolution, avoiding expensive remeshing of Finite Element meshes. Complex behavior can be simulated in real time such as friction along the shaft of the needle, puncture and cutting force resulting from interactions of the needle with the tissue. The method is illustrated both in an interactive simulation of a needle insertion/cutting and in a robotic needle insertion in liver tissue during the breathing motion.
Auto-rigging 3D Bipedal Characters in Arbitrary Poses
(The Eurographics Association, 2021) Kim, Jeonghwan; Son, Hyeontae; Bae, Jinseok; Kim, Young Min; Theisel, Holger and Wimmer, Michael
We present an end-to-end algorithm that can automatically rig a given 3D character such that it is ready for 3D animation. The animation of a virtual character requires the skeletal motion defined with bones and joints, and the corresponding deformation of the mesh represented with skin weights. While the conventional animation pipeline requires the initial 3D character to be in the predefined default pose, our pipeline can rig a 3D character in arbitrary pose. We handle the increased ambiguity by fixing the skeletal topology and solving for the full deformation space. After the skeletal positions and orientations are fully discovered, we can deform the provided 3D character into the default pose, from which we can animate the character with the help of recent motion-retargeting techniques. Our results show that we can successfully animate initially deformed characters, which was not possible with previous works.
VisGuided: A Community-driven Approach for Education in Visualization
(The Eurographics Association, 2021) Diehl, Alexandra; Firat, Elif E.; Torsney-Weir, Thomas; Abdul-Rahman, Alfie; Bach, Benjamin; Laramee, Robert; Pajarola, Renato; Chen, Min; Sousa Santos, Beatriz and Domik, Gitta
We propose a novel educational approach for teaching visualization, using a community-driven and participatory methodology that extends the traditional course boundaries from the classroom to the broader visualization community.We use a visualization community project, VisGuides, as the main platform to support our educational approach. We evaluate our new methodology by means of three use cases from two different universities. Our contributions include the proposed methodology, the discussion on the outcome of the use cases, the benefits and limitations of our current approach, and a reflection on the open problems and noteworthy gaps to improve the current pedagogical techniques to teach visualization and promote critical thinking. Our findings show extensive benefits from the use of our approach in terms of the number of transferable skills to students, educational resources for educators, and additional feedback for research opportunities to the visualization community.
Algorithms for Microscopic Crowd Simulation: Advancements in the 2010s
(The Eurographics Association and John Wiley & Sons Ltd., 2021) Toll, Wouter van; Pettré, Julien; Bühler, Katja and Rushmeier, Holly
The real-time simulation of human crowds has many applications. Simulating how the people in a crowd move through an environment is an active and ever-growing research topic. Most research focuses on microscopic (or 'agent-based') crowdsimulation methods that model the behavior of each individual person, from which collective behavior can then emerge. This state-of-the-art report analyzes how the research on microscopic crowd simulation has advanced since the year 2010. We focus on the most popular research area within the microscopic paradigm, which is local navigation, and most notably collision avoidance between agents. We discuss the four most popular categories of algorithms in this area (force-based, velocity-based, vision-based, and data-driven) that have either emerged or grown in the last decade. We also analyze the conceptual and computational (dis)advantages of each category. Next, we extend the discussion to other types of behavior or navigation (such as group behavior and the combination with path planning), and we review work on evaluating the quality of simulations. Based on the observed advancements in the 2010s, we conclude by predicting how the research area of microscopic crowd simulation will evolve in the future. Overall, we expect a significant growth in the area of data-driven and learning-based agent navigation, and we expect an increasing number of methods that re-group multiple 'levels' of behavior into one principle. Furthermore, we observe a clear need for new ways to analyze (real or simulated) crowd behavior, which is important for quantifying the realism of a simulation and for choosing the right algorithms at the right time.
Virtual Creature Morphology - A Review
(The Eurographics Association and John Wiley & Sons Ltd., 2021) Lai, Gorm; Leymarie, Frederic Fol; Latham, William; Arita, Takaya; Suzuki, Reiji; Bühler, Katja and Rushmeier, Holly
We present a review of methods for procedurally generating the morphology of virtual creatures. We include a range of methods, with the main groups being from ALife over art to video games. Even though at times these groups overlap, for clarity we have kept this distinction. By including the word virtual, we mean that we focus on methods for simulation in silico, and not physical robots. We also include a historical perspective, with information on methods such as cellular automata, L-systems and a focus on earlier pioneers in the field.
Modeling and Actuation of Cable-driven Silicone Soft Robots
(The Eurographics Association, 2021) Frâncu, Mihail; Theisel, Holger and Wimmer, Michael
In this paper we present a framework for modeling cable-driven soft robots fabricated from silicone rubber - an incompressible material. Our forward simulation model can use either the standard or the mixed formulation of the finite element method (FEM). The latter prevents volumetric locking for incompressible materials and is more accurate for low resolution meshes. Hence, we show that mixed FEM is well suited for estimating elastic parameters and simulator validation. We also introduce a cable actuation model using barycentric coordinates and then use it to solve some simple control problems.
Bregman Approach to Single Image De-Raining
(The Eurographics Association, 2021) Szirmay-Kalos, Laszlo; Tóth, Márton; Theisel, Holger and Wimmer, Michael
Surveillance cameras are expected to work also in bad visibility conditions, which requires algorithmic solutions to improve the captured image and to eliminate image degradation caused by these weather conditions. Algorithms for such tasks belong to the field of computational photography and have been successful in eliminating haze, fog, motion blur, etc. This paper presents a simple algorithm to suppress rain or snow from single images. The algorithm uses energy minimization, and we propose a novel data term and a Bregman distance based regularization term reflecting the particular properties of precipitation.
Visual Analysis of Point Cloud Neighborhoods via Multi-Scale Geometric Measures
(The Eurographics Association, 2021) Ritter, Marcel; Schiffner, Daniel; Harders, Matthias; Theisel, Holger and Wimmer, Michael
Point sets are a widely used spatial data structure in computational and observational domains, e.g. in physics particle simulations, computer graphics or remote sensing. Algorithms typically operate in local neighborhoods of point sets, for computing physical states, surface reconstructions, etc. We present a visualization technique based on multi-scale geometric features of such point clouds. We explore properties of different choices on the underlying weighted co-variance neighborhood descriptor, illustrated on different point set geometries and for varying noise levels. The impact of different weighting functions and tensor centroids, as well as point set features and noise levels becomes visible in the rotation-invariant feature images. We compare to a curvature based scale space visualization method and, finally, show how features in real-world LiDAR data can be inspected by images created with our approach in an interactive tool. In contrast to the curvature based approach, with our method line structures are highlighted over growing scales, with clear border regions to planar or spherical geometric structures.
Automatic Hierarchical Arrangement of Vector Designs
(The Eurographics Association, 2021) Fisher, Matthew; Agarwal, Vineet; Beri, Tarun; Theisel, Holger and Wimmer, Michael
We present a method that transforms an unstructured vector design into a logical hierarchy of groups of objects. Each group is a meaningful collection, formed by proximity in visual characteristics (like size, shape, color, etc.) and spatial location of objects and models the grouping principles designers use. We first simplify the input design by partially or completely flattening it and isolate duplicate geometries in the design (for example, repeating patterns due to copy and paste operations). Next we build the object containment hierarchy by assigning objects that are wholly enclosed inside the geometry of other objects as children of the enclosing parent. In the final clustering phase, we use agglomerative clustering to obtain a bottom-up hierarchical grouping of all objects by comparing and ranking all pairs of objects according to visual and spatial characteristics. Spatial proximity segregates far apart objects, but when they are identical (or near identical) designers generally prefer to keep (and edit) them together. To accommodate this, we detect near identical objects and group them together during clustering despite their spatial separation. We further restrict group formation so that z-order disturbances in the design keep the visual appearance unaffected for tightly-overlapping geometry. The generated organization is equivalent to the original design and the organization results are used to facilitate abstract navigation (hierarchical, lateral or near similar) and selections in the design. Our technique works well with a variety of input designs with commonly identifiable objects and structural patterns.
Rendering 2D Vector Graphics on Mobile GPU Devices
(The Eurographics Association, 2021) Kumar, Harish; Sud, Anmol; Bittner, Jirí and Waldner, Manuela
Designers and artists world-wide rely on vector graphics to design and edit 2D artwork, illustrations and typographic content. There is a recent trend of vector graphic applications moving to mobile platforms such as iPads, iPhone and mobile phones and with that there is new interest in optimised techniques of rendering vector graphics on these devices. These vector applications are not read only but also requires real time vector editing experience. Our solution builds upon standard 'stencil then cover' paradigm and develops an algorithm targeted for GPUs based on tile based deferred rendering architecture. Our technique provides an efficient way to use signed distance based anti-aliasing techniques with 'stencil then cover' paradigm by employing a state machine during the fragment shader stage of graphics pipeline.
Volumetric Video - Acquisition, Compression, Interaction and Perception
(The Eurographics Association, 2021) Zell, Eduard; Castan, Fabien; Gasparini, Simone; Hilsmann, Anna; Kazhdan, Misha; Tagliasacchi, Andrea; Zarpalas, Dimitris; Zioulis, Nick; O'Sullivan, Carol and Schmalstieg, Dieter
Volumetric video, free-viewpoint video or 4D reconstruction refer to the process of reconstructing 3D content over time using a multi-view setup. This method is constantly gaining popularity both in research and industry. In fact, volumetric video is more and more considered to acquire dynamic photorealistic content instead of relying on traditional 3D content creation pipelines. The aim of the tutorial is to provide an overview of the entire volumetric video pipeline. Furthermore, it presents existing projects that may serve as a starting point to this topic at the intersection of computer vision and graphics. The first part of the tutorial will focus on the process of computing 3D models from captured videos. Topics will include content acquisition with affordable hardware, photogrammetry, and surface reconstruction from point clouds. A remarkable contribution of the presenters to the graphics community is that they will not only provide an overview of their topic but have in addition open sourced their implementations. Topics of the second part will focus on usage and distribution of volumetric video, including data compression, streaming or post-processing like pose-modification or seamless blending. The tutorial will conclude with an overview of perceptual studies focusing on quality assessment of 3D and 4D content.
To Splat Straight with Crooked Points: Rendering Noisy Meshes and Point Clouds using Coherent Tangent Vector Fields
(The Eurographics Association, 2021) Anjos, Rafael Kuffner dos; Lopes, Daniel S.; Bittner, Jirí and Waldner, Manuela
Surface aligned splatting is a popular rendering technique to visualize reconstructed meshes and point clouds scanned from the real world. Such data typically presents some degree of noise that jeopardizes any attempt to render a perfectly smooth normal field and, more importantly, the estimated tangent vector fields are not locally continuous, thus affecting the overall visual quality. In this work, we compare two splat orientation techniques for rendering 3D noisy data, namely, the Covariance Matrix and the Householder formula. We evaluate both techniques using four publicly available meshes with synthetic noise, and four scanned point clouds with natural noise. Results indicate that the Householder technique is better suited for surface aligned splatting as it generates more coherent tangent vector fields, while Covariance Matrix reacts poorly to noise.
An Unbiased Hybrid Rendering Approach to Path Guiding
(The Eurographics Association, 2021) Jhang, Jia-Wun; Chang, Chun-Fa; Bittner, Jirí and Waldner, Manuela
When we think of hybrid rendering of rasterization and ray tracing, we often consider rasterization as a mean to solve the primary rays and then consider ray tracing as a mean to add secondary effects. We take a different approach to combine ray tracing and rasterization, in which our final output images are still produced with a path tracer. We leverage the GPU rasterization to build the necessary data that are required for path guidng, thus improves the convergence of our path tracer. We borrow the ideas of Voxel Cone Tracing and implement it in GPU shaders to build the path guiding data. The advantage of our proposed hybrid approach is that it maintains the unbiased results of a Monte Carlo path tracer while incurring relatively small performance hit in path guiding, as shown in our preliminary results.
Generative Landmarks
(The Eurographics Association, 2021) Ferman, David; Bharaj, Gaurav; Bittner, Jirí and Waldner, Manuela
We propose a general purpose approach to detect landmarks with improved temporal consistency, and personalization. Most sparse landmark detection methods rely on laborious, manually labelled landmarks, where inconsistency in annotations over a temporal volume leads to sub-optimal landmark learning. Further, high-quality landmarks with personalization is often hard to achieve. We pose landmark detection as an image translation problem. We capture two sets of unpaired marked (with paint) and unmarked videos. We then use a generative adversarial network and cyclic consistency to predict deformations of landmark templates that simulate markers on unmarked images until these images are indistinguishable from ground-truth marked images. Our novel method does not rely on manually labelled priors, is temporally consistent, and image class agnostic - face, and hand landmarks detection examples are shown.
2D Points Curve Reconstruction Survey and Benchmark
(The Eurographics Association and John Wiley & Sons Ltd., 2021) Ohrhallinger, Stefan; Peethambaran, Jiju; Parakkat, Amal Dev; Dey, Tamal Krishna; Muthuganapathy, Ramanathan; Bühler, Katja and Rushmeier, Holly
Curve reconstruction from unstructured points in a plane is a fundamental problem with many applications that has generated research interest for decades. Involved aspects like handling open, sharp, multiple and non-manifold outlines, run-time and provability as well as potential extension to 3D for surface reconstruction have led to many different algorithms. We survey the literature on 2D curve reconstruction and then present an open-sourced benchmark for the experimental study. Our unprecedented evaluation of a selected set of planar curve reconstruction algorithms aims to give an overview of both quantitative analysis and qualitative aspects for helping users to select the right algorithm for specific problems in the field. Our benchmark framework is available online to permit reproducing the results and easy integration of new algorithms.
Illumination-driven Light Probe Placement
(The Eurographics Association, 2021) Vardis, Konstantinos; Vasilakis, Andreas Alexandros; Papaioannou, Georgios; Bittner, Jirí and Waldner, Manuela
We introduce a simplification method for light probe configurations that preserves the indirect illumination distribution in scenes with diverse lighting conditions. An iterative graph simplification algorithm discards the probes that, according to a set of evaluation points, have the least impact on the global light field. Our approach is simple, generic and aims at improving the repetitive and often non-intuitive and tedious task of placing light probes on complex virtual environments.
Interactive Synthesis of 3D Geometries of Blood Vessels
(The Eurographics Association, 2021) Rauch, Nikolaus; Harders, Matthias; Theisel, Holger and Wimmer, Michael
In surgical training simulators, where various organ surfaces make up the majority of the scene, the visual appearance is highly dependent on the quality of the surface textures. Blood vessels are an important detail in this; they need to be incorporated into an organ's texture. Moreover, the actual blood vessel geometries also have to be part of the simulated surgical procedure itself, e.g. during cutting. Since the manual creation of vessel geometry or branching details on textures is highly tedious, an automatic synthesis technique capable of generating a wide range of blood vessel patterns is needed.We propose a new synthesis approach based on the space colonization algorithm. As extension, physiological constraints on the proliferation of branches are enforced to create realistic vascular structures. Our framework is capable of generating three-dimensional blood vessel networks in a matter of milliseconds, thus allowing a 3D modeller to tweak parameters in real-time to obtain a desired appearance.

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