EG2021

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State of the Art on Computational Design of Assemblies with Rigid Parts
(The Eurographics Association and John Wiley & Sons Ltd., 2021) Wang, Ziqi; Song, Peng; Pauly, Mark; Bühler, Katja and Rushmeier, Holly
An assembly refers to a collection of parts joined together to achieve a specific form and/or functionality. Designing assemblies is a non-trivial task as a slight local modification on a part's geometry or its joining method could have a global impact on the structural and/or functional performance of the whole assembly. Assemblies can be classified as structures that transmit force to carry loads and mechanisms that transfer motion and force to perform mechanical work. In this state-of-the-art report, we focus on computational design of structures with rigid parts, which generally can be formulated as a geometric modeling and optimization problem. We broadly classify existing computational design approaches, mainly from the computer graphics community, according to high-level design objectives, including fabricability, structural stability, reconfigurability, and tileability. Computational analysis of various aspects of assemblies is an integral component in these design approaches. We review different classes of computational analysis and design methods, discuss their strengths and limitations, make connections among them, and propose possible directions for future research.
Unsupervised Learning of Disentangled 3D Representation from a Single Image
(The Eurographics Association, 2021) Lv, Junliang; Jiang, Haiyong; Xiao, Jun; Bittner, Jirí and Waldner, Manuela
Learning 3D representation of a single image is challenging considering the ambiguity, occlusion, and perspective project of an object in an image. Previous works either seek image annotation or 3D supervision to learn meaningful factors of an object or employ a StyleGAN-like framework for image synthesis. While the first ones rely on tedious annotation and even dense geometry ground truth, the second solutions usually cannot guarantee consistency of shapes between different view images. In this paper, we combine the advantages of both frameworks and propose an image disentanglement method based on 3D representation. Results show our method facilitates unsupervised 3D representation learning while preserving consistency between images.
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.
Film Directing for Computer Games and Animation
(The Eurographics Association and John Wiley & Sons Ltd., 2021) Ronfard, Rémi; Bühler, Katja and Rushmeier, Holly
Over the last forty years, researchers in computer graphics have proposed a large variety of theoretical models and computer implementations of a virtual film director, capable of creating movies from minimal input such as a screenplay or storyboard. The underlying film directing techniques are also in high demand to assist and automate the generation of movies in computer games and animation. The goal of this survey is to characterize the spectrum of applications that require film directing, to present a historical and up-to-date summary of research in algorithmic film directing, and to identify promising avenues and hot topics for future research.
Interactive Simulation for easy Decision-making in Fluid Dynamics
(The Eurographics Association, 2021) Wang, Mengchen; Férey, Nicolas; Magoulès, Frédéric; Bourdot, Patrick; Theisel, Holger and Wimmer, Michael
A conventional study of fluid simulation involves different stages including conception, simulation, visualization, and analysis tasks. It is, therefore, necessary to switch between different software and interactive contexts which implies costly data manipulation and increases the time needed for decision making. Our interactive simulation approach was designed to shorten this loop, allowing users to visualize and steer a simulation in progress without waiting for the end of the simulation. The methodology allows the users to control, start, pause, or stop a simulation in progress, to change global physical parameters, to interact with its 3D environment by editing boundary conditions such as walls or obstacles. This approach is made possible by using a methodology such as the Lattice Boltzmann Method (LBM) to achieve interactive time while remaining physically relevant. In this work, we present our platform dedicated to interactive fluid simulation based on LBM. The contribution of our interactive simulation approach to decision making will be evaluated in a study based on a simple but realistic use case.
Gaming in Elliptic Geometry
(The Eurographics Association, 2021) Szirmay-Kalos, Laszlo; Magdics, Milán; Theisel, Holger and Wimmer, Michael
An interesting way to explore curved spaces is to play games governed by the rules of non-Euclidean geometries. However, modeling tools and game engines are developed with Euclidean geometry in mind. This paper addresses the problem of porting a game from Euclidean to elliptic geometry. We consider primarily the geometric calculations and the transformation pipeline.
Data-driven Garment Pattern Estimation from 3D Geometries
(The Eurographics Association, 2021) Goto, Chihiro; Umetani, Nobuyuki; Theisel, Holger and Wimmer, Michael
Three-dimensional scanning technology recently becomes widely available to the public. However, it is difficult to simulate clothing deformation from the scanned people because scanned data lacks information required for the clothing simulation. In this paper, we present a technique to estimate clothing patterns from a scanned person in cloth. Our technique uses image-based deep learning to estimate the type of pattern on the projected image. The key contribution is converting image-based inference into three-dimensional clothing pattern estimation. We evaluate our technique by applying our technique to an actual scan.
EUROGRAPHICS 2021: Education Papers Frontmatter
(Eurographics Association, 2021) Sousa Santos, Beatriz; Domik, Gitta; Sousa Santos, Beatriz and Domik, Gitta
EUROGRAPHICS 2021: CGF 40-2 STARs Frontmatter
(The Eurographics Association and John Wiley & Sons Ltd., 2021) Bühler, Katja; Rushmeier, Holly; Bühler, Katja and Rushmeier, Holly
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EUROGRAPHICS 2021: Tutorials Frontmatter
(Eurographics Association, 2021) O'Sullivan, Carol; Schmalstieg, Dieter; O'Sullivan, Carol and Schmalstieg, Dieter
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.
Teaching 3D Computer Animation to Non-programming Experts
(The Eurographics Association, 2021) Casas, Dan; Sousa Santos, Beatriz and Domik, Gitta
This paper describes a Computer Animation course aimed at novice Computer Science and Engineering students with minimal programming skills. We observe that students enrolled in Computer Graphics (and related) undergraduate degrees usually face a Computer Animation subject early in their programs, sometimes even before they develop strong software development and programming skills. This causes that assignments and tasks where students should focus on the Computer Animation concepts, end up in frustration and massive efforts to just get over-complicated developing frameworks running. Instead, we propose a Computer Animation course based on small MATLAB tasks that covers a large range of topics and it is adapted to students with minimal programming skills. For each topic, we provide a brief theoretical summary and links to fundamental literature, as well as a set of hands-on tasks with the necessary source code to get started. A user study shows that students who took this course were able to better focus on the fundamental concepts of the subject, circumventing the need to learn advanced programming skills. Course material is available on a public GitHub repository, and solutions are provided upon request from course tutors.
Tetrahedral Interpolation on Regular Grids
(The Eurographics Association, 2021) Bán, Róbert; Valasek, Gábor; Bittner, Jirí and Waldner, Manuela
This work proposes the use of barycentric interpolation on enclosing simplices of sample points to infer a reconstructed function from discrete data. In particular, we compare the results of trilinear and tetrahedral interpolation over regular 3D grids of second order spherical harmonics (SH) light probes. In general, tetrahedral interpolation only requires four data samples per query in contrast to the 8 samples necessary for trilinear interpolation, at the expense of a more expensive weight computation. Our tetrahedral implementation subdivides the cubical cells into six tetrahedra and uses the barycentric coordinates of the query position as weights to blend the probe data. We show that barycentric coordinates can be calculated efficiently in shaders for our particular tetrahedral decomposition of the cube, resulting only in simple arithmetic and conditional move operations.
A Virtual Reality Platform for Immersive Education in Computer Graphics
(The Eurographics Association, 2021) Hácha, Filip; Vanecek, Petr; Váša, Libor; Sousa Santos, Beatriz and Domik, Gitta
We present a general framework for teaching 3D imagination demanding topics using commonly available hardware for virtual reality (VR). Our software allows collaborating on 3D objects, interaction and annotation in a simple and intuitive manner. Students can follow the exposition from an arbitrary, naturally chosen point of view, and they interact with the shared scene by adding annotations and using a pointing metaphore. The software allows using various VR headsets as well as opting for a traditional 3D rendering on a 2D screen. The framework has been tested in a small course on polygon mesh processing, identifying and eliminating the most serious flaws. In its current form, most of the sources of friction have been addressed and the system can be employed in a variety of teaching scenarios.
Project in Visualization and Data Analysis: Experiences in Designing and Coordinating the Course
(The Eurographics Association, 2021) Kucher, Kostiantyn; Martins, Rafael M.; Kerren, Andreas; Sousa Santos, Beatriz and Domik, Gitta
Visual analytics involves both visual and computational components for empowering human analysts who face the challenges of making sense and making use of large and heterogeneous data sets in various application domains. In order to facilitate the learning process for the students at higher education institutions with regard to both the theoretical knowledge and practical skills in visual analytics, the respective courses must cover a variety of topics and include multiple assessment methods and activities. In this paper, we report on the design and first instantiation of a full term project-based course in visualization and data analysis, which was recently offered to graduate and post-graduate students at our department and met with positive feedback from the course participants.
Inverse Computational Spectral Geometry
(The Eurographics Association, 2021) Rodolà, Emanuele; Melzi, Simone; Cosmo, Luca; Bronstein, Michael; Ovsjanikov, Maks; O'Sullivan, Carol and Schmalstieg, Dieter
In the last decades, geometry processing has attracted a growing interest thanks to the wide availability of new devices and software that make 3D digital data available and manipulable to everyone. Typical issues that are faced by geometry processing algorithms include the variety of discrete representations for 3D data (point clouds, polygonal or tet-meshes and voxels), or the type of deformation this data may undergo. Powerful approaches to address these issues come from looking at the spectral decomposition of canonical differential operators, such as the Laplacian, which provides a rich, informative, robust, and invariant representation of the 3D objects. Reasoning about spectral quantities is at the core of spectral geometry, which has enabled unprecedented performance in many tasks of computer graphics (e.g., shape matching with functional maps, shape retrieval, compression, and texture transfer), as well as contributing in opening new directions of research. The focus of this tutorial is on inverse computational spectral geometry. We will offer a different perspective on spectral geometric techniques, supported by recent successful methods in the graphics and 3D vision communities, as well as older, but notoriously overlooked results. Here, the interest shifts from studying the “forward” path typical of spectral geometry pipelines (e.g., computing Laplacian eigenvalues and eigenvectors of a given shape) to studying the inverse path (e.g., recovering a shape from given Laplacian eigenvalues, like in the classical “hearing the shape of the drum” problem). As is emblematic of inverse problems, the ill-posed nature of the reverse direction requires additional effort, but the benefits can be quite considerable as showcased on several challenging tasks in graphics and geometry processing. The purpose of the tutorial is to overview the foundations and the current state of the art on inverse computational spectral geometry, to highlight the main benefits of inverse spectral pipelines, as well as their current limitations and future developments in the context of computer graphics. The tutorial is aimed at a wide audience with a basic understanding of geometry processing, and will be accessible and interesting to students, researchers and practitioners from both the academia and the industry.
Color Reproduction Framework for Inkjet FDM 3D Printers
(The Eurographics Association, 2021) Silapasuphakornwong, Piyarat; Punpongsanon, Parinya; Panichkriangkrai, Chulapong; Sueeprasan, Suchitra; Uehira, Kazutake; Bittner, Jirí and Waldner, Manuela
Recent advances in consumer-grade 3D printers have enabled the fabrication of personal artifacts in aesthetically pleasing full color. However, the printed colors are usually different from the actual user desired colors due to the mismatching of droplets when the color reproduction workflow has been changed or the color profile setup is missing. In this paper, we present a preliminary experiment to investigate color reproduction errors in consumer-grade inkjet FDM 3D printers. Our results suggest that solving the problem requires initiating the workflow to minimize color reproduction errors such as using CMYK or sRGB color profiles. We also found that the mismatched color gamut between the input's desired texture and the 3D printed output depends on different file formats, and this finding requires future investigation.
EUROGRAPHICS 2021: Posters Frontmatter
(Eurographics Association, 2021) Bittner, Jirí; Waldner, Manuela; Bittner, Jirí and Waldner, Manuela

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