42-Issue 1

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https://diglib.eg.org/handle/10.2312/2633291

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HardVis: Visual Analytics to Handle Instance Hardness Using Undersampling and Oversampling Techniques
(Eurographics ‐ The European Association for Computer Graphics and John Wiley & Sons Ltd., 2023) Chatzimparmpas, A.; Paulovich, F. V.; Kerren, A.; Hauser, Helwig and Alliez, Pierre
Despite the tremendous advances in machine learning (ML), training with imbalanced data still poses challenges in many real‐world applications. Among a series of diverse techniques to solve this problem, sampling algorithms are regarded as an efficient solution. However, the problem is more fundamental, with many works emphasizing the importance of instance hardness. This issue refers to the significance of managing unsafe or potentially noisy instances that are more likely to be misclassified and serve as the root cause of poor classification performance.This paper introduces HardVis, a visual analytics system designed to handle instance hardness mainly in imbalanced classification scenarios. Our proposed system assists users in visually comparing different distributions of data types, selecting types of instances based on local characteristics that will later be affected by the active sampling method, and validating which suggestions from undersampling or oversampling techniques are beneficial for the ML model. Additionally, rather than uniformly undersampling/oversampling a specific class, we allow users to find and sample easy and difficult to classify training instances from all classes. Users can explore subsets of data from different perspectives to decide all those parameters, while HardVis keeps track of their steps and evaluates the model's predictive performance in a test set separately. The end result is a well‐balanced data set that boosts the predictive power of the ML model. The efficacy and effectiveness of HardVis are demonstrated with a hypothetical usage scenario and a use case. Finally, we also look at how useful our system is based on feedback we received from ML experts.
Novel View Synthesis Of Transparent Object From a Single Image
(Eurographics ‐ The European Association for Computer Graphics and John Wiley & Sons Ltd., 2023) Zhou, Shizhe; Wang, Zezu; Ye, Dongwei; Hauser, Helwig and Alliez, Pierre
We propose a method for converting a single image of a transparent object into multi‐view photo that enables users observing the object from multiple new angles, without inputting any 3D shape. The complex light paths formed by refraction and reflection makes it challenging to compute the lighting effects of transparent objects from a new angle. We construct an encoder–decoder network for normal reconstruction and texture extraction, which enables synthesizing novel views of transparent object from a set of new views and new environment maps using only one RGB image. By simultaneously considering the optical transmission and perspective variation, our network learns the characteristics of optical transmission and the change of perspective as guidance to the conversion from RGB colours to surface normals. A texture extraction subnetwork is proposed to alleviate the contour loss phenomenon during normal map generation. We test our method using 3D objects within and without our training data, including real 3D objects that exists in our lab, and completely new environment maps that we take using our phones. The results show that our method performs better on view synthesis of transparent objects in complex scenes using only a single‐view image.
ZeroEGGS: Zero‐shot Example‐based Gesture Generation from Speech
(Eurographics ‐ The European Association for Computer Graphics and John Wiley & Sons Ltd., 2023) Ghorbani, Saeed; Ferstl, Ylva; Holden, Daniel; Troje, Nikolaus F.; Carbonneau, Marc‐André; Hauser, Helwig and Alliez, Pierre
We present ZeroEGGS, a neural network framework for speech‐driven gesture generation with zero‐shot style control by example. This means style can be controlled via only a short example motion clip, even for motion styles unseen during training. Our model uses a Variational framework to learn a style embedding, making it easy to modify style through latent space manipulation or blending and scaling of style embeddings. The probabilistic nature of our framework further enables the generation of a variety of outputs given the input, addressing the stochastic nature of gesture motion. In a series of experiments, we first demonstrate the flexibility and generalizability of our model to new speakers and styles. In a user study, we then show that our model outperforms previous state‐of‐the‐art techniques in naturalness of motion, appropriateness for speech, and style portrayal. Finally, we release a high‐quality dataset of full‐body gesture motion including fingers, with speech, spanning across 19 different styles. Our code and data are publicly available at .
Visual Exploration of Financial Data with Incremental Domain Knowledge
(Eurographics ‐ The European Association for Computer Graphics and John Wiley & Sons Ltd., 2023) Arleo, Alessio; Tsigkanos, Christos; Leite, Roger A.; Dustdar, Schahram; Miksch, Silvia; Sorger, Johannes; Hauser, Helwig and Alliez, Pierre
Modelling the dynamics of a growing financial environment is a complex task that requires domain knowledge, expertise and access to heterogeneous information types. Such information can stem from several sources at different scales, complicating the task of forming a holistic impression of the financial landscape, especially in terms of the economical relationships between firms. Bringing this scattered information into a common context is, therefore, an essential step in the process of obtaining meaningful insights about the state of an economy. In this paper, we present , a Visual Analytics (VA) approach for exploring financial data across different scales, from individual firms up to nation‐wide aggregate data. Our solution is coupled with a pipeline for the generation of firm‐to‐firm financial transaction networks, fusing information about individual firms with sector‐to‐sector transaction data and domain knowledge on macroscopic aspects of the economy. Each network can be created to have multiple instances to compare different scenarios. We collaborated with experts from finance and economy during the development of our VA solution, and evaluated our approach with seven domain experts across industry and academia through a qualitative insight‐based evaluation. The analysis shows how enables the generation of insights, and how the incorporation of transaction models assists users in their exploration of a national economy.
Remeshing‐free Graph‐based Finite Element Method for Fracture Simulation
(Eurographics ‐ The European Association for Computer Graphics and John Wiley & Sons Ltd., 2023) Mandal, A.; Chaudhuri, P.; Chaudhuri, S.; Hauser, Helwig and Alliez, Pierre
Fracture produces new mesh fragments that introduce additional degrees of freedom in the system dynamics. Existing finite element method (FEM) based solutions suffer from increasing computational cost as the system matrix size increases. We solve this problem by presenting a graph‐based FEM model for fracture simulation that is remeshing‐free and easily scales to high‐resolution meshes. Our algorithm models fracture on the graph induced in a volumetric mesh with tetrahedral elements. We relabel the edges of the graph using a computed damage variable to initialize and propagate fracture. We prove that non‐linear, hyper‐elastic strain energy density is expressible entirely in terms of the edge lengths of the induced graph. This allows us to reformulate the system dynamics for the relabelled graph without changing the size of the system dynamics matrix and thus prevents the computational cost from blowing up. The fractured surface has to be reconstructed explicitly only for visualization purposes. We simulate standard laboratory experiments from structural mechanics and compare the results with corresponding real‐world experiments. We fracture objects made of a variety of brittle and ductile materials, and show that our technique offers stability and speed that is unmatched in current literature.
Efficient Storage and Importance Sampling for Fluorescent Reflectance
(Eurographics ‐ The European Association for Computer Graphics and John Wiley & Sons Ltd., 2023) Hua, Q.; Tázlar, V.; Fichet, A.; Wilkie, A.; Hauser, Helwig and Alliez, Pierre
We propose a technique for efficient storage and importance sampling of fluorescent spectral data. Fluorescence is fully described by a re‐radiation matrix, which for a given input wavelength indicates how much energy is re‐emitted at other wavelengths. However, such representation has a considerable memory footprint. To significantly reduce memory requirements, we propose the use of Gaussian mixture models for the representation of re‐radiation matrices. Instead of the full‐resolution matrix, we work with a set of Gaussian parameters that also allow direct importance sampling. Furthermore, if accuracy is of concern, a re‐radiation matrix can be used jointly with efficient importance sampling provided by the Gaussian mixture. In this paper, we present our pipeline for efficient storage of bispectral data and provide its extensive evaluation on a large set of bispectral measurements. We show that our method is robust and colour accurate even with its comparably minor memory requirements and that it can be seamlessly integrated into a standard Monte Carlo path tracer.
Differentiable Depth for Real2Sim Calibration of Soft Body Simulations
(Eurographics ‐ The European Association for Computer Graphics and John Wiley & Sons Ltd., 2023) Arnavaz, K.; Nielsen, M. Kragballe; Kry, P. G.; Macklin, M.; Erleben, K.; Hauser, Helwig and Alliez, Pierre
In this work, we present a novel approach for calibrating material model parameters for soft body simulations using real data. We use a fully differentiable pipeline, combining a differentiable soft body simulator and differentiable depth rendering, which permits fast gradient‐based optimizations. Our method requires no data pre‐processing, and minimal experimental set‐up, as we directly minimize the L2‐norm between raw LIDAR scans and rendered simulation states. In essence, we provide the first marker‐free approach for calibrating a soft‐body simulator to match observed real‐world deformations. Our approach is inexpensive as it solely requires a consumer‐level LIDAR sensor compared to acquiring a professional marker‐based motion capture system. We investigate the effects of different material parameterizations and evaluate convergence for parameter optimization in both single and multi‐material scenarios of varying complexity. Finally, we show that our set‐up can be extended to optimize for dynamic behaviour as well.
Monolithic Friction and Contact Handling for Rigid Bodies and Fluids Using SPH
(Eurographics ‐ The European Association for Computer Graphics and John Wiley & Sons Ltd., 2023) Probst, T.; Teschner, M.; Hauser, Helwig and Alliez, Pierre
We propose a novel monolithic pure SPH formulation to simulate fluids strongly coupled with rigid bodies. This includes fluid incompressibility, fluid–rigid interface handling and rigid–rigid contact handling with a viable implicit particle‐based dry friction formulation. The resulting global system is solved using a new accelerated solver implementation that outperforms existing fluid and coupled rigid–fluid simulation approaches. We compare results of our simulation method to analytical solutions, show performance evaluations of our solver and present a variety of new and challenging simulation scenarios.
PDViz: A Visual Analytics Approach for State Policy Data
(Eurographics ‐ The European Association for Computer Graphics and John Wiley & Sons Ltd., 2023) Han, Dongyun; Nayeem, Abdullah‐Al‐Raihan; Windett, Jason; Cho, Isaac; Hauser, Helwig and Alliez, Pierre
Sub‐national governments across the United States implement a variety of policies to address large societal problems and needs. Many policies are picked up or adopted in other states. This process is called policy diffusion and allows researchers to analyse and compare the social, political, and contextual characteristics that lead to adopting certain policies, as well as the efficacy of these policies once adopted. In this paper, we introduce PDViz, a visual analytics approach that allows social scientists to dynamically analyse the policy diffusion history and underlying patterns. It is designed for analysing and answering a list of research questions and tasks posed by social scientists in prior work. To evaluate our system, we present two usage scenarios and conduct interviews with domain experts in political science. The interviews highlight that PDViz provides the result of policy diffusion patterns that align with their domain knowledge as well as the potential to be a learning tool for students to understand the concept of policy diffusion.
Decision Boundary Visualization for Counterfactual Reasoning
(Eurographics ‐ The European Association for Computer Graphics and John Wiley & Sons Ltd., 2023) Sohns, Jan‐Tobias; Garth, Christoph; Leitte, Heike; Hauser, Helwig and Alliez, Pierre
Machine learning algorithms are widely applied to create powerful prediction models. With increasingly complex models, humans' ability to understand the decision function (that maps from a high‐dimensional input space) is quickly exceeded. To explain a model's decisions, black‐box methods have been proposed that provide either non‐linear maps of the global topology of the decision boundary, or samples that allow approximating it locally. The former loses information about distances in input space, while the latter only provides statements about given samples, but lacks a focus on the underlying model for precise ‘What‐If'‐reasoning. In this paper, we integrate both approaches and propose an interactive exploration method using local linear maps of the decision space. We create the maps on high‐dimensional hyperplanes—2D‐slices of the high‐dimensional parameter space—based on statistical and personal feature mutability and guided by feature importance. We complement the proposed workflow with established model inspection techniques to provide orientation and guidance. We demonstrate our approach on real‐world datasets and illustrate that it allows identification of instance‐based decision boundary structures and can answer multi‐dimensional ‘What‐If'‐questions, thereby identifying counterfactual scenarios visually.
HDRNet: High‐Dimensional Regression Network for Point Cloud Registration
(Eurographics ‐ The European Association for Computer Graphics and John Wiley & Sons Ltd., 2023) Gao, Jian; Zhang, Yuhe; Liu, Zehua; Li, Siyi; Hauser, Helwig and Alliez, Pierre
Abstract‐3D point cloud registration is a crucial topic in the reverse engineering, computer vision and robotics fields. The core of this problem is to estimate a transformation matrix for aligning the source point cloud with a target point cloud. Several learning‐based methods have achieved a high performance. However, they are challenged with both partial overlap point clouds and multiscale point clouds, since they use the singular value decomposition (SVD) to find the rotation matrix without fully considering the scale information. Furthermore, previous networks cannot effectively handle the point clouds having large initial rotation angles, which is a common practical case. To address these problems, this paper presents a learning‐based point cloud registration network, namely HDRNet, which consists of four stages: local feature extraction, correspondence matrix estimation, feature embedding and fusion and parametric regression. HDRNet is robust to noise and large rotation angles, and can effectively handle the partial overlap and multi‐scale point clouds registration. The proposed model is trained on the ModelNet40 dataset, and compared with ICP, SICP, FGR and recent learning‐based methods (PCRNet, IDAM, RGMNet and GMCNet) under several settings, including its performance on moving to invisible objects, with higher success rates. To verify the effectiveness and generality of our model, we also further tested our model on the Stanford 3D scanning repository.
Mesh Draping: Parametrization‐Free Neural Mesh Transfer
(Eurographics ‐ The European Association for Computer Graphics and John Wiley & Sons Ltd., 2023) Hertz, A.; Perel, O.; Giryes, R.; Sorkine‐Hornung, O.; Cohen‐Or, D.; Hauser, Helwig and Alliez, Pierre
Despite recent advances in geometric modelling, 3D mesh modelling still involves a considerable amount of manual labour by experts. In this paper, we introduce Mesh Draping: a neural method for transferring existing mesh structure from one shape to another. The method drapes the source mesh over the target geometry and at the same time seeks to preserve the carefully designed characteristics of the source mesh. At its core, our method deforms the source mesh using progressive positional encoding (PE). We show that by leveraging gradually increasing frequencies to guide the neural optimization, we are able to achieve stable and high‐quality mesh transfer. Our approach is simple and requires little user guidance, compared to contemporary surface mapping techniques which rely on parametrization or careful manual tuning. Most importantly, Mesh Draping is a parameterization‐free method, and thus applicable to a variety of target shape representations, including point clouds, polygon soups and non‐manifold meshes. We demonstrate that the transferred meshing remains faithful to the source mesh design characteristics, and at the same time fits the target geometry well.
Test‐Time Optimization for Video Depth Estimation Using Pseudo Reference Depth
(Eurographics ‐ The European Association for Computer Graphics and John Wiley & Sons Ltd., 2023) Zeng, Libing; Kalantari, Nima Khademi; Hauser, Helwig and Alliez, Pierre
In this paper, we propose a learning‐based test‐time optimization approach for reconstructing geometrically consistent depth maps from a monocular video. Specifically, we optimize an existing single image depth estimation network on the test example at hand. We do so by introducing pseudo reference depth maps which are computed based on the observation that the optical flow displacement for an image pair should be consistent with the displacement obtained by depth‐reprojection. Additionally, we discard inaccurate pseudo reference depth maps using a simple median strategy and propose a way to compute a confidence map for the reference depth. We use our pseudo reference depth and the confidence map to formulate a loss function for performing the test‐time optimization in an efficient and effective manner. We compare our approach against the state‐of‐the‐art methods on various scenes both visually and numerically. Our approach is on average 2.5× faster than the state of the art and produces depth maps with higher quality.
Priority‐based encoding of triangle mesh connectivity for a known geometry
(Eurographics ‐ The European Association for Computer Graphics and John Wiley & Sons Ltd., 2023) Dvořák, Jan; Káčereková, Zuzana; Vaněček, Petr; Váša, Libor; Hauser, Helwig and Alliez, Pierre
In certain practical situations, the connectivity of a triangle mesh needs to be transmitted or stored given a fixed set of 3D vertices that is known at both ends of the transaction (encoder/decoder). This task is different from a typical mesh compression scenario, in which the connectivity and geometry (vertex positions) are encoded either simultaneously or in reversed order (connectivity first), usually exploiting the freedom in vertex/triangle re‐indexation. Previously proposed algorithms for encoding the connectivity for a known geometry were based on a canonical mesh traversal and predicting which vertex is to be connected to the part of the mesh that is already processed. In this paper, we take this scheme a step further by replacing the fixed traversal with a priority queue of open expansion gates, out of which in each step a gate is selected that has the most certain prediction, that is one in which there is a candidate vertex that exhibits the largest advantage in comparison with other possible candidates, according to a carefully designed quality metric. Numerical experiments demonstrate that this improvement leads to a substantial reduction in the required data rate in comparison with the state of the art.
ComBiNet: Visual Query and Comparison of Bipartite Multivariate Dynamic Social Networks
(Eurographics ‐ The European Association for Computer Graphics and John Wiley & Sons Ltd., 2023) Pister, A.; Prieur, C.; Fekete, J.‐D.; Hauser, Helwig and Alliez, Pierre
We present ComBiNet, a visualization, query, and comparison system for exploring bipartite multivariate dynamic social networks. Historians and sociologists study social networks constructed from textual sources mentioning events related to people, such as marriage acts, birth certificates and contracts. We model this type of data using bipartite multivariate dynamic networks to maintain a representation faithful to the original sources while not too complex. Relying on this data model, ComBiNet allows exploring networks using both visual and textual queries using the Cypher language, the two being synchronized to specify queries using the most suitable modality; simple queries are easy to express visually and can be refined textually when they become complex. These queries are used for applying topological and attribute‐based selection on the network. Query results are visualized in the context of the whole network and over a geographical map for geolocalized entities. We also present the design of our interaction techniques for querying social networks to visually compare the selections in terms of topology, measures and attribute distributions. We validate the query and comparison systems by showing how they have been used to answer historical questions and by explaining how they have been improved through a usability study conducted with historians.
Investigation and Simulation of Diffraction on Rough Surfaces
(Eurographics ‐ The European Association for Computer Graphics and John Wiley & Sons Ltd., 2023) Clausen, O.; Chen, Y.; Fuhrmann, A.; Marroquim, R.; Hauser, Helwig and Alliez, Pierre
Simulating light–matter interaction is a fundamental problem in computer graphics. A particular challenge is the simulation of light interaction with rough surfaces due to diffraction and multiple scattering phenomena. To properly model these phenomena, wave‐optics have to be considered. Nevertheless, the most accurate BRDF models, including wave‐optics, are computationally expensive, and the resulting renderings have not been systematically compared to real‐world measurements. This work sheds more light on reflectance variations due to surface roughness. More specifically, we look at wavelength shifts that lead to reddish and blueish appearances. These wavelength shifts have been scarcely reported in the literature, and, in this paper, we provide the first thorough analysis from precise measured data. We measured the spectral in‐plane BRDF of aluminium samples with varying roughness and further acquired the surface topography with a confocal microscope. The measurements show that the rough samples have, on average, a reddish and blueish appearance in the forward and back‐scattering, respectively. Our investigations conclude that this is a diffraction‐based effect that dominates the overall appearance of the samples. Simulations using a virtual gonioreflectometer further confirm our claims. We propose a linear model that can closely fit such phenomena, where the slope of the wavelength shifts depends on the incident and reflection direction. Based on these insights, we developed a simple BRDF model based on the Cook–Torrance model that considers such wavelength shifts.
ComVis‐Sail: Comparative Sailing Performance Visualization for Coaching
(Eurographics ‐ The European Association for Computer Graphics and John Wiley & Sons Ltd., 2023) Pieras, M.; Marroquim, R.; Broekens, D.; Eisemann, E.; Vilanova, A.; Hauser, Helwig and Alliez, Pierre
During training sessions, sailors rely on feedback provided by the coaches to reinforce their skills and improve their performance. Nowadays, the incorporation of sensors on the boats enables coaches to potentially provide more informed feedback to the sailors. A common exercise during practice sessions, consists of two boats of the same class, sailing side by side in a straight line with different boat handling techniques. Coaches try to understand which techniques are that make one boat go faster than the other. The analysis of the obtained data from the boats is challenging given its multi‐dimensional, time‐varying and spatial nature. At present, coaches only rely on aggregated statistics reducing the complexity of the data, hereby losing local and temporal information. We describe a new domain characterization and present a visualization design that allows coaches to analyse the data, structuring their analysis and explore the data from different perspectives. A central element of the tool is the glyph design to intuitively represent and aggregate multiple aspects of the sensor data. We have conducted multiple user studies with naive users, sailors and coaches to evaluate the design and potential of the overall tool.
Editorial
(Eurographics ‐ The European Association for Computer Graphics and John Wiley & Sons Ltd., 2023) Alliez, Pierre; Hauser, Helwig; Hauser, Helwig and Alliez, Pierre
Improved Evaluation and Generation Of Grid Layouts Using Distance Preservation Quality and Linear Assignment Sorting
(Eurographics ‐ The European Association for Computer Graphics and John Wiley & Sons Ltd., 2023) Barthel, K. U.; Hezel, N.; Jung, K.; Schall, K.; Hauser, Helwig and Alliez, Pierre
Images sorted by similarity enables more images to be viewed simultaneously, and can be very useful for stock photo agencies or e‐commerce applications. Visually sorted grid layouts attempt to arrange images so that their proximity on the grid corresponds as closely as possible to their similarity. Various metrics exist for evaluating such arrangements, but there is low experimental evidence on correlation between human perceived quality and metric value. We propose distance preservation quality (DPQ) as a new metric to evaluate the quality of an arrangement. Extensive user testing revealed stronger correlation of DPQ with user‐perceived quality and performance in image retrieval tasks compared to other metrics. In addition, we introduce Fast linear assignment sorting (FLAS) as a new algorithm for creating visually sorted grid layouts. FLAS achieves very good sorting qualities while improving run time and computational resources.
Issue Information
(Eurographics ‐ The European Association for Computer Graphics and John Wiley & Sons Ltd., 2023) Hauser, Helwig and Alliez, Pierre

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