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Gao, Shan; Ye, Qixiang; Liu, Li; Kuijper, Arjan; Ji, Xiangyang

A Graphical Social Topology Model for RGB-D Multi-Person Tracking

2021

IEEE Transactions on Circuits and Systems for Video Technology (TCSVT)

Tracking multiple persons is a challenging task especially when persons move in groups and occlude one another. Existing research have investigated the problems of group division and segmentation; however, lacking overall person-group topology modeling limits the ability to handle complex person and group dynamics. We propose a Graphical Social Topology (GST) model in the RGB-D data domain, and estimate object group dynamics by jointly modeling the group structure and states of persons using RGB-D topological representation. With our topology representation, moving persons are not only assigned to groups, but also dynamically connected with each other, which enables in-group individuals to be correctively associated and the cohesion of each group to be precisely modeled. Using the learned typical topology pattern and group online update modules, we infer the birth/death and merging/splitting of dynamic groups. With the GST model, the proposed multi-person tracker can naturally facilitate the occlusion problem by treating the occluded object and other in-group members as a whole, while leveraging overall state transition. Experiments on different RGB-D and RGB datasets confirm that the proposed multi-person tracker improves the state-of-the-arts.

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Ferreira, Stephanie; Stork, André [1. Review]; Weber, Daniel [2. Review]

A Projection-based Approachfor Solving Quadratic Programs in Contact Mechanics

2021

Darmstadt, TU, Master Thesis, 2021

In this thesis the application of projection-based methods to solve the quadratic program arising in contact mechanics is explored. The projected conjugate gradient method is combined with an active-set strategy. In each active-set iteration the projected conjugate gradient method is used to solve the equality constrained subproblem. The projected conjugate gradient method combines the advantages of the conjugate gradient method with the capability to handle equality constraints indirectly by projecting the search directions to the feasible space. A new method, the active-set conjugate gradient method, is introduced to handle inequality constraints inside the conjugate gradient algorithm. Heavy weight active-set iterations are not needed, as the active-set functionalities are incorporated directly inside the conjugate gradient routine. The active constraints are enforced by using the projection technique of the projected conjugate gradient method. Both methods provided accurate results in reasonable run times when solving the linear contact mechanics problem. The active-set conjugate gradient method showed the potential to be able to significantly increase efficiency especially on large models.

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A Visualization Interface to Improve the Transparency of Collected Personal Data on the Internet

2021

IEEE Transactions on Visualization and Computer Graphics

Online services are used for all kinds of activities, like news, entertainment, publishing content or connecting with others. But information technology enables new threats to privacy by means of global mass surveillance, vast databases and fast distribution networks. Current news are full of misuses and data leakages. In most cases, users are powerless in such situations and develop an attitude of neglect for their online behaviour. On the other hand, the GDPR (General Data Protection Regulation) gives users the right to request a copy of all their personal data stored by a particular service, but the received data is hard to understand or analyze by the common internet user. This paper presents TransparencyVis - a web-based interface to support the visual and interactive exploration of data exports from different online services. With this approach, we aim at increasing the awareness of personal data stored by such online services and the effects of online behaviour. This design study provides an online accessible prototype and a best practice to unify data exports from different sources.

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Analyzing and Improving the Parametrization Quality of Catmull-Clark Solids for Isogeometric Analysis

2021

IEEE Computer Graphics and Applications

In the field of physically based simulation, high quality of the simulation model is crucial for the correctness of the simulation results and the performance of the simulation algorithm. When working with spline or subdivision models in the context of isogeometric analysis, the quality of the parametrization has to be considered in addition to the geometric quality of the control mesh. Following Cohen et al.'s concept of model quality in addition to mesh quality, we present a parametrization quality metric tailored for Catmull-Clark (CC) solids. It measures the quality of the limit volume based on a quality measure for conformal mappings, revealing local distortions and singularities. We present topological operations that resolve these singularities by splitting certain types of boundary cells that typically occur in interactively designed CC-solid models. The improved models provide higher parametrization quality that positively affects the simulation results without additional computational costs for the solver.

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Deep Learning Models for Optically Characterizing 3D Printers

2021

Optics Express

Multi-material 3D printers are able to create material arrangements possessing various optical properties. To reproduce these properties, an optical printer model that accurately predicts optical properties from the printer’s control values (tonals) is crucial. We present two deep learning-based models and training strategies for optically characterizing 3D printers that achieve both high accuracy with a moderate number of required training samples. The first one is a Pure Deep Learning (PDL) model that is essentially a black-box without any physical ground and the second one is a Deep-Learning-Linearized Cellular Neugebauer (DLLCN) model that uses deep-learning to multidimensionally linearize the tonal-value-space of a cellular Neugebauer model. We test the models on two six-material polyjetting 3D printers to predict both reflectances and translucency. Results show that both models can achieve accuracies sufficient for most applications with much fewer training prints compared to a regular cellular Neugebauer model.

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Baumgartl, Tom; Petzold, Markus; Wunderlich, Marcel; Höhn, Markus; Archambault, Daniel; Lieser, M.; Dalpke, Alexander; Scheithauer, Simone; Marschollek, Michael; Eichel, V. M.; Mutters, N. T.; Landesberger, Tatiana von

In Search of Patient Zero: Visual Analytics of Pathogen Transmission Pathways in Hospitals

2021

IEEE Transactions on Visualization and Computer Graphics

Pathogen outbreaks (i.e., outbreaks of bacteria and viruses) in hospitals can cause high mortality rates and increase costs for hospitals significantly. An outbreak is generally noticed when the number of infected patients rises above an endemic level or the usual prevalence of a pathogen in a defined population. Reconstructing transmission pathways back to the source of an outbreak – the patient zero or index patient – requires the analysis of microbiological data and patient contacts. This is often manually completed by infection control experts. We present a novel visual analytics approach to support the analysis of transmission pathways, patient contacts, the progression of the outbreak, and patient timelines during hospitalization. Infection control experts applied our solution to a real outbreak of Klebsiella pneumoniae in a large German hospital. Using our system, our experts were able to scale the analysis of transmission pathways to longer time intervals (i.e., several years of data instead of days) and across a larger number of wards. Also, the system is able to reduce the analysis time from days to hours. In our final study, feedback from twenty-five experts from seven German hospitals provides evidence that our solution brings significant benefits for analyzing outbreaks.

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Yang, Heyun; Guthe, Stefan [Betreuer]; Knauthe, Volker [Betreuer]

Influence of Container Resolutions on the Visualizations Created by State-of-the-Art Treemap Layout Algorithms

2021

Darmstadt, TU, Bachelor Thesis, 2021

Nowadays, the standard of representing data becomes higher and higher. We need as many details as possible on a limited screen without losing any information about what the raw data show. Treemaps are powerful tools to illustrate hierarchical data which seems to be a solution to the problem. However, a treemap layout structure may variate on different display screens like cell phones and tablets. Large layout changes are undesirable, since they make it hard to track an individual item, and find items on the treemap from memory, which decreases efficacy for long-term users. Which algorithms have this potential disadvantage and how stable they are in practical use, is a relevant new topic. This thesis is inspired by a real-life case and aims to find out the influence of different resolutions of the same data set on layouts generated by different treemap algorithms. 600 trees are generated and tested in 100 resolutions with five algorithms using four stability metrics. The comparison shows that Hilbert treemaps and Moore treemaps are relatively stable, but they may generate bad aspect ratios. Two Neighborhood treemaps are more stable, if the previous and the latter resolution both have a larger width or a larger height. Greedy-insertion treemaps hold a good balance between spatial quality and stability. These findings might help while choosing a standard visualization treemap algorithm. 3

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Stober, Gunter; Janches, Diego; Matthias, Vivien; Fritts, Dave; Marino, John; Moffat-Griffin, Tracy; Baumgarten, Kathrin; Lee, Wonseok; Murphy, Damian; Kim, Yong Ha; Mitchell, Nicholas; Palo, Scott

Seasonal Evolution of Winds, Atmospheric Tides, and Reynolds Stress omponents in the Southern Hemisphere Mesosphere–Lower Thermosphere in 2019

2021

Annales Geophysicae (ANGEO)

In this study we explore the seasonal variability of the mean winds and diurnal and semidiurnal tidal amplitude and phases, as well as the Reynolds stress components during 2019, utilizing meteor radars at six Southern Hemisphere locations ranging from midlatitudes to polar latitudes. These include Tierra del Fuego, King Edward Point on South Georgia island, King Sejong Station, Rothera, Davis, and McMurdo stations. The year 2019 was exceptional in the Southern Hemisphere, due to the occurrence of a rare minor stratospheric warming in September. Our results show a substantial longitudinal and latitudinal seasonal variability of mean winds and tides, pointing towards a wobbling and asymmetric polar vortex. Furthermore, the derived momentum fluxes and wind variances, utilizing a recently developed algorithm, reveal a characteristic seasonal pattern at each location included in this study. The longitudinal and latitudinal variability of vertical flux of zonal and meridional momentum is discussed in the context of polar vortex asymmetry, spatial and temporal variability, and the longitude and latitude dependence of the vertical propagation conditions of gravity waves. The horizontal momentum fluxes exhibit a rather consistent seasonal structure between the stations, while the wind variances indicate a clear seasonal behavior and altitude dependence, showing the largest values at higher altitudes during the hemispheric winter and two variance minima during the equinoxes. Also the hemispheric summer mesopause and the zonal wind reversal can be identified in the wind variances.

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The Effect of Alignment on Peoples Ability to Judge Event Sequence Similarity

2021

IEEE Transactions on Visualization and Computer Graphics

Event sequences are central to the analysis of data in domains that range from biology and health, to logfile analysis and people's everyday behavior. Many visualization tools have been created for such data, but people are error-prone when asked to judge the similarity of event sequences with basic presentation methods. This paper describes an experiment that investigates whether local and global alignment techniques improve people's performance when judging sequence similarity. Participants were divided into three groups (basic vs. local vs. global alignment), and each participant judged the similarity of 180 sets of pseudo-randomly generated sequences. Each set comprised a target, a correct choice and a wrong choice. After training, the global alignment group was more accurate than the local alignment group (98% vs. 93% correct), with the basic group getting 95% correct. Participants' response times were primarily affected by the number of event types, the similarity of sequences (measured by the Levenshtein distance) and the edit types (nine combinations of deletion, insertion and substitution). In summary, global alignment is superior and people's performance could be further improved by choosing alignment parameters that explicitly penalize sequence mismatches.

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The Effect of Alignment on People’s Ability to Judge Event Sequence Similarity

2021

IEEE Transactions on Visualization and Computer Graphics

Event sequences are central to the analysis of data in domains that range from biology and health, to logfile analysis and people's everyday behavior. Many visualization tools have been created for such data, but people are error-prone when asked to judge the similarity of event sequences with basic presentation methods. This paper describes an experiment that investigates whether local and global alignment techniques improve people's performance when judging sequence similarity. Participants were divided into three groups (basic vs. local vs. global alignment), and each participant judged the similarity of 180 sets of pseudo-randomly generated sequences. Each set comprised a target, a correct choice and a wrong choice. After training, the global alignment group was more accurate than the local alignment group (98% vs. 93% correct), with the basic group getting 95% correct. Participants' response times were primarily affected by the number of event types, the similarity of sequences (measured by the Levenshtein distance) and the edit types (nine combinations of deletion, insertion and substitution). In summary, global alignment is superior and people's performance could be further improved by choosing alignment parameters that explicitly penalize sequence mismatches.

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Spitzenberg, David; Stork, André [1. Review]; Grasser, Tim [2. Review]

Topology and Material Optimization for Microstructure-Based Multimaterial 3D-Printing

2021

Darmstadt, TU, Master Thesis, 2021

Microstructure-based meta-materials have facilitated the design of additively manufactured objects featuring rich, spatially varying mechanical properties. However, originatingin the context of 3D printing, microstructures are typically modeled using cube-shapedvoxels filled with a small set of base materials preventing the underlying two-scale approach from being transferred to other applications. To date, little work has been put intothe design of microstructures using other, wide-spread cell types. Throughout this thesis,we study base material arrangements employing tetrahedral cells resulting in microstructures of diverse applicability. To this end, we give a sound reasoning on the design oftetrahedral microstructures at the micro-scale which, ensured by our construction, resultin orientation-agnostic cubic meta-materials, experimentally explore the correspondingspace of meta-materials and apply this meta-material space to macro-scale, real-worlddesign tasks again defined over tetrahedral meshes. Our discussion shows the applicabilityof the discussed two-scale approach to the design of objects featuring spatially varyingmechanical properties using tetrahedral cells instead of a printer’s cube-shaped voxels.