Schreck, Tobias

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Visual cluster analysis of trajectory data with interactive Kohonen maps

2009, Schreck, Tobias, Bernard, Jürgen, von Landesberger, Tatiana, Kohlhammer, Jörn

Visual-interactive cluster analysis provides valuable tools for effectively analyzing large and complex data sets. Owing to desirable properties and an inherent predisposition for visualization, the Kohonen Feature Map (or Self-Organizing Map or SOM) algorithm is among the most popular and widely used visual clustering techniques. However, the unsupervised nature of the algorithm may be disadvantageous in certain applications. Depending on initialization and data characteristics, cluster maps (cluster layouts) may emerge that do not comply with user preferences, expectations or the application context. Considering SOM-based analysis of trajectory data, we propose a comprehensive visual-interactive monitoring and control framework extending the basic SOM algorithm. The framework implements the general Visual Analytics idea to effectively combine automatic data analysis with human expert supervision. It provides simple, yet effective facilities for visually monitoring and interactively controlling the trajectory clustering process at arbitrary levels of detail. The approach allows the user to leverage existing domain knowledge and user preferences, arriving at improved cluster maps. We apply the framework on several trajectory clustering problems, demonstrating its potential in combining both unsupervised (machine) and supervised (human expert) processing, in producing appropriate cluster results.

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A Visual Analysis of Multi-Attribute Data Using Pixel Matrix Displays

2007-01-28, Hao, Ming C., Dayal, Umeshwar, Keim, Daniel A., Schreck, Tobias

Charts and tables are commonly used to visually analyze data. These graphics are simple and easy to understand, but charts show only highly aggregated data and present only a limited number of data values while tables often show too many data values. As a consequence, these graphics may either lose or obscure important information, so different techniques are required to monitor complex datasets. Users need more powerful visualization techniques to digest and compare detailed multi-attribute information to analyze the health of their business. This paper proposes an innovative solution based on the use of pixel-matrix to represent transaction-level information within graphics. With pixel-matrixes, users can visualize areas of importance at a glance, a capability not provided by common charting techniques. Our solutions are based on colored pixel-matrixes, which are used in (1) charts for visualizing data patterns and discovering exceptions, (2) tables for visualizing correlations and finding root-causes, and (3) time series for visualizing the evolution of long-running transactions. The solutions have been applied with success to product sales, Internet network performance analysis, and service contract applications demonstrating the benefits of our method over conventional graphics. The method is especially useful when detailed information is a key part of the analysis.

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Content-Based 3D Object Retrieval

2007, Bustos Cárdenas, Benjamin Eugenio, Keim, Daniel A., Saupe, Dietmar, Schreck, Tobias

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Visual Rank Analysis for Search Engine Benchmarking and Efficient Navigation

2007, Catarci, Tiziana, Keim, Daniel A., Santucci, Giuseppe, Schreck, Tobias, Iervella, Gloria, Iannarelli, Stefano, Veltri, Fabio

In many important applications, the search for non-standard data types is essential. E.g., digital libraries and multimedia database systems offer content-based search functionality for images and 3D documents. Contrary to the annotation-based approach, where information manually attached to the data objects if used for retrieval, in content-based retrieval, automatically derived meta-data is used. However, the quality of the meta data is crucial, and often, it a priori is not clear which meta data is best suited to execute a user-issued query. Owing to the multi-meta data problem, two crucial questions arise: (a) how can different meta data (feature vector) schemas be benchmarked to assess their suitability for solving the retrieval problem effectively, and (b) how to support the user with issuing queries to the retrieval system, considering different choices for the type of meta data to engage in the search. In this paper, we address these questions in a two-fold contribution. Based on the DARE visualization system, we first introduce an approach for the visual benchmarking of multiple meta data formats on a ground truth benchmark, supporting the optimization stage of the multimedia database design. We secondly propose a simple, yet effective visual interface to multiple, long lists (rankings) of answer objects for the user. The latter, based on relevance feedback information supplied by the user, allows the effective identification of the meta data schema best suited for executing the similarity queries at hand.

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An Image-Based Approach to Visual Feature Space Analysis

2008, Schreck, Tobias, Schneidewind, Jörn, Keim, Daniel A.

Methods for management and analysis of non-standard data often rely on the so-called feature vector approach. The technique describes complex data instances by vectors of characteristic numeric values which allow to index the data and to calculate similarity scores between the data elements. Thereby, feature vectors often are a key ingredient to intelligent data analysis algorithms including instances of clustering, classification, and similarity search algorithms. However, identification of appropriate feature vectors for a given database of a given data type is a challenging task. Determining good feature vector extractors usually involves benchmarks relying on supervised information, which makes it an expensive and data dependent process. In this paper, we address the feature selection problem by a novel approach based on analysis of certain feature space images. We develop two image-based analysis techniques for the automatic discrimination power analysis of feature spaces. We evaluate the techniques on a comprehensive feature selection benchmark, demonstrating the effectiveness of our analysis and its potential toward automatically addressing the feature selection problem.

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A New Metaphor for Projection-Based Visual Analysis and Data Exploration

2007-01-28, Schreck, Tobias, Panse, Christian

In many important application domains such as Business and Finance, Process Monitoring, and Security, huge and quickly increasing volumes of complex data are collected. Strong efforts are underway developing automatic and interactive analysis tools for mining useful information from these data repositories. Many data analysis algorithms require an appropriate definition of similarity (or distance) between data instances to allow meaningful clustering, classification, and retrieval, among other analysis tasks. Projection-based data visualization is highly interesting (a) for visual discrimination analysis of a data set within a given similarity definition, and (b) for comparative analysis of similarity characteristics of a given data set represented by different similarity definitions. We introduce an intuitive and effective novel approach for projection-based similarity visualization for interactive discrimination analysis, data exploration, and visual evaluation of metric space effectiveness. The approach is based on the convex hull metaphor for visually aggregating sets of points in projected space, and it can be used with a variety of different projection techniques. The effectiveness of the approach is demonstrated by application on two well-known data sets. Statistical evidence supporting the validity of the hull metaphor is presented. We advocate the hull-based approach over the standard symbol-based approach to projection visualization, as it allows a more effective perception of similarity relationships and class distribution characteristics.

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Effective Retrieval and Visual Analysis in Multimedia Databases

2007, Schreck, Tobias

Basierend auf Fortschritten bei der digitalen Erfassung, Speicherung und Übermittlung multimedialer Inhalte werden zunehmend große Mengen von Multimedia Objekten wie z.B. Bilder, Audio, Videos, und 3D Modellen verfügbar. Das Feature Vector Paradigma ist aufgrund seiner Einfachheit und Allgemeinheit einer der populärsten Ansätze zum Management von Multimedia Inhalten. Es bildet die Elemente eines Multimedia Objektraumes in einen metrischen Raum ab und ermöglicht hierdurch, von den Distanzen im metrischen Raum auf Ähnlichkeitsbeziehungen im Objektraum rück schließen zu können. Für einen gegebenen Multimedia Datentyp sind prinzipiell viele verschiedene Abbildungen in einen metrischen Raum denkbar. Die Effektivität einer gegebenen Abbildung kann als der Grad der Übereinstimmung der Distanzen im metrischen Raum mit dem Grad der Ähnlichkeiten im Objektraum verstanden werden. Die Effektivität der Abbildung mit Feature Vektoren ist von grundlegender Bedeutung für alle auf dieser Abbildung aufsetzenden Anwendungen. Zwei grundlegende Ideen liegen dieser Arbeit zugrunde. Zum einen stellen wir fest, dass der Feature Vektor Ansatz der geeigneten Auswahl und Konfiguration der Feature Vektoren bedarf, um effektive Anwendungen zu ermöglichen. Zum anderen sind wir überzeugt davon, dass bestimmte Visualisierungstechniken als effektive Schnittstellen für den Feature und den Objektraum geeignet sind. Im Rahmen dieser Arbeit werden innovative Methoden (a) zur effektiven Ausführung von Ähnlichkeits-Suchanfragen, (b) zur visuellen Diskriminierunganalyse, sowie (c) zur Layouterzeugung für die Präsentation und Analyse von Multimedia Daten entwickelt. Die Nützlichkeit der Methoden wird durch Anwendung auf eine Reihe von verschiedenen Multimedia Datentypen wie 3D Objekte und Zeitreihendaten aufgezeigt.

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Towards Automatic Feature Vector Optimization for Multimedia Applications

2008, Schreck, Tobias, Fellner, Dieter W., Keim, Daniel A.

We systematically evaluate a recently proposed method for unsupervised discrimination power analysis for feature selection and optimization in multimedia applications. A series of experiments using real and synthetic benchmark data is conducted, the results of which indicate the suitability of the method for unsupervised feature selection and optimization. We present an approach for generating synthetic feature spaces of varying discrimination power, modeling main characteristics from real world feature vector extractors. A simple, yet powerful visualization is used to communicate the results of the automatic analysis to the user.

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DelosDLMS - The integrated DELOS digital library management system

2007, Agosti, Maristella, Berretti, Stefano, Brettlecker, Gert, Del Bimbo, Alberto, Ferro, Nicola, Fuhr, Norbert, Keim, Daniel A., Klas, Claus-Peter, Lidy, Thomas, Milano, Diego, Norrie, Moira C., Ranaldi, Paola, Rauber, Andreas, Schek, Hans-Jörg, Schreck, Tobias, Schuldt, Heiko, Signer, Beat, Springmann, Michael

DelosDLMS is a prototype of a next-generation Digital Library (DL) management system. It is realized by combining various specialized DL functionalities provided by partners of the DELOS network of excellence. Currently, DelosDLMS combines text and audio-visual searching, offers new information visualization and relevance feedback tools, provides novel interfaces, allows retrieved information to be annotated and processed, integrates and processes sensor data streams, and finally, from a systems engineering point of view, is easily configured and adapted while being reliable and scalable. The prototype is based on the OSIRIS/ISIS platform, a middleware environment developed by ETH Zürich and now being extended at the University of Basel.

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Methoden und Benutzerschnittstellen für effektives Retrieval in 3D-Datenbanken

2007, Bustos Cárdenas, Benjamin Eugenio, Keim, Daniel A., Saupe, Dietmar, Schreck, Tobias, Tatu, Andrada

3D Objekte sind ein wichtiger Typ Multimedia Daten mit einer Reihe vielversprechender Anwendungsmöglichkeiten etwa in der industriellen Produktion, in Simulation, Unterhaltung und Visualisierung. Die Definition von Ähnlichkeit zwischen 3D Objekten und die Implementierung von entsprechenden Ähnlichkeitssuchalgorithmen sind interessant für den Einsatz in 3D-Datenbanksystemen, repräsentieren aber gleichzeitig schwierige Probleme. In dieser Arbeit stellen wir Methoden dar, um effektives Retrieval in 3D-Datenbanken zu realisieren. Wir besprechen zudem Methoden, um Ergebnisse von Ähnlichkeitssuchanfragen sowie ganze 3D Objekträume visuell zu analysieren.