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  1. Article ; Online: Large-Scale Evaluation of Topic Models and Dimensionality Reduction Methods for 2D Text Spatialization.

    Atzberger, Daniel / Cech, Tim / Trapp, Matthias / Richter, Rico / Scheibel, Willy / Dollner, Jurgen / Schreck, Tobias

    IEEE transactions on visualization and computer graphics

    2023  Volume 30, Issue 1, Page(s) 902–912

    Abstract: Topic models are a class of unsupervised learning algorithms for detecting the semantic structure within a text corpus. Together with a subsequent dimensionality reduction algorithm, topic models can be used for deriving spatializations for text corpora ... ...

    Abstract Topic models are a class of unsupervised learning algorithms for detecting the semantic structure within a text corpus. Together with a subsequent dimensionality reduction algorithm, topic models can be used for deriving spatializations for text corpora as two-dimensional scatter plots, reflecting semantic similarity between the documents and supporting corpus analysis. Although the choice of the topic model, the dimensionality reduction, and their underlying hyperparameters significantly impact the resulting layout, it is unknown which particular combinations result in high-quality layouts with respect to accuracy and perception metrics. To investigate the effectiveness of topic models and dimensionality reduction methods for the spatialization of corpora as two-dimensional scatter plots (or basis for landscape-type visualizations), we present a large-scale, benchmark-based computational evaluation. Our evaluation consists of (1) a set of corpora, (2) a set of layout algorithms that are combinations of topic models and dimensionality reductions, and (3) quality metrics for quantifying the resulting layout. The corpora are given as document-term matrices, and each document is assigned to a thematic class. The chosen metrics quantify the preservation of local and global properties and the perceptual effectiveness of the two-dimensional scatter plots. By evaluating the benchmark on a computing cluster, we derived a multivariate dataset with over 45 000 individual layouts and corresponding quality metrics. Based on the results, we propose guidelines for the effective design of text spatializations that are based on topic models and dimensionality reductions. As a main result, we show that interpretable topic models are beneficial for capturing the structure of text corpora. We furthermore recommend the use of t-SNE as a subsequent dimensionality reduction.
    Language English
    Publishing date 2023-12-25
    Publishing country United States
    Document type Journal Article
    ISSN 1941-0506
    ISSN (online) 1941-0506
    DOI 10.1109/TVCG.2023.3326569
    Database MEDical Literature Analysis and Retrieval System OnLINE

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  2. Article: Object class segmentation of massive 3D point clouds of urban areas using point cloud topology

    Richter, Rico / Behrens, Markus / Döllner, Jürgen

    International journal of remote sensing. 2013 Dec. 10, v. 34, no. 23

    2013  

    Abstract: A large number of remote-sensing techniques and image-based photogrammetric approaches allow an efficient generation of massive 3D point clouds of our physical environment. The efficient processing, analysis, exploration, and visualization of massive 3D ... ...

    Abstract A large number of remote-sensing techniques and image-based photogrammetric approaches allow an efficient generation of massive 3D point clouds of our physical environment. The efficient processing, analysis, exploration, and visualization of massive 3D point clouds constitute challenging tasks for applications, systems, and workflows in disciplines such as urban planning, environmental monitoring, disaster management, and homeland security. We present an approach to segment massive 3D point clouds according to object classes of virtual urban environments including terrain, building, vegetation, water, and infrastructure. The classification relies on analysing the point cloud topology; it does not require per-point attributes or representative training data. The approach is based on an iterative multi-pass processing scheme, where each pass focuses on different topological features and considers already detected object classes from previous passes. To cope with the massive amount of data, out-of-core spatial data structures and graphics processing unit (GPU)-accelerated algorithms are utilized. Classification results are discussed based on a massive 3D point cloud with almost 5 billion points of a city. The results indicate that object-class-enriched 3D point clouds can substantially improve analysis algorithms and applications as well as enhance visualization techniques.
    Keywords algorithms ; environmental monitoring ; infrastructure ; photogrammetry ; remote sensing ; spatial data ; topology ; urban areas ; urban planning ; vegetation
    Language English
    Dates of publication 2013-1210
    Size p. 8408-8424.
    Publishing place Taylor & Francis
    Document type Article
    ZDB-ID 1497529-4
    ISSN 1366-5901 ; 0143-1161
    ISSN (online) 1366-5901
    ISSN 0143-1161
    DOI 10.1080/01431161.2013.838710
    Database NAL-Catalogue (AGRICOLA)

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