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Journal of the Brazilian Computer Society, Volume: 15, Issue: 2, Published: 2009
  • Letter from the editor-in-chief

    Oliveira, Maria Cristina Ferreira de
  • Volume sculpting based on geometric tools

    Huff, Rafael; Rosa Jr., Roberto Silveira da; Nedel, Luciana; Freitas, Carla Maria Dal Sasso

    Abstract in English:

    The analysis of volumetric datasets is the main concern in many areas ranging from geophysics to biomedical sciences. The direct visualization of these data plays an important role in this scenario, and in spite of developments in volume visualization techniques, interacting with large datasets still demands research efforts due to perceptual and performance issues. There is a need of interactive sculpting tools which can provide an intuitive way to examine and explore inner parts of the datasets, as well as to fill missing data for specific purposes. In this paper we report the development of interactive, intuitive and easy-to-use sculpting tools, which specify regions within the volume to be discarded from rendering, thus allowing inspection of the volume interior, and to be filled with material to build virtual structures in the volume. Interactive rates for these sculpting tools were obtained by running special fragment programs on the graphics hardware. The tools were implemented using two interaction metaphors (virtual pointer and virtual hand) and following different approaches in terms of devices and single versus two-handed interaction. We report the evaluation of these approaches in detail and concluded that the use of two different devices together presents a better performance and are preferred by users. Moreover, the use of virtual hand interaction provided better results than using the virtual pointer during the tests.
  • The impact of spatial data redundancy on SOLAP query performance

    Siqueira, Thiago Luís Lopes; Ciferri, Cristina Dutra de Aguiar; Times, Valéria Cesário; Oliveira, Anjolina Grisi de; Ciferri, Ricardo Rodrigues

    Abstract in English:

    Geographic Data Warehouses (GDW) are one of the main technologies used in decision-making processes and spatial analysis, and the literature proposes several conceptual and logical data models for GDW. However, little effort has been focused on studying how spatial data redundancy affects SOLAP (Spatial On-Line Analytical Processing) query performance over GDW. In this paper, we investigate this issue. Firstly, we compare redundant and non-redundant GDW schemas and conclude that redundancy is related to high performance losses. We also analyze the issue of indexing, aiming at improving SOLAP query performance on a redundant GDW. Comparisons of the SB-index approach, the star-join aided by R-tree and the star-join aided by GiST indicate that the SB-index significantly improves the elapsed time in query processing from 25% up to 99% with regard to SOLAP queries defined over the spatial predicates of intersection, enclosure and containment and applied to roll-up and drill-down operations. We also investigate the impact of the increase in data volume on the performance. The increase did not impair the performance of the SB-index, which highly improved the elapsed time in query processing. Performance tests also show that the SB-index is far more compact than the star-join, requiring only a small fraction of at most 0.20% of the volume. Moreover, we propose a specific enhancement of the SB-index to deal with spatial data redundancy. This enhancement improved performance from 80 to 91% for redundant GDW schemas.
  • A progressive vector map browser for the web

    Ramos, José Augusto Sapienza; Esperança, Claudio; Clua, Esteban Walter Gonzales

    Abstract in English:

    With the increasing popularity of web-based map browsers, remotely obtaining a high quality depiction of cartographic information has become commonplace. Most web mapping systems, however, rely on high-capacity servers transmitting pre-rendered tiled maps in raster format. That approach is capable of producing good quality renderings on the client side while using limited bandwidth and exploiting the browser's image cache. These goals are harder to achieve for maps in vector format. In this work, we present an alternative client-server architecture capable of progressively transmitting vector maps in levels-of-detail (LOD) by using techniques such as polygonal line simplification, spatial data structures and, most importantly, a customized memory management algorithm. A multiplatform implementation of this system is described, where the client application is written entirely in JavaScript and processed within the web browser, avoiding the need of external applications or plug-ins. Results of experiments aimed at gauging both the performance and the display quality obtained with the system are presented and explained. Extensions to the system are also discussed, including issues such as level-of-detail versus visual importance tradeoffs and the handling of closed polygonal lines.
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