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Boletim de Ciências Geodésicas, Volume: 26, Número: 3, Publicado: 2020
  • The quality of OpenStreetMap in a large metropolis in northeast Brazil: Preliminary assessment of geospatial data for road axes Original Article

    Elias, Elias Nasr Naim; Fernandes, Vivian de Oliveira; Alixandrini Junior, Mauro José; Schmidt, Marcio Augusto Reolon

    Resumo em Inglês:

    Abstract: This paper evaluates the data quality of road axes using the OpenStreetMap (OSM) collaborative mapping platform. OSM was chosen owing to the abundance of data and registered contributors (~ 6 million). We assumed the OSM collaborative data could complement the reference mappings by its quality parameters. We used the cartographic quality indicators of positional accuracy, thematic accuracy, and completeness to validate vector files from OSM. We analyzed the positional accuracy of linear features and we developed the automation of the positional accuracy process. The tool verified the completeness of road axes and thematic accuracy. The positional accuracy of linear features was also used, performed to obtain a range of scales, which reflected the characteristics of mapped areas and varied from 1:22,500 to 1:25,000. The completeness of road axes was 82% of the checked areas. By evaluating the thematic accuracy, we found that the absence of road axes toponymy in editions caused errors in the OSM features (i.e., 58% of road axes without information). As such, we concluded that collaborative data complements the reference cartography by measuring the heterogeneity of information in various regions and filtering the OSM data, despite its being useful for certain analyses.
  • ASSESSMENT OF HYDROLOGICAL MASS LOSSES IN THE NORTHEAST ATLANTIC EASTERN HYDROGRAPHIC REGION, BRAZIL Original Article

    Lima, Fábio Vinícius Marley Santos; Gonçalves, Rodrigo Mikosz; Castro, Henry Diverth Montecino; Nova, Raquel Arcoverde Vila

    Resumo em Inglês:

    Abstract: Freshwater monitoring globally is fundamental to support decision-making. However, long-term hydrological data for some regions are lacking due to limited of observational networks. Remote sensing products come to aggregate the in situ observations and overcome obstacles about data availability. This study assesses the hydrological mass losses in the Northeast Atlantic Eastern Hydrographic Region (NAEHR) in Brazil through temporal data sources. GRACE RL06 Mascon solutions, reservoirs volume, vegetation index and rainfall stations are used. The results confirm the cohesion between the TWS variations with water volume and NDVI, obtaining a strong correlation of 0.78 and 0.77 respectively. The Standardized Precipitation Index scales (12, 24 and 36 months) showed a moderate and strong correlation with the TWS of 0.57, 0.73 and 0.72 respectively and identified the last regional severe drought from 2012 to 2017. The NEAHR is located almost entirely in the Brazilian semiarid region, comprises about 24 million inhabitants, it is high vulnerable to drought, thus justifying the importance of monitoring its water resources availability.
  • EVALUATION OF THE GNSS POSITIONING PERFORMANCE UNDER INFLUENCE OF THE IONOSPHERIC SCINTILLATION Original Article

    Caldeira, Mayara Cobacho Ortega; Caldeira, Carlos Rodrigo Tanajura; Cereja, Samara Sunny dos Anjos; Alves, Daniele Barroca Marra; Aguiar, Claudinei Rodrigues de

    Resumo em Inglês:

    Abstract: The ionosphere may not only degrade the accuracy of the GNSS positioning but also reduce its availability because there is a high dependence between signal losses and ionospheric irregularities. Irregularities in the Earth’s ionosphere may produce rapid fluctuations in phase and amplitude. These rapid fluctuations are called ionospheric scintillation. Thus, loss of signal can occur due to the effects of diffraction and refraction, which cause a weakening in the signal received by the GNSS receivers. In this way, this paper aims to evaluate the magnitude of ionospheric scintillation in Brazil and the performance of the positioning under its influence in the period of high solar activity in the current cycle (24), through the Spearman correlation analysis and the Wavelet periodogram. For that, three-year time series (2012 to 2014) of the S4 index and 3D MSE (Mean Squared Error) of three Brazilian stations with different ionospheric conditions were considered, PALM (near the Geomagnetic Equator) PRU2 (Equatorial region and Anomalies) and POAL (Mid-latitude region). Thus, it was possible to evaluate the correlation between the accuracy of the precise point positioning using only the C/A code of the GPS satellite and the S4 index. As a result, there was a correlation of 53% and 51%, using the Spearman method, for the PALM and PRU2 series, respectively. In addition, considering the analysis of space-frequency in relation to time by the Wavelet coherence method, a correlation of more than 70% is noted in the period of greatest 3D MSE concerning the spring and autumn equinox months.
  • A PERCEPTRON-BASED FEATURE SELECTION APPROACH FOR DECISION TREE CLASSIFICATION Original Article

    Casaroti, Carla Jaqueline; Centeno, Jorge Antonio Silva; Fuchs, Stephan

    Resumo em Inglês:

    Abstract: The use of OBIA for high spatial resolution image classification can be divided in two main steps, the first being segmentation and the second regarding the labeling of the objects in accordance with a particular set of features and a classifier. Decision trees are often used to represent human knowledge in the latter. The issue falls in how to select a smaller amount of features from a feature space with spatial, spectral and textural variables to describe the classes of interest, which engenders the matter of choosing the best or more convenient feature selection (FS) method. In this work, an approach for FS within a decision tree was introduced using a single perceptron and the Backpropagation algorithm. Three alternatives were compared: single, double and multiple inputs, using a sequential backward search (SBS). Test regions were used to evaluate the efficiency of the proposed methods. Results showed that it is possible to use a single perceptron in each node, with an overall accuracy (OA) between 77.6% and 77.9%. Only SBS reached an OA larger than 88%. Thus, the quality of the proposed solution depends on the number of input features.
  • Erratum: EVALUATION OF THE GNSS POSITIONING PERFORMANCE UNDER INFLUENCE OF THE IONOSPHERIC SCINTILLATION Erratum

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