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Boletim de Ciências Geodésicas, Volume: 25, Número: 4, Publicado: 2019
  • VERTICAL ACCURACY ASSESSMENT OF THE PROCESSED SRTM DATA FOR THE BRAZILIAN TERRITORY Original Article

    Orlandi, Alex Gois; Carvalho Júnior, Osmar Abílio de; Guimarães, Renato Fontes; Bias, Edilson de Souza; Corrêa, Douglas Corbari; Gomes, Roberto Arnaldo Trancoso

    Resumo em Inglês:

    Abstract: This research aims to determine the vertical accuracy of the Interferometric Digital Elevation Model (DEM) obtained from the processed Shuttle Radar Topographic Mission (SRTM) data. The research compared the SRTM-GL1 (Shuttle Radar Topographic Mission-Global 1) with 30-meter resolution and the following 90-meter resolution models: (a) EMBRAPA; (b) Hydrological data and maps based on Shuttle Elevation Derivatives at multiple Scales (HydroSHEDS) (HydroSHEDS), provided by the United States Geological Survey (USGS); (c) Consultative Group for International Agricultural Research-Consortium for Spatial Information (CGIAR-CSI); and (d) Jonathan de Ferranti. The accuracy analysis considered the diverse Brazilian regions, adopting 1,087 field points from the Global Navigation Satellite System (GNSS) trackers or topography methods. The Jonathan de Ferranti model achieved the best accuracy with RMSE of 9.61m among the 90-meter resolution models. Most SRTM models at 1:100,000 scale reached Grade A of the Cartographic Accuracy Standard. However, the accuracy at the 1: 50,000 scale did not achieve the same performance. SRTM errors are linearly related to slope and the most significant errors always occur in forest areas. The 30-meter resolution SRTM showed an accuracy of around 10% better (RMSE of 8.52m) than the model of Jonathan de Ferranti with 90-meter resolution (RMSE of 9.61m).
  • A QUANTITATIVE EVALUATION OF DGPS PERFORMANCE IN THE POSITION AND PSEUDORANGE DOMAINS Original Article

    Lima, Erly Caldas de; Pissardini, Rodrigo de Sousa; Oliveira, Rafael Henrique de; Fonseca Junior, Edvaldo Simões da; Cintra, Jorge Pimentel

    Resumo em Inglês:

    Abstract: This study compares in quantitative terms two methods of differential corrections to GPS positioning from the code-based pseudoranges. The differential method calculated from the coordinates (Latitude, Longitude and Altitude), called Position-Domain DGPS, has simple implementation and easy transmission by the correction vector. The second method, called Pseudorange-Domain DGPS has a more elaborate algorithm, focused on the pseudorange correction for each visible satellite, which consumes more processing time and increases the complexity in the transmission of the corrections. Notwithstanding a few variations from this DGPS techniques proposed, this work intends to verify in a numeric way the bias and precision offered by these two well-known methods in different devices and situations, to assess in which context each method would be more advantageous when one what to apply a simple DGPS correction; showing how much is the gain by way of bias the more elaborated method is. The results demonstrate that in favorable conditions, the Position-Domain offered an improvement of approximately 50% in positioning, 35% in dispersion, but without any significant bettering in altimetry or in the maximum values; wile the Pseudorange-Domain method showed 70% in positioning, 75% in precision, 60% for maximum values and numbers close to zero on average altimetry.
  • LANDMARKS EVALUATION WITH USE OF QR-CODE FOR POSITIONING INDOOR ENVIRONMENT Original Article

    Antunes, Amanda Pereira; Delazari, Luciene Stamato

    Resumo em Inglês:

    Abstract: People tend to lose their sense of direction in closed environments and the role of indoor maps is to assist the user in navigating in these spaces, through understanding the environment, identifying reference points or positioning. Among the several forms of achieving positioning in indoor environments, this research used the method based on image recognition through identification of QR-Code labels, because of their low cost, easy implementation, and because their accuracy is not affected by the environment. As such, this article presents the use of QR-Code markers affixed to possible reference points to determine user positioning in an indoor environment using a mobile device. This study seeks to discover which are the most appropriate sites for placing QR-Codes in an environment, by evaluating what reference points and what type thereof are most used in indoor environments. This study is therefore based on the hypothesis that if initial positioning is obtained only through reference points this is sufficient for users to orient themselves. Through analysis of the results obtained from navigation tasks done by users we were able to obtain data regarding elements most cited as references. The results show that people orient themselves in distinct ways in the same environment and use as their main reference points structural elements of the environment such as stairways, lifts, and decision-making points; in general structural reference points were those most used to support orientation and navigation.
  • A PROPOSAL FOR MODELING AND IMPLEMENTING AN INTEGRATED SYSTEM FOR BRAZILIAN CADASTRES ACCORDING TO ISO 19152:2012 LAND ADMINISTRATION DOMAIN MODEL Original Article

    Purificação, Nathalia Rose Silva da; Carneiro, Andrea Flávia Tenório; Julião, Rui Pedro

    Resumo em Inglês:

    Abstract: This article proposes the modelling and implementation of an integrated system for Brazilian cadastres, based on the standardized model of land administration described in the ISO 19152:2012 LADM. The model was developed from the identification of the essential elements of the urban, the National Rural Cadastre System and the cadastres of public assets of the Secretariat of the Patrimony of the Union. At all stages of this work, free and/or open source software was used to validate this proposal. The results confirm the viability of the application of the concepts proposed by LADM to the Brazilian system of cadastres, allowing the integration between the systems of different institutions. The model is flexible and allows for the inclusion of additional classes according to changing needs of land administration data users. The current form of the model can be regarded as the basic module to be used as a starting point in the structuring of the National System of Management of Territorial Information, which is aimed at the integration of all existing cadastres and land registries in Brazil.
  • ERROR BEHAVIOR OF ATOMIC CLOCKS ABOARD GPS SATELLITES Original Article

    Mansur, Gustavo Bento; Ferreira, Luiz Danilo Damasceno

    Resumo em Inglês:

    Abstract: The signal transmission and position quality obtained by GNSS positioning directly depends on the time control. The atomic clocks aboard the satellites are responsible for this control. In this research, the satellites clock errors of GPS are studied, using data from the pseudorange, the satellite semi-major axis and the correction parameters of the satellites’ clock errors found in the RINEX navigation and observation files. From these data, the satellites’ clock errors are calculated using the IGS mathematical model for rubidium and cesium clocks, and then an adjustment technique is applied in order to estimate the new parameters of the clock corrections. For cesium atomic clocks, the periodic part of the mathematical model was adapted. The correction parameters adjusted were applied in the IGS and the adapted model; finally, the results were compared with the IGS data from the clk_30s file. The experiments carried out show an improvement of 50 cm in the cesium satellites’ clock errors. In addition, the research concludes that the satellites’ clock errors do not depend on the station where the data were collected and the equipment’s antenna.
  • THE USE OF THE AUTOMATED DIGITAL ZENITH CAMERA SYSTEM IN ISTANBUL FOR THE DETERMINATION OF ASTROGEODETIC VERTICAL DEFLECTION Original Article

    Albayrak, Müge; Halıcıoğlu, Kerem; Özlüdemir, Mustafa Tevfik; Başoğlu, Burak; Deniz, Rasim; Tyler, Allison RB; Aref, Mohammed Mohseni

    Resumo em Inglês:

    Abstract: The Digital Zenith Camera Systems (DZCSs) are dedicated astrogeodetic instruments used to obtain highly accurate astrogeodetic vertical deflection (VD) data. The first Turkish DZCS, the Astrogeodetic Camera System (ACSYS), was developed in Istanbul, Turkey in 2015. The ACSYS was capable of determining astrogeodetic VDs with an accuracy of ~0.3 arcseconds. However, it had some limitations in observation duration: because of the semi-automated mechanical design, levelling the system towards zenith was a time-consuming process. Since 2016, the ACSYS has been modernized through system upgrades and new technological components. In this paper, we describe the instrument design of the new DZCS-ACSYS2-observation procedures, evaluation of the test data and calculations of these data. The preliminary ACSYS2 astrogeodetic test observations were conducted at Istanbul Technical University (ITU) test station. The standard deviation results of the repeated observations reveal a VD measurement precision of ~0.3 arcseconds for both the North-South and East-West components. To investigate the accuracy of the system, a lightweight total station based-geodetic system-QDaedalus-was also used at the ITU test station. The comparison of the VDs data between ACSYS2 and QDaedalus system shows that the ACSYS2 can produce reliable VDs data.
  • SPATIAL OUTLIERS DETECTION ALGORITHM (SODA) APPLIED TO MULTIBEAM BATHYMETRIC DATA PROCESSING Original Article

    Ferreira, Italo Oliveira; Santos, Afonso de Paula dos; Oliveira, Júlio César de; Medeiros, Nilcilene das Graças; Emiliano, Paulo César

    Resumo em Inglês:

    Abstract: The amount of data produced in an echosounder has increased dramatically with scanning systems such as multibeam echo sounders and interferometric sonars, providing a considerable improvement in the submerged terrain representation, especially when it comes to detecting hazardous objects to the navigator. However, the available processing algorithms did not come along with this evolution; manual processing or, at least, constant intervention is usually necessary, which makes this task arduous with a high degree of subjectivity. In addition, statistical inconsistencies do not appear to be uncommon in most of the algorithms and filters available. Thus, SODA (Spatial Outliers Detection Algorithm) was recently presented, being a methodology directed, at first, to echosounder data treatment. Considering this, this article aims to evaluate the SODA efficiency for real data treatment from a multibeam sonar. SODA, in some cases, was capable to identify up to 74% of spikes with the δ-Method, which means that this technique detected 28 out of the 38 confirmed spikes in the data set, reassuming the methodology strength regarding the search for spikes in echosounder data.
  • G-SIVAR: A GLOBAL SPATIAL INDICATOR BASED ON VARIOGRAM Original Article

    Naizer, Cláudia Cristina Baptista Ramos; Rodrigues, David Souza; Pedreira Junior, Jorge Ubirajara; Pitombo, Cira Souza

    Resumo em Inglês:

    Abstract: Among the exploratory spatial data analysis tools, there are indicators of spatial association, which measure the degree of spatial dependence of analysed data and can be applied to quantitative data. Another procedure available is geostatistics, which is based on the variogram, describing quantitatively and qualitatively the spatial structure of a variable. The aim of this paper is to use the concept of the variogram to develop a global indicator of spatial association (Global Spatial Indicator Based on Variogram - G-SIVAR). The G-SIVAR indicator has a satisfactory performance for spatial association, with sensibility for anisotropy cases. Because the indicator is based on geostatistics, it is appropriate for quantitative and qualitative data. The developed indicator is derived from theoretical global variogram, providing more details of the spatial structure of the data. The G-SIVAR indicator is based on spatial dissimilarity, while traditional indexes, such as Moran’s I, are based on spatial similarity.
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