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Structural integrity verification of cable stayed footbridge based on FEM analyses and geodetic surveying techniques / Vassilis Gikas in Survey review, vol 48 n° 346 (January 2016)  

Public [article]  inSurvey review > vol 48 n° 346 (January 2016) . - pp 1 - 10 Titre : Structural integrity verification of cable stayed footbridge based on FEM analyses and geodetic surveying techniques Type de document : Article/Communication Auteurs : Vassilis Gikas, Auteur ; P. Karydakis, Auteur ; Thanassis Mpimis, Auteur ; et al., Auteur Année de publication : 2016 Article en page(s) : pp 1 - 10 Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Topographie [Termes IGN] construction [Termes IGN] GPS-INS [Termes IGN] modèle mathématique [Termes IGN] pont [Termes IGN] surveillance d'ouvrage Résumé : (auteur) This paper presents the mathematical models developed for the design of a pedestrian, cable stayed bridge, the geodetic monitoring procedures and their detailed cross-comparisons and analyses undertaken during the phases of construction and at commissioning stage. Because of the asymmetric design, the relative flexibility of the pylons, the eccentric positioning of the central joint and the off-plane low angles of the cables, a multi-sensor, event based geodetic monitoring scheme was adopted to assess the structural integrity of the bridge. During construction, the bridge kinematics were measured along both sides of the deck and at selected points on the pylon facades using a digital level and a high accuracy total station used in metrology respectively. At a commissioning stage, a number of load test series were undertaken using conventional geodetic techniques and a tactical grade Inertial Measurement Unit (IMU). Analysis confirmed the overall mathematical modelling assumptions made for the individual stages of construction and for the completed structure. However, analysis also revealed the increased structural rigidity of the structure. This particularly applies for the torsional stiffness of the deck that exhibits low (by a factor of 0·5) rotation angles compared to those obtained from the analytical models. Numéro de notice : A2016-043 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article DOI : 10.1080/00396265.2015.1097582 En ligne : https://doi.org/10.1080/00396265.2015.1097582 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=79636 [article]

Investigating efficacy of robust M-estimation of deformation from observation differences / Krzysztof Nowel in Survey review, vol 48 n° 346 (January 2016)  

Public [article]  inSurvey review > vol 48 n° 346 (January 2016) . - pp 21 - 30 Titre : Investigating efficacy of robust M-estimation of deformation from observation differences Type de document : Article/Communication Auteurs : Krzysztof Nowel, Auteur Année de publication : 2016 Article en page(s) : pp 21 - 30 Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Navigation et positionnement [Termes IGN] analyse de données [Termes IGN] déformation géométrique [Termes IGN] estimation statistique [Termes IGN] méthode de Monte-Carlo [Termes IGN] méthode des moindres carrés [Termes IGN] modèle stochastique [Termes IGN] test de performance Résumé : (auteur) In deformation analysis of geodetic control networks, it is important to know whether the estimated displacement value of a given point is the effect of displacement or only the effect of random measurement errors. The F-test of statistical significance is used to answer this question. This test is applied both in conventional deformation analysis (CDA) based on least square (LS) estimation and in deformation analysis based on robust M-estimation. Unfortunately, the F-test is strongly flawed in the latter case. As a consequence, its results are significantly different here than assumed/expected. This paper analyses how flawed the F-test is and proposes a new solution. First, the algorithm of the global and local F-tests was derived. It was then demonstrated that for deformation analysis based on robust M-estimation, this algorithm has theoretical flaws. Next, it was shown how these problems can be solved numerically. The basis of the solutions proposed involves the use of stochastic simulations and, more specifically, the Monte Carlo (MC) method. Moreover, it was noted that other statistical test problems which also occur in deformation analysis based on robust M-estimation can be solved using present-day computers. The numerical approach can be a good support here in the selection of the proper significance level as well as in the correct performance of the test sensitivity analysis. All theoretical discussions were verified on an example simulated control network. Numéro de notice : A2016-044 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article DOI : 10.1080/00396265.2015.1097585 En ligne : https://doi.org/10.1080/00396265.2015.1097585 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=79637 [article]

External error modelling with combined model in terrestrial laser scanning / J. Wang in Survey review, vol 48 n° 346 (January 2016)  

Public [article]  inSurvey review > vol 48 n° 346 (January 2016) . - pp 40 - 50 Titre : External error modelling with combined model in terrestrial laser scanning Type de document : Article/Communication Auteurs : J. Wang, Auteur ; H. Kutterer, Auteur ; X. Fang, Auteur Année de publication : 2016 Article en page(s) : pp 40 - 50 Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Lasergrammétrie [Termes IGN] étalonnage de capteur (imagerie) [Termes IGN] itération [Termes IGN] modèle de Gauss-Helmert [Termes IGN] réfraction atmosphérique [Termes IGN] télémétrie laser sur satellite [Termes IGN] télémétrie laser terrestre Résumé : (auteur) Terrestrial laser scanning (TLS) is a promising tool in geodetic applications. Data quality of outdoor TLS measurements is considerably limited by external errors caused by atmospheric variations and object related factors. In this study, external models related to atmospheric refraction, beam wander and incidence angle were introduced and integrated into a seven-parameter similarity transformation (7PST) model to compose a combined model. The combined model was rigorously adjusted by an iterative Gauss–Helmert (GH) model primarily to estimate external calibration parameters and transformation parameters simultaneously. In the application on a dam surface, a t-test showed that a significant external calibration parameter was the range scale, which mainly corresponded with the incidence angle model. The precision of estimated representative points was improved by approximately 50% with the proposed method. The presented models show a great potential for detecting external errors and registering multiple scans in outdoor applications. Numéro de notice : A2016-045 Affiliation des auteurs : non IGN Thématique : IMAGERIE Nature : Article DOI : 10.1080/00396265.2015.1097589 En ligne : https://doi.org/10.1080/00396265.2015.1097589 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=79638 [article]

Static GNSS precise point positioning using free online services for Africa / Anis Abdallah in Survey review, vol 48 n° 346 (January 2016)  

Public [article]  inSurvey review > vol 48 n° 346 (January 2016) . - pp. 61 - 77 Titre : Static GNSS precise point positioning using free online services for Africa Type de document : Article/Communication Auteurs : Anis Abdallah, Auteur ; B. V. Schwieger, Auteur Année de publication : 2016 Article en page(s) : pp. 61 - 77 Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Navigation et positionnement [Termes IGN] Afrique (géographie politique) [Termes IGN] positionnement par GNSS [Termes IGN] positionnement ponctuel précis [Termes IGN] positionnement statique [Termes IGN] retard troposphérique zénithal [Termes IGN] service fondé sur la position [Termes IGN] station GNSS Résumé : (auteur) The GNSS precise point positioning (PPP) technique has been extensively covered in recent research. In this study, six International global navigation satellite system (GNSS) Service (IGS) stations defined by 4-digits code in Africa were selected to be processed. The stations cover different climates in Africa. HARB, SUTH and WIND stations cover the mid-latitude area and NKLG, NURK and MAL2 are located in the equatorial region. Two data sessions were selected in processing to cover the winter and summer seasons: the first session of 3 days [01–03 January 2013 (DOY: 001–003/2013)] and the second session of 3 days [01–03 July 2013 (DOY: 182–184/2013)]. This paper aims to evaluate the accuracy of static PPP coordinate solution in Africa for different convergence times using free online services: Canadian Spatial Reference System (CSRS)-PPP, Automatic Precise Point Service (APPS)-PPP and GPS Analysis and Positioning Software (GAPS)-PPP. The stations’ observation times were divided into different observation times (1, 2, 4, 8, 12, and 24 h).The PPP coordinate solution was compared to the reference solution of those stations. The investigation is continued by estimating the PPP total tropospheric zenith delay (TZD) parameters, which were obtained by the different online services. These parameters were compared to the published parameters from IGS. The comparison between the different online services shows that the CSRS-PPP provides the best solution after 4 and 8 h. The APPS-PPP and CSRS-PPP provides the same solution in millimeters level after 12 h. In the equatorial region, the PPP coordinate solution is significantly improved between 12 and 24 h. Moreover, GAPS-PPP is not recommended to be used in the equatorial stations, where it shows a high error compared to CSRS-PPP and APPS-PPP even after 24 h. The mid-latitude stations show a better PPP coordinate solution in the winter than in the summer, but the equatorial stations present a low accuracy for the two sessions. Regarding the PPP tropospheric delay estimation, an additional station (HNUS) is used in the mid-latitude area, which has a low ellipsoidal height. APPS-PPP shows the best solution in the TZD estimation. The GAPS-PPP online service shows a systemic error in estimation and a high RMS relative to the TZD values known from IGS. The ellipsoidal height for antenna indicates a negative correlation to the estimated tropospheric values, but there is no effect for the variation of the ellipsoidal height in the estimated RMS. The estimated tropospheric parameters are correlated with the PPP coordinate estimation, where the GAPS-PPP service provides the worst PPP coordinate solution and at the same time, it shows the worst accuracy for tropospheric parameters estimation. Moreover, the estimated tropospheric parameters for the mid-latitude stations in the summer season show a higher RMS than in the winter season, which matches the same sequence of the PPP coordinates. The NKLG and NURK stations present a low accuracy for the tropospheric estimation, which is matching to the low accuracy of the PPP coordinates obtained from the different online services. Numéro de notice : A2016-046 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article DOI : 10.1080/00396265.2015.1097595 En ligne : https://doi.org/10.1080/00396265.2015.1097595 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=79639 [article]