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Using direct transformation approach as an alternative technique to fuse global digital elevation models with GPS/levelling measurements in Egypt / Hossam Talaat Elshambaky in Journal of applied geodesy, vol 13 n° 3 (July 2019)  

Public [article]  inJournal of applied geodesy > vol 13 n° 3 (July 2019) . - pp 159 - 177 Titre : Using direct transformation approach as an alternative technique to fuse global digital elevation models with GPS/levelling measurements in Egypt Type de document : Article/Communication Auteurs : Hossam Talaat Elshambaky, Auteur Année de publication : 2019 Article en page(s) : pp 159 - 177 Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Nivellement [Termes descripteurs IGN] collocation par moindres carrés [Termes descripteurs IGN] Egypte [Termes descripteurs IGN] formule de Molodensky [Termes descripteurs IGN] fusion de données [Termes descripteurs IGN] méthode fiable [Termes descripteurs IGN] MNS GTOPO30 [Termes descripteurs IGN] MNS SRTM [Termes descripteurs IGN] modèle numérique de surface [Termes descripteurs IGN] réseau neuronal artificiel [Termes descripteurs IGN] séparateur à vaste marge Résumé : (auteur) Open global digital elevation models (GDEMs) represent a free and important source of information that is available to any country. Fusion processing between global and national digital elevation models is neither easy nor inexpensive. Hence, an alternative solution to fuse a GDEM (GTOPO30 or SRTM 1) with national GPS/levelling measurements is adopted. Herein, a transformation process between the GDEMs and national GPS/levelling measurements is applied using parametric and non-parametric equations. Two solutions are implemented before and after the filtration of raw data from outliers to assess the ability of the generated corrector surface model to absorb the effect of the outliers’ existence. In addition, a reliability analysis is conducted to select the most suitable transformation technique. We found that when both the fitting and prediction properties have equal priority, least-squares collocation integrated with a least-squares support vector machine inherited with a linear or polynomial kernel function exhibits the most accurate behavior. For the GTOPO30 model, before filtration of the raw data, there is an improvement in the mean and root mean square of errors by 39.31 % and 68.67 %, respectively. For the SRTM 1 model, the improvement in mean and root mean square values reached 86.88 % and 75.55 %, respectively. Subsequently, after the filtration process, these values became 3.48 % and 36.53 % for GTOPO30 and 85.18 % and 47.90 % for SRTM 1. Furthermore, it is found that using a suitable mathematical transformation technique can help increase the precision of classic GDEMs, such as GTOPO30, making them to be equal or more accurate than newer models, such as SRTM 1, which are supported by more advanced technologies. This can help overcome the limitation of shortage of technology or restricted data, particularly in developed countries. Henceforth, the proposed direct transformation technique represents an alternative faster and more economical way to utilize unfiltered measurements of GDEMs to estimate national digital elevations in areas with limited data. Numéro de notice : A2019-283 Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1515/jag-2018-0050 date de publication en ligne : 05/03/2019 En ligne : https://doi.org/10.1515/jag-2018-0050 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=93118 [article]

Empirical stochastic model of detected target centroids: Influence on registration and calibration of terrestrial laser scanners / Tomislav Medic in Journal of applied geodesy, vol 13 n° 3 (July 2019)  

Public [article]  inJournal of applied geodesy > vol 13 n° 3 (July 2019) . - pp 179 – 197 Titre : Empirical stochastic model of detected target centroids: Influence on registration and calibration of terrestrial laser scanners Type de document : Article/Communication Auteurs : Tomislav Medic, Auteur ; Christoph Holst, Auteur ; Jannik Janssen, Auteur ; Heiner Kuhlmann, Auteur Année de publication : 2019 Article en page(s) : pp 179 – 197 Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Lasergrammétrie [Termes descripteurs IGN] centroïde [Termes descripteurs IGN] compensation par moindres carrés [Termes descripteurs IGN] détection de cible [Termes descripteurs IGN] données lidar [Termes descripteurs IGN] données localisées 3D [Termes descripteurs IGN] étalonnage d'instrument [Termes descripteurs IGN] incertitude de mesurage [Termes descripteurs IGN] modèle stochastique [Termes descripteurs IGN] télémètre laser terrestre Résumé : (auteur) The target-based point cloud registration and calibration of terrestrial laser scanners (TLSs) are mathematically modeled and solved by the least-squares adjustment. However, usual stochastic models are simplified to a large amount: They generally employ a single point measurement uncertainty based on the manufacturers’ specifications. This definition does not hold true for the target-based calibration and registration due to the fact that the target centroid is derived from multiple measurements and its uncertainty depends on the detection procedure as well. In this study, we empirically investigate the precision of the target centroid detection and define an empirical stochastic model in the form of look-up tables. Furthermore, we compare the usual stochastic model with the empirical stochastic model on several point cloud registration and TLS calibration experiments. There, we prove that the values of usual stochastic models are underestimated and incorrect, which can lead to multiple adverse effects such as biased results of the estimation procedures, a false a posteriori variance component analysis, false statistical testing, and false network design conclusions. In the end, we prove that some of the adverse effects can be mitigated by employing the a priori knowledge about the target centroid uncertainty behavior. Numéro de notice : A2019-284 Thématique : IMAGERIE Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1515/jag-2018-0032 date de publication en ligne : 22/03/2019 En ligne : https://doi.org/10.1515/jag-2018-0032 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=93119 [article]

Accuracy assessment of relative and precise point positioning online GPS processing services / Ahmed El Shouny in Journal of applied geodesy, vol 13 n° 3 (July 2019)  

Public [article]  inJournal of applied geodesy > vol 13 n° 3 (July 2019) . - pp 215 – 227 Titre : Accuracy assessment of relative and precise point positioning online GPS processing services Type de document : Article/Communication Auteurs : Ahmed El Shouny, Auteur ; Yehia Miky, Auteur Année de publication : 2019 Article en page(s) : pp 215 – 227 Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Navigation et positionnement [Termes descripteurs IGN] Egypte [Termes descripteurs IGN] estimation de précision [Termes descripteurs IGN] positionnement différentiel [Termes descripteurs IGN] positionnement par GNSS [Termes descripteurs IGN] positionnement par GPS [Termes descripteurs IGN] positionnement ponctuel précis [Termes descripteurs IGN] traitement de données GNSS Résumé : (auteur) Over the last few years, several institutions, research centers, and organizations have developed different strategies for GPS data processing and analysis to obtain high accurate coordinates. They are taking into considerations overcoming restrictions and limitations such as necessity of using relative positioning, time consuming, and high cost of different processing software. One of these developed strategies is the web–based online GNSS (Global Navigation Satellite Systems) processing service which estimates coordinates with centimeter or decimeter level accuracy. This study aims to represent the most popular of these services, namely AUSPOS, OPUS, APPS, GAPS, Trimble RTX, and CSRS–PPP, also to perform in-between comparison of these services with respect to their achieved accuracy using field observations with different durations. The obtained results were compared with a real field data measured using traditional relative positioning technique with high accuracy standards. The set of data used in this study was performed in the Eastern zone in Egypt. The results of this comparison indicate that these services can be used as an alternative method for relative positioning technique due to their simplicity, cost-effective and saving in time. They saved about 75 % from the time required for traditional method to produce coordinate with reasonable accuracy. The maximum standard deviation obtained was 15.4 cm from APPS service with time less than two hours, while the minimum standard deviation was 0.07 cm and obtained from CSRS–PPP with time duration from 6 to 12 hours. For achieving more accurate results, it is recommended to use time duration more than two hours. Numéro de notice : A2019-285 Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1515/jag-2018-0046 date de publication en ligne : 24/04/2019 En ligne : https://doi.org/10.1515/jag-2018-0046 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=93120 [article]

Monitoring of extreme land hydrology events in central Poland using GRACE, land surface models and absolute gravity data / Joanna Kuczynska-Siehien in Journal of applied geodesy, vol 13 n° 3 (July 2019)  

Public [article]  inJournal of applied geodesy > vol 13 n° 3 (July 2019) . - pp 229 – 243 Titre : Monitoring of extreme land hydrology events in central Poland using GRACE, land surface models and absolute gravity data Type de document : Article/Communication Auteurs : Joanna Kuczynska-Siehien, Auteur ; Dimitrios Piretzidis, Auteur ; Michael G. Sideris, Auteur ; et al., Auteur Année de publication : 2019 Article en page(s) : pp 229 – 243 Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Applications de géodésie spatiale [Termes descripteurs IGN] analyse diachronique [Termes descripteurs IGN] analyse spectrale [Termes descripteurs IGN] données GLDAS [Termes descripteurs IGN] données GRACE [Termes descripteurs IGN] gravimètre absolu [Termes descripteurs IGN] inondation [Termes descripteurs IGN] levé gravimétrique [Termes descripteurs IGN] modèle numérique de surface [Termes descripteurs IGN] Pologne [Termes descripteurs IGN] risque naturel [Termes descripteurs IGN] sécheresse [Termes descripteurs IGN] surveillance hydrologique [Termes descripteurs IGN] variation temporelle Résumé : (auteur) This study deals with the analysis of temporal gravity variations in central Poland, deduced from multiple sources and covering the period from 2002–2016. The gravity data sets used comprise GRACE monthly solutions, GLDAS land surface models and absolute gravimeter measurements from the FG-5 gravimeter located in Józefosław, Poland. All data are corrected using standard processing methods in order to include the same gravity effects. After removing the annual and semi-annual components from all data using least-squares spectral analysis and seasonal-trend decomposition, the deseasoned time series are derived and examined for signatures of extreme hydrological events. The signatures of several severe drought and flood conditions affecting Poland and central Europe are identified. A complementary correlation analysis is performed to assess the level of agreement between different data sources. A higher correlation is shown when the analysis is restricted in the 2009–2012 period that includes the 2010 extreme flood and 2011 increased precipitation events, both affecting Poland. Numéro de notice : A2019-286 Thématique : IMAGERIE/POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1515/jag-2019-0003 date de publication en ligne : 20/04/2019 En ligne : https://doi.org/10.1515/jag-2019-0003 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=93121 [article]

Geometric and statistical interpretation of correlation between fault tests in integrated GPS/INS systems / Ali Almagbile in Journal of applied geodesy, vol 13 n° 3 (July 2019)  

Public [article]  inJournal of applied geodesy > vol 13 n° 3 (July 2019) . - pp 267 – 278 Titre : Geometric and statistical interpretation of correlation between fault tests in integrated GPS/INS systems Type de document : Article/Communication Auteurs : Ali Almagbile, Auteur Année de publication : 2019 Article en page(s) : pp 267 – 278 Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie spatiale [Termes descripteurs IGN] coefficient de corrélation [Termes descripteurs IGN] détection d'erreur [Termes descripteurs IGN] données GPS [Termes descripteurs IGN] erreur de positionnement [Termes descripteurs IGN] fiabilité des données [Termes descripteurs IGN] GPS-INS [Termes descripteurs IGN] incertitude géométrique Résumé : (auteur) Fault detection and identification (FDI) in either a stand-alone GPS or in integrated GPS/INS systems is essential for improving the quality of positioning, navigation, and many other applications. The assumption that the observations include a single fault has been considered intensively in literature. However, this assumption may not necessarily be valid due to the fact that multiple faults may exist simultaneously. In this study, separability of multiple faults in GPS/INS integration systems has been analysed geometrically and statistically. This has been achieved through testing how large correlation coefficient between any pair of fault tests statistics increases the probability of faults misidentification. In addition, a new calculation procedure of correlation coefficient when four faults appear in the observations has been developed. This procedure considers calculation the correlation between a single and a punch of measurements combined together. The results show that there is a strong relationship between the value of correlation coefficient and the probability of misidentification. Furthermore, a significant relationship between the correlation and the fault test values can be found when splitting the measurements combinations into groups based on the combination similarity. Nevertheless, this relationship can be defined without splitting the measurements into groups when using a new correlation procedure for four faults case. The geometric representation shows that large correlation coefficient reflects small angle between the correlation and the x-axis; whereas the angle between the fault-test vectors and the x-axis becomes wider when a tiny correlation exist. Numéro de notice : A2019-287 Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1515/jag-2019-0008 date de publication en ligne : 05/06/2019 En ligne : https://doi.org/10.1515/jag-2019-0008 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=93123 [article]