| 1. |
- Alizadeh-Khameneh, Amin, et al.
(författare)
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A field method to estimate the uncertainty of RTK measurements
- 2023
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Ingår i: Survey review - Directorate of Overseas Surveys. - : Informa UK Limited. - 0039-6265 .- 1752-2706. ; , s. 1-8
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Tidskriftsartikel (refereegranskat)abstract
- The expected accuracies obtainable with Network Real-Time Kinematic (NRTK) measurements are of interest to surveyors working on construction projects. This study introduces an NRTK-based free stationing method called RUFRIS (Real Time Updated Free Station) which is independent from physically marked points. Integration of total station distance and direction observations with NRTK measurements enables uncertainty estimation of both total station and surveyed NRTK points. In Sweden, NRTK is conducted using the national network of permanent reference stations with different densifications (10, 35, 70 km). This paper investigates the applicability of the RUFRIS-method to estimate the uncertainty of NRTK measurements in the field.
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| 2. |
- Alizadeh Khameneh, Mohammad Amin, et al.
(författare)
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Investigation of the RUFRIS Method with GNSS and Total Station for Leveling
- 2017
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Konferensbidrag (refereegranskat)abstract
- The establishment of leveling benchmarks for performing geodetic measurements, for instance in construction works, is usually costly and laborious due to a mass of field works in transferring the height from nearby known benchmarks. In this study, a real-time updated free station (RUFRIS) method is investigated to be used as an alternative approach for the traditional leveling. The coordinates of a RUFRIS station are determined by establishing a total station on the point, and performing a free-station by observing some points with both Real-Time Kinematic (RTK) GNSS and total station distance and direction observations. The study is conducted based on data from the East Link project in Sweden, where a 150 km long high-speed railway is to be constructed. The results show a standard deviation of 7 mm between the RUFRIS and leveling heights in this project and imply the feasibility of replacing the traditional leveling methods with RUFRIS in projects with low accessibility to benchmarks.
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| 3. |
- Alizadeh Khameneh, Mohammad Amin, 1983-
(författare)
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Optimal Design in Geodetic GNSS-based Networks
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- An optimal design of a geodetic network helps the surveying engineers maximise the efficiency of the network. A number of pre-defined quality requirements, i.e. precision, reliability, and cost, of the network are fulfilled by performing an optimisation procedure. Today, this is almost always accomplished by implementing analytical solutions, where the human intervention in the process cycle is limited to defining the requirements. Nevertheless, a trial and error method can be beneficial to some applications. In order to analytically solve an optimisation problem, it can be classified to different orders, where an optimal datum, configuration, and optimal observation weights can be sought such that the precision, reliability and cost criteria are satisfied.In this thesis, which is a compilation of six peer-reviewed papers, we optimised and redesigned a number of GNSS-based monitoring networks in Sweden by developing new methodologies. In addition, optimal design and efficiency of total station establishment with RTK-GNSS is investigated in this research.Sensitivity of a network in detecting displacements is of importance for monitoring purposes. In the first paper, a precision criterion was defined to enable a GNSS-based monitoring network to detect 5 mm displacements at each network point. Developing an optimisation model by considering this precision criterion, reliability and cost yielded a decrease of 17% in the number of observed single baselines implying a reliable and precise network at lower cost. The second paper concerned a case, where the precision of observations could be improved in forthcoming measurements. Thus a new precision criterion was developed to consider this assumption. A significant change was seen in the optimised design of the network for subsequent measurements. As yet, the weight of single baselines was subject to optimisation, while in the third paper, the effect of mathematical correlations between GNSS baselines was considered in the optimisation. Hence, the sessions of observations, including more than two receivers, were optimised. Four out of ten sessions with three simultaneous operating receivers were eliminated in a monitoring network with designed displacement detection of 5 mm. The sixth paper was the last one dealing with optimisation of GNSS networks. The area of interest was divided into a number of three-dimensional elements and the precision of deformation parameters was used in developing a precision criterion. This criterion enabled the network to detect displacements of 3 mm at each point.A total station can be set up in the field by different methods, e.g. free station or setup over a known point. A real-time updated free station method uses RTK-GNSS to determine the coordinates and orientation of a total station. The efficiency of this method in height determination was investigated in the fourth paper. The research produced promising results suggesting using the method as an alternative to traditional levelling under some conditions. Moreover, an optimal location for the total station in free station establishment was studied in the fifth paper. It was numerically shown that the height component has no significant effect on the optimal localisation.
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| 4. |
- Alizadeh Khameneh, Mohammad Amin, et al.
(författare)
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Optimal Vertical Placement of Total Station
- 2018
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Ingår i: Journal of Surveying Engineering. - 0733-9453 .- 1943-5428.
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Tidskriftsartikel (refereegranskat)abstract
- When using the free station method, a Total Station (TS) is established by performing distance and angle observations toward a number of Control Points (CPs). The quality of the establishment is crucial for the quality of subsequent measurements. The optimal horizontal location of the TS has been investigated in previous studies. Even the vertical precision is important in many applications, especially with significant height variations. Therefore in this paper, we focus on the optimality of vertical location of the TS. As an optimality criterion, the sum of TS coordinates and orientation variances is used. To investigate the optimization problem, an analytical as well as a trial and error method is developed. Both methods showed that the height component has no significant influence on the optimal vertical placement of the TS. Inspection of results from the trial and error method, where the CPs are moved in different height layers, indicates differences in the height uncertainty of the establishment in micrometer range, which is negligible for most engineering applications.
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| 5. |
- Andersson, Johan Vium, 1971-
(författare)
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A Complete Model for Displacement Monitoring Based on Undifferenced GPS Observations
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- During recent years there has been a great focus on the climate changes within the media. More or less every day more newspaper articles are presented about the global warming issue and the effect on us human race. Climate models predict higher temperatures and more rain in the northern part of Europe. It is also predicted that the weather will become more extreme e.g. it will rain a lot during longer periods than has been the norm. If these predictions are correct, the amount of water that is going to be transported away in streams and rivers will increase and so also will the subsoil water level. The latter increases the risk for landslides in areas with fine grained soils. An early warning system that is able to alert people before a landslide take place would be of great interest. The purpose of this work is to develop a complete real-time displacement monitoring system based on observations from several GPS-receivers that could be used as an early warning system. Due to the complex correlation structure of the traditionally used double differences, an alternative method based on undifferenced observations is used. Theoretically this approach shows some advantages and simplifies the correlative structure of observables compared to the double differenced method. A complete model for the undifferenced approach is presented in this thesis including its software implementation. A displacement detection system includes not only the positioning algorithms, but also methods to detect if any displacement occurs. There are many methods available to discriminate displacements, which are used in the traditional control of manufacturing processes. Several of these methods are compared in this thesis, such as the Shewhart chart, different Weighted Moving Average (WMA) charts and the CUmulative SUMmation (CUSUM). Practical tests show that it is possible to detect an abrupt shift on sub centimetre level at the same epoch as the shift occurs. Smaller shifts are also detectable with the applied approach but with a slightly longer detection time.
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| 6. |
- Andersson, Johan Vium
(författare)
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Undifferenced GPS for Deformation Monitoring
- 2006
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis contains the development of a deformation monitoring software based on undifferenced GPS observations. Software like this can be used in alarm systems placed in areas where the earth is unstable. Systems like this can be used in areas where people are in risk of getting hurt, like in earthquake zones or in land slide areas, but they can also be useful when monitoring the movements in buildings, bridges and other artefacts. The main hypotheses that are tested are whether it is possible to detect deformations with undifferenced observations and if it is possible to reach the same accuracy in this mode as when working in a traditional mode where the observations are differenced. The development of a deformation monitoring software based on undifferenced GPS observations is presented. A complete mathematical model is given as well as implementation details. The software is developed in Matlab together with a GPS observation simulator. The simulator is mainly used for debugging purposes. The developed software is tested with both simulated and real observations. Results from tests with simulated observations show that it is possible to detect deformations in the order of a few millimetres with the software. Calculations with real observations give the same results. Further, the result from calculations in static mode indicates that the commercial software and the undifferenced software diverge a few millimetres, which probably depends on different implementations of the tropospheric corrections. In kinematic mode the standard deviation is about 1 millimetre larger in the undifferenced mode than in the double differenced mode. An initial test with different observation weighting procedures indicates that there is a lot of potential to improve the result by applying correct weights to the observations. This is one of the aims in the future work within this project. This thesis are sponsored by the Swedish Research Council for Enviroment, Agricultural Sciences and Spatial Planning, FORMAS within the framework “Monitoring of construction and detection of movements by GPS ref no. 2002-1257"
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| 7. |
- Horemuz, Milan, PhD. 1964-, et al.
(författare)
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Geometry of Reference Stations in Network RTK
- 2023
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Ingår i: FIG Working Week 2023.
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Konferensbidrag (refereegranskat)abstract
- Using the Global Navigation Satellite System (GNSS) surveying methods give the users anadvantage over the other traditional methods, where for instance, measurements betweenpoints with longer distances can be performed with no line of sight. Furthermore, the GNSStechnology, through its real-time applications, can provide a basis for more efficient datacollection and product automation, e.g., machine guidance. Nowadays, users do not need tohave deep theoretical knowledge of GNSS to survey. They only expect a reliable and preciseestimation of coordinates from the surveying instruments and GNSS services. It is the systemproviders, who face challenges to ensure a reliable delivery with consistent quality to theusers and are, therefore, in need of planning tools and models to operate more efficientservices. The developed simulation model in this paper provides an overview of uncertaintiesfor the network Real Time Kinematic (RTK) measurements and investigates the effect ofnetwork geometry on users’ precision. Besides, the model is used to study the possibledeterioration in users’ precision if any reference station in the network stops working. Thisinformation provides a theoretical basis for densification strategies and evaluates if anyreference station is more important than the others to maintain consistent quality in thenetwork.
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| 8. |
- Horemuz, Milan, et al.
(författare)
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Polynomial interpolation of GPS satellite coordinates
- 2006
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Ingår i: GPS Solutions. - : Springer Science and Business Media LLC. - 1080-5370 .- 1521-1886. ; 10:1, s. 67-72
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Tidskriftsartikel (refereegranskat)abstract
- This article describes an algorithm for polynomial interpolation of GPS satellite coordinates and its implementation in MATLAB. The algorithm is intended for realtime processing software and computes the position and velocity of GPS satellites from both broadcast and precise ephemerides. Tests with different orders of polynomials, and with different time spans used for polynomial fitting, show suitable settings with respect to the required interpolation precision.
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