scholarly journals A New Asynchronous RTK Method to Mitigate Base Station Observation Outages

Sensors ◽  
2019 ◽  
Vol 19 (15) ◽  
pp. 3376 ◽  
Author(s):  
Yuan Du ◽  
Guanwen Huang ◽  
Qin Zhang ◽  
Yang Gao ◽  
Yuting Gao
Keyword(s):  
Real Time ◽  
Base Station ◽  
Global Navigation Satellite Systems ◽  
Observation Data ◽  
Post Processing ◽  
Positioning Accuracy ◽  
Real Time Processing ◽  
Phase Measurements ◽  
Satellite Systems ◽  
Precise Ephemeris

Real-time kinematic (RTK) positioning is a satellite navigation technique that is widely used to enhance the precision of position data obtained from global navigation satellite systems (GNSS). This technique can reduce or eliminate significant correlation errors via the enhancement of the base station observation data. However, observations received by the base station are often interrupted, delayed, and/or discontinuous, and in the absence of base station observation data the corresponding positioning accuracy of a rover declines rapidly. With the strategies proposed till date, the positioning accuracy can only be maintained at the centimeter-level for a short span of time, no more than three min. To address this, a novel asynchronous RTK method (that addresses asynchronous errors) that can bridge significant gaps in the observations at the base station is proposed. First, satellite clock and orbital errors are eliminated using the products of the final precise ephemeris during post-processing or the ultra-rapid precise ephemeris during real-time processing. Then the tropospheric error is corrected using the Saastamoinen model and the asynchronous ionospheric delay is corrected using the carrier phase measurements from the rover receiver. Finally, a straightforward first-degree polynomial function is used to predict the residual asynchronous error. Experimental results demonstrate that the proposed approach can achieve centimeter-level accuracy for as long as 15 min during interruptions in both real-time and post-processing scenarios, and that the accuracy of the real-time scheme can be maintained for 15 min even when a large systematic error is projected in the U direction.

Advances in smartphone positioning in forests: dual-frequency receivers and raw GNSS data

2020 ◽  
Author(s):  
Julián Tomaštík ◽  
Juliána Chudá ◽  
Daniel Tunák ◽  
František Chudý ◽  
Miroslav Kardoš
Keyword(s):  
Real Time ◽  
Mean Shift ◽  
Global Navigation Satellite Systems ◽  
Single Frequency ◽  
Dual Frequency ◽  
Post Processing ◽  
Open Area ◽  
Satellite Systems ◽  
Gnss Data ◽  
Mean Square Errors

Abstract Smartphones with their capability to receive Global Navigation Satellite Systems (GNSS) signals can be currently considered the most common devices used for positioning tasks, including forestry applications. This study focuses on possible improvements related to two crucial changes implemented into Android smartphone positioning in the last 3 years – dual-frequency (L1/L5) GNSS receivers and the possibility of recording raw GNSS data. The study comprises three experiments: (1) real-time measurements of individual points, (2) real-time recording of trajectories, and (3) post-processing of raw GNSS data provided by the smartphone receiver. The real-time tests were conducted using final positions provided by the internal receiver, i.e. without further processing or averaging. The test on individual points has proven that the Xiaomi Mi8 smartphone with a multi-constellation, dual-frequency receiver was the only device whose accuracy was not significantly different from single-frequency mapping-grade receiver under any conditions. The horizontal accuracy of most devices was lower during leaf-on season (root mean square errors between 5.41 and 12.55 m) than during leaf-off season (4.10–11.44 m), and the accuracy was significantly better under open-area conditions (1.72–4.51 m) for all tested devices when compared with forest conditions. Results of the second experiment with track recording suggest that smartphone receivers are better suited for dynamic applications – the mean shift between reference and measured trajectories varied from 1.23 to 5.98 m under leaf-on conditions. Post-processing of the raw GNSS data in the third experiment brought very variable results. We achieved centimetre-level accuracy under open-area conditions; however, in forest, the accuracies varied from meters to tens of meters. Observed loss of the signal strength in the forest represented ~20 per cent of the open-area value. Overall, the multi-constellation, dual-frequency receiver provided more robust and accurate positional solutions compared with single-frequency smartphones. Applicability of the raw GNSS data must be further studied especially in forests, as the provided data are highly susceptible to multipath and other GNSS adverse effects.

scholarly journals Evaluation of Real-Time Kinematic Positioning and Deformation Monitoring Using Xiaomi Mi 8 Smartphone

2022 ◽  
Vol 12 (1) ◽  
pp. 435
Author(s):  
Shulin Zeng ◽  
Cuilin Kuang ◽  
Wenkun Yu
Keyword(s):  
Real Time ◽  
Low Cost ◽  
Density Ratio ◽  
Deformation Monitoring ◽  
Global Navigation Satellite Systems ◽  
Single Frequency ◽  
Short Baseline ◽  
Positioning Accuracy ◽  
Satellite Systems ◽  
Real Time Kinematic

Modern low-cost electronic devices can achieve high precision for global navigation satellite systems (GNSSs) and related applications. Recently, the pseudo-range and carrier phase have been directly obtained from a smartphone to establish a professional-level surveying device. Although promising results have been obtained by linking to an external GNSS antenna, the real-time kinematic (RTK) positioning performance requires further improvement when using the embedded smartphone antenna. We first investigate the observation quality characteristics of the Xiaomi Mi 8 smartphone. The carrier-to-noise-density ratio of L5/E5a signals is below that of L1/E1 signals, and the cycle slip and loss of lock are severe, especially for L5/E5a signals. Therefore, we use an improved stochastic model and ambiguity-resolution strategies to improve the short-baseline RTK positioning accuracy. Experimental results show that the ambiguity fixing rate can reach approximately 90% in 3 h of observations when using the embedded antenna, while the GPS/Galileo/BDS single-frequency combination is more suitable for smartphones. On the other hand, convergence takes 10–30 min, and the RTK positioning accuracy can reach 1 and 2 cm along the horizontal and vertical directions, respectively, if ambiguity is resolved correctly. Moreover, we verify the feasibility of using a mass-produced smartphone for deformation monitoring. Results from a simulated dynamic deformation experiment indicate that a smartphone can recognise deformations as small as 2 cm.

Technical Considerations for Modernizing Nova Scotia’s Coordinate Referencing System

GEOMATICA ◽  
2016 ◽  
Vol 70 (2) ◽  
pp. 85-96 ◽  
Author(s):  
Jason Bond
Keyword(s):  
Passive Control ◽  
Global Navigation Satellite Systems ◽  
Observation Data ◽  
Crowd Sourcing ◽  
Satellite Systems ◽  
Network Location ◽  
Land Administration ◽  
New Strategy ◽  
Global Navigation Satellite ◽  
Technical Considerations

The Nova Scotia Coordinate Referencing System (NSCRS) is Nova Scotia's current framework for providing location-based information. The NSCRS is the foundation for the province's geographic data, includ ing the land administration system. In 2012, the province began developing a modernization strategy to better execute its coordinate referencing program to address ongoing accuracy and accessibility needs. A net work of active control stations (ACSs) tracking global navigation satellite systems (GNSS) is at the core of the new strategy. In addition to providing better accuracy and accessibility to the NSCRS, the tech nol ogy has created new opportunities to sustain its passive control infrastructure. In 2015, the installation of 40 ACSs across the province was completed, providing industry with access to real-time, centimetre-level positioning. Over the course of the NSCRS modernization project, several tech nical considerations needed to be addressed pertaining to the design of the network, location of the ACSs, flow of the ACS data and the crowd sourcing of GNSS observation data to maintain the passive con trol sys tem. These technical considerations are reviewed and the solutions implemented to address the needs of this initiative are presented.

scholarly journals Performance Evaluation of GPS Auto-Surveying Techniques

Sensors ◽  
2021 ◽  
Vol 21 (21) ◽  
pp. 7374
Author(s):  
João Manito ◽  
José Sanguino
Keyword(s):  
Kalman Filter ◽  
Least Squares ◽  
Unscented Kalman Filter ◽  
Weighted Least Squares ◽  
Base Station ◽  
Global Navigation Satellite Systems ◽  
Precise Position ◽  
Satellite Systems ◽  
Global Navigation Satellite ◽  
Position Estimate

With the increase in the widespread use of Global Navigation Satellite Systems (GNSS), increasing numbers of applications require precise position data. Of all the GNSS positioning methods, the most precise are those that are based in differential systems, such as Differential GNSS (DGNSS) and Real-Time Kinematics (RTK). However, for absolute positioning, the precision of these methods is tied to their reference position estimates. With the goal of quickly auto-surveying the position of a base station receiver, four positioning methods are analyzed and compared, namely Least Squares (LS), Weighted Least Squares (WLS), Extended Kalman Filter (EKF) and Unscented Kalman Filter (UKF), using only pseudorange measurements, as well as the Hatch Filter and position thresholding. The research results show that the EKF and UKF present much better mean errors than LS and WLS, with an attained precision below 1 m after about 4 h of auto-surveying. The methods that presented the best results are then tested against existing implementations, showing them to be very competitive, especially considering the differences between the used receivers. Finally, these results are used in a DGNSS test, which verifies a significant improvement in the position estimate as the base station position estimate improves.

scholarly journals Sensitivity of GNSS tropospheric gradients to processing options

2019 ◽  
Vol 37 (3) ◽  
pp. 429-446 ◽  
Author(s):  
Michal Kačmařík ◽  
Jan Douša ◽  
Florian Zus ◽  
Pavel Václavovic ◽  
Kyriakos Balidakis ◽  
...  
Keyword(s):  
Real Time ◽  
Elevation Angle ◽  
Mapping Function ◽  
Global Navigation Satellite Systems ◽  
Gradient Estimates ◽  
Post Processing ◽  
Data Set ◽  
Mapping Functions ◽  
Gradient Mapping

Abstract. An analysis of processing settings impacts on estimated tropospheric gradients is presented. The study is based on the benchmark data set collected within the COST GNSS4SWEC action with observations from 430 Global Navigation Satellite Systems (GNSS) reference stations in central Europe for May and June 2013. Tropospheric gradients were estimated in eight different variants of GNSS data processing using precise point positioning (PPP) with the G-Nut/Tefnut software. The impacts of the gradient mapping function, elevation cut-off angle, GNSS constellation, observation elevation-dependent weighting and real-time versus post-processing mode were assessed by comparing the variants by each to other and by evaluating them with respect to tropospheric gradients derived from two numerical weather models (NWMs). Tropospheric gradients estimated in post-processing GNSS solutions using final products were in good agreement with NWM outputs. The quality of high-resolution gradients estimated in (near-)real-time PPP analysis still remains a challenging task due to the quality of the real-time orbit and clock corrections. Comparisons of GNSS and NWM gradients suggest the 3∘ elevation angle cut-off and GPS+GLONASS constellation for obtaining optimal gradient estimates provided precise models for antenna-phase centre offsets and variations, and tropospheric mapping functions are applied for low-elevation observations. Finally, systematic errors can affect the gradient components solely due to the use of different gradient mapping functions, and still depending on observation elevation-dependent weighting. A latitudinal tilting of the troposphere in a global scale causes a systematic difference of up to 0.3 mm in the north-gradient component, while large local gradients, usually pointing in a direction of increasing humidity, can cause differences of up to 1.0 mm (or even more in extreme cases) in any component depending on the actual direction of the gradient. Although the Bar-Sever gradient mapping function provided slightly better results in some aspects, it is not possible to give any strong recommendation on the gradient mapping function selection.

scholarly journals Feasibility of Using Low-Cost Dual-Frequency GNSS Receivers for Land Surveying

Sensors ◽  
2021 ◽  
Vol 21 (6) ◽  
pp. 1956
Author(s):  
Natalia Wielgocka ◽  
Tomasz Hadas ◽  
Adrian Kaczmarek ◽  
Grzegorz Marut
Keyword(s):  
Real Time ◽  
Field Experiments ◽  
Low Cost ◽  
Base Station ◽  
Global Navigation Satellite Systems ◽  
Single Frequency ◽  
Signal Acquisition ◽  
Dual Frequency ◽  
Static Mode ◽  
Land Surveying

Global Navigation Satellite Systems (GNSS) have revolutionized land surveying, by determining position coordinates with centimeter-level accuracy in real-time or up to sub-millimeter accuracy in post-processing solutions. Although low-cost single-frequency receivers do not meet the accuracy requirements of many surveying applications, multi-frequency hardware is expected to overcome the major issues. Therefore, this paper is aimed at investigating the performance of a u-blox ZED-F9P receiver, connected to a u-blox ANN-MB-00-00 antenna, during multiple field experiments. Satisfactory signal acquisition was noticed but it resulted as >7 dB Hz weaker than with a geodetic-grade receiver, especially for low-elevation mask signals. In the static mode, the ambiguity fixing rate reaches 80%, and a horizontal accuracy of few centimeters was achieved during an hour-long session. Similar accuracy was achieved with the Precise Point Positioning (PPP) if a session is extended to at least 2.5 h. Real-Time Kinematic (RTK) and Network RTK measurements achieved a horizontal accuracy better than 5 cm and a sub-decimeter vertical accuracy. If a base station constituted by a low-cost receiver is used, the horizontal accuracy degrades by a factor of two and such a setup may lead to an inaccurate height determination under dynamic surveying conditions, e.g., rotating antenna of the mobile receiver.

scholarly journals ANALYSIS OF POSITIONING RESULTS OBTAINED BY A SINGLE BASE RTK WITH AUTONOMOUS BASE START AND TILT OPTION

2018 ◽  
Vol 13 (1) ◽  
Author(s):  
Danijel Šugar
Keyword(s):  
Real Time ◽  
Reliable Method ◽  
Base Station ◽  
Communication Link ◽  
Post Processing ◽  
Single Base ◽  
Gnss Receiver ◽  
Clear Sky ◽  
Differential Corrections ◽  
Set Up

HPPS service of the CROPOS system is today a fast, reliable, precise and commonly used tool for coordinates determination in Croatia. The advantages of a networked RTK method are well known, but in some situations, a single-base RTK method could be a reliable method for coordinates determination, even without a base station having known coordinates. Single-base RTK method with Autonomous base start can be set up on any (unknown) station with a clear sky and GNSS satellites visibility enabled. Differential corrections are usually broadcast to the rover GNSS receiver via a communication link, enabling the coordinates determination with cm-level precision in real time. Simultaneously, the base GNSS receiver collects static observations for base station determination in post-processing and subsequent rover coordinates shift. In this paper, the above mentioned method was tested on the ground, together with TILT option integrated into newest Topcon GNSS receiver.

scholarly journals ANALYSIS OF POSITIONING DEVIATION BETWEEN BEIDOU AND GPS BASED ON NATIONAL REFERENCE STATIONS IN CHINA

2021 ◽  
Vol XLIII-B1-2021 ◽  
pp. 209-214
Author(s):  
M. Chen ◽  
Q. Zhang
Keyword(s):  
Satellite System ◽  
Global Navigation Satellite Systems ◽  
Global Coordinate System ◽  
Gps Data ◽  
Observation Data ◽  
Navigation Satellite ◽  
Satellite Systems ◽  
National Reference ◽  
The North ◽  
Processing Modes

Abstract. In order to probe into the characteristics of positioning deviation between Beidou Navigation Satellite System (Beidou) and global positioning system (GPS), and investigate possible contribution of Beidou data to refinement of global coordinate system, refined calculation is made on observation data of 240 national reference stations that are distributed uniformly across China on the whole in this study. These stations support satellite signals of four global navigation satellite systems, including Beidou, GPS, GLONASS and Galileo, and a 5-year time span from 2016 to 2020 is adopted. In this study, PPP is calculated based on GPS data and Beidou single system data in no-difference resolution network mode, and accurate coordinates of national reference stations in two processing modes are obtained. Analysis of difference between the calculations based on Beidou data and on GPS data shows that the consistency between Beidou and GPS positioning results reaches about 5 mm in the east and in the north, and about 1.3 cm in the height direction.

scholarly journals Positioning Accuracy Comparison of GNSS Receivers Used for Mapping and Guidance of Agricultural Machines

Agronomy ◽  
2020 ◽  
Vol 10 (7) ◽  
pp. 924 ◽  
Author(s):  
Pietro Catania ◽  
Antonio Comparetti ◽  
Pierluigi Febo ◽  
Giuseppe Morello ◽  
Santo Orlando ◽  
...  
Keyword(s):  
Real Time ◽  
Precision Agriculture ◽  
Low Cost ◽  
Global Navigation Satellite Systems ◽  
Reference Trajectory ◽  
Positioning Error ◽  
Differential Correction ◽  
Positioning Accuracy ◽  
Real Time Kinematic ◽  
Gnss Receivers

Global Navigation Satellite Systems (GNSS) allow the determination of the 3D position of a point on the Earth’s surface by measuring the distance from the receiver antenna to the orbital position of at least four satellites. Selecting and buying a GNSS receiver, depending on farm needs, is the first step for implementing precision agriculture. The aim of this work is to compare the positioning accuracy of four GNSS receivers, different for technical features and working modes: L1/L2 frequency survey-grade Real-Time Kinematic (RTK)-capable Stonex S7-G (S7); L1 frequency RTK-capable Stonex S5 (S5); L1 frequency Thales MobileMapper Pro (TMMP); low-cost L1 frequency Quanum GPS Logger V2 (QLV2). In order to evaluate the positioning accuracy of these receivers, i.e., the distance of the determined points from a reference trajectory, different tests, distinguished by the use or not of Real-Time Kinematic (RTK) differential correction data and/or an external antenna, were carried out. The results show that all satellite receivers tested carried out with the external antenna had an improvement in positioning accuracy. The Thales MobileMapper Pro satellite receiver showed the worst positioning accuracy. The low-cost Quanum GPS Logger V2 receiver surprisingly showed an average positioning error of only 0.550 m. The positioning accuracy of the above-mentioned receiver was slightly worse than that obtained using Stonex S7-G without the external antenna and differential correction (maximum positioning error 0.749 m). However, this accuracy was even better than that recorded using Stonex S5 without differential correction, both with and without the external antenna (average positioning error of 0.962 m and 1.368 m).

scholarly journals Asynchronous RTK Method for Detecting the Stability of the Reference Station in GNSS Deformation Monitoring

Sensors ◽  
2020 ◽  
Vol 20 (5) ◽  
pp. 1320
Author(s):  
Yuan Du ◽  
Guanwen Huang ◽  
Qin Zhang ◽  
Yang Gao ◽  
Yuting Gao
Keyword(s):  
Real Time ◽  
Reference Frame ◽  
Deformation Monitoring ◽  
Global Navigation Satellite Systems ◽  
Reference Station ◽  
Monitoring Station ◽  
Landslide Monitoring ◽  
Satellite Systems ◽  
Local Reference ◽  
Global Navigation Satellite

The real-time kinematic (RTK) positioning technique of global navigation satellite systems (GNSS) has been widely used for deformation monitoring in the past several decades. The RTK technique can provide relative displacements in a local reference frame defined by a highly stable reference station. However, the traditional RTK solution does not account for reference stations that experience displacement. This presents a challenge for establishing a near real-time GNSS monitoring system, as since the displacement of a reference station can be easily misinterpreted as a sign of rapid movement at the monitoring station. In this study, based on the reference observations in different time domains, asynchronous and synchronous RTK are proposed and applied together to address this issue, providing more reliable displacement information. Using the asynchronously generated time difference of a reference frame, the proposed approach can detect whether a measured displacement has occurred in the reference or the monitoring station in the current epoch. This allows for the separation of reference station movements from monitoring station movements. The results based on both simulated and landslide monitoring data demonstrate that the proposed method can provide reliable displacement determinations, which are critical in deformation monitoring applications, such as the early warning of landslides.

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