GNSS Measurements Research Articles

GNSS and Photogrammetric UAV Derived Data for Coastal Monitoring: A Case of Study in Emilia-Romagna, Italy

GNSS real-time techniques and UAV photogrammetry can be alternative methods for the monitoring of sand beaches. This activity is particularly important in environments such as the Emilia-Romagna coastline. In this paper, two couples of surveys (year 2019 and 2020) performed using GNSS or a low-cost UAV equipment over a common area were compared in order to analyse: point-wise height differences, profile shapes along defined sections, and volumes variations over time. Both surveys were aligned to the same reference benchmark through GNSS measurements. The highest discrepancies between the two surveying methods (tens of cm) were found in vegetated areas and along the shoreline, otherwise, the height differences are mainly within the 10 cm level. In terms of volumes, excluding the most critical areas, differences close to zero can be found. Obtained results show that GNSS and UAV photogrammetry provides similar results, at least for quite flat terrains and when decimetre-level accuracy is required.

Intelligent Active Correction Technology and Application of Tower Displacement in Arch Bridge Cable Lifting Construction

In order to control the tower deviation in the cable hoisting process of long-span concrete-filled steel tubular arch bridge during construction monitoring, a practical method of tower deviation correction was studied and established. In the paper, based on the studies about the deviation error formation mechanism of tower in the process of cable lifting, the relevant formulas of the arch rib elevation changes caused by the change of tower state were deduced. The traditional control methods including increase of tower stiffness and strength of the anchor cable, are not effective, costly, and require a longer construction period. To overcome these defects, in virtue of the Beidou GNSS measurement system and hydraulic jack active control system, the active control technology of the CFST (Concrete Filled Steel Tube) arch bridge tower deviation was thoroughly studied. Besides, a perfect active control theory was established. Finally, the author puts forward the idea of reverse pulling tower deviation. The field measurement and comparative study show that after the optimization of this method, the tower deviation is within 2 cm, and the error meets the specification requirements. The proposed method can accurately control the tower deviation in the process of arch bridge cable hoisting, and establish a set of perfect active control related systems and theories, which is especially suitable for the construction monitoring and adjustment in the construction stage of arch bridge, and can provide reference for the construction control of tower deviation of the same type of bridge.

Fusing GNSS/INS/Vision With A Priori Feature Map for High-Precision and Continuous Navigation

Nowadays, the autonomous vehicle has undergone an impressive development, in which one of the most challenging tasks is to pursue high-precision and continuous navigation in complex scenarios. However, GNSS signals are very likely to be blocked and the inertial system suffers from error drift over time. To achieve centimeter-level positioning accuracy, a tightly-coupled model is built via fusing visual, GNSS, and INS measurements, based on a priori visual feature map. The visual map is first generated by a visual mobile surveying system, and the quality of the map is improved by outlier elimination and road lane tracking. This visual feature map consists of two layers that involve 3D coordinates of robust visual features and road lane markings, then two GNSS/INS/Vision fusion models are developed. The first one fuses visual 2D-3D feature matching, GNSS, and INS measurement. The proposed system is effective even when satellites are all out of lock. The second one fuses lane line constraints with GNSS, INS, and distance measurement indicator (DMI). In the experiment part, we show how a visual feature map is generated and refined, then, the performance of the positioning algorithm is evaluated. For the first fusion model, we achieve 10 cm RMS accuracy when only one feature point was matched and all GNSS signals are blocked for 20 minutes. For the other fusion model, the system maintained 10 cm RMS accuracy or even better when a few GNSS satellites are out of lock for 300 seconds.

Ionospheric tomographic common clock model of undifferenced uncombined GNSS measurements

In this manuscript, we introduce the Ionospheric Tomographic Common Clock (ITCC) model of undifferenced uncombined GNSS measurements. It is intended for improving the Wide Area precise positioning in a consistent and simple way in the multi-GNSS context, and without the need of external precise real-time products. This is the case, in particular, of the satellite clocks, which are estimated at the Wide Area GNSS network Central Processing Facility (CPF) referred to the reference receiver one; and the precise realtime ionospheric corrections, simultaneously computed under a voxel-based tomographic model with satellite clocks and other geodetic unknowns, from the uncombined and undifferenced pseudoranges and carrier phase measurements at the CPF from the Wide Area GNSS network area. The model, without fixing the carrier phase ambiguities for the time being (just constraining them by the simultaneous solution of both ionospheric and geometric components of the uncombined GNSS model), has been successfully applied and assessed against previous precise positioning techniques. This has been done by emulating real-time conditions for Wide Area GPS users during 2018 in Poland.

Conceptual Framework for the Analysis and Modeling of GNSS Measurements based on Gaussian Process

Conceptual Framework for the Analysis and Modeling of GNSS Measurements based on Gaussian Process

Prediction on the Urban GNSS Measurement Uncertainty Based on Deep Learning Networks With Long Short-Term Memory

The GNSS performance could be significantly degraded by the interferences in an urban canyon, such as the blockage of the direct signal and the measurement error due to reflected signals. Such interferences can hardly be predicted by statistical or physical models, making urban GNSS positioning unable to achieve satisfactory accuracy. The deep learning networks, specializing in extracting abstract representations from data, may learn the representation about the GNSS measurement quality from existing measurements, which can be employed to predict the interferences in an urban area. In this study, we proposed a deep learning network architecture combining the conventional fully connected neural networks (FCNNs) and the long short-term memory (LSTM) networks, to predict the GNSS satellite visibility and pseudorange error based on GNSS measurement-level data. The performance of the proposed deep learning networks is evaluated by real experimental data in an urban area. It can predict the satellite visibility with 80.1% accuracy and predict the pseudorange errors with an average difference of 4.9 meters to the labeled errors. Experiments are conducted to investigate what representations have been learned from data by the proposed deep learning networks. Analysis results show that the LSTM layer within the proposed networks may contain representations about the environment, which affects the prediction behavior and can associate with the real environment information.

GNSS and RPAS Integration Techniques for Studying Landslide Dynamics: Application to the Areas of Victoria and Colinas Lojanas, (Loja, Ecuador)

This research tests the application of GNSS and RPAS techniques to the spatiotemporal analysis of landslide dynamics. Our method began by establishing non-permanent GNSS networks on the slope surfaces to perform periodic measurements by differential GNSS. Similarly, RPAS flights were made to acquire high-resolution images, which were oriented and georeferenced using ground control points and structure-from-motion algorithms to ultimately obtain digital surface models and orthophotos. Based on GNSS measurements, the direction and velocity of displacements were accurately calculated, and orthophotos and DSMs were used to calculate horizontal and vertical displacements in a set of significant points throughout the study area, reaching accuracies higher than 0.035 m in the GNSS data and 0.10 m in the RPAS data. These values were within the accuracy required for such studies. Based on the field observations and the results from the photogrammetric studies, the two studied landslides were classified as very slow flows. These techniques are the basis for establishing early warning systems in areas of natural hazards based on the calculation of displacement speeds of the surface of slopes.

Assimilation of OLCI total column water vapour in the Met Office global numerical weather prediction system

AbstractThe representation of water vapour in numerical weather prediction models is still subject to significant uncertainties, which are partly due to the lack of observations of water vapour in the lower troposphere over land and sea‐ice areas. There are now several satellite datasets of total column water vapour available, which make use of the reflected radiances from the surface in the near‐infrared spectral region where there are water vapour absorption bands. The ocean and land cover imager (OLCI) on the Sentinel‐3A and 3B satellites measures the top of atmosphere radiances in the near infrared, and a total column water vapour product is retrieved and made available in near real time. Comparisons of the total column water vapour from OLCI with NWP model 6‐h forecasts, collocated ground‐based GNSS measurements and radiosonde profiles have been undertaken to determine the accuracy of the product. Following the monitoring, some experiments were made to assimilate the OLCI total column water vapour over land using the Met Office 4D‐Var assimilation system. A 5‐month trial assimilating the OLCI data has shown consistently positive impacts on the forecast scores with some changes to the water vapour distribution in the model.

Диференціація кінематики греблі Дністровської ГЕС-1 (за даними ГНСС-моніторингу просторових зміщень)

The purpose of study is to generalize the vertical displacements of the GNSS network of spatial monitoring of the Dnister HPP-1 dam for the differentiation of its kinematics as well as to evaluate the impact of short-term geodynamic processes in the region. Object of study. The object of the study is the monitoring of the Dniester HPP-1 dam according to the GNSS network data of the stationary system for monitoring the spatial displacement of structures (SSMSDS) of the Dniester HPP-1. The basis of the Dnister SSMSDS are two base GNSS stations additionally equipped with a robotic total station, which are installed on a strong foundation and located at a distance of several hundred meters from the dam. There are control points equipped with a GNSS receiver, antenna and an angle reflector with a 3600 viewing angle on the crest of the dam. The results of GNSS measurements are transmitted to the Leica GNSS Spider software, which processes and determines the coordinates of the base and control points. The GEOMOS software performs a joint estimation of GNSS results and linear-angular measurements. Methodology. To generalize the displacements of GNSS stations of Dnister HPP-1 the method of statistical analysis of time series is used. Authors examine the covariance interrelationships between all GNSS stations of the stationary system for monitoring the spatial displacement of structures (SSMSDS) of the Dnister HPP-1, which are placed on the dam based on the results of measurements from 1.07.2017 to 31.03.2021. For the selected periods of anomalous short-term displacements, the average values of covariance for each GNSS station are calculated. Results. During the period from 1.07.2017 to 31.03.2021 and according to the results of covariance interrelation for most GNSS stations, 3 epochs of anomalous altitude displacements are established (T = 2017.8 ± 0.1, T = 2019.0 ± 0.1, T = 2019.4 ± 0.1). Based on the covariance analysis, it was found that for periods of anomalous vertical displacements, the kinematics of the GNSS station MP01 differs significantly from the kinematics of GNSS stations MP02-MP05. The kinematics of GNSS-stations MP02-MP05 is constant, which indicates the anomalous movement of the unit on which the GNSS-station MP01 is installed in relation to the other blocks of the dam of the Dnister HPP-1. Scientific novelty and practical significance. Authors proposed the method for studying the geodynamics possesses of large industrial areas covered by a network of GNSS stations. Based on the GNSS measurements the periods of anomalous displacement are reveled and further search for spatial kinematic interrelationships between pair of GNSS stations is established. The developed methodology can be used to differentiate the kinematics of structural elements with installed GNSS stations such as engineering structures, industrial areas, geodynamic polygons.

Data‐driven protection levels for camera and 3D map‐based safe urban localization

<h3>Abstract</h3> Reliably assessing the error in an estimated vehicle position is integral for ensuring the vehicle’s safety in urban environments. Many existing approaches use GNSS measurements to characterize protection levels (PLs) as probabilistic upper bounds on position error. However, GNSS signals might be reflected or blocked in urban environments, and thus additional sensor modalities need to be considered to determine PLs. In this paper, we propose an approach for computing PLs by matching camera image measurements to a LiDAR-based 3D map of the environment. We specify a Gaussian mixture model probability distribution of position error using deep neural-network-based data-driven models and statistical outlier weighting techniques. From the probability distribution, we compute PL by evaluating the position error bound using numerical line-search methods. Through experimental validation with real-world data, we demonstrate that the PLs computed from our method are reliable bounds on the position error in urban environments.

Результаты калибровки альтиметрических измерений космической геодезической системы «ГЕО-ИК-2» на акватории Рыбинского водохранилища

The authors present the results of satellite altimetry measurements calibration from the space geodetic system “GEO-IK-2” in the water area of the Rybinsk reservoir, obtained through two independent methods. In the first case, the altimetry measurements were calibrated by comparing the sea surface heights with respect to the reference ellipsoid, which were calculated from radio altimeter measurements, and from the processing of ground GNSS measurements performed at the sub-satellite point at the time of passing the GEO-IK-2 spacecraft. For this, in the summer of 2020, special geodetic measurements were carried out in the water area of the Rybinsk reservoir. The GNSS receiver was mounted on the Sea Buoy, which was towed by boat to the specified sub-satellite points, the coordinates of which were predetermined from the forecast of satellite orbits. At the same time, base stations for GNSS observations were installed on the coast. The largest difference in the sea surface height does not exceed 13,9 cm. The second method is cross-calibration by radio altimeter measurements from other altimetry spacecraft. In this case, the tracks of the first and second satellites within a relatively short time interval cross one common point, at which the sea surface height is determined. For this, the Jason-3 spacecraft was selected, the track of which was crossed by the GEO-IK-2 vehicle track on September 11, 2020 over the water area of the Rybinsk Reservoir. The difference in sea surface heights was 9,6 cm.

GNSS Signal Processing with EKF and UKF for Stationary User Position Estimation

Precise and accurate estimation of state vectors is an important process during position determination. In this study, Extended Kalman Filter (EKF) and Unscented Kalman Filter (UKF) of stationary user, state vectors defined in Earth Centered Inertial (ECI) coordinate system, accompanied by GNSS measurement data. It is aimed to make estimations with methods. EKF and UKF methods were compared with each other. In this study, the effects of nonlinear motion analysis and linearization methods on state vector estimations were investigated. Thanks to this study, estimations of the positioning information required during the specific tasks of many moving platforms have been made.

Effects of ionospheric constraints in Precise Point Positioning processing of geodetic, low-cost and smartphone GNSS measurements

The proliferation of low-cost GNSS hardware smartphones providing multi-constellation, multi-frequency carrier-phase and pseudorange measurements for the Android platform offer an avenue for Precise Point Positioning (PPP) GNSS use in recent years. However, smartphone PPP is restricted due to high multipath effects and signal loss leading to metre-level accuracy and longer convergence time compared against professional-grade GNSS receivers. Proven by previous research, the combination of ionospheric constraints and receiver differential code bias (DCB) estimation is an efficient approach to improve PPP solution initialization. Therefore, this study analyzes the performance improvements by applying ionospheric constraints (IC) to PPP in comparison to conventional PPP solutions for different grades of GNSS receivers (geodetic, low-cost, and smartphone hardware) in open-sky and suburban environments. The results reveal that smartphone PPP enjoys more beneficial effects from ionospheric constraints (IC) than low-cost and geodetic hardware, as a significant 30% improvement in horizontal rms is observed in the first epoch of examined datasets, and a 57% improvement in the first 20 min of data collection. For low-cost and geodetic equipment, the first epoch improvement is only 21% and 18%, respectively. Furthermore, a 44% convergence time reduction for smartphone PPP-IC is observed to attain 1 m level of horizontal accuracy. Based on these investigations, PPP-IC can provide greater impact for those low-quality measurements before convergence, showing potential in achieving fast initialization and accurate positioning within a short time for autonomous vehicles, precision agriculture, and smartphone location-based services.

Sea-level variations from co-located tide gauge and GNSS stations using GNSS-Reflectometry in Indonesia

Sea level variation is an important key for hazard mitigation in the coastal region to study climate change. In the last decade, reflected GNSS signals have been used in many applications, such as snow, sea level, and ocean storm monitoring. In this research, we use GNSS-Reflectometry co-located with a tide gauge station to monitor sea-level variations. We use the Signal Noise to Ratio (SNR) data to derive sea-level height from GNSS. One-month comparison of sea-level variations has been made from a tide gauge and a GNSS measurement in Barus, North Sumatra Indonesia. The results have a mean bias of about 2 cm with a root mean square error of 11 cm and a correlation coefficient value of 0.90. Our result demonstrates that the GNSS-Reflectometry technique is potential to provide a new approach to monitor sea-level changes that complement the existing tide-gauge networks in Indonesia.

Using Android smartphones with dual-frequency multi-GNSS receiver to measure the total electron content of the ionosphere

The results of raw GNSS data recorded using a Xiaomi Mi 8 android smartphone equipped with a dual-frequency GNSS module BCM47755 capable of receiving and processing signals from the GPS, Galileo, QZSS systems in the L1 and L5 frequency sub-bands are presented in the paper. The indices of ionospheric activity that as variations in the relative slant total electron content, the rate of total electron content, the rate of total electron content index, root-mean-square deviation of relative slant total electron content on the base of raw GNSS data are calculated. A comparison study of the data obtained with the data from the KZN2 station of the International GNSS Service network, equipped with a professional GNSS receiver of a geodetic class is carried out. It is shown that the median value of signal strength at frequencies L1 and L5 for the data obtained from the satellites G08, G10, G27, G32, E09 on the Xiaomi Mi 8 smartphone is ≈ 5-25% lower than data from the KZN2 station. The indices of ionospheric activity registered by the Xiaomi Mi 8 smartphone have a higher signal-to-noise ratio in comparison with the data of the KZN2 station. Median levels of variations of the relative slant TEC, ROT, ROTI, and RMSTEC obtained by the Trimble Alloy receiver at KZN2 station were 45÷70% lower than that for the Xiaomi Mi 8 smartphone. Nonetheless, the possibility of registering the indices of ionospheric activity such as relative slant total electron content and others based on dual-frequency raw GNSS measurements (primarily carrier-phase and pseudorange) of GNSS signals received by smartphones opens up prospects for attracting as wide a community as possible for collecting GNSS data and monitoring the ionosphere.

ГЕОДИНАМІКА

The goal. Identify the relationship between seasonal temperature changes and vertical and horizontal displacements of GNSS control points based on data obtained by the automated monitoring system of the Dnipro HPP dam in the period from 2016 to 2020. Input data. The research used data of uninterrupted GNSS measurements obtained at 16 points of the Dnipro HPP dam from mid-2016 to mid-2020. Method. A specially developed software product analyzes the GNSS time series of measurements pre-processed by the GeoMoS system to determine the parameters of seasonal displacements and their relationship with seasonal changes in air temperature. The GNSS time series analysis. Based on the conducted research, the influence of environmental temperature has a decisive effect on the cyclicity of dam deformations. This applies to both horizontal and vertical displacements but in the absence of significant changes in the water level in the upper reservoir. Values of extreme displacements increase closer to the middle of the dam and decrease at the edges. This tendency is observed every year in the study period. According to the three-year GNSS dam monitoring, the amplitude of semi-annual horizontal oscillations of the control points relative to the dam axis is in the range of 15-18 mm. Almost all vectors of horizontal displacements are perpendicular to the axis of the arcuate dam. In the first half of the year, the vectors of horizontal displacements aim to widen the dam, and in the second half of the year - at compressing the dam. The analysis of the data represents that almost every year, extreme deviations, both horizontal and vertical, occur in February and August. Temperature extremes occur faster than excessive GNSS displacements. For the dam of the Dnipro HPP, the extreme horizontal displacements lag on average by 37 days, and the vertical ones - by 32 days from the extreme temperatures. The deformations of the dam are related to the concrete structure temperature, which changes with a certain delay relative to the air temperature. The magnitudes of extreme displacements and the epoch of their manifestation depend on the dam's design and its technical parameters. For each dam, these extreme displacements and the periods of their representation will be different. Accordingly, monitoring these displacements and their changes over time is one of the criteria for assessing the general condition of the dam. Scientific novelty and practical significance. The regularities of the connection between the change of temperature and the displacements of the GNSS points, revealed during the research, can be used for the further study of data processing and analysis of the hydraulic structures monitoring.

DEVELOPMENT OF A LOW-COST, HAND-HELD MULTI-SENSOR SYSTEM FOR THE MONITORING OF SMALL WATER BODIES

Abstract. For small-scale monitoring of small water bodies, conventional methods such as GNSS or total station measurements are used. The data acquisition is usually carried out in profile form supplemented with extra measurements of break edges, slope edges or bank courses. However, these methods can be used efficiently only on small sections and with low temporal resolution. At the same time, as the length of rivers or creeks to be monitored increases, the cost-effectiveness of the above methods decreases. Further limitations such as very small sections that are difficult to access and also sections that are sometimes heavily overgrown also prevent the use of large measuring platforms. By contrast, with use of a hand-held compact multi-sensor platform it is possible to survey several hundred kilometres of the smallest rivers and creeks. This publication demonstrates the use of such a platform to record micro-watersheds. For this purpose, the Creek4D project, the measurement principle and the sensor technology used are shown. In addition, first measurement data and the calibration strategy are shown.

Tropospheric Correction of Sentinel-1 Synthetic Aperture Radar Interferograms Using a High-Resolution Weather Model Validated by GNSS Measurements

Synthetic Aperture Radar Interferometry (InSAR) is a space geodetic technique used for mapping deformations of the Earth’s surface. It has been developed and used increasingly during the last thirty years to measure displacements produced by earthquakes, volcanic activity and other crustal deformations. A limiting factor to this technique is the effect of the troposphere, as spatial and temporal variations in temperature, pressure, and relative humidity introduce significant phase delays in the microwave imagery, thus “masking” surface displacements due to tectonic or other geophysical processes. The use of Numerical Weather Prediction (NWP) models as a tropospheric correction method in InSAR can tackle several of the problems faced with other correction techniques (such as timing, spatial coverage and data availability issues). High-resolution tropospheric modelling is particularly useful in the case of single interferograms, where the removal of the atmospheric phase screen (and especially the highly variable turbulent component) can reveal large-amplitude deformation signals (as in the case of an earthquake). In the western Gulf of Corinth, prominent topography makes the removal of both the stratified and turbulent atmospheric phase screens a challenging task. Here, we investigate the extent to which a high-resolution WRF 1-km re-analysis can produce detailed tropospheric delay maps of the required accuracy by coupling its output (in terms of Zenith Total Delay or ZTD) with the vertical delay component in GNSS measurements. The model is operated with varying physical parameterization in order to identify the best configuration, and validated with GNSS zenithal tropospheric delays, providing a benchmark of real atmospheric conditions. We correct sixteen Sentinel-1A interferograms with differential delay maps at the line-of-sight (LOS) produced by WRF re-analysis. In most cases, corrections lead to a decrease in the phase gradient, with average root-mean-square (RMS) and standard deviation (SD) reductions in the wrapped phase of 6.0% and 19.3%, respectively. Results suggest a high potential of the model to reproduce both the long-wavelength stratified atmospheric signal and the short-wave turbulent atmospheric component which are evident in the interferograms.

Real-time interpolation of global ionospheric maps by means of sparse representation

In this paper, we propose a method for the generation of real-time global ionospheric map (RT-GIM) of vertical total electron content (VTEC) from GNSS measurements. The need for interpolation arises from the fact that the ionospheric pierce point (IPP) measurements from satellites to stations are not distributed uniformly over the ionosphere, leaving unfilled gaps at oceans or poles. The method we propose is based on using a high-quality historical database of post-processed GIMs that comprises more than two solar cycles, calculates the GIM by weighted superposition on a subset of the database with the compatible solar condition. The linear combination of GIMs in the database was obtained by minimizing a $$\ell _2$$ distance between VTEC measurements at the IPPs and the VTECs from the database, adding a $$\ell _1$$ penalization on the weights to assure a sparse solution. The process uses a Sun-fixed geomagnetic reference frame. This method uses the atomic decomposition/least absolute shrinkage and selection operator (LASSO), which will be denoted as atomic decomposition interpolator of GIMs (ADIGIM). As the computation is done in milliseconds, the interpolation is performed in real time. In this work, two products were developed, denoted as UADG and UARG, the UADG in real time and UARG with a latency of 24 h to benefit from the availability of a greater number of stations. The altimeter JASON3 VTEC measurements were used as reference. The quality of interpolated RT-GIMs from day 258 of 2019 to 155 of the year 2020 is compared with other RT/non-RT GIM products such as those from International GNSS Service (IGS), Centre National d’Etudes Spatiales (CNES), Chinese Academy of Sciences (CAS), Polytechnic University of Catalonia (UPC) and others. The RT ADIGIM performance proved to be better, nearly as good as the rapid or final GIMs computed retrospectively with delays of hours to days. Besides, the non-RT ADIGIM quality is as good or better than most GIM products. The oceanic regions have been included in the assessment which showed that ADIGIM interpolation gives the best estimation (referred to JASON3). The developed method, UADG, will constitute the next-generation UPC RT-GIM, and also UARG will improve the current product UQRG (the current UPC rapid GIM product computed retrospectively) due to its complementary information.

EXPERIMENTAL RESEARCH OF THE ACCURACY OF NAVIGATION GNSS - RECEIVERS IN CONDITIONS OF THE CONSTRUCTED TERRITORY

Use of digital geodetic support technologies with the use of GNSS satellite systems in combination with electronic geodetic instruments, introduction of new methods of construction of geodetic networks, collection of information by ground and aerospace surveying, unification of exchange formats of measurement results based on computer technologies and their application conditions. Substantiation and development of remote methods of spatial information collection requires analysis and consideration of a number of errors in order to improve accuracy.&#x0D; Wikimapia is a map project for shared use with open content, which aims to identify all geographical objects with the introduction of useful information about them. It combines an interactive web map and a Wiki system.&#x0D; One of the features of the Wikimapia resource is that it is possible to determine geographical coordinates. To do this, you need to move the cross cursor on the object of interest and get its coordinates visually.&#x0D; The purpose of the study was to determine the accuracy of the coordinates of GPS receivers Garmin Oregon 450 in the built-up area, using as a basis for calibration, the resource "Wikimapia".&#x0D; In order to determine the accuracy of the location with the help of GARMIN Oregon 450 GPS receivers, GNSS measurements were performed at 30 marker points.&#x0D; Ellipsoidal coordinates were recalculated into spatial rectangles according to known formulas.&#x0D; In order to assess the accuracy of determining the location of marker points, the differences in the coordinates of their position were found and the root mean square error from a number of measurements was found.&#x0D; The average error of coordinate measurements was ± 4.79 m for the GPS receiver.&#x0D; Based on experimental research, the possibility of using the resource "Wikimapia" not only to quickly determine the coordinates of topographic objects, determine their categories, but also with sufficient accuracy to apply for the calibration of navigation GNSS receivers when there is no network of geodetic points.&#x0D; A promising direction in the process of scientific and practical research should be the creation of a general mathematical model for predicting the influence of the plurality on the location and improvement of navigation aids.