RTK Mode Research Articles

Geodetic support for the construction of in-farm roads in rural settlements

The article is about the analysis of geodetic methods used to realize in-farm road projects. The issue of high-quality provision of geospatial data is considered in this paper. The authors compared two methods: using electronic total station, and GNSS technology in RTK mode. The paper presents the sequence of research and the results, and proposes the most effective method to ensure quality and save time during construction.

Low-Cost Dual-Frequency GNSS Receivers and Antennas for Surveying in Urban Areas.

Low-cost dual-frequency global navigation satellite system (GNSS) receivers have recently been tested in various positioning applications. Considering that these sensors can now provide high positioning accuracy at a lower cost, they can be considered an alternative to high-quality geodetic GNSS devices. The main objectives of this work were to analyze the differences between geodetic and low-cost calibrated antennas on the quality of observations from low-cost GNSS receivers and to evaluate the performance of low-cost GNSS devices in urban areas. In this study, a simple RTK2B V1 board u-blox ZED-F9P (Thalwil, Switzerland) was tested in combination with a low-cost calibrated and geodetic antenna in open-sky and adverse conditions in urban areas, while a high-quality geodetic GNSS device was used as a reference for comparison. The results of the observation quality check show that low-cost GNSS instruments have a lower carrier-to-noise ratio (C/N0) than geodetic instruments, especially in the urban areas where the difference is larger and in favor of the geodetic GNSS instruments. The root-mean-square error (RMSE) of the multipath error in the open sky is twice as high for low-cost as for geodetic instruments, while this difference is up to four times greater in urban areas. The use of a geodetic GNSS antenna does not show a significant improvement in the C/N0 and multipath of low-cost GNSS receivers. However, the ambiguity fix ratio is larger when geodetic antennas are used, with a difference of 1.5% and 18.4% for the open-sky and urban conditions, respectively. It should be noted that float solutions may become more evident when low-cost equipment is used, especially for short sessions and in urban areas with more multipath. In relative positioning mode, low-cost GNSS devices were able to provide horizontal accuracy lower than 10 mm in urban areas in 85% of sessions, while the vertical and spatial accuracy was lower than 15 mm in 82.5% and 77.5% of the sessions, respectively. In the open sky, low-cost GNSS receivers achieve a horizontal, vertical, and spatial accuracy of 5 mm for all sessions considered. In RTK mode, positioning accuracy varies between 10-30 mm in the open-sky and urban areas, while better performance is demonstrated for the former.

Research on the Positioning Performance of GNSS with a Low-Cost Choke Ring Antenna

One of the technologies used for localization is GNSS (Global Navigation Satellite Systems), which is exposed to many phenomena, i.e., the occurrence of terrain covers, reflections of the radio waves, and the multipath nature of the radio waves in the propagation environment. To increase the resistance to environmental phenomena, special types of antennas are used, which include, among others, choke ring antennas. The article describes the design and construction of the choke ring antenna and the impact of the mentioned device on the quality of GNSS positioning. The accuracy of the constructed antenna (based on selected accuracy measures: DRMS, 2DRMS, SEP, MRSE, SAE) is calculated together with positioning errors determined for two types of antennas: choke ring antenna and the dedicated antenna supplied by the manufacturer in RTK mode. The results confirm that the designed choke ring antenna can be used for positioning without significantly losing accuracy in the RTK mode.

Use of UAS and TLS technology in 3D modeling of constructions with complex architecture

3D building models are widely used in many applications. The use of terrestrial laser scanning and UAS photogrammetry for 3D modelling is a popular practice especially for constructions with complex architecture. The present article presents an example of using these technologies successfully for 3D modelling of the Episcopal Cathedral of the Holy Trinity from Baia Mare, Romania. A number of 51 control and verification points were determined by the closed circuit travel method and the intersection method. All measurements were processed in Terramodel software. The control points used in the georeferencing of the scans were materialized by metal stakes and the verification points were materialized by reflective targets. Depending on the construction configuration, the field of view and the minimum/maximum scanning distances were subsequently set. A total of 45 scans were performed to model the entire cathedral. The photogrammetric flight was performed in RTK mode, with corrections being transmitted from the DJI D-RTK-2 Mobile Station base to the RTK drone. All retrieved frames had geolocation and frame orientation elements recorded by the IMU module. A total number of 222 photograms were taken, as a result of a double grid photogrammetric flight, with the camera oriented at 60 degrees, but also as a result of manual acquisition by performing orbital flights at different heights: an orbital flight on the ground floor, an orbital flight at the level of about 40 meters and an orbital flight around the tower.

ACCURACY OF COORDINATE DETERMINATIONS OF THE NETWORK OF PROTECTED ZONE POINTS ACCORDING TO THE RESULTS OF GNSS OBSERVATIONS

The article examines errors of the planned position of the points of the educational and research site “Fortuna” of the Chernihiv Polytechnic National University (Ukraine), located in a forested area. Kinematic positioning has been performed using a GNSS receiver GeoMax Zenith 10/20 in real time mode. The network of permanent satellite GNSS stations System NET has been used as a coordinate basis. RTK Master Auxiliary Corrections (MAX) technology has been used to form the corrective amendments. The calculation of RTK corrections has been performed using the software package Leica GNSS Spider v4.3. The Transverse Mercator cartographic projection has been used to determine the flat rectangular coordinates in the USK-2000 system. The values of the coordinates determined in the RTK mode have been compared with the coordinates obtained by the method of electronic polygonometry, which are estimated to be 3 times more accurate. Coordinate differences have formed error vectors. As a result of analysis of the vector field, a stable tendency has been established: the deviation of the planned coordinates of the site points, determined by the method of GNSS-observations in real time mode and located in the forest park zone, in the direction of the base station.

Evaluation of Different LiDAR Technologies for the Documentation of Forgotten Cultural Heritage under Forest Environments.

In the present work, three LiDAR technologies (Faro Focus 3D X130—Terrestrial Laser Scanner, TLS-, Kaarta Stencil 2–16—Mobile mapping system, MMS-, and DJI Zenmuse L1—Airborne LiDAR sensor, ALS-) have been tested and compared in order to assess the performances in surveying built heritage in vegetated areas. Each of the mentioned devices has their limits of usability, and different methods to capture and generate 3D point clouds need to be applied. In addition, it has been necessary to apply a methodology to be able to position all the point clouds in the same reference system. While the TLS scans and the MMS data have been geo-referenced using a set of vertical markers and sphere measured by a GNSS receiver in RTK mode, the ALS model has been geo-referenced by the GNSS receiver integrated in the unmanned aerial system (UAS), which presents different characteristics and accuracies. The resulting point clouds have been analyzed and compared, focusing attention on the number of points acquired by the different systems, the density, and the nearest neighbor distance.

Evaluation of Forest Features Determining GNSS Positioning Accuracy of a Novel Low-Cost, Mobile RTK System Using LiDAR and TreeNet

Accurate positioning is one of the main components and challenges for precision forestry. This study was established to test the feasibility of a low-cost GNSS receiver, u-blox ZED-F9P, in movable RTK mode with features that determine its positioning accuracy following logging trails in the forest environment. The accuracy of the low-cost receiver was controlled via a geodetic-grade receiver and high-density LiDAR data. The features of nearby logging trails were extracted from the LiDAR data in three main categories: tree characteristics; ground-surface conditions; and crown-surface conditions. An object-based TreeNet approach was used to explore the influential features of the receiver’s positioning accuracy. The results of the TreeNet model indicated that tree height, ground elevation, aspect, canopy-surface elevation, and tree density were the top influencing features. The partial dependence plots showed that tree height above 14 m, ground elevation above 134 m, western direction, canopy-surface elevation above 138 m, and tree density above 30% significantly increased positioning errors by the low-cost receiver over southern Finland. Overall, the low-cost receiver showed high performance in acquiring reliable and consistent positions, when integrated with LiDAR data. The system has a strong potential for navigating machinery in the pathway of precision harvesting in commercial forests.

Investigation of determining the accuracy of spatial vectors by the satellite method in a real time mode

Abstract The study of determining the accuracy of spatial vectors by the global navigation satellite system (GNSS) in real time (RTK) was conducted. The possibility of construction of precision geodetic networks by the combined method of static and RTK GNSS measurements which correspond to the set accuracy and reach the maximum economic efficiency is investigated. A technique providing the densification of GNSS network and the use of two simultaneously operating GNSS receivers (Rover) is proposed. The research was carried out at the points of the GNSS network of Dnister Pumped Storage Power Plant (PSPP) (Ukraine). As a result of comparison of reference and measured elements of vectors, it was found that the average absolute error in determining the spatial distance of 14 vectors was 5.3 mm. Rejection of vectors with a closed horizon reduced the error to 2.1 mm. The vectors are most accurately determined from two satellite systems (GPS, GLONASS) and from a single base station. The recommended distance to the base station is within one kilometer. Increasing the accuracy by 75 % in determining the vector by the proposed method in RTK mode is also shown. As a result of a posteriori optimization of combined GNSS networks, high accuracy on the reliability of vectors determined by the method in RTK mode was confirmed. The technique can be used to construct precision networks, to carry out repeated measurements for the monitoring of large engineering structures with an open horizon.

Использование БПЛА Geoscan 201 для съемки линейного объекта трассы Хива–Ургенч

The aim of this work is to perform a linear aerial survey of the Khiva–Urgench highway using the Geoscan 210 UAV, the results of which will create orthophotomaps at a scale of 1:1 000, which are necessary for designing bicycle and sidewalk paths along this route. Surveyors of the Applied Geodesy Department of UZGASHKLITI performed a field planned-altitude reference at this object. 48 control points were determined. Characteristic solid contours along the route were chosen as reference points. The binding of control points was carried out from the starting points of the State Geodetic Networks, using satellite receivers (SN 5242498595, 5243499034, 4827155394) in the RTK mode in a radial way, by the calibration method on the ground. The coverage area was 17.4 sq. km. Aerial photography was carried out at a height of 211 m by a Geoscan 201 unmanned aerial vehicle at a scale of 1:500 with a DSC RXIR digital camera with a focal length of 35 mm. Forward overlap of aerial photographs was 70 %, and lateral—50 %. 4 aerial routes were made at this facility, the photography basis was 42 m. The number of aerial photographs at the facility was 3 868 pieces, and the coverage of aerial photography was 300 m. The images and their EXIF files were georeferenced by performing field processing using the Geoscan Planner program. Before the start of field work, the GNSS receiver (Trimble R6) was installed at a known point on the ground and started in static mode (10 Hz). The aircraft has a GNSS receiver (Topcon) operating in fast static mode (10 Hz). The GNSS data on the ground and on board the aircraft are balanced. Image center coordinates are calculated from the base station GNSS receiver data using MAGNET Tools software. Then the data is imported into Agisoft Metashape software for automatic processing. In this case, the coordinates of the image centers were recalculated from the WGS-84 system into the SK-42 (Pulkovo 1942) system adopted in our country. The process of optimization and alignment of aerial photographs was carried out. After that, in order to obtain a high image quality, the orthophoto map was built using a height map built on the basis of a dense point cloud. The result of the work performed are orthophoto maps for the Khiva–Urgench highway, which will be used to design the location of bicycle and sidewalk paths.

Implementation of engineering and geodetic works in the framework of research work, which are aimed at developing proposals for the development of settlements of the municipality

At any stage of urban planning activities, it may be necessary to plan the territory. The territory planning project can be created on topographic plans of a scale of 1: 2000. Modern needs for cadastre maintenance, land management, and design of territories require high quality topographic material obtained in almost real time with high image resolution. This problem is effectively solved by aerial photography from unmanned aerial vehicles (UAVs). Airborne laser scanning allows you to survey difficult terrain and large areas. To clarify the position of some terrain objects, a GNSS survey in RTK mode was used. The combined survey method provides the necessary accuracy of surveying the situation and the terrain, the measurement accuracy corresponds to the possibility of creating engineering-topographic plans at a scale of 1: 2000. In the course of the work, engineering digital terrain models and orthophotomaps were formed. Based on the data obtained, a digital topographic plan of 1: 2000 scale was compiled.

Аналіз похибок еліпсоїдних висот на основі результатів GNSS-нівелювання

Research the influence of errors on the measurement results is always an urgent task. Analysis of such values makes it possible to assess the nature of the change and the magnitude of the impact of errors for their further consideration or compensation, or minimization. In this paper, the errors in determining ellipsoidal heights from GNSS observations are considered. In determining the ellipsoidal heights, this method can achieve an accuracy of 1–2 cm in static mode (Static) and 2–4 cm in real time mode (RTK). Thus, the accuracy of the chosen mode of observations will indicate the initial limits of the ellipsoidal heights errors influence, and the factors that arise directly during observations and data processing will determine the extent to which these errors will change relative to the initial limits. The purpose of this work is to analyze the errors of ellipsoidal heights based on the results of GNSS-leveling obtained in the static and RTK modes. Method. The study used GNSS-leveling data at 17 points (wall and soil benchmarks) of leveling lines of I–II classes, which are located within a radius of 15 km from the permanent station SULP of the Lviv Polytechnic National University. Observations were performed in static mode (4-hour) and RTK (8–10 measurements). Points are divided into three categories (5–6 points): 1) statics on wall benchmarks; 2) real-time mode on wall benchmarks; 3) static mode on soil benchmarks. By combining methods and categories, four GNSS networks were formed, including 11, 11, 12 and 17 points. Results. For each category, the percentages within which the errors of ellipsoidal heights change in static observation mode and real-time mode using the GNSS leveling method are presented. On the basis of the received information it is established that for the first case errors of ellipsoidal heights on the average change within ± 43 %, for the second ± 36 %, and for the third ± 14 %. The analysis of statistical characteristics for each category shows that the standard deviation of the static mode data is 2 % and 19 %, and the RTK mode – 12 %, respectively. Scientific novelty and practical significance. The nature of the change in the error limits of the ellipsoidal heights determination gives an idea of what accuracy should be expected when performing GNSS-leveling depending on the mode of observation. Such data play an important role in solving scientific and applied problems by GNSS leveling, such as the constructions of new leveling networks or monitoring the height points of existing networks.

Analysis of the current state of unstable geomorphological structures with modern methods

The paper gives results of the digitization of the status and spatial position of a cliff in the Western Crimea coastal zone. The modern equipment and methods accelerate the survey from the time perspective and improve the quality of the outcomes; namely a high precision GNSS receiver in RTK mode and PHANTOM-3 PRO copter. The digital terrain model was generated with used the Agisoft Photoscan software. The paper shows that the precision of the mathematical model of the relief constructed by aerial photographs provides more detailed data in comparison to those obtained in the field observations. Furthermore, aerial photography makes it possible to calculate the number of spatial characteristics of hazardous for surveying and latent natural objects out of reach for an on-location investigation. As a result, the very detailed data about current condition of dangerous cliff were obtained. The paper also evaluates the linear and volumetric characteristics of cleavages that are prone to collapse.

Assessment of the Single Frequency Low Cost GPS RTK Positioning

The Global Navigation Satellite System (GNSS), nowadays, is to be an important tool for determining positions and times on the real-time and post-processing applications. This study aims to assess the performance of the single frequency L1-GPS using low cost receivers. The performance will be evaluated by comparing with the geodetic L1+L2 GPS receiver to positioning performance. The low cost receivers used were Ublox NEO-M8T and Allystar HD9100. While, the dual frequency GPS TOPCON was used as reference receiver. The results show, RTK mode can improve the accuracy compare with single positioning up to centimetres. In this experiment, the Allystar HD9100 gives a better result than Ublox Neo M8T. However, the result discrepancies may be caused by the simple antenna splitter.

Tendencies of development of local geodetic network in Riga city

Local geodetic network is very important in harmonic development of city territory. On the base of the local geodetic network, cadastral and topographic surveying works, engineering geodetic works and executive measurements of newly built buildings and engineering networks are carried out. In the territory of Riga, the local geodetic network was started to create in 1880, and in the course of time, as the city expanded, necessity to have wider reference network emerged. In 2005, in the territory of Latvia, network of continuously working base stations LatPos was launched, which ensured completely new trends in execution of measurements and accuracy reached. One year later, base station network EUPOS-RIGA was launched in the territory of Riga. It can be regarded as consistent part of Riga local geodetic network. The purpose of the research was to state, what are differences between historically used coordinates of points of the local geodetic network, and coordinates that are determined by use of real time corrections of LatPos and EUPOS-RIGA base station network. Measurements were made in the territory of Riga in period from December 2016 until April 2017. In the framework of the research, 61 point of the local geodetic network was inspected and in 38 cases GNSS observations in RTK mode were completed. In the research, catalogues of coordinates of polygonometry points of sixties and eighties were used in order to compare what differences of coordinates existed historically. The main conclusion drawn during the research – historical points of the local geodetic network shall not be used for surveying works of any kind before improvement of them and before they comply with requirements of normative acts.

"A review of bathymetric measurements from August 2018 campaign on the lower course of the Danube "

The presented paper shows a combination of different methods and techniques for high precision depth measurements. The results show the procedures for collecting field data from the bathymetric measurement campaign of August 2018, developed along the lower course of the Danube. Measurements were made over a total distance of 20 km. The main purpose of the measurements is to create bathymetric maps and to generate depth maps. To achieve the main purpose of this research paper, single beam bathymetric measurements were made, and they were combined with GPS RTK mode determination, in local Stereo 70 coordinate system. Repeated measurements in different quarters of the year will determine the morphometric changes in time of the riverbed on this study area. Furthermore, based on the bathymetric maps, in the future, a coherent river terrain model can be created, and it can be used for other purposes, like 1D/2D or 3D hydrodynamic modeling and flood inundation mapping.

Application of analytic hierarchy process, frequency ratio, and statistical index to landslide susceptibility: an approach to endangered cultural heritage

This paper presents the applicability of the analytic hierarchy process, frequency ratio, and statistical index in landslide susceptibility mapping for an area from north-eastern Romania. The dependent factor (in this case the landslides) was determined by combining seven conditioning factors: elevation, slope angle, curvature, normalised difference vegetation index, roughness, distance to rivers, and landforms. A landslide inventory was prepared using topographic plans and orthophotos and by carrying out field surveys with the total station (Leica TCR1201) and geodetic GPS (Leica System 1200) in RTK mode. The final susceptibility maps were made with the help of GIS and validated by carrying out the receiver operating characteristics (ROC) curves. ROC plots for training data have shown that the susceptibility map generated using the analytic hierarchy process with AUC value of 79.46 has a better prediction accuracy compared with frequency ratio method (AUC = 75.24), and statistical index method, which had an AUC value of 61.46. The prediction rate of the three models is over 50% (79.64% for the analytic hierarchy process model, 75.65% for the frequency ratio model, and 66.36% for the statistical index model). More than a half of the cultural heritage sites are located in areas with a very high and high vulnerability to landslides. Taking into consideration that multi-stratified settlements are located in areas with low and medium landslide susceptibility, this fact can indicate a possible awareness of prehistoric people from natural hazards. The final susceptibility maps can be used for land use planning, risk reduction, hazard mitigation, to evaluate the present state of cultural heritage sites in danger and to predict which of the sites will be in more danger in the future.

A new TEC interpolation method based on the least squares collocation for high accuracy regional ionospheric maps

The ionosphere plays a crucial role in space weather that affects satellite navigation as the ionospheric delay is one of the major errors in GNSS. On the other hand, GNSS observations are widely used to determine the amount of ionospheric total electron content (TEC). An important aspect in the electron content estimation at regional and global scale is adopting the appropriate interpolation strategy. In this paper we propose and validate a new method for regional TEC modeling based on least squares collocation (LSC) with noise variance estimation. This method allows for providing accurate TEC maps with high spatial and temporal resolution. Such maps may be used to support precise GNSS positioning and navigation, e.g. in RTK mode and also in the ionosphere studies. To test applicability of new TEC maps to positioning, double-difference ionospheric corrections were derived from the maps and their accuracy was analyzed. In addition, the corrections were applied to GNSS positioning and validated in ambiguity resolution domain. The tests were carried out during a strong ionospheric storm when the ionosphere is particularly difficult to model. The performance of the new approach was compared to IGS and UPC global, and CODE regional TEC maps. The results showed an advantage of our solution with resulting accuracy of the relative ionospheric corrections usually better than 10 cm, even during the ionospheric disturbances. This proves suitability of our regional TEC maps for, e.g. supporting fast ambiguity resolution in kinematic GNSS positioning.

Transect based analysis versus area based analysis to quantify shoreline displacement: spatial resolution issues.

Field surveys, aerial photographs, and satellite images are the most commonly employed sources of data to analyze shoreline position, which are further compared by area based analysis (ABA) or transect based analysis (TBA) methods. The former is performed by computing the mean shoreline displacement for the identified coastal segments, i.e., dividing the beach area variation by the segment length; the latter is based on the measurement of the distance between each shoreline at set points along transects. The present study compares, by means of GIS tools, the ABA and TBA methods by computing shoreline displacements recorded on two stretches of the Tuscany coast (Italy): the beaches of Punta Ala, a linear coast without shore protection structures, and the one at Follonica, which is irregular due to the presence of groins and detached breakwaters. Surveys were carried out using a differential global positioning system (DGPS) in RTK mode. For each site, a 4800-m-long coastal segment was analyzed and divided into ninety-six 50-m-long sectors for which changes were computed using both the ABA and TBA methods. Sectors were progressively joined to have a length of 100, 200, 400, and 800m to examine how this influenced results. ABA and TBA results are highly correlated for transect distance and sector length up to 100m at both investigated locations. If longer transects are considered, the two methods still produce good correlated data on the smooth shoreline (i.e. at Punta Ala), but correlation became significantly lower on the irregular shoreline (i.e., at Follonica).

POLE PHOTOGRAMMETRY WITH AN ACTION CAMERA FOR FAST AND ACCURATE SURFACE MAPPING

Abstract. High resolution and high accuracy terrain mapping can provide height change detection for studies of erosion, subsidence or land slip. A UAV flying at a low altitude above the ground, with a compact camera, acquires images with resolution appropriate for these change detections. However, there may be situations where different approaches may be needed, either because higher resolution is required or the operation of a drone is not possible. Pole photogrammetry, where a camera is mounted on a pole, pointing to the ground, is an alternative. This paper describes a very simple system of this kind, created for topographic change detection, based on an action camera. These cameras have high quality and very flexible image capture. Although radial distortion is normally high, it can be treated in an auto-calibration process. The system is composed by a light aluminium pole, 4 meters long, with a 12 megapixel GoPro camera. Average ground sampling distance at the image centre is 2.3 mm. The user moves along a path, taking successive photos, with a time lapse of 0.5 or 1 second, and adjusting the speed in order to have an appropriate overlap, with enough redundancy for 3D coordinate extraction. Marked ground control points are surveyed with GNSS for precise georeferencing of the DSM and orthoimage that are created by structure from motion processing software. An average vertical accuracy of 1 cm could be achieved, which is enough for many applications, for example for soil erosion. The GNSS survey in RTK mode with permanent stations is now very fast (5 seconds per point), which results, together with the image collection, in a very fast field work. If an improved accuracy is needed, since image resolution is 1/4 cm, it can be achieved using a total station for the control point survey, although the field work time increases.

POLE PHOTOGRAMMETRY WITH AN ACTION CAMERA FOR FAST AND ACCURATE SURFACE MAPPING

High resolution and high accuracy terrain mapping can provide height change detection for studies of erosion, subsidence or land slip. A UAV flying at a low altitude above the ground, with a compact camera, acquires images with resolution appropriate for these change detections. However, there may be situations where different approaches may be needed, either because higher resolution is required or the operation of a drone is not possible. Pole photogrammetry, where a camera is mounted on a pole, pointing to the ground, is an alternative. This paper describes a very simple system of this kind, created for topographic change detection, based on an action camera. These cameras have high quality and very flexible image capture. Although radial distortion is normally high, it can be treated in an auto-calibration process. The system is composed by a light aluminium pole, 4 meters long, with a 12 megapixel GoPro camera. Average ground sampling distance at the image centre is 2.3 mm. The user moves along a path, taking successive photos, with a time lapse of 0.5 or 1 second, and adjusting the speed in order to have an appropriate overlap, with enough redundancy for 3D coordinate extraction. Marked ground control points are surveyed with GNSS for precise georeferencing of the DSM and orthoimage that are created by structure from motion processing software. An average vertical accuracy of 1 cm could be achieved, which is enough for many applications, for example for soil erosion. The GNSS survey in RTK mode with permanent stations is now very fast (5 seconds per point), which results, together with the image collection, in a very fast field work. If an improved accuracy is needed, since image resolution is 1/4 cm, it can be achieved using a total station for the control point survey, although the field work time increases.