Network RTK

Get up to speed on all existing GNSS with this practical guide. Covering everything from GPS, GLONASS, Galileo, and BeiDou orbits and signals to multi-GNSS receiver design, AGPS, RTK, and VRS, you will understand the complete global range of mobile positioning systems. Step-by-step algorithms and practical methods provide the tools you need to develop current mobile systems, whilst coverage of cutting edge techniques, such as the instant positioning method, gives you a head-start in unlocking the potential of future mobile positioning. Whether you are an engineer or business manager working in the mobile device industry, a student or researcher, this is your ideal guide to GNSS.
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Academia, Industry and Government are investigating the reliability to use the real time kinematic (RTK) Global Navigation Satellite System (GNSS) techniques for centimetre level positioning of many existing and emerging applications. These include for instance mobile mapping and airborne laser scanning systems. The classical RTK methodology allows for an operational distance between the reference station and the user, within a range of 10-15 kilometres, due to the effect of correlation of some GNSS errors which tend to increase with distance. The adoption of a network-based RTK (NRTK) allow to extend centimetric level positioning within continuously operating reference station network (CORS) with separation distance up to 70 kilometres. One of the research aim was to evaluate the positional accuracy of the GNSS NRTK for mobile mapping applications. In order to understand the potentiality and the limitations of this methodology a testing procedure was designed using the BO-POS Netwo...

Inexpensive and small unmanned aerial vehicles (UAVs) provide high-accuracy positional data and enable users to collect high-resolution aerial images. The analysis of images captured using UAVs in a specific reference system is traditionally accomplished using the georeferencing method with high-accuracy ground control points (GCPs). This study aims to test and compare the benchmarks and point clouds’ positional accuracy produced on three consecutive days with different flight combinations at 75 and 100 m flight altitude by means of network-based continuously operating reference stations and differential-based real-time kinematic georeferencing systems without using GCPs. A root mean squared error values were obtained 1–3 cm for the horizontal accuracy and 4–6 cm for the vertical accuracy values. Thus, the proposed system proved an acceptable positional accuracy level. According to the results of the proposed approach, it can be said that the evaluation and use of UAV data without u...

Total electron content (TEC) fluctuation in the ionosphere is one of the main unresolved problems degrading ambiguity resolution and thus affect the reliability of satellite positioning. With regard to conditions prevailing at mid-latitudes, the impact of the upper atmospheric layers is primarily associated with the occurrence of medium-scale traveling ionospheric disturbances (MSTIDs). This study contains the combined analysis involving MSTIDs patterns observed in raw phase data and their impact on rapid static positioning. The first part is aimed at discrepancies in wavelike MSTIDs signatures detected in time series of high elevated measurements. It was demonstrated that the differences in slant ionospheric delays at medium baselines often exceed 0.5 TEC units and more importantly, the detected MSTIDs patterns were highly mutable. The next section presents the impact of MSTIDs on double differenced ionospheric delays and performance of rapid static positioning. The positioning was...

Unmanned air vehicle (UAV) has become an indispensable mobile mapping technology of remote sensing thanks to offering low cost and high resolution spatial data. Particularly, camera equipped optical UAVs are large in demand by land-related professions, including mapping, agriculture and forestry. Regarding the requirements, the technological level of the optical UAVs rises day by day by adding novel payloads. For instance, global navigation satellite system (GNSS) receivers with real-time kinematic (RTK) positioning capability were added to facilitate the fieldwork for ground control point (GCP) set up and measurements before UAV flights. Multispectral cameras were added to increase the automatic land cover classification potential of generated ortho-mosaics. At this point, the most significant question is the contribution level of these technological payloads. In this study, our research group evaluated the RTK GNSS positioning accuracy and automatic land cover classification potential of "DJI Phantom IV Multispectral RTK", which is one of the most common optical UAVs for scientific and commercial applications. For the evaluations, a study area that includes a large variety of land cover classes was selected. The UAV RTK GNSS positioning accuracy was calculated by comparing the RTK GNSS data obtained from the UAV with the measured GCPs in the study area. Furthermore, the land cover classification performance of Multispectral UAV was analysed by pixel and object-based classification techniques separately. For this purpose, while spectral angle mapper (SAM), minimum distance (MD) and maximum likelihood (ML) classifiers were applied to perform pixel-based classification, nearest neighbour (NN) classifier was employed to utilize object-based classification. The positioning accuracy results demonstrated that the root mean square error (RMSE) of UAV RTK GNSS is ±1.1 cm in X, ±2.7 cm in Y, and ±5.7 cm in Z. The classification results showed that the highest overall accuracy was estimated as 93.56% with ML classifier and its classification performance was found to be superior compared to those of SAM (73.46%) and MD (75.27%) classifiers. On the other hand, the overall accuracy was calculated as 90.09% for object-based classification and it was 3% lower than the pixel-based ML classification result. This could be the result of heterogeneity of the image objects created during the segmentation stage. Further studies are required to improve the object-based classification accuracy by applying different segmentation methods and quality measures.

Kinematic service to support its cadastral surveying applications. The service implements a Virtual Reference Station (VRS) concept based on a network of 11 CORS stations located mainly in the Central Thailand. Such service reduces several technical limitations of conventional RTK method and increases the productivity in a cost effective manner. This also opens the question how feasible DOL-VRS service may be for establishing survey control. The conventional way to set up high accuracy survey control for geospatial applications is in post processing mode using relative positioning method and double differenced carrier phase algorithms. Apart of the rover, the user needs a second receiver to collect data simultaneously and at the same epoch rate at a known point. VRS eliminates this requirement by creating synthetic observations for a non-physical, un-occupied, invisible reference station situated only few meters from the approximate location of the rover. On the other hand, previous...