scholarly journals LOW-COST DGPS ASSISTED AERIAL TRIANGULATION FOR SUB-DECIMETRIC ACCURACY WITH NON-RTK UAVS

2021 ◽  
Vol XLIII-B2-2021 ◽  
pp. 25-32
Author(s):  
F. Ioli ◽  
L. Pinto ◽  
F. Ferrario
Keyword(s):  
Low Cost ◽  
Field Work ◽  
Single Frequency ◽  
Gnss Receiver ◽  
Emergency Situations ◽  
Aerial Triangulation ◽  
Ground Control Points ◽  
Bundle Block Adjustment ◽  
Gnss Receivers ◽  
Camera Position

Abstract. The possibility of equipping UAVs with lightweight GNSS receivers in order to estimate the camera position within a photogrammetric block allows for a reduction of the number of Ground Control Points (GCP), saving time during the field work and decreasing operational costs. Additionally, this makes it possible to build photogrammetric models even in morphologically complex areas or in emergency situations. This work is proposing a non-intrusive and low-cost procedure to retrieve the coordinates of the camera projection centre with decimetric accuracy. The method was designed and tested with the quadcopter DJI Matrice 210 V2 drone equipped with a DJI ZENMUSE X5S camera and an Emlid reach M, a low-cost, single-frequency (L1) GNSS receiver. GNSS observations are post-processed in PPK in order to obtain the UAV trajectory. Synchronization between the camera and the GNSS receiver is achieved by looking at the camera triggering timestamps in flight telemetry data, without requiring an electronic connection between camera and the GNSS that may be troublesome with commercial UAVs. Two surveys were carried out, respectively to calibrate and validate the procedure. The validation test evidenced the possibility of obtaining the coordinates of the camera projection centres with decimetric accuracy. The centre of projections can then be employed for GNSS-assisted aerial triangulation as input of the bundle block adjustment. Provided that at least one GCP is used, it is possible to reach centimetric accuracy on the ground.

scholarly journals Georeferencing experiments with UAS imagery

2014 ◽  
Vol II-1 ◽  
pp. 25-29 ◽  
Author(s):  
G. Jóźków ◽  
C. Toth
Keyword(s):  
Low Cost ◽  
Field Work ◽  
Single Frequency ◽  
Gps Data ◽  
Dual Frequency ◽  
Quality Of Data ◽  
Advantages And Disadvantages ◽  
Ground Control Points ◽  
Active Imaging ◽  
Application Potential

Comparing typical airborne mapping systems with Unmanned Airborne Systems (UAS) developed for mapping purposes, there are several advantages and disadvantages of both systems. The unquestionable benefits of UAS are the much lower costs of equipment and the simple operation; though, the regulations to fly UAS greatly vary by country. Low cost, however, means small sensor size and low weight, thus, sensors usually lack the quality, negatively impacting the accuracy of UAS data and, consequently, any derived mapping products. This work compares the performance of three different positioning approaches used for UAS image geolocation. The first one is based on using dual-frequency GPS data, post-processed in kinematic mode. The second approach uses the single frequency, code only GPS data that was acquired and processed by a geotagger, attached to mapping camera. Finally, the third one employs indirect image georeferencing, based on aerial triangulation using ground controls. As expected, the quality of data provided by the inexpensive GPS receiver (geotagger) is not suitable for mapping purposes. The two other approaches provided similar and reliable results, confirming that commonly used indirect georeferencing, which usually assures good solution, can be replaced by direct georeferencing. The latter technique results not only in reduction of field work, e.g. Ground Control Points (GCPs) surveying, but is appropriate for use with other sensors, such as active imaging technology, LiDAR, further extending UAS application potential.

Reducing multipath effect of low-cost GNSS receivers for monitoring by considering temporal correlations

2020 ◽  
Vol 14 (2) ◽  
pp. 167-175
Author(s):  
Li Zhang ◽  
Volker Schwieger
Keyword(s):  
Low Cost ◽  
Ground Plane ◽  
Single Frequency ◽  
Spatial Correlations ◽  
Raw Data ◽  
Multipath Effect ◽  
Temporal Correlations ◽  
Multipath Effects ◽  
Gnss Receivers ◽  
Multipath Signals

AbstractThe investigations on low-cost single frequency GNSS receivers at the Institute of Engineering Geodesy (IIGS) show that u-blox GNSS receivers combined with low-cost antennas and self-constructed L1-optimized choke rings can reach an accuracy which almost meets the requirements of geodetic applications (see Zhang and Schwieger [25]). However, the quality (accuracy and reliability) of low-cost GNSS receiver data should still be improved, particularly in environments with obstructions. The multipath effects are a major error source for the short baselines. The ground plate or the choke ring ground plane can reduce the multipath signals from the horizontal reflector (e. g. ground). However, the shieldings cannot reduce the multipath signals from the vertical reflectors (e. g. walls).Because multipath effects are spatially and temporally correlated, an algorithm is developed for reducing the multipath effect by considering the spatial correlations of the adjoined stations (see Zhang and Schwieger [24]). In this paper, an algorithm based on the temporal correlations will be introduced. The developed algorithm is based on the periodic behavior of the estimated coordinates and not on carrier phase raw data, which is easy to use. Because, for the users, coordinates are more accessible than the raw data. The multipath effect can cause periodic oscillations but the periods change over time. Besides this, the multipath effect’s influence on the coordinates is a mixture of different multipath signals from different satellites and different reflectors. These two properties will be used to reduce the multipath effect. The algorithm runs in two steps and iteratively. Test measurements were carried out in a multipath intensive environment; the accuracies of the measurements are improved by about 50 % and the results can be delivered in near-real-time (in ca. 30 minutes), therefore the algorithm is suitable for structural health monitoring applications.

scholarly journals IMPROVING UAV TELEMETRY POSITIONING FOR DIRECT PHOTOGRAMMETRY

2021 ◽  
Vol XLIII-B2-2021 ◽  
pp. 61-68
Author(s):  
L. Rossi ◽  
F. Ioli ◽  
E. Capizzi ◽  
L. Pinto ◽  
M. Reguzzoni
Keyword(s):  
Low Cost ◽  
Three Dimensional ◽  
Control Points ◽  
Three Dimensional Model ◽  
Commercial Software ◽  
Ground Control Points ◽  
Lower Accuracy ◽  
Least Squares Adjustment ◽  
Gnss Receivers

Abstract. A fundamental step of UAV photogrammetric processes is to collect Ground Control Points (GCPs) by means of geodetic-quality GNSS receivers or total stations, thus obtaining an absolutely oriented model with a centimetric accuracy. This procedure is usually time-consuming, expensive and potentially dangerous for operators who sometimes need to reach inaccessible areas. UAVs equipped with low-cost GNSS/IMU sensors can provide information about position and attitude of the images. This telemetry information is not enough for a photogrammetric restitution with a centimetric accuracy, but it can be usefully exploited when a lower accuracy is required. The algorithm proposed in this paper aims at improving the quality of this information, in order to introduce it into a direct-photogrammetric process, without collecting GCPs. In particular, the estimation of an optimal trajectory is obtained by combining the camera positions derived from UAV telemetry and from the relative orientation of the acquired images, by means of a least squares adjustment. Then, the resulting trajectory is used as a direct observation of the camera positions into a commercial software, thus replacing the information of GCPs. The algorithm has been tested on different datasets, comparing the classical photogrammetric solution (with GCPs) with the proposed one. These case-studies showed that using the improved trajectory as input to the commercial software (without GCPs) the reconstruction of the three-dimensional model can be improved with respect to the solution computed by using the UAV raw telemetry only.

scholarly journals PERFORMANCE ASSESSMENT OF INTEGRATED SENSOR ORIENTATION WITH A LOW-COST GNSS RECEIVER

2017 ◽  
Vol IV-2/W3 ◽  
pp. 75-80 ◽  
Author(s):  
M. Rehak ◽  
J. Skaloud
Keyword(s):  
Position Control ◽  
Low Cost ◽  
Satellite System ◽  
Bundle Adjustment ◽  
Single Frequency ◽  
Reference Trajectory ◽  
Integrated Sensor ◽  
Homogeneous Surface ◽  
Gnss Receiver ◽  
Sensor Orientation

Mapping with Micro Aerial Vehicles (MAVs whose weight does not exceed 5&amp;thinsp;kg) is gaining importance in applications such as corridor mapping, road and pipeline inspections, or mapping of large areas with homogeneous surface structure, e.g. forest or agricultural fields. In these challenging scenarios, integrated sensor orientation (ISO) improves effectiveness and accuracy. Furthermore, in block geometry configurations, this mode of operation allows mapping without ground control points (GCPs). Accurate camera positions are traditionally determined by carrier-phase GNSS (Global Navigation Satellite System) positioning. However, such mode of positioning has strong requirements on receiver’s and antenna’s performance. In this article, we present a mapping project in which we employ a single-frequency, low-cost (<&amp;thinsp;$100) GNSS receiver on a MAV. The performance of the low-cost receiver is assessed by comparing its trajectory with a reference trajectory obtained by a survey-grade, multi-frequency GNSS receiver. In addition, the camera positions derived from these two trajectories are used as observations in bundle adjustment (BA) projects and mapping accuracy is evaluated at check points (ChP). Several BA scenarios are considered with absolute and relative aerial position control. Additionally, the presented experiments show the possibility of BA to determine a camera-antenna spatial offset, so-called lever-arm.

Ionosphere Sensing With a Low-Cost, Single-Frequency, Multi-GNSS Receiver

2019 ◽  
Vol 57 (2) ◽  
pp. 881-892 ◽  
Author(s):  
Chuanbao Zhao ◽  
Yunbin Yuan ◽  
Baocheng Zhang ◽  
Min Li
Keyword(s):  
Low Cost ◽  
Single Frequency ◽  
Gnss Receiver

The use of low-cost, single-frequency GNSS receivers in mapping surveys

Survey Review ◽  
2016 ◽  
Vol 50 (358) ◽  
pp. 46-56 ◽  
Author(s):  
M. Tsakiri ◽  
A. Sioulis ◽  
G. Piniotis
Keyword(s):  
Low Cost ◽  
Single Frequency ◽  
Gnss Receivers

scholarly journals CORS ARCHITECTURE AND EVALUATION OF POSITIONING BY LOW-COST GNSS RECEIVER

2018 ◽  
Vol 44 (2) ◽  
pp. 36-44 ◽  
Author(s):  
Massimiliano Pepe
Keyword(s):  
Low Cost ◽  
Satellite System ◽  
Ease Of Use ◽  
Quality Data ◽  
Gnss Receiver ◽  
Stop And Go ◽  
Gnss Receivers ◽  
Spatial Positioning ◽  
Global Navigation Satellite

In recent years, the use of low cost GNSS receivers is becoming widespread due to their increasing performance in the spatial positioning, flexibility, ease of use and really interesting price. In addition, a recent technique of Global Navigation Satellite System (GNSS) survey, called Network Real Time Kinematic (NRTK), allows to obtain to rapid and accurate positioning measurements. The main feature of this approach is to use the raw measurements obtained and stored from a network of Continuously Operating Reference Stations (CORS) in order to generate more reliable error models that can mitigate the distance-dependent errors within the area covered by the CORS. Also, considering the huge potential of this GNSS positioning system, the purpose of this paper is to analyze and investigate the performance of the NTRK approach using a low cost GNSS receiver, in stop-and-go kinematic technique. By several case studies it was shown that, using a low cost RTK board for Arduino environment, a smartphone with open source application for Android and the availability of data correction from CORS service, a quick and accurate positioning can be obtained. Because the measures obtained in this way are quite noisy and, more in general, increasing with the baseline, by a simple and suitable statistic treatment, it was possible to increase the quality of the measure. In this way, this low cost architecture could be applied in many geomatics fields. In addition to presenting the main aspects of the NTRK infrastructure and a review of several types of correction, a general workflow in order to obtain quality data in NRTK mode, regardless of the type of GNSS receiver (multi constellations, single or many frequencies, etc.) is discussed.

scholarly journals Towards Automatic UAS-Based Snow-Field Monitoring for Microclimate Research

Sensors ◽  
2019 ◽  
Vol 19 (8) ◽  
pp. 1945 ◽  
Author(s):  
Petr Gabrlik ◽  
Premysl Janata ◽  
Ludek Zalud ◽  
Josef Harcarik
Keyword(s):  
Rapid Development ◽  
Field Work ◽  
Satellite System ◽  
Mountain Range ◽  
Ground Control Points ◽  
Snow Covered Area ◽  
Covered Area ◽  
Gnss Receivers ◽  
Global Navigation Satellite ◽  
Optimum Solution

This article presents unmanned aerial system (UAS)-based photogrammetry as an efficient method for the estimation of snow-field parameters, including snow depth, volume, and snow-covered area. Unlike similar studies employing UASs, this method benefits from the rapid development of compact, high-accuracy global navigation satellite system (GNSS) receivers. Our custom-built, multi-sensor system for UAS photogrammetry facilitates attaining centimeter- to decimeter-level object accuracy without deploying ground control points; this technique is generally known as direct georeferencing. The method was demonstrated at Mapa Republiky, a snow field located in the Krkonose, a mountain range in the Czech Republic. The location has attracted the interest of scientists due to its specific characteristics; multiple approaches to snow-field parameter estimation have thus been employed in that area to date. According to the results achieved within this study, the proposed method can be considered the optimum solution since it not only attains superior density and spatial object accuracy (approximately one decimeter) but also significantly reduces the data collection time and, above all, eliminates field work to markedly reduce the health risks associated with avalanches.

Pemanfaatan Receiver Gnss Berbiaya Rendah “Expandable-Gnss” dengan Metode Post-Processing Kinematic dalam Pengukuran Kadastral

Tunas Agraria ◽  
2018 ◽  
Vol 1 (1) ◽  
Author(s):  
Rizka Dita Samsudin Al Chodiq ◽  
Tanjung Nugroho ◽  
Bambang Suyudi
Keyword(s):  
Statistical Analysis ◽  
Spatial Planning ◽  
Low Cost ◽  
Data Communication ◽  
Tolerance Test ◽  
Static Method ◽  
Baseline Length ◽  
Post Processing ◽  
Gnss Receiver ◽  
Gnss Receivers

Abstract: Utilization of GNSS receiver by RTK method is expected to accelerate the land parcels measurement in the Ministry of Agrarian Affairs and Spatial Planning/National Land Agency. However, due to the expensive price, the number of current GNSS receivers is not yet comparable with the existing targets and work loads. Utilization of low-cost GNSS receiver can be a solution to the situation. One of the low-cost GNSS receivers is Expandable-GNSS (E-GNSS). The limitation of RTK method, related to the dependence of data communication during observation can be solved by the Post-Processing Kinematic (PPK) method. This research aims to test the accuracy of observations using E-GNSS with PPK method. The comparator in this research is the result of observation using GNSS receiver with static method. Data were analyzed by comparing the differences of coordinates between the three sample groups based on the baseline length classification, and also compared the coordinate differences between the two methods and the tolerance test based on the provisions of the PMNA / KBPN Technical Guidelines Number 3 of 1997. Based on the analysis indicates an increase in coordinate difference proportional to the length of the baseline. Statistical analysis also shows that there are significant differences between the coordinates of both methods, but still meet the fault tolerance point of 0.250 m. The length of the measured land parcels also meets the tolerance based on the provisions of the PMNA / KBPN Technical Guidelines Number 3 of 1997.Keywords: Cadastral, Low-Cost GNSS Receiver, Post-Processing Kinematic Intisari: Pemanfaatan receiver GNSS dengan metode RTK diharapkan dapat mempercepat kegiatan pengukuran bidang tanah di Kementerian ATR/BPN. Akan tetapi, karena harga receiver GNSS yang relatif mahal menyebabkan jumlahnya belum sebanding dengan target dan beban pekerjaan yang ada. Pemanfaatan receiver GNSS berbiaya rendah dapat menjadi solusi keadaan tersebut. Salah satu receiver GNSS berbiaya rendah adalah Expandable-GNSS (E-GNSS). Sedangkan keterbatasan metode RTK, terkait ketergantungan akan komunikasi data selama pengamatan dapat di atasi dengan penggunaan metode Post-Processing Kinematic (PPK). Pada penelitian ini, dilakukan pengujian ketelitian hasil pengamatan menggunakan E-GNSS dengan metode PPK. Sebagai pembanding dalam penelitian ini adalah hasil pengamatan menggunakan receiver GNSS dengan metode statik. Analisis dilakukan dengan membandingkan perbedaan koordinat kedua metode antar kelompok sampel berdasarkan klasifikasi panjang baseline, selain itu juga dibandingkan perbedaan koordinat hasil pengamatan antara kedua metode serta uji toleransi berdasarkan ketentuan pada Petunjuk Teknis PMNA/KBPN Nomor 3 Tahun 1997. Berdasarkan analisis hasil penelitian menunjukkan adanya peningkatan perbedaan koordinat sebanding dengan semakin panjang baseline. Analisis statistik juga menunjukkan terdapat perbedaan signifikan koordinat yang dihasilkan kedua metode, akan tetapi masih memenuhi toleransi kesalahan titik sebesar 0,250 m. Panjang sisi bidang tanah hasil pengukuran juga memenuhi toleransi berdasarkan ketentuan Petunjuk Teknis PMNA/KBPN Nomor 3 Tahun 1997.Kata kunci: Kadastral, Receiver GNSS Berbiaya Rendah, Post-Processing Kinematic

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