We present an error tolerant path planning algorithm for Micro Aerial Vehicle (MAV) swarms. We assume navigation without GPS-like techniques. The MAVs find their path using sensors and cameras, ...identifying and following a series of visual landmarks. The visual landmarks lead the MAVs towards their destination. MAVs are assumed to be unaware of the terrain and locations of the landmarks. They hold a priori information about landmarks, whose interpretation is prone to errors. Errors are of two types,
or
. Recognition errors follow from misinterpretation of sensed data or a priori information, or confusion of objects, e.g., due to faulty sensors. Advice errors are consequences of outdated or wrong information about landmarks, e.g., due to weather conditions. Our path planning algorithm is cooperative. MAVs communicate and exchange information wirelessly, to minimize the number of recognition and advice errors. Hence, the quality of the navigation decision process is amplified. Our solution successfully achieves an adaptive error tolerant navigation system. Quality amplification is parameterized with respect to the number of MAVs. We validate our approach with theoretical proofs and numeric simulations.
Extreme medium‐scale traveling ionospheric disturbances (MSTIDs) occurred at midlatitudes in East Asia during a geomagnetically active time on 10 November 2004. Using the Global Positioning System ...(GPS) observation data from Korean GPS reference stations, the characteristics of the MSTIDs on 10 November 2004 and their potential impact on GPS‐based navigation systems in the Korean region are analyzed. The MSTIDs were first observed in the northeast part of South Korea at about 10:00 UT and propagated southwestward with successive wavefronts which extended from northwest to southeast. The peak‐to‐peak amplitudes of vertical total electron content (TEC) disturbances decreased from about 29 to 10 total electron content unit (1 TECU = 1016 el m−2), and the wavelengths lengthened from about 360 to 580 km from 12:53 to 14:38 UT. The propagation velocity of MSTID wavefronts was estimated using three nearby reference stations showing that velocity gradually decreased from about 254 m/s at 11:46 UT to 76 m/s at 21:26 UT. The ionospheric irregularities in small‐scale regions accompanied by the MSTIDs were spatially and temporally varied from about 10:00 to 22:00 UT in response to the movement and intensity change of the MSTIDs. This event also generated anomalously large ionospheric spatial gradients which could cause unacceptable residual pseudorange errors for users of GPS augmentation systems. Frequent loss of the GPS signals, which occurred due to the intense ionospheric irregularities, could also degrade the continuity and availability of GPS‐based navigation systems.
Key Points
Highly intense MSTIDs were observed in the Korean region on 10 November 2004
Large ionospheric gradients and loss of GPS signals occurred during MSTIDs
MSTIDs can potentially degrade the performance of GPS‐based navigation systems
Introduction: Accuracy in guided implant surgery means that pre-determined position of the implant by the software matches the position of the implant in the patient's mouth. The aim of this study ...was to evaluate the impact of initial prediction by navigation in the DIOnavi system on the accuracy of implant placement.
Materials & Methods: In this interventional study, two samples of 17 and 25 patients) in total 42 patient) requesting navigation method for implant placement were selected. First, a cone beam computed tomography (CBCT) was taken from each patient and then its virtual model was prepared using the DIO NAVI system (South Korean DIO company. Two to three months following the implant placement by the surgeon, the CBCT from the same section was obtained again and the thickness of the buccal bone on the implant, the thickness of the lingual bone on the implant, the distance of the implant apex to the apical anatomic regions (Nasal cavity, Maxillary sinus and Mental foramen), Implant depth from crest edge and implant distance from adjacent teeth if present in the two obtained images were compared. Data were analyzed using paired t test and Pearson Correlation Coefficient (α = 0.05).
Results: The mean of all measurements in both groups in the initial prediction was significantly related to after surgery (r = 0.99, p value < 0.001) and in the group of 17, 98% and in the group of 25, 97.4% of the variances of the means of the total measurements were explained by the initial prediction.
Conclusion: The accuracy of implant placement with the help of dionavi system is estimated to be more than 97%.
An accurately linearized in-motion alignment with a large heading error is proposed for a low-cost inertial navigation system with the aiding of global positioning system. The linearization is ...designed for both the coarse and the fine stages in the local level frame. A criterion is constructed to determine the time to switch the alignment from the coarse stage to the fine one automatically. A vehicle test demonstrates that the proposed alignment converges fast and accurately.
Great strides have been made in Geographic Information Systems (GIS) research over the past half-century. However, this progress has created both opportunities and challenges. From a geographic ...perspective, certain challenges remain, including the modelling of geographic-featured environments with GIS data model, the enhancement of GIS's analysis functions for comprehensive geographic analysis and achieving human-oriented geographic information presentation. Several basic theoretical and technical ideas that follow the workflow and processes of geographic information induction, geographic scenario modelling, geographic process analysis and geographic environment representation are proposed to fill the gaps between GIS and geography. We also call for designing methods for big geographic data-oriented analysis, making best use of videos and developing virtual geographic scenario-based GIS for further evolution.
On 17 April 2011, all analysis centers (ACs) of the International GNSS Service (IGS) adopted the reference frame realization IGS08 and the corresponding absolute antenna phase center model igs08.atx ...for their routine analyses. The latter consists of an updated set of receiver and satellite antenna phase center offsets and variations (PCOs and PCVs). An update of the model was necessary due to the difference of about 1 ppb in the terrestrial scale between two consecutive realizations of the International Terrestrial Reference Frame (ITRF2008 vs. ITRF2005), as that parameter is highly correlated with the GNSS satellite antenna PCO components in the radial direction.
For the receiver antennas, more individual calibrations could be considered and GLONASS-specific correction values were added. For the satellite antennas, all correction values except for the GPS PCVs were newly estimated considering more data than for the former model. Satellite-specific PCOs for all GPS satellites active since 1994 could be derived from reprocessed solutions of five ACs generated within the scope of the first IGS reprocessing campaign. Two ACs separately derived a full set of corrections for all GLONASS satellites active since 2003.
Ignoring scale-related biases, the accuracy of the satellite antenna PCOs is on the level of a few cm. With the new phase center model, orbit discontinuities at day boundaries can be reduced, and the consistency between GPS and GLONASS results is improved. To support the analysis of low Earth orbiter (LEO) data, igs08.atx was extended with LEO-derived PCV estimates for big nadir angles in June 2013.
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•BDS-3 on-board clock was evaluated and compared to GPS/GLONASS/Galileo/ BDS-2.•The prediction accuracy of BDS-3 satellite clock was investigated and presented.•The performance of ...BDS-3 PPP time transfer was studied and assessed.
The atomic clock is the heart of a satellite navigation system and limits the user positioning, navigation and timing (PNT) accuracy; hence, it is necessary to acquire more information about the BDS-3 on-board clocks. In this contribution, sixty days of BDS-3 clock results were analyzed in terms of their stability and prediction accuracy and compared with the results from BDS-2 (BDS: BeiDou Navigation Satellite System), GPS (Global Positioning System), GLONASS (Global Navigation Satellite System) and Galileo clocks. The results show that BDS-3 clocks have greater stability than BDS-2 and BDS-3 s clocks, GPS Block IIA, Block IIR, and Block IIR-M clocks, and GLONASS clocks, while their stability is comparable to that of Block IIF clocks and inferior to that of Galileo clocks. In comparison with the stability of BDS-2 clocks, the percentages of improvement in the stability of BDS-3 clocks range from 5% to 65%. Overall, the stabilities of BDS-3 clocks at 1000 s, 10000 s and 86400 s are nearly 3 ~ 6E-14, 2 ~ 8E-14 and 1 ~ 24E-14, respectively. Furthermore, the prediction accuracy of BDS-3 clocks is 0.24 ns, which is smaller than that of BDS-2 and GPS clocks. Finally, preliminary experiments were conducted with regard to precise point positioning (PPP) time transfer using BDS-3 signals. The four solutions, namely, the BDS-2, BDS-2 + BDS-3, BDS-3, and GPS solutions, were compared in terms of their frequency stability. As a slight imperfection, BDS-3 applications are restricted by the limited number of satellites. Nevertheless, the link results based on BDS-3 are more stable than those based on BDS-2 and BDS-2 + BDS-3. In particular, the BDS-3 results outperform the GPS results in their long-term stability. At typical averaging times, namely, 1000 s, 10,000 s, and 86,400 s, in comparison with the GPS results, the percentages of improvement in the link stability are 22.91, 38.40 and 19.03%, respectively, while those in comparison with the BDS-2 results are 40.08, 34.06 and 10.90%, respectively.
Global Satellite Navigation System (GNSS) has been widely used in various high-precision positioning services and has become an indispensable part of daily production and life. However, in urban ...environments, GNSS is highly susceptible to interference from non-line-of-sight (NLOS) signals, resulting in a sharp deterioration in positioning accuracy. The use of machine learning methods for NLOS detection has become a research hotspot due to its advantages of no need to change hardware devices and high accuracy. However, in existing machine learning NLOS detection work, the machine learning models used to detect NLOS are usually simple versions. In practice, these existing methods using a single model may fall into the local optimal solution. Therefore, we propose a GNSS NLOS detection method based on the stacking ensemble learning (SEL) model, which reduces the bias of each base model and reduces generalization error by fusing different and heterogeneous base models. The experiment used collected multi-scene smartphone GNSS data to conduct a detailed evaluation of the characteristics of GNSS observations, the accuracy of the models for NLOS detection, and the impact of the SEL NLOS detection model on smartphone GNSS positioning performance. The results show that the GNSS NLOS detection method based on the SEL model has higher detection accuracy and generalization ability than base models. Under static conditions, smartphones can achieve more than 90% recognition accuracy, and dynamic scenes can achieve 75% to 85% recognition accuracy. After NLOS detection based on the SEL model, the horizontal and vertical CEP95 positioning accuracy of the Vivo smartphone has been improved by 21.9% and 24.5%, respectively, and the positioning accuracy of other smartphones has also been improved. This method does not require additional improvements to the receiver hardware and has the potential to be widely applied to various GNSS terminals.
This paper presents an enhanced time-delay controller (TDC) for the position control of an autonomous underwater vehicle (AUV) under disturbances. A conventional TDC performs well when the involved ...data acquisition rate is fast. However, in AUV control applications that use a Doppler velocity log (DVL) navigation system, we cannot keep the data acquisition rate sufficiently fast because a DVL sensor generally supplies data at a slow acquisition rate, which degrades the performance of the TDC. To overcome this problem, we propose an integral sliding-mode controller to be supplemented to the conventional TDC to improve the control precision even if the DVL navigation system is in operation. The proposed controller is computationally simple and robust to unmodeled dynamics and disturbances. We performed computer simulations and experiments with the Cyclops AUV to demonstrate the validity of the proposed controller.
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