Yuneec International’s commercial hexacopter, the H520, will now optionally be available with an RTK (real-time kinematic) system from the Swiss company Fixposition.
Under difficult GPS conditions, such as in cities or canyons, the RTK system ensures maximum precision and centimeter-precise positioning. The fully integrated RTK satellite navigation enables extremely accurate recurring images and faster 3D mapping. It also makes automated inspection flights easier and more precise, the company said.
The new H520 RTK is suitable for commercial applications that require maximum precision. By using RTK technology, the H520 can now fly much closer to objects for inspection as the UAV positions itself precisely in the centimeter range (1 cm + ppm horizontal / 1.5 cm + ppm vertical) rather than in the meter range, which is standard for the H520.
This accuracy is paramount for applications where several images need to be taken at the same location on different days including:
documenting progress on construction sites,
inspecting mountain landscapes to prevent natural hazards such as rock falls or avalanches, and
forensic accident scene reconstruction.
In addition, the satellite navigation system makes it possible to significantly reduce image overlaps, which means fewer photos and shorter model calculation times, maximizing efficiency in workflows.
The RTK system is not only fully integrated into the hardware, but also into the UAV’s software. This means the user retains the full range of functions of the DataPilot software, including mission flights.
The H520 RTK works with two components: the RTK module on board the H520 and a base station on the ground. For precise navigation, the module supports constellations of up to three different satellite systems from GPS, GLONASS, Galileo and BeiDou.
If the use of a ground station is not possible, the system can also be operated with a national reference station network (network RTK). The network RTK is provided by third-party providers and requires an internet connection, such as a mobile hotspot. All data including satellite data is recorded, which makes the H520 RTK suitable for post-processed kinematics (PPK).
The H520 RTK will be available in the second quarter of 2019. Technical specifications are available here.
Dime-sized INS with RTK paves the way for high accuracy in mass-market consumer applications.
Photo: Inertial Sense
Inertial Sense has released a new micro-sized inertial navigation system (INS) with precise real-time-kinematic (RTK)-level accuracy. The company says the new solution paves the way for high accuracy in mass-market consumer applications.
The new micro INS with RTK solution offers an accuracy of 2-3 centimeters using GPS positioning in combination with inertial sensors (including on-board sensor fusion).
Inertial Sense designs and manufactures precision INS+RTK GPS sensors that deliver fast, accurate and reliable altitude, velocity and position for a wide range of autonomous vehicle applications, the company said.
The new micro INS with RTK provides a high degree of precision for orientation and GPS in a tiny package. Standard INS/GPS sensors offer accuracy in the range of 1.5 to 2 meters. Inertial Sense’s micro INS with RTK offers accuracy of 2-3 centimeters.
In the image above, a vehicle travels under an overpass. The 3-cm accurate RTK-inertial navigation track holds true to the vehicle’s position while the standard GPS signal is lost. (Image: Inertial Sense)
“The incredibly small size of our new micro INS with RTK sensor, in combination with its extremely affordable price point, will make this type of highly sophisticated technology accessible for general consumer applications for the very first time,” said Walt Johnson, founder and CTO, Inertial Sense. “We are offering RTK at a size, accuracy and price point that the market has never seen before.”
By optimizing the manufacturing processes for high volume applications, the micro INS with RTK sensor is as small and lightweight as a dime, and is available at a low price point.
Sensor fusion. Sensor data from MEMs gyros, accelerometers, magnetometers, barometric pressure and u-blox GPS/GNSS are fused to provide optimal position estimation. Data out includes angular rate, linear acceleration, magnetic field, barometric altitude and GPS time.
The miniature module provides orientation, velocity and position. Base station corrections data can be applied to achieve centimeter-level precision.
Autonomous vehicles. The sensor will enable the navigation of all types of autonomous vehicles with a very high degree of precision, Inertial Sense said.
Inertial Sense patented modules are currently being sold worldwide at volume for a broad variety of applications including:
Aerial surveys: UAV Payloads for 3D mapping, photogrammetry, orthomosaics
Gimbal stabilization and antenna pointing
3D motion capture and personnel tracking
Evaluation kits. Inertial Sense has bundled evaluation kits it says are simple to use and contain everything needed to begin logging RTK-accurate data. The evaluation boards can be utilized in both rover and base station configurations and include 900-mhz radios with onboard logging capabilities.
Sokkia introduced the latest addition to its GNSS integrated receiver line — the GRX3. According to the company, the GRX3 is designed to provide a smaller, lighter and fully integrated GNSS solution.
Photo: Sokkia
“The multi-constellation GRX3 receiver is built to offer a complete and versatile solution to provide best-in-class positioning performance for a wide variety of precision applications,” said Alok Srivastava, director of product management.
“Whether using the receiver for GNSS post-processed surveying, or RTK using wireless technologies including network RTK option with a cellular-equipped field computer, a SiteComm RTK rover, or paired with a Sokkia total station for fusion positioning, the GRX3 provides the most advanced and powerful GNSS technology available in a more compact and lightweight housing that can withstand the harshest of environmental conditions. Combine it with one of Sokkia’s data collectors and field software for maximum versatility and convenience, increasing fieldwork efficiency from start to finish.”
The receiver features Sokkia Tilt technology, which includes a 9-axis inertial measurement unit and ultra-compact eCompass designed to compensate for mis-leveled field measurements by as much as 15 degrees.
“The GRX3 is designed as a ‘future-proof’ solution with an advanced GNSS chipset with Universal Tracking Channels technology that automatically tracks signals from all available and planned constellations — including GPS, GLONASS, Galileo, Beidou, IRNSS, QZSS, SBAS,” Srivastava said.
The receiver has been tested to meet IP67 certification for protection against harsh environmental weather conditions.
Tersus GNSS Inc. has launched Tersus Oscar, its new generation GNSS real-time kinematic (RTK) system.
Oscar is an all-in-one GNSS receiver that can be used as rover or base system. Paired with a Tersus TC20 controller or A11 mobile terminal, Oscar can more efficiently meet customer application requirements for the optimal surveying solution, according to Xiaohua Wen, founder and CEO of Tersus GNSS.
“Last year, we launched the David GNSS receiver,” Xiaohua said. “This year, we are very excited to introduce an advanced version of David; we named it Oscar.”
Oscar supports calibration-free tilt compensation function, meaning a leveling pole is no longer required. Configuration is made easy with a 1.3-inch interactive screen. With an internal high-performance multi-constellation and multi-frequency GNSS board, the Oscar GNSS receiver can provide high accuracy and stable signal detection, the company said.
The high-performance antenna can speed the time to first fix and improve anti-jamming performance. The built-in large capacity battery can support up to 10 hours of fieldwork.
A radio module in the package supports long-distance communication. With its rugged housing material, Oscar is protected from harsh environments.
Agriculture equipment maker Case IH is enhancing the robustness of its RTK+ correction signal network by adding the European Galileo system to the compatible satellites with which it works.
The move will increase levels of signal reception and reliability for farmers using Case IH RTK+-guided autosteering and related technologies.
Real-time kinematic (RTK) systems typically depend on signals from the American GPS or Russian GLONASS satellite networks, both designed primarily for non-civilian use. To give European Case IH users a reliable alternative when using RTK+-guided steering systems with their sub-1.5-centimeter repeatable accuracy, Case IH AFS RTK+ now also uses Galileo.
The addition of Galileo to the global GNSS constellation helps minimize the risk of signal failure, a key driver for the integration of its signals into the Case IH AFS RTK+ signal system. European satellite network independence is a principal objective, but Case IH AFS RTK+ is also designed to be compatible with existing and planned GNSS satellites and interoperable with GPS and GLONASS.
Galileo benefits farmers by minimizing downtime from waiting for lost signals to be regained, and ensures consistent efficient use of seed, fertilizer and crop protection products through parallel passes with minimal overlap, thereby maximizing crop potential.
“The use of GNSS technology is opening up new productivity levels and opportunities in European agriculture, providing farmers with an unprecedented level of knowledge about their crops, livestock and operations while making the sector more efficient, economically competitive and environmentally sustainable,” said Maxime Rocaboy, product marketing manager, AFS technology, at Case IH.
“Enhanced RTK+ accuracy through incorporation of signals from the Galileo satellite system is a core way in which we can help Case IH tractor and combine users be innovative and competitive as they seek to help develop a sustainable agriculture to feed an ever-increasing world population in an environmentally responsible way,” Rocaboy said.
The technique of precise point positioning (PPP) is making inroads in the positioning industry. However, one issue hampering its more widespread adoption is the convergence time required for the carrier-phase ambiguities to be fully resolved so that the 10-centimeter-accuracy threshold can be surpassed. By using a multi-system, multi-carrier-frequency approach, instantaneous centimeter-level PPP can be achieved.
Innovation Insights with Richard Langley
CARRIER PHASE. It’s one of the two main measurement types or observables used by all GNSS receivers. Fundamentally, it is the instantaneous phase of a GNSS signal’s carrier, an electromagnetic wave of fixed amplitude and frequency (when transmitted), which is (optionally) modulated by a ranging code and a navigation message. It’s measured in radians, degrees or cycles and can be converted to a biased measure of the range between the receiver and satellite antennas by multiplying the value in cycles by the wavelength of the carrier in meters. The other GNSS observable is the phase of the ranging code. Initially measured in code chips or units of time, it is converted to a biased measure of the receiver-satellite range by multiplying it by the speed of light. This value is then typically called the code measurement or the pseudorange. The carrier phase is much more precise than the pseudorange by something like a factor of 100. So, while pseudoranges can be measured to a precision of tens of centimeters, carrier phases can be measured to millimeters or better.
Most GNSS receivers use pseudorange measurements to determine their position. In fact, this is the standard approach to satellite-based positioning that was introduced by GPS in the 1970s. While carrier-phase measurements, or rather their time-rate-of-change, are used for precise velocity determination, it wasn’t originally recognized that carrier-phase measurements could be used for position determination, too. The problem with the carrier phase as a measure of the range is that it has an initially unknown and potentially huge bias. This is because when a receiver starts tracking a signal’s carrier, it doesn’t know the exact number of cycles of the carrier wave stretching all the way from the satellite to the receiver. Hence, carrier-phase measurements are ambiguous as a result of this initial bias. If this ambiguity can be resolved, then carrier-phase measurements can be used for very precise positioning — positioning at the centimeter level or even better.
Over the years, various techniques have been developed to use carrier-phase measurements for positioning, most notably in differential positioning where one or more reference stations are used to position a user receiver or rover. But the technique of precise point positioning, which only requires direct uncombined measurements from the user receiver, is being actively developed and is making inroads in the positioning industry. However, one continuing issue hampering its more widespread adoption is the convergence time required for the carrier-phase ambiguities to be fully resolved so that the 10-centimeter-accuracy threshold can be surpassed. Research by the authors of this month’s article shows that by using a multi-system, multi-carrier-frequency approach, instantaneous centimeter-level PPP can be achieved. They call their technique Optimal Estimation using Uncombined Four-frequency Signals or OEUFS for short. Those of us who remember a smattering of our high-school French will agree that it is quite an eggceptional technique.
Instantaneous centimeter-level positioning used to be synonymous with the single-baseline real-time kinematic (RTK) technique. The rover was constrained to be within a few kilometers of the base station to ensure that errors would remain spatially correlated. Modeling error sources using a regional network of stations later allowed users to retain this level of accuracy within the area of network coverage. A global network of reference stations enabled the determination of precise satellite orbit and clock products, paving the way for precise point positioning (PPP).
Global centimeter-level accuracy can be achieved with PPP, at the cost of a long convergence time, often measured in hours. An additional layer of corrections, including satellite code (pseudorange) and carrier-phase biases, has enabled PPP with ambiguity resolution (PPP-AR). While an improvement in convergence time can be obtained, PPP-AR still cannot compete with RTK or network RTK in terms of time to first fix. Only by providing precise atmospheric information to PPP users, in the form of zenith tropospheric and slant ionospheric delays, can instantaneous centimeter-level accuracy be obtained. This approach led to a unification of PPP and RTK, often referred to as PPP-RTK. This scalable approach has allowed PPP users to obtain accurate positioning globally, while achieving rapid convergence when located within the regional reference network boundaries.
The modernization of GNSS includes satellites transmitting signals on multiple frequencies. The 12 GPS Block IIF satellites currently in orbit already broadcast the L5 signal, and all Galileo and BeiDou satellites launched so far have triple-frequency capabilities. In November 2017, the BeiDou constellation began a new phase of its development with the launch of the Beidou-3S satellites offering new signals compatible with the GPS L1/L5 bands. In March 2018, the European Union decided to open its Commercial Service (CS), offering at no cost the signal and correction stream for the “CS high accuracy” service. As a result, the E6 signal is now available on 14 satellites and can be tracked by modern GNSS receivers. FIGURE 1 depicts the frequency plan of the open GNSS signals, including these last evolutions, as of May 2018.
FIGURE 1. GNSS open signals (as of May 2018). (Image: authors)
With three or more frequencies, a series of widelane ambiguities can be resolved in a cascading scheme. These unambiguous widelane signals can be used to form an ionosphere-free phase measurement with lower noise than code measurements, but typically still at the decimeter level. The availability of the Galileo E6 signal provides a significant step forward for PPP-AR, permitting instantaneous convergence. As a result of frequency separation, unambiguous widelane signals have low noise characteristics, which further benefits the resolution of the whole set of ambiguities. The strategy used in our study is a generalization of the widelaning technique, based on uncombined observations, which we describe as Optimal Estimation using Uncombined Four-frequency Signals (OEUFS).
We explain how instantaneous centimeter-level PPP is achieved by first analyzing the precision of the ambiguity and range parameters in the single-satellite case. The network estimation of the uncombined Galileo phase biases is then described, followed by epoch-by-epoch and 5-minute PPP solutions based on OEUFS.
SINGLE-SATELLITE PROCESSING
To get a first grasp of the benefits of using four frequencies, we first look into single-satellite data. The aim of this analysis is twofold: first, to evaluate the ability of fixing linear combinations of ambiguities and, second, to determine the resulting precision of the unbiased range estimate once these ambiguities are fixed.
Uncombined observations on four Galileo frequencies (E1, E5a, E5b and E6) are used to model an ionosphere-free range, a slant ionospheric delay, and four carrier-phase ambiguities. It should be noted that measurements on a fifth frequency (E5) are available but, due to the proximity of E5 with respect to E5a and E5b, its impact was found to be almost negligible. We will, therefore, restrict ourselves to the four-frequency case. Only two code observations are included in the model — in this case E1 and E5a — since adding other frequencies would require the estimation of differential code biases. Thus, for single-epoch processing, additional code measurements would not usefully contribute to the solution. Observable standard deviations are set to 3 millimeters and 30 centimeters for carrier phase and code, respectively. An analysis using a zero-length baseline revealed that weak correlations do exist between signals, and multipath effects could further increase this correlation. Although taking into consideration correlations among observations would lead to a more realistic covariance matrix, these correlations were neglected in producing the results shown in this article. This is justified by the fact that correlation coefficients are usually not available, especially for real-time processing.
The above-mentioned model was inverted in a least-squares adjustment to perform covariance analysis. While the Least‐squares AMBiguity Decorrelation Adjustment (LAMBDA) method can be used for the identification of optimal linear combinations of ambiguities, the classic widelane ambiguities were found to perform equally well and were used in our work to simplify the exposition. When no ambiguities are fixed, the quality of the solution is driven by the noise on the code observations. TABLE 1 shows that, in this case, the receiver-satellite range parameter can be estimated with a precision of 0.776 meters. This value can be translated into a 3D-position precision by using the position dilution of precision (PDOP) factor. As a rule of thumb, if the PDOP for all satellites in view is equal to 1, the resulting 3D precision should be around 78 centimeters.
TABLE 1. Precision of parameters in the Galileo four-frequency (E1, E5a, E5b, E6) single-satellite case.
Even though the range is not very precise, forming the E5a-E5b widelane ambiguity from the estimated uncombined ambiguities gives a precision of 0.034 cycles, which can be reliably fixed due to the very long wavelength of the signal (9.77 meters). Adding this constraint to the system allows us to estimate the E5b-E6 widelane ambiguity with a standard deviation of 0.041 cycles (although it could also have been fixed initially). Interestingly, fixing both extra-widelane ambiguities does not significantly improve the precision of the range information derived from a single satellite. Nevertheless, due to correlations among ambiguity parameters, a precision of 0.183 cycles is now obtained for the E1-E5a widelane, an improvement of approximately 35 percent over the initial estimate.
While the E1-E5a ambiguity is not sufficiently precise for reliable instantaneous fixing based on single-satellite data from one epoch, using the geometric information from several satellites will enable single-epoch ambiguity resolution for three widelane ambiguities per satellite, as we show in the following sections. Assuming for the moment that ambiguity resolution was indeed successful on all three widelanes, Table 1 indicates that the range parameter can now be estimated with a standard deviation of 19 centimeters, a substantial improvement over the initial 78-centimeter precision. Recalling the PDOP factor introduced above, instantaneous 3D position precision at the 20-centimeter mark should then be possible with good geometry.
Including all available measurements in the model necessarily leads to the best performance. Still, TABLE 2 presents the conditional precision of parameters in three-frequency configurations. The precision for the widelane ambiguity is conditioned on first fixing the extra-widelane ambiguity, while that for the range assumes fixed extra-widelane and widelane ambiguities. The table highlights that frequency spacing plays a key role in the system performance. After fixing two widelane ambiguities, the Galileo E1-E5a-E5b configuration provides a range with a standard deviation of approximately 42 centimeters. The E1-E5a-E6 configuration is the best option, with a precision of the range parameter equal to the four-frequency case. In other words, the contribution of the E5b signal is almost negligible once the E5a-E6 ambiguity, having a wavelength of 2.93 meters, is resolved. For comparison purposes, the values for GPS are included and show that Galileo has the potential for significantly more precise instantaneous positioning.
TABLE 2. Conditional precision of parameters for three-frequency single-satellite configurations.
NETWORK SOLUTION
To demonstrate the concept of four-frequency ambiguity resolution for PPP, a phase-bias network solution for the Galileo constellation must be generated. Our solution is based on the precise satellite orbit and clock corrections produced by the Centre National d’Études Spatiales (CNES) as a part of the International GNSS Service (IGS) Multi-GNSS Experiment (MGEX). These products contain satellite clock corrections at a 30-second interval, as well as widelane biases allowing for GPS ambiguity resolution in the L1 and L2 frequency bands. For this reason, the following analysis considers both GPS and Galileo constellations.
Consistent processing of multi-frequency and multi-modulation signals requires code-bias corrections. The differential code-bias products from the German Aerospace Center (DLR), including the Galileo E6 signals, are used. Ambiguity resolution for Galileo can only be enabled with corresponding phase biases for all frequencies. To this date, the main contributors to the IGS for E6-compatible receivers are Natural Resources Canada (NRCan), CNES and Geoscience Australia. Since a global network of ground receivers tracking all four Galileo frequencies is not yet available, our solution is computed from a regional, but wide-area, network in Australia. The network consists of six reference stations with multi-system, multi-frequency receivers as depicted with red triangles in FIGURE 2. (Station CEDU is not included in the network solution because it is used later as a rover for PPP testing.) Measurements collected at a 30-second interval are retrieved from the Crustal Dynamics Data Information System (CDDIS) data archive. For the purpose of our demonstration, data from April 1, 2018, from 13:45:00 to 14:35:00 GPS Time is selected. During this period, five Galileo satellites were continuously tracked by the Australian stations, allowing the computation of a Galileo-only solution.
The phase-bias solution is a generalization in the multi-frequency case of the well-known widelane/narrowlane GPS scheme. The first step consists of resolving all integer ambiguities in the network. As we deal with four frequencies, it is required to fix four ambiguities, or their combinations, per satellite-station pass. The first three combinations used for this study are the widelanes defined from E5a-E1, E5b-E1 and E6-E1. Their ambiguities are solved, as for the dual-frequency GPS case, thanks to the Melbourne-Wübbena combination. Then, one remaining integer ambiguity (here, E1) is solved by forming the ionosphere-free phase combination between E1 and E5a (with the corresponding widelane ambiguity already resolved as an integer value). The second step aims at recovering the uncombined phase biases from the estimated linear combinations of biases. By a simple system inversion, it is possible to reconstruct the phase biases on each frequency.
FIGURE 2. Stations used to generate the Galileo phase-bias solution are represented by red triangles, while the PPP user is represented by a black square. (Image: authors)
FIGURE 3 shows the estimated biases for each frequency over the study period. The values were shifted by an integer number of the carrier wavelength for plotting purposes. The uncombined biases obtained are relatively stable, although they vary by a few centimeters over this one-hour period. These fluctuations are correlated among frequencies due to the transformation from linear combinations to uncombined biases. It should be understood that the resulting biases are not true phase biases, but rather biases to be applied to the carrier-phase observations.
FIGURE 3. Estimated Galileo phase biases for the four frequency bands over the study period. (Image: authors)
PRECISE POINT POSITIONING
We assessed the impact of using four frequencies transmitted by Galileo (E1, E5a, E5b and E6) on positioning performance by using station CEDU in Australia (see Figure 2). It is equipped with a multi-frequency receiver collecting multi-GNSS observations at 30-second intervals. Position estimates are derived from the PPP methodology using the satellite orbit and clock corrections, along with the carrier-phase and code biases, described in the previous section.
We computed three different solutions:
a GPS-only solution;
a Galileo-only solution; and
a GPS and Galileo combined solution.
For all solutions, all error sources affecting observations are modeled, including relativistic and wind-up effects, solid Earth tides and ocean loading. The a priori tropospheric zenith delay (TZD) is computed using the Vienna Mapping Function 1 (VMF1) grids, while a priori ionospheric delays are obtained from a global ionospheric map (GIM) generated at the Center for Orbit Determination in Europe (CODE). The eccentricity between the satellite antenna phase centers and the satellite center of mass is obtained from the latest version of the IGS ANTEX file, which includes frequency-dependent phase-center offsets and variations for Galileo. Since there are no Galileo-specific ground-antenna calibrations available, GPS values are used as approximations.
In all cases, we processed uncombined observations corresponding to the OEUFS strategy. For GPS, the L1C and L2W carrier-phase observations are used, along with the C1W and C2W code observations. For Galileo, the L1C, L5Q, L6C and L7Q carrier phases are used, with identical modulations for code measurements. Note that this signal identification uses the RINEX 3 conventions where, for Galileo, the L5 and L7 signals correspond to those in the E5a and E5b bands, respectively. Carrier-phase observations are given a standard deviation of 2 millimeters at zenith, while code observations are deweighted by a factor of 100. An elevation-angle-dependent weighting strategy also assigns lesser weight to satellites closer to the local horizon. Therefore, the value of 3 millimeters used in the single-satellite analysis above corresponds to a satellite tracked at an elevation angle of approximately 40 degrees.
The PPP filter includes states for the three position components, one receiver clock parameter per satellite system, inter-frequency code biases, one phase-bias parameter per frequency, a residual TZD, a residual slant ionospheric delay per satellite and carrier-phase ambiguities. To confirm the theoretical analysis from a previous section, the empirical single-epoch ambiguity-fixing success rate is first evaluated using a bootstrapping algorithm. The full vector of estimated float ambiguities is first decorrelated using the LAMBDA method, and all ambiguities having a success rate larger than 99 percent are fixed to integers. FIGURE 4 shows the number of fixed ambiguities for each solution.
FIGURE 4. Number of fixed ambiguities using a bootstrapping approach for independent, single-epoch, solutions. Number of frequencies in parentheses. (Image: authors)
Not surprisingly, the dual-frequency GPS solution is incapable of reliably fixing ambiguities within a single epoch. During this time period, five Galileo satellites are tracked. If we first consider all four frequencies from Galileo, and use the ambiguities on one satellite to provide the datum, then a total of 16 ambiguities are being estimated in the PPP filter, 12 of which are considered widelanes. Figure 4 confirms that using correlations introduced by the geometry allows instantaneous fixing of all widelane ambiguities for Galileo for most epochs. Adding GPS to the Galileo solution makes Galileo widelane fixing more reliable, but does not allow fixing of additional ambiguities. The three-frequency (E1, E5a and E6) Galileo configuration also enables instantaneous fixing of all eight widelane ambiguities, since the inclusion of E5b brings minimal additional information.
In all subsequent solutions, ambiguity estimation is performed using a more sophisticated method referred to as the best integer equivariant (BIE) approach. Because it is expected that not all ambiguities can be fixed simultaneously, a partial ambiguity resolution scheme is required. The BIE method fulfills this criterion by computing a weighted average of integer vectors. The outcome is a constrained ambiguity vector whose entries take either integer or float values. The key point of this approach is that the BIE float estimates can be improved by the averaging process with respect to the least-squares float estimates. Furthermore, by exploiting the correlations contained in the ambiguity covariance matrix, this method can effectively fix linear combinations of ambiguities. Therefore, we are not explicitly forming widelane ambiguities, but rather optimal linear combinations of ambiguities are fixed through the BIE averaging process. This strategy is implemented using the LAMBDA method to decorrelate ambiguities. Even though the BIE estimates are independent of the decorrelation, this step improves the computational efficiency of the approach.
As we explained in the previous sections, positioning with fixed widelane ambiguities can potentially allow for instantaneous precise positioning. FIGURE 5 demonstrates the epoch-by-epoch position estimates for the three solutions. As the strategy implies, the filter is entirely reset between epochs, and each point in the time series is independently determined. As expected, instantaneous ambiguity resolution with GPS alone is not feasible. Although the external information provided by the GIM is beneficial in reducing the errors, the root-mean-square (RMS) error is at the decimeter level for all components (see TABLE 3).
FIGURE 5. Instantaneous (epoch by epoch) PPP-AR solutions for GPS only, Galileo only and GPS and Galileo combined. Number of frequencies in parentheses. (Image: authors)TABLE 3. RMS errors for each instantaneous PPP-AR solution (meters).
The Galileo-only solution offers a substantial improvement in the horizontal components. These results are explained by the ambiguity-resolved widelane signals providing precise range estimates. It should be noted that only five Galileo satellites are visible during this period with a PDOP slightly exceeding a value of 3. When the full constellation of satellites will be in orbit, even better results could be obtained from a Galileo-only solution. The three-frequency (E1, E5a, E6) Galileo solution offers almost identical position estimates and is not shown here for conciseness. Combining GPS and Galileo yields the best solution with centimeter-level instantaneous positioning (refer to Table 3). For several epochs, a fully converged position is even obtained within a single epoch.
While the RMS errors of the combined GPS + Galileo solution is at the centimeter level, individual epochs can still exhibit decimeter-level errors. To demonstrate the convergence capabilities of the OEUFS strategy, we computed 5-minute PPP sessions. Even though the station is stationary, we added a large amount of process noise to the position states to simulate kinematic processing. FIGURE 6 shows the results of all 10 sessions: horizontal convergence to a few centimeters could be achieved within two epochs in all but one session.
FIGURE 6. Independent 5-minute kinematic PPP solutions using GPS and Galileo. Each trace represents a different session. (Image: authors)
CONCLUSION
We have shown that GNSS modernization is a key component for reducing the convergence time of PPP solutions. Combining multiple constellations strengthens the geometry, and using multiple frequencies allows for improved ambiguity resolution performance. In particular, tracking of the E6 Galileo commercial service signal turns out to be particularly beneficial in terms of instantaneous positioning capabilities. We demonstrated that ambiguities can be instantaneously resolved on Galileo satellites, leading to a range estimate approximately four times better than that provided using code measurements. With good satellite geometry, these frequencies can enable instantaneous 3D positioning with an accuracy of around 20 centimeters. Combining Galileo and GPS allows for single-epoch centimeter-level PPP solutions and full convergence within a few epochs.
We expect that the robustness and accuracy of the OEUFS strategy will improve in the future, with an increasing number of multi-frequency satellites and ground stations. Specifically, the additional frequencies provided by BeiDou and the Quasi-Zenith Satellite System will enhance the geometry of the solution and will further expedite convergence. Within a few years, instantaneous PPP might very well become a practical alternative to RTK for a wide range of applications.
ACKNOWLEDGMENTS
The authors acknowledge Geoscience Australia for making publicly available modernized GNSS data, as well as Paul Collins from NRCan for the review of our manuscript and technical advice. This article is published as NRCan Contribution 20180102.
MANUFACTURER
All of the stations used for the tests described in this article have PolaRx5 reference receivers manufactured by Septentrio (www.septentrio.com).
DENIS LAURICHESSE is a member of the Navigation Systems Department at CNES in Toulouse, France. He has been in charge of the DIOGENE GPS orbital navigation filter, and is now involved in navigation algorithms for GNSS. He is in charge of the CNES IGS real-time analysis center. Laurichesse was the co-recipient of the 2009 Institute of Navigation Burka Award for his work on phase ambiguity resolution.
SIMON BANVILLE is a senior geodetic engineer with the Canadian Geodetic Survey of NRCan, Ottawa, Canada, working on PPP. He obtained his Ph.D. degree in 2014 from the Department of Geodesy and Geomatics Engineering at the University of New Brunswick, under the supervision of Richard B. Langley. He is the recipient of the Institute of Navigation 2014 Parkinson Award.
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• Multi-GNSS Experiment
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“Carrier Phase Integer Ambiguity Resolution” by P.J.G. Teunissen, Chapter 23 in Springer Handbook of Global Navigation Satellite Systems, edited by P.J.G. Teunissen and O. Montenbruck, published by Springer International Publishing AG, Cham, Switzerland, 2017.
“Theory of Integer Equivariant Estimation with Application to GNSS” by P.J.G. Teunissen in Journal of Geodesy, Vol. 77, No. 7-8, Oct. 2003, pp. 402–410, doi: 10.1007/s00190-003-0344-3.
u-blox, a global provider of leading positioning and wireless communication technologies, has released the ZED-F9P multi-band GNSS module with integrated multi-band real-time kinematics (RTK) technology for machine control, ground robotic vehicles and high-precision unmanned aerial vehicles (UAV) applications.
The ZED‑F9P measures 22 x 17 x 2.4 millimeters and uses technology from the recently announced u‑blox F9 platform to deliver robust high-precision positioning performance in seconds.
The u-blox ZED-F9P is a mass market multi-band receiver that concurrently uses GNSS signals from all four GNSS constellations (GPS, GLONASS, Galileo and BeiDou). Combining GNSS signals from multiple frequency bands (L1/L2/L5) and RTK technology lets the ZED‑F9P achieve centimeter-level accuracy in seconds, the company said.
Receiving more satellite signals at any given time maximizes the availability of centimeter-level accuracy even in challenging environments such as in cities.
With its high update rate, the ZED‑F9P is suitable for highly dynamic applications such as UAVs. Featuring on-chip integration of advanced multi-band RTK algorithms, it requires no additional hardware or third-party RTK libraries. Ready to use on delivery and easy to integrate, it helps product developers quickly bring their ideas to the market.
ZED-F9P is fully geared to clearing the three main hurdles that have kept centimeter-level positioning accuracy from breaking into mass-market applications: cost, size and power consumption. Significantly smaller and more energy efficient than existing solutions, and as a cost efficient alternative, the ZED-F9P will enable new high-precision positioning applications for the mass market.
“The new ZED-F9P GNSS receiver builds on the success of our NEO-M8P high-precision GNSS module, but takes performance to another level by leveraging all the available GNSS signals,” said Mårten Ström, senior principal product management, product center positioning at u‑blox. “By making robust and affordable high-precision positioning technology more accessible, we hope to fuel innovation and enable a new generation of high-precision GNSS navigation applications.”
Engineering samples will be available at the end of July.
Harxon Corporation is launching the single-frequency, multi-GNSS real-time-kinematic (RTK) enabled Smart Antenna TS300 series, designed for manual guidance and autosteer agriculture applications that benefit from scalable performance in positioning accuracy.
The TS300 series smart antennas are designed for manual guidance and autosteer agriculture applications. (Photo: Harxon)
The TS300 series is a multi-GNSS compatible system using GPS, GLONASS, BeiDou and Galileo for simultaneous satellite tracking to offer RTK positioning.
It is able to track any visible satellites under challenging conditions, ensuring a stable signal quality with higher precision and reliable data. Farm tractors and machines can still receive a healthy signal when the sky is partially visible or there are obstructions around the farmland.
The TS300 series features patented T-DIFF technology, providing smooth positioning and exceptional pass-to-pass accuracy. Its steady, smooth output is well suited for autosteer applications and helps the machines operate in a steady path. By reducing the impact of machine vibration during farming on complex landforms, T-DIFF technology ensures machine controlling and positioning accuracy at a centimeter level.
Powered by the latest stand-alone algorithmic technology, the TS300 series can maintain the RTK positioning accuracy for a certain period when the RTK difference link is disconnected during machine operation. It guarantees that farm machines operate effectively and accurately under poor positioning conditions.
Moreover, the TS300 series can output real-time tilt information for machines on rugged farmland. By optimizing the backend operation, it is convenient for users to improve positioning accuracy through a tilt compensation algorithm.
The data links — 3G/4G modules, external/internal radio transmission modems and Bluetooth — of the TS300 series are designed as multiple selections as required, allowing customers flexible and convenient operation in different environmental conditions.
Purpose-built for challenging environments, TS300 Series has built-in magnets to simplify mounting; fixed mounting options are also available as 5/8-inch screws and M4 screws, providing convenient and quick installation. Its IP67 ruggedized enclosure works reliably in harsh environments and is designed for professional precision agriculture applications requiring high-precision RTK positioning.
Geneq has launched the SXblue Premier GNSS receiver, which is available in a submetric version (GNSS) or centimetric version (real-time kinematic, RTK).
The new SXblue Premier GNSS receiver is equipped with the Pacific Crest Maxwell 6 Trimble technology with BD910 (GNSS version) and BD930 (RTK version) OEM boards, delivering 220 channels to acquire and track GNSS signals from all constellations in view. It makes effective use of GPS, GLONASS, Galileo, BeiDou, QZSS and SBAS signals for outstanding highly precise positioning.
The SXblue Premier is small and light weight, and rugged for field work. It is equipped with dual mode for Bluetooth V2.1 and Bluetooth V4.0, ensuring the unit’s wireless communication with any Android or Windows terminal. With its two models, the user will have large efficiency and flexibility on the field either with SBAS corrections or RTK reference networks.
In addition, SXblue Premier can be configured for Wi-Fi hotspots, allowing users to connect and access a web management platform. It also can be used as a data link, providing a quick connection to the internet to receive corrections from reference station (CORS) networks so that it can process RTK measurements.
With its internal memory using an 8-GB solid state disk, SXblue Premier provides enough storage space for field data collection or raw data recording for a high data sampling rate.
Multiple compatible software programs — including FieldGenius, Carlson, Collector for ArcGIS — will meet the users’ diverse need, making SXblue Premier more powerful and flexible.
After years of development and an intensive beta testing phase with key partners, Qinertia post-processing kinematic software is now being offered by SBG Systems.
Qinertia has been designed to help surveyors get the most of their surveys, according to SBG Systems.
After the mission, Qinertia gives access to offline real-time kinematic (RTK) corrections from more than 7,000 base stations in 164 countries — and always up-to-date. By creating a virtual base station near a project, the software delivers the highest level of accuracy without having to set up your own base station.
An advanced tight coupling algorithm has been designed by SBG Systems to deliver the highest accuracy and maximize RTK availability. Trajectory and orientation are greatly improved by processing inertial data and raw GNSS observables in forward and backward directions, especially in GNSS challenging environments (urban canyons, forest, etc.).
With advanced quality control indicators such as standard deviation, separations and GNSS quality feedback, Qinertia provides full understanding of a survey. With Qinertia, surveyors can quickly identify and solve issues such as mechanical installations or sensor alignment.
Qinertia has been designed to be easily integrated in a production workflow. It supports RINEX industry standard, and Septentrio, Novatel and Trimble native binary format.
A powerful ASCII export feature allows seamless integration with any third-party software. SBET and Google Earth are also supported for improved interoperability.
u‑blox has rolled out the u-blox F9 technology platform, which was designed to deliver high-precision positioning solutions for mass market industrial and automotive applications.
The platform combines multi-band GNSS technology with dead-reckoning, high-precision algorithms, and compatibility with a variety of GNSS correction data services, to achieve precision down to the centimeter level.
u‑blox F9 paves the way for the next generation of high precision navigation, augmented reality, and unmanned vehicles, the company said.
The u-blox F9 platform will underpin the next wave of u‑blox positioning modules targeting mass market industrial and automotive applications. It uses GNSS signals in multiple frequency bands (L1/L2/L5) to correct positioning errors caused by the ionosphere and deliver fast time to first fix (Fast TTFF).
Its ability to receive signals from all GNSS constellations (GPS, GLONASS, Galileo, Beidou) further improves performance by increasing the number of satellites visible at any given time. Stand-alone u‑blox F9 solutions robustly achieve meter-level accuracy.
To achieve centimeter-level accuracy, u‑blox F9 offers optional on-chip real-time knematic (RTK) technology. In addition to offering an open interface to legacy GNSS correction service providers, it supports the main GNSS correction services, bringing RTK high-precision positioning to the mass market.
“High precision is the next frontier in positioning for mass markets, with countless applications in need of a robust and scalable high precision positioning solution. u‑blox F9 provides the hardware and integrated software components to address these needs,” said Daniel Ammann, executive director of positioning product development at u-blox.
Optimized for low power consumption, the u‑blox F9 platform sets a high standard for security with built-in jamming and spoofing detection systems that protect against intentional and unintentional interference. Dead-reckoning technology based on inertial sensors extends high-precision performance to otherwise challenging urban environments.
Automotive applications of the technology include lane-level navigation for head-up displays and vehicular infotainment systems as well as for vehicle-to-everything (V2X) communication, a prerequisite for highly automated and fully autonomous vehicles.
In the industrial realm, u‑blox F9 will enable mass adoption of commercial unmanned vehicle applications including drones and ground vehicles such as heavy trucks or robotic lawnmowers.
The u‑blox F9 platform’s technology will be showcased at Embedded World in Nuremberg, Germany from Feb. 27-March 1 at Booth #3-139. Product samples will be available later in the year.
SimActive Inc., a developer of photogrammetry software, has launched an automated solution for direct georeferencing from real-time kinematic (RTK) positioning.
Within the new workflow feature, users can achieve get high accuracy in projects without the use of ground control points (GCP), saving time in collecting and processing data.
Martin Instrument, a reseller of SimActive and surveying equipment, is benefitting from the automation. “Direct georeferencing greatly helps reducing cost for applications like corridor mapping,” said Mike Minick, vice president of sales at Martin Instrument. “The new automated option within SimActive software for direct georeferencing greatly facilitates the user workflow.”
“With RTK GPS available on drones, the use of direct georeferencing is growing within the industry,” said Louis Simard, CTO of SimActive. “Correlator3D allows users to maximize their hardware and software investment.”
For a live demonstration at the Commercial UAV Show (Nov. 15-16, London, United Kingdom), visit SimActive’s booth or send an email to [email protected].
