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Single-base RTK is an excellent choice for many uses but mixing different baseline lengths can yield inconsistent results

By Gavin Schrock, PLS

The surveying lead for a construction firm started getting calls from his crews — suddenly they were not checking in to existing control with the accuracy required. This presented a conundrum and an immediate resolution was needed to stay on schedule. What had changed? A nearby permanent base, part of the regional real-time GNSS network (RTN), had suddenly gone dark, and when the crews switched to other bases, they got the inconsistent results. Time to call the RTN. (See a primer on RTN.)

I have been operating a regional cooperative RTN for 19 years, and I get these kinds of support calls regularly, but typically only from users of the single-base mountpoints. Most RTN provide, via NTRIP casters, both network RTK (NRTK) solutions — such as master-auxiliary, VRS and FKP — and single-base solutions for each base. The base they had been using was down while the roof of the city building on which it is mounted was undergoing some maintenance.

The construction firm, halfway through a multi-year transportation project, had used the base when they established project control, and for layout and as-built tasks. Using the base, which was slightly more than 4 km from the site, the crews were used to seeing check-in results of 0.3′ (9 mm) or better (horizontal). When they switched to different bases, 23 km and 25 km distant, the results were now inconsistent, and in many instances, double.

This was an easy fix. We met on site and checked results using the network solution; it closely matched the results they were seeing from the original base. Until the original base was restored, this would meet their needs.

It made a lot of sense to use the nearby base, as setting a temporary project base on the congested and sky-view challenged site was impractical. Furthermore, the baseline length of 4 km yields excellent results. Single-base RTK is a powerful tool, and a default for many construction projects, provided that:

• the base has an unobstructed view of the sky
• the base is free of nearby multi-path hazards
• the base receiver and the antenna are of the same or better quality as the rovers
• the base receiver and the antenna support the constellations and the signals desired.

In many ways, it is hard to beat single-base RTK. For instance, if you set up a base right on the site, say less than a kilometer away, this should yield the best results possible for RTK, and can be better than network RTK.

However, there are challenges. Single-base, typically “iono-free” solutions common in today’s rovers, degrades over the baseline length. The rule of thumb for many is that the degradation becomes noticeable when baseline lengths exceed 10 km. It is not uncommon for rovers to fix at much longer baseline lengths; 20 km, 30 km, 50 km or more — but results will likely vary from hour to hour or day to day. Changes in ionospheric and tropospheric conditions can bring inconsistencies, particularly over longer baseline lengths.

Network RTK may not beat single-base over very short baselines, but as it uses 5 to 15 bases (depending on the implementation) it can better model in the varied conditions. It can provide great consistency and repeatability, even if an individual base is unavailable, as was the case for this conduction site. There are strengths and weaknesses for both. NRTK brings consistency over a wide area, you do not have to set up (and guard) your own base, and the geodetic values are solved.

If you can have an on-site base, you can under certain conditions see a gain in results. This is especially important for certain applications, such as machine control and precision agriculture, for which tight year-to-year and row-to-row repeatability is key. However, if you may need to use another base at some point, you may be better off starting with NRTK, if it yields the results you seek.

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Gavin Schrock is a practicing surveyor, technology writer, editor of xyHt Magazine and operator of a cooperative GNSS network.

The European Railway Traffic Management System (ERTMS) could start using Europe’s space solutions to manage rail traffic.

A project funded by the European Union Space Program Agency (EUSPA) is taking steps toward providing a cost-efficient train-tracking solution based on satellite technology, together with other sensors and data.

Knowing the exact position of each train is at the heart of rail operations across the European Union (EU). ERTMS is a major industrial EU project to create a more efficient and safer interoperable railway system. It currently relies on a series of costly ground instruments. In the coming years, ERTMS could switch to EU space solutions.

In a project dubbed CLUG — short for Certifiable Localization Unit with GNSS — experienced rail operators and infrastructure managers came together to define a set of specifications and operational scenarios that meet the most stringent safety needs of the rail sector. The specifications are used by the architects of the CLUG consortium, who are in the process of rolling out the system.

The project’s goal is to assess the creation of a failsafe train localization onboard unit (TLOBU) interoperable across the entire European railway network. The TLOBU will provide trains and railway operators with critical information such as positioning and velocity, complemented by acceleration, heading and attitude for applications.

GPS and airborne light detection and ranging (lidar) have revolutionized archaeology. In just a little more than a decade, dozens of previously hidden cities and settlements have been discovered under heavy tree canopy and in other terrain. Many of the sites are in difficult-to-access areas, such as high atop mountains, in vast deserts, or enclosed in thick, nearly impenetrable foliage. Many were only the stuff of legend.

Others are right under our feet. In 2018, early settlements were uncovered in New England, including now-abandoned walls, roads and building foundations.

With the development of lidar, archaeologists gained perhaps their most powerful tool since carbon dating. Lidar began as a million-dollar classified technology. Now lidar units are small enough to attach to unmanned aerial vehicles (UAVs).

Lidar devices send more than 100,000 laser pulses to the ground every second and use their return times to calculate precise elevation data that allow researchers to build three-dimensional maps of a landscape, while GPS receivers provide its coordinates. Lidar fly-overs have revealed ancient cities, temples, causeways, irrigation systems and other structures, which are then ground-truthed by excavation teams.

“Lidar has completely changed the way we survey ancient Maya cities and what we can know about them, and it is a thousand times better than [what we used] before,” Francisco Estrada-Belli told GPS World. Estrada-Belli is a research professor at Tulane University’s Middle American Research Institute.

The application of lidar to archaeology began in 2009, when NASA sponsored a remote-sensing project that showed lidar’s usefulness below the forest canopy. The project revealed the surprisingly vast scope of Caracol, the largest Mayan archaeological site in Belize. Urban Caracol maintained a population of more than 100,000 people with an immense agricultural field system and elaborate city planning.

Since then, lidar has been used the world over to uncover buried secrets from early Roman fortifications in Italy to landscape changes from World War I. Just this August, lidar unearthed sobering evidence of a massacre by Nazi Germany in Poland during World War II.

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A landmark project in Guatemala illustrates the benefits of lidar. The ancient city of Tikal was one of the best-mapped regions of the Mayan world, but the Pacunam Lidar Initiative quintupled the amount of mapping done in 50 years in a single summer, with 61,000 structures found in an 810-square-mile area invisible to the naked eye because of overgrown vegetation. What experts had mistaken for unusable swampland, for instance, had actually been farmland, crisscrossed with canals. The area may have been home to a population of up to 10 million people. Results were published in Science in 2018.

“Seen & Heard” is a monthly feature of GPS World magazine, traveling the world to capture interesting and unusual news stories involving the GNSS/PNT industry.

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SMARTWATCH REVEALS RUNNER’S FATE

On the morning of July 10, Berkeley resident Philip Kreycik went for a run in Pleasanton, California. That day, temperatures reached 106 degrees, and he didn’t return home. His body was found Aug. 3, reports the San Francisco Chronicle. His Suunto smartwatch stopped tracking movement 4.5 hours after he started his run. GPS data from the watch showed him moving in erratic zigzags and circles before he stopped. Experts concluded he experienced delirium before succumbing to heat exhaustion.

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GANGS TARGET FARM DEVICES

Organized gangs riding e-scooters are stealing high-value GPS/GNSS technology from farms in the United Kingdom, reports BBC News. Insurer NFU Mutual said the cost of replacing the stolen equipment nearly doubled in a year to £2.9 million. The technology, in worldwide demand, has become the “rural thieves’ top target,” the insurer said. GPS/GNSS equipment on tractors can cost up to £10,000 per unit.

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SPACE FORCE RECRUITS WITH GPS

A 13-minute recruitment commercial from the U.S. Space Force debuted
Aug. 24, with GPS as a star. “There’s no such thing as a day without space operations. You just don’t see them,” explains the video, mentioning how GPS is key to the operation of ATMs, cell phones, gas pumps, traffic lights, power grids, guided missiles and more. The commercial states that the Space Force is seeking guardians who will help protect satellites from attack and debris. Current guardians describe the importance of GPS. “We won’t just think outside the box, we’ll think outside the atmosphere, in one of the most challenging environments ever known,” concludes the video. “The sky is not the limit.”

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THIEVES STEAL TRACKERS AND… (GUESS THE REST)

Two burglars who stole a package from a drop-off box were quickly apprehended — the package was filled with Roambee GPS-based trackers heading to a COVID-19 vaccine maker for use in tracking shipments. The Santa Clara Police Department was ecstatic to learn what the thieves had stolen, reports Roambee, who knew the package had gone missing. Unaware of what was in their trunk, the thieves traveled more than 761 miles around the Bay Area before being arrested 14 days later on July 18.

2J Antennas has introduced the Stellar series, antennas designed for a large suite of devices with a focus on GNSS, sub-6 GHz, 5G NR, 4G LTE, 3G, 2G and WiFi-6E technologies.

The Stellar Series is suitable for law enforcement, medical transportation, fire rescue and other applications where mission-critical communication is a requirement. The antennas are designed to reliably provide real-time connectivity in a small size.

This series includes single or up to 9-in-1 configuration choices within the range of 617 MHz to 7125 MHz frequency bands.

The patent-pending technology reduces the antenna footprint by 55% while implementing a new double trifilar design and longitudinal resonances for MIMO/ARRAY configurations that traditionally have more complex size restrictions (such as B71 band/600 MHz).

Each antenna configuration uses symmetrical or asymmetrical resonators for negative sections of the antenna, resulting in maximum performance at low and mid frequencies. The Stellar series offers magnetic and adhesive mounting choices, making them suitable for temporary installations.

For permanent installation, 2J Antennas also offers the screw mount option in its roof series. The low-profile and lightweight housing introduces a new design that offers a more cost-effective solution for suppliers and distributors.

“We are excited to reinvent antenna designs to meet the fast-growing global markets and offer antenna solutions with the highest quality while reducing antenna sizes as much as possible,” said Ruben Cuadras, director of engineering. “We are proud to continue to bring antenna solutions to customers that require small device integration, reliability and new designs.”

The National Geospatial-Intelligence Agency launches Phase 4a of MagQuest Challenge to advance NASA’s ability to measure Earth’s magnetic field

The National Geospatial-Intelligence Agency (NGA) has launched the Demonstration Phase (Phase 4a) of its MagQuest Challenge to develop novel data-collection approaches for the World Magnetic Model.

The WMM ultimately ensures the accuracy of navigation, because it corrects for differences in magnetic forces at a user’s location. The model is used by thousands of systems for mobile navigation apps and is critical for military and commercial uses around the world.

Produced since 1905, the WMM originated with data collection from two ships surveying 500,000 miles of ocean. Today, the data is collected by satellites operated by the European Space Agency that will eventually reach the end of their useful life.

NGA’s MagQuest Challenge is promoting the development of miniaturized solutions to determine whether they can produce data useful to support WMM production. NGA has an extensive network of government partners collaborating on the WMM production, including the National Oceanic and Atmospheric Administration (NOAA), the British Geological Survey, the Federal Aviation Administration (FAA), the Department of Defense (DOD), the United States Geological Survey (USGS), and the United States Naval Observatory (USNO) among others.

As part of its core mission, NGA provides geospatial intelligence products and services to decision makers, military service members, and first responders.

The MagQuest Demonstration Phase 4a will take place on HeroX, a social network platform for crowdsourced solutions.

Three winning teams from Phase 3 of MagQuest each proposed a magnetometer design to measure the Earth’s magnetic field. In this new phase, the teams will receive several million dollars in awards, including a $1.55 million incentive prize purse, to develop their proposed magnetometers. NASA Goddard Space Flight Center will conduct independent testing on each team’s prototype.

Following Phase 4a, successful teams will integrate their magnetometers into their satellites and launch their systems, acquire data and share their results with NGA.

“Our ultimate goal is for all three teams to successfully develop a magnetometer, each of which can be sent into orbit to determine viability for WMM production,” said Mike Paniccia, NGA program manager for the World Magnetic Model. “We want to test as many innovative and groundbreaking magnetometers as possible to ensure that NGA has a robust set of data suppliers to support the future of the WMM. We intend to have a competitive procurement for a data-buy contract following MagQuest and hope that these three teams, in addition to others from industry, will be able to supply comprehensive data sets to support the future of the WMM.”

Three of the teams that participated in Phase 3 were selected to participate in Phase 4:

• Iota Technology, the first-place Phase 3 winner, works alongside experienced teams from Oxford Space Systems and AAC Clyde Space. Their combined expertise in sensor technology, deployable structures and mission design informed the design of their SIGMA solution — a 3U CubeSat featuring a novel deployable boom and a 3D magnetometer array.
• University of Colorado Boulder is one second-place Phase 3 winner, and their solution, COSMO, leverages recent innovations in CubeSat technology and novel magnetometer technology. The University of Colorado Boulder team includes experts and faculty from the Department of Aerospace Engineering Sciences, the Department of Mechanical Engineering, and the Laboratory for Atmospheric and Space Physics, and they operate their missions entirely at the university, including using their own ground stations.
• Spire Global and SBQuantum formed a partnership with a promising approach to become the other second-place Phase 3 winner. SBQuantum’s novel diamond-based quantum magnetometer technology is coupled with Spire’s expertise and existing infrastructure in satellites, ground stations and data processing to produce a unique solution.

“This MagQuest Challenge is a testament to the power of the crowd,” said Kal K. Sahota, CEO, HeroX. “We are pleased to be part of securing the future of geomagnetic data collection and consequently contributing to the resilience and continued crucial work of the WMM.”

Geoscience Australia is developing open-source software — named Ginan — that will provide real-time corrections to positioning signals of all the GNSS constellations.

Once operational, Ginan will improve the accuracy of location data from 10 meters down to 3 to 5 centimeters for users with an internet and mobile connection. It will enable industry to provide reliable centimeter positioning to their customers, the agency said in a press release.

“Ginan is part of an exciting and innovative Australian Government program to enable precise positioning technology across the whole of the Australian continent,” said Martine Woolf, head of Geoscience Australia’s National Positioning Infrastructure Branch. “It will provide industry with the ability to use precise point positioning, bringing significant economic and social benefits to Australia.”

Examples of how this data could be used include reducing fertilizer and chemical spray waste in agriculture. It could also improve the operational efficiency of large mine sites through greater use of automation.

“Ginan will allow Australians to enjoy the benefits of precise positioning through the creation of new services and products, and in doing so, drive Australia’s economic growth,” Woolf said. “Our precise location data will inform of near real-time atmospheric conditions, which is already being used by the Bureau of Meteorology to assist with their weather predictions. It will also enable a greater understanding of movements in the Earth’s crust and provide insight into earthquakes, sea-level changes and the atmosphere.”

Ginan 1.0 will be publicly released in June 2022. An alpha version is now available on the Ginan GitHub repository, with a beta version planned for user testing from February 2022.

A thoughtful name

Ginan is named for a star that aided the First Australians as they navigated across the continent.

Woolf said the name of the software is a gift from the Wardaman people from the Northern Territory. Geoscience Australia sought permission to use the name Ginan as part of its commitment to respectfully engage and collaborate with Australia’s First Peoples.

“In the language of the Wardaman people, Ginan means ‘a red dilly-bag filled with songs of knowledge’. We like to think of this software as being similar to a dilly-bag full of knowledge because of the benefits it will unlock,” Woolf said. “Ginan is also the name of the fifth-brightest star in the Southern Cross. Just as the Southern Cross helped the First Australians to navigate this land, the positioning capability we are developing here at Geoscience Australia will enable us to know exactly where we are and where we are going.”

Wardaman Elder Diganbal Rosas said the dilly-bag was an important part of the Wardaman songline of the Katherine region. Songlines help to culturally and physically map land and seas through the transmission of traditional knowledge, cultural values, lore and wisdom across the landscapes. They are a living ancient memory code linking the environment, language and culture.

“Ginan [in our language] has all of the Wardaman knowledge regarding connection to country — all of the stars, the skies, the country, the people and the kinship. Everything we do is held in that dilly-bag, in that Ginan,” Rosas said. “The star teaches us many aspects of that spiritual connection to country, how it all began through those songlines, and how that story connects country to the stars. It is significant [that the Wardaman people have allowed Geoscience Australia to use this name] and I think it is a great opportunity for us to showcase our partnership.”

The Ginan initiative is part of Geoscience Australia’s Positioning Australia program, which is improving the accuracy of location-based data across the nation, bringing it from meters to centimeters.

Further information

Ginan Analysis Centre Software
Ginan GitHub repository
Positioning Australia

Septentrio now offers Qinertia post-processing software from SBG Systems on AsteRx-i3 D Pro+, AsteRx-i3 S Pro+ and AsteRx SBi3 Pro+ receivers

Septentrio will now offer post-processing solutions for its GNSS/INS (inertial navigation system) receivers, using SBG Systems’ Qinertia software.

The AsteRx-i3 Pro+ receivers are fully compatible with Qinertia post-processing software, so no data manipulation is required before the post-processing step.

Land or aerial mapping applications, which do not have access to real-time GNSS corrections, benefit from post-processing software for higher positioning and orientation (heading, pitch and roll) accuracy. With the addition of post-processing, Septentrio GNSS/INS products cover the full mapping workflow.

“As a result of our cooperation with SBG Systems, Septentrio’s mapping customers who use GNSS/INS are benefiting from a quicker and more reliable workflow,” said Danilo Sabbatini, product manager at Septentrio. “The intuitive user interface of Qinertia software makes it easy for users to further improve their positioning and orientation accuracy in the post-processing step.”

In case of GNSS outage or correction link failure, post-processing recovers accuracy for recorded positioning and inertial data.

After the mission, Qinertia gives access to real-time kinematic (RTK) corrections from more than 8,000 base stations to deliver centimeter level accuracy. Trajectory and orientation are greatly improved by post processing GNSS and IMU data forward and backward. The Qinertia GNSS/INS post-processed kinematic (PPK)  solution provides accuracy, reliability, advanced quality-control indicators, and a modern application programming interface (API).

Qinertia recently added an image geotagging feature, and specific outputs dedicated to photogrammetry.

The Institute of Navigation’s (ION) Satellite Division presented two prestigious awards Sept. 24 at its ION GNSS+ 2021 Conference, which took place in St. Louis, Missouri.

Mark Psiaki received the  Johannes Kepler Award for setting a standard of rigor, clarity and thoroughness in addressing key estimation and signal processing problems in positioning, navigation and timing (PNT).

The Johannes Kepler Award recognizes and honors an individual for sustained and significant contributions to the development of satellite navigation. It is the highest honor bestowed by the ION’s Satellite Division.

Psiaki originated the technique of bit-wise parallel RF signal processing for use in general-purpose processors. This enabler of software-defined GNSS led to the first space deployment of a fully software-defined GNSS receiver on a general-purpose digital signal processor (DSP) and to the widespread adoption of software-defined GNSS across the aerospace industry.

Psiaki’s real-time software radio expertise also enabled the development of a spoofer cultivated in his research group. He led the development of spoofing detection algorithms based on cross-correlation of unknown P(Y) codes and based on direction-of-arrival sensing.

Psiaki was the lead signal processing designer/analyst for the iGPS program that combined Iridium L-band downlink signals, GPS signals and inertial navigation system (INS) data to enhance GPS anti-jam capabilities. Recent work on navigation based on low-Earth-orbit (LEO) satellites fuses observables from an existing global communications constellation with INS and other sensor data to provide a backup to GPS.

Another contribution demonstrates how Doppler-based navigation could replace pseudorange-based navigation if implemented using a large LEO constellation.

DPsiaki has made many contributions to the practice of modeling, estimation, and detection applied to GNSS, including the study of GNSS carrier phase modeling for space-based applications.  His campaign to decode the GIOVA-A L1 BOC(1,1) PRN codes enabled Galileo receiver manufacturers to test their systems before the ESA published the codes.  His group’s work on ionospheric scintillations led to the first commercially-available scintillation simulators.

Psiaki holds the Kevin T. Crofton Faculty Chair of Aerospace & Ocean Engineering at Virginia Tech.  He studied at Princeton University, completing a B.A. in physics in 1979 (magna cum laude) followed by an M.A. (1984) and a Ph.D. (1987) in mechanical and aerospace engineering.

He is a past recipient of the ION’s Burka Award, its Tycho Brahe Award, and the Pride at Boeing Accomplishment Award. He is a Fellow of both the AIAA and the ION.

PARKINSON AWARD

The Institute of Navigation’s (ION) Satellite Division also presented Lakshay Narula with its Bradford W. Parkinson Award for his thesis, “Towards Secure & Robust PNT for Automated Systems.”

The Bradford W. Parkinson Award is given annually to an outstanding graduate student in the field of GNSS. The award, which honors Parkinson for his leadership in establishing both GPS and the Satellite Division of the ION, includes a personalized plaque and a $2,500 honorarium.

Any ION member who is a graduate student completing a degree program with an emphasis in GNSS technology, applications or policy is eligible for the award.

News from the National Institutes of Health

A new robotic cane can help the visually impaired navigate indoors. The cane is equipped with a color 3D camera, an inertial measurement sensor, and its own on-board computer.

When paired with a building’s architectural drawing, the device can accurately guide a user to a desired location with sensory and auditory cues, while simultaneously helping the user avoid obstacles like boxes, furniture and overhangs.

Development of the device was co-funded by the National Institutes of Health’s National Eye Institute (NEI) and the National Institute of Biomedical Imaging and Bioengineering (NIBIB). Details of the updated design were published in the journal IEEE/CAA Journal of Automatica Sinica.

“Many people in the visually impaired community consider the white cane to be their best and most functional navigational tool, despite it being century-old technology,” said Cang Ye, Ph.D., lead author of the study and professor of computer science at the College of Engineering at the Virginia Commonwealth University, Richmond. “For sighted people, technologies like GPS-based applications have revolutionized navigation. We’re interested in creating a device that closes many of the gaps in functionality for white cane users.”

While cellphone-based applications can provide navigation assistance — helping blind users stay within crosswalks, for example — large spaces inside buildings are a major challenge, especially when those spaces are unfamiliar.

Earlier versions of Ye’s robotic cane began tackling this problem by incorporating building floorplans; the user could tell the cane where he or she wished to go, and the cane — by a combination of auditory cues and a robotic rolling tip — could guide the user to the destination. But when used over long distances, the inaccuracies in the user’s location could build up, eventually leaving the user at an incorrect location.

To help correct this issue, Ye and colleagues have added a color-depth camera to the system. Using infrared light, much like a mobile phone’s front-facing camera, the system can determine the distance between the cane and other physical objects, including the floor, doorways and walls, as well as furniture and other obstacles. Using this information, along with data from an inertial sensor, the cane’s onboard computer can map the user’s precise location to the existing architectural drawing or floorplan, while also alerting the user to obstacles in their path.

“While some cell phone apps can give people auditory navigation instructions, when going around a corner for example, how do you know you’ve turned just the right amount?” said Ye. “The rolling tip on our robotic cane can guide you to turn at just the right point and exactly the right number of degrees, whether it’s 15 or 90. This version can also alert you to overhanging obstacles, which a standard white cane cannot.”

There are still a few kinks to be worked out before the system will be market-ready — it’s still too heavy for regular use, for example, and Ye’s team is looking for a way to slim down the device.

Nevertheless, with the ability to easily switch between its automated mode and a simpler, non-robotic “white cane mode,” Ye believes the device could provide a key independence tool for the blind and visually impaired, without losing the characteristics of the white cane that have stood the test of time.

The study was funded by NEI and NIBIB through grant EB018117.

Reference: Zhang H, Jin LQ, Ye C. “An RGB-D camera based visual positioning system for assistive navigation by a robotic navigation aid,” IEEE/CAA J. Autom. Sinica. 2021. 8(8):1389-1400. doi:10.1109/JAS.2021.1004084