There’s no denying that GPS technology has transformed our lives. From its introduction in the 1970s to its proliferation over the ensuing decades, GPS became an essential tool for U.S. consumers and businesses, so much so that it now travels with us everywhere in our pockets.
Everyday Americans use GPS signals to navigate with their phones and share their location with friends. Companies rely on it for everything from vehicle fleet management to construction surveying.
In short, GPS tools make countless tasks possible — or at least more accurate. But, as any engineer knows, they can only go so far. When it comes to numerous modern applications, GPS simply isn’t precise enough to make the grade.
The good news is that GPS can now be corrected to be 100 times more accurate than it is on its own.
What’s Wrong with Your GPS?
Before we get into the shortcomings of GPS, let’s get our terms straight. GPS stands for Global Positioning System. Although often used in the U.S. as a shorthand for any satellite-based navigation system, GPS is only the American constellation of satellites — just one of several satellite constellations around the world, such as Galileo, GLONASS, and Beidou.
Together, these satellite constellations are known as Global Navigation Satellite Systems, or GNSS. Satellites in these arrays transmit signals to GNSS receivers around the world, and the receivers use those signals to determine absolute position.
To properly reflect the worldwide use of this technology going forward, GNSS is the preferred term.
Causes and Consequences of GNSS Errors
So, to reframe the question: What’s wrong with your GNSS?
In short, GNSS signals are subject to several types of interference that make it difficult to achieve extreme precision when solely relying on satellites and receivers. The satellites themselves, while quite precise in their orbits and clock timing, can experience slight drift in both areas, leading to significant discrepancies in geospatial measurements on the ground.
Conditions in the ionosphere and troposphere — two layers of the Earth’s atmosphere — can also create distortions in signals as they are transmitted from satellites, causing measurements to veer even further off course. Finally, ground-level interference from surrounding buildings can deflect signals, adding additional variance to positioning measurements.
Atmospheric interference leads to what are called “ephemeris errors” in positioning measurements. These errors must be corrected to achieve precision. Image: Point One Navigation.
All told, the effect of these various layers of interference can lead to positioning estimates that are several meters off the mark. In applications such as construction, autonomous driving, and robotics, a few meters is more than enough to cause serious problems.
Consider the outcome if, for instance, digging coordinates for a construction site are several meters off of design specifications. Diggers could strike underground utilities, leading to a gas leak or electrical outage, or builders may run into delays or other problems when pouring the foundation for a building. Needless to say, the consequences of imprecise autonomous vehicle coordinates could be even more drastic.
Options for GNSS Correction
With such potential for inaccuracy, GNSS measurements have always required correction. In the past, however, these corrections were highly cost-prohibitive, amounting to $50,000 and up to install site-specific base stations.
Today, companies can leverage several types of GNSS correction technology to achieve measurements that are precise to within a few centimeters or less:
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Precise point positioning (PPP): PPP relies on a collection of precise stations to refine the data from GNSS receivers and correct errors. The results are accurate, but the limited PPP network provides extremely slow signal convergence — leading to convergence delays of 20 minutes or more.
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State space representation (SSR): This newer type of GNSS correction technology allows for the most in-depth analysis of signal data. However, it usually requires specific vendor support to integrate with existing technology, making it a costly option. And often, provider companies will sacrifice accuracy to save bandwidth, base station cost, or both.
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Real-time kinematics (RTK): RTK relies on a network of base stations and correction devices to deliver immediate signal analysis and correction. Because base stations are installed at known fixed positions, rovers, drones, and other devices can check GNSS data against base station position for centimeter-level accuracy.
RTK positioning uses fixed base stations in communication with satellite constellations to achieve centimeter-level accuracy. Image: Point One Navigation.
Dialing in Precision with Real-Time Kinematic (RTK) Positioning
Real-time kinematic positioning dodges the extremes of PPP and SSR technology. With a wide enough network of base stations and correction devices, RTK can provide correction in real time. It also easily integrates with existing technology, making it a cost-effective solution for a wide range of applications.
Even better, RTK corrections are consistently some of the most accurate and reliable available. With sufficient network coverage, it’s possible to achieve near-universal uptime and pinpoint precision of even a few millimeters.
The benefits of such real-time precision are far-reaching for numerous industries and engineering/design applications.
In the aforementioned case of pre-construction digging, companies like Radiodetection are using RTK corrections to pinpoint the location of underground utility lines and other hidden structures. By ensuring digging crews avoid these important structures, Radiodetection helps them avoid costly delays and potential disasters.
RTK proves essential for above-ground applications, too. Civ Robotics, which builds robots for surveying, can accurately survey and mark construction sites up to six times as fast by connecting to a reliable RTK network. When relying on RTK, Civ Robotics also avoids substantial expenses it would otherwise incur for installing its own base stations for corrections.
Civ Robotics Rovers communicate with RTK base stations to create precise survey markings. Image courtesy of Civ Robotics.
Further, RTK can also facilitate precision with autonomous vehicles in everyday applications. For instance, Faction deploys autonomous delivery vehicles — supported by remote human operators — to facilitate last-mile curbside delivery. Its vehicles rely on RTK positioning to place packages within centimeters of their target drop-off points.
This level of precision geospatial positioning can even be applied in autonomous race car driving. Even in an application with virtually no margin for error, RTK technology delivers. Recently, the Indy Autonomous Challenge (IAC) race opted for an RTK location system to guide dozens of self-driving race cars around the track at the Las Vegas Motor Speedway at CES 2024. The cars safely circumnavigated the track driver-free at up to 180 miles per hour.
RTK technology drives accuracy in autonomous race cars at the Indy Autonomous Challenge in Las Vegas. Image: Indy Autonomous Challenge.
Bringing GPS Measurements Into the 21st Century
GPS systems and other GNSS around the globe radically changed life for consumers and businesses alike. Engineers, in particular, have been able to leverage such technology to bring design concepts to life with more precision than ever before.
Yet, the demands of precision are only growing more extreme. As engineers and designers rely more on robots and other autonomous devices to realize their plans, they can no longer lean on uncorrected GNSS signals to ensure precision.
RTK positioning makes it possible to achieve precise correction in real time and without the costly expense of other correction options on the market. It brings GNSS technology decisively out of the past and into the 21st century, enabling designers and engineers to continue building for an exciting future.
