RF & Microwave

Why RTK will be essential GPS tech for precision positioning

15 May 2024
Civ Robotics Rovers can communicate with RTK base stations to ensure precise location for survey markings. Source: Civ Robotics

Precise positioning has never been more important in surveying and other engineering applications. Measurements have always mattered for ensuring on-paper designs can withstand real-world applications. But now, with robots and automation moving into industries like construction, surveying, and damage prevention, precision is critical to job-site success.

Robots are already in use to assist with land surveying and construction planning. Drones and robots — either independently operated or handheld — can be used for in-process assessments of work in progress. Yet, to ensure those applications are effective, we must be sure those robots have accurate positioning measurements.

Technologies like the Global Positioning System (GPS) and other Global Navigation Satellite Systems (GNSS) are setting the stage for achieving high degrees of precision in modern engineering. They’ve been in use for decades now, but on their own, GNSS do not provide the level of accuracy that’s required in today’s projects. Errors in GNSS signals can range up to a few meters, but surveyors require accuracies that are less than 5 centimeters.

The good news is that the technology is already available to enhance the precision of satellite signals. It’s called real-time kinematic (RTK) corrections, and it’s going to play an essential role in tomorrow’s engineering tasks.

Figure 1: RTK positioning technology uses a network of base stations in communication with satellites and rovers to achieve centimeter-level accuracy in geospatial positioning estimates. Source: Point One NavigationFigure 1: RTK positioning technology uses a network of base stations in communication with satellites and rovers to achieve centimeter-level accuracy in geospatial positioning estimates. Source: Point One Navigation

Why uncorrected GNSS falls short for autonomous vehicles, construction and surveying

To better understand the need for RTK, let’s explore a few common use cases for GNSS measurements and how they fall short. This technology is already in use in a wide range of industries, from construction surveying to autonomous vehicles.

For instance, construction firms often rely on satellite signals to verify the coordinates of precise spots for digging or building. Site surveyors check these against building plans and underground utility schematics to verify construction can safely proceed without damaging underground cables and pipelines.

By equipping drones and rovers with GNSS capabilities, these construction firms can automate and/or accelerate the task of surveying, mapping, or construction planning. To do this, the drones need accurate, precise, real-time positioning to within a few centimeters.

However, GNSS signals have inherent error sources, including signal delay due to ionospheric conditions, multi-path errors, clock errors, and satellite ephemeris errors. Until recently, the standard for correcting these errors was for construction companies to install expensive and hard-to-calibrate base stations, eating up valuable technician time. This has made precise positioning a costly and time-consuming endeavor.

At their best, GNSS signals are only accurate to within a meter or two. For a construction or survey drone, being off by 2 meters might mean you build on the wrong side of a property line or damage valuable infrastructure like gas lines or water mains.

Likewise, consider an application like photogrammetry, which uses photography to measure distances and construct detailed maps. Errors in GNSS are often non-homogenous, meaning they will vary in direction and degree across a construction site. Historically, drone pilots have had to install ground control points, a time consuming process similar to base-station installation to provide a reference frame for building maps. Alternatively, they would use computationally intensive post-processing techniques to “stitch” images together with a map. GNSS, with its non-predictable error profile, did not aid in reducing the processing time or setup time for mapping. Getting an accurate location, with little setup would alleviate these problems.

Using a real-time kinematics (RTK) for survey-level precision

RTK, specifically modern RTK Networks, provide the precision required by survey applications without the extensive manpower cost of legacy corrections methods. RTK Networks consist of hundreds or thousands off-base stations, usually installed and maintained by a corrections provider like Point One Navigation. These base stations are precisely surveyed and measure the common sources of GNSS error. They then provide this data over the internet (usually cellular connections) to robots, survey devices, and drones. With a wide enough network of base stations and correctional devices, RTK can provide measurements that are 100 times more accurate than typical stand-alone GNSS measurements — as precise as 1 or 2 centimeters.

For instance, the drone in the above example can connect to an RTK network to verify its positioning for photographs in real time. This enables those drones to create highly accurate maps with far less processing and setup time. Sky Eye Imagery, a U.K.-based aerial photography and surveying company, has used RTK to create maps that are accurate to within 6 millimeters.

Real-time correction capabilities are especially helpful for robotics applications where the devices change locations frequently. Rather than installing its own expensive base stations for GNSS corrections at every location, a company like Civ Robotics can connect its land survey rovers to an existing RTK network to ensure survey accuracy for constructing solar farms and other outdoor projects across the country.

Applications extend well beyond land surveying. Consider a company like Faction, which uses autonomous delivery vehicles with the support of remote human operators to facilitate last-mile curbside delivery. Faction relies on RTK positioning to ensure packages are placed within centimeters of their target location.

Figure 2: Faction’s delivery vehicles rely on Point One’s RTK network to guarantee accurate curbside deliveries. Source: FactionFigure 2: Faction’s delivery vehicles rely on Point One’s RTK network to guarantee accurate curbside deliveries. Source: Faction

RTK can be used to achieve precision in even more demanding autonomous driving situations. Recently, the Indy Autonomous Challenge (IAC) race at the Las Vegas Motor Speedway at CES 2024 chose to use an RTK location system to safely guide dozens of self-driving race cars as they zipped around the track at up to 180 miles per hour.

Figure 3: RTK technology can push the limits of precision demands, ensuring some of the world’s fastest race cars can employ autonomous driving safely and accurately. Source: IACFigure 3: RTK technology can push the limits of precision demands, ensuring some of the world’s fastest race cars can employ autonomous driving safely and accurately. Source: IAC

RTK vs. other GNSS corrections options

As you may know, RTK isn’t the only option on the market for GNSS corrections, but no other method consistently achieves RTK’s level of measurement precision and correctional speed without costly equipment upgrades. The two most common options are as follows:

Precise point positioning (PPP): Thanks to its reliance on a network of highly precise stations, PPP is an accurate alternative to RTK positioning. However, it has significant delays in signal convergence — causing corrections to take at least 20 minutes and often more than an hour. It is not a good solution for any application that requires near-real time corrections data (including robotics).

State space representation (SSR): This is the newest form of GNSS correction technology on the market, and it can provide a detailed analysis of factors that affect signal accuracy. However, most applications call for additional vendor support or service upgrades, making this an expensive option.

In contrast, RTK positioning technology relies on an extensive (and growing) network of correction devices, and it easily integrates into existing tools without the need for expensive upgrades. In other words, only RTK can achieve centimeter-level accuracy in real time and at an affordable price.

The next frontier of geospatial positioning and automation

Thanks to the advent of AI and other advancements in robotics, the field is wide open for using these technologies to accomplish more with less time and effort. From surveying to autonomous racing, the possibilities are nearly limitless.

Yet, using such tools effectively requires extreme levels of precision. GNSS technology gets close to a solution, but it doesn’t go quite far enough.

Not only is RTK technology easy to use, affordable, and widely available, it provides unparalleled levels of precision. With RTK, engineers can step into the next phase of automation with confidence.

About the author

Aaron Nathan, founder and CEO of Point One Navigation, is an entrepreneur and technical leader with over a decade of experience in cutting edge robotics and critical software/hardware development. He has led multi-disciplinary teams building complex systems in financial, defense and enterprise markets and has founded two venture backed startups. He has deep domain experience in sensor fusion, computer vision, navigation and embedded systems, specifically in the context of self-driving vehicles and other robotic applications.

About Point One Navigation

Point One Navigation, headquartered in San Francisco, specializes in building precise location services with accuracy down to a few centimeters at a cost hundreds times less than existing solutions. State of the art sensor fusion techniques and a proprietary network of sensors enable Point One to determine location with unrivaled precision and cost. To learn more about Point One Navigation and its products, visit pointonenav.com.



Powered by CR4, the Engineering Community

Discussion – 0 comments

By posting a comment you confirm that you have read and accept our Posting Rules and Terms of Use.
Engineering Newsletter Signup
Get the GlobalSpec
Stay up to date on:
Features the top stories, latest news, charts, insights and more on the end-to-end electronics value chain.
Advertisement
Weekly Newsletter
Get news, research, and analysis
on the Electronics industry in your
inbox every week - for FREE
Sign up for our FREE eNewsletter
Advertisement
Find Free Electronics Datasheets
Advertisement