GPS World • July 2022 • Upgrade Your Survey GNSS

It’s about more than advances in technology — peak times demand peak productivity

Trusty legacy rovers have served surveyors well. Under the right conditions and with proper procedures, a 20-year-old rover might still deliver precisions that could match the latest and greatest.

We’ve become so used to the limitations of legacy gear that we’ve built our workflows, expectations, and job estimates around them. However, in the past few years, the state of GNSS rovers has experienced a sea change, with gains in productivity, the ability to work in mixed environments, ease of use, and increased speed, repeatability and reliability — these developments have come at an opportune time.

Surveying always has been a feast-or-famine prospect; the rises and dips in economics are felt sharply within the profession.

In many places, there is more work than surveyors can accommodate, with competition to recruit and retain enough field personnel to meet demand. It is unclear how long this peak will last. Surveying firms recognize this and do their best to take on as many projects as they can.

Staffing is an acute challenge. Firms have had to dip into incentives beyond the usual pay and benefits packages to attract and retain qualified field personnel. Having the latest gear is a definite plus. Experienced surveyors know much they struggled with legacy gear: GPS-only or GPS + GLONASS only, slow processors, poor multipath performance, and field-data-collector operating systems and software that are obsolete or no longer supported.

Despite the immediate need, it’s generally less desirable to hire people with no surveying experience and train them from scratch. However, newer rovers and field software often do not have the same steep learning curve posed by legacy systems and methods.

It is hard to say how much of the productivity gains, stated by various manufacturers for their newest systems, will be realized for your specific workflows, but simple testing can give you an idea.

When surveyors try out new rovers, they tend to find themselves so impressed by the first unit tried, they conclude it must be “the best” and eschew due diligence in the selection process. That aside, I believe it is safe to say that there is a near across-the-board productivity improvement with the latest generation of rovers.

We haven’t seen such a sea change in GNSS rover technology in decades; most gains have been incremental. Similar jumps in the past included going from the static-only world to real-time and the first additional constellation beyond GPS.

While the early days of GLONASS were rocky, and most manufacturers were hesitant to productize an unreliable and noisy solution, it did eventually improve. The effect of nearly doubling satellites in view translated to productivity gains. But that was two decades ago.

The recent advent of true, multi-constellation GNSS has had a profound impact on the state of rovers. In 2020, both the Galileo and BeiDou constellations reached a full level of global coverage and signal integration.

Many rovers were already equipped to utilize some (but not all) of the newest satellites and signals. Interface control documents (ICD) for some of the signals have only been released by the constellation providers in the past few years. ICDs provide signal specifics that manufacturers need to integrate them into GNSS solutions.

Some rovers (and base receivers) developed four or more years ago may not be able to take advantage of the full complement of signals. And many did not have the processing power to utilize so many signals from so many satellites in real-time solutions.

By contrast, nearly every new GNSS board released in the past few years has greatly increased processing power, often double that of legacy gear.

Newer rovers are able to work better in sky-view-challenged and multipath hazard-prone places than rovers from only a few short years ago. And it is not just about the total number of channels on a rover datasheet, it is about how many are actually being utilized, how much of that data the processors and real-time kinematic (RTK) engine can handle, and how modernized signals are being leveraged.

Modernized signals are yielding additional advantages. The expected benefits of L5 for the GPS constellation have been widely promoted. L5 was designed to be robust enough for certain safety-of-life applications. The L5 signal is being deployed incrementally to the GPS constellation and should be broadcast from 24 satellites by 2027.

I have heard surveyors say they won’t bother upgrading until L5 is complete. But wait — two other constellations already have third-signal capabilities. Indeed, there are 3, 4, 5, even 6 usable signals (in the case of Galileo) already available — modernized, robust signals.

Although L5 will only make this better, you can reap the benefits of signal modernization right now. Some of the innovation put into these modernized signals contributes to reducing certain sources of error. For instance, the Galileo E5a-E5b AltBOC — multiplexing signals in a wide band — is particularly beneficial for dealing with multipath.

Rovers have evolved in other ways besides multi-constellation integration. The decades between these sea changes brought developments such as electronic bubbles, better operating systems, and automation of some functions, but essentially the form factor and functionality of a surveying rover has not changed much. There have been some gadgets and gimmicks along the way, but otherwise rovers had remained pretty much standard in those intervening years.

Real-time precise-point positioning (PPP) has matured to the point that it could be viewed as survey-grade (at least in the horizontal). The delivery of clock, orbit and other data broadcast from geostationary communications satellites (as a service) for PPP means that, for many applications, high-precision positions can be processed by a rover over much of the globe — no base, no radio, no network and no cell phone connection required.

Once research and development removed the lengthy convergence times that plagued legacy PPP, it became commercially viable for many applications. Commercial providers such as Trimble (RTX), Hexagon | Leica (SmartLink), Hemisphere GNSS (Atlas) and others provide subscription services for surveying, construction, agriculture and the growing autonomy market. Most new survey rovers have a PPP option.

Multi-sensor integration, particularly of inertial measurement units (IMU), is becoming standard on new rovers. While there was some value from magnetometer-oriented tilt compensation in the past (though it could be cumbersome and somewhat unreliable), it served as a precursor to modern-day integrated GNSS/IMU no-calibration tilt.

The first no-calibration tilt system hit the market as recently as 2017; now it is hard to find a rover without it. Accessing hard-to-reach points and improved stakeout workflows are some of the benefits of tilt compensation. The development of reliable IMU/GNSS processing was also the key to fully integrating camera-based offset point capture — and soon other sensors such as lidar might be incorporated.

Another set of changes in the high-precision GNSS industry coincided with the above developments, growing a more competitive marketplace. This equates to more choice. The secret sauce of high-precision GNSS is no longer in the hands of the few. The glass floor has been broken, with more rovers than ever available.

The Top End. The manufacturers traditionally considered to be the top end continue to innovate and are usually the first to productize developments such as multi-sensor integration and PPP. They continue to lead in integrated surveying solutions, track record, performance, quality, service, support and peer user networks — which continues to appeal to many users. However, they also have second-tier offerings to suit various markets, regions and value propositions.

Whether to Use OEM Devices. For many users, there are compelling reasons to stick with top-end solutions, but there always has been room for other price point options. Until recently, most lesser-known rover brands exclusively integrated GNSS boards from a handful of well-known original equipment manufacturers (OEMs) such as Trimble and NovAtel. Sometimes new developments hit the OEM market quite rapidly — for instance, IMU integration. These third-party manufacturers may add their own touches, but in effect, nearly every rover out there offered a narrow set of DNA — until recently.

Rolling Their Own. Globally, technical universities are graduating GNSS engineers at an unprecedented rate; the prospect of mass applications such as vehicular autonomy and robotics are driving demand. With this expanding pool of engineers, it is now much more practical to develop GNSS solutions from scratch and to fully leverage multiple constellations.

Some third-party manufacturers began working with OEMs but have started developing their own boards and related technologies. I’ve tried several, and performance is, in most cases, as good as that of new boards from traditional sources..

The Rise of Mid-Price Rovers. There are a growing number of breakout rovers from lesser-known brands or rebranded models. These are about half the price of some of the top-end models, yet performance is in most cases nearly par. Some include OEM boards, or the new wave of independent boards.

I’ve seen a sharp rise in the popularity of mid-level rovers among small and mid-sized firms. However, there has not been a corresponding drop in sales of top-end rovers. It seems that surveyors are simply buying more rovers during this peak time.

Receivers-as-a-Service. Another approach for surveying and asset-mapping rovers is pay-as-you-go. This means you do not have to make large up-front investments in hardware. Instead, you pay for high-precision capabilities through subscriptions or tokens when you need it. This can be a good choice for occasional or seasonal users.

One example is Trimble’s Catalyst system. For Catalyst, the hardware investment is an inexpensive antenna, and then you access a subscription service via your mobile field data collector, tablet or smartphone to activate the software-defined receiver (SDR).

Another such model is Flex. With Flex, you have the option to pay full price for the full receiver/antenna to operate as a conventional rover. Alternatively, you can choose to pay a lower up-front price for the rover and use tokens to activate the high-precision capabilities.

Low-Priced Rovers. Two external factors have fostered a mini boom in low-cost rovers: R&D for mass markets such as autonomy, and RTK/post-processed kinematic (PPK) solutions for drones, which are often used to reduce the need to set ground control points.

In both segments, inexpensive and often small GNSS boards have been developed. For drone applications where a base was needed for RTK/PPK methods, developers sometimes took the same GNSS board in the drone and packaged it as a base. It did not take long for some of these developers to package the rover for surveying or asset mapping (with geographic information system, or GIS).

While these rovers can perform just as well as top-end or mid-priced rovers in optimal conditions, they may struggle in mixed environments. I’ve tried some, and I can see why every surveyor I’ve asked about performance adds “for the price” to their assessment.

Other developers have taken this a step further, selling a bare-bones rover for less than $1,000, though these can take a lot of tinkering and extra attention to fit into a production workflow. There are even folks creating do-it-yourself rovers. I am not seeing many large firms, who have high-ticket projects and need to conduct integrated surveying, opting for lower priced systems.

We are riding a new wave of GNSS rovers, awash with more choices than ever. In this period of increased demand for surveying services, it might be a great time to upgrade and boost productivity.

Industry Insights

GNSS executives told Gavin Schrock about recent developments in their companies.

NEIL GEREIN, Senior Director of Marketing, Autonomy & Positioning Division, Hexagon

As satellite constellations were modernized, GNSS receivers kept pace to offer multi-constellation and multi-frequency capabilities to culminate in the latest technologies in PPP corrections.

For example, Hexagon’s RTK From the Sky technology is able to achieve highly available corrections with centimeter-level accuracy globally. However, modern GNSS receivers also offer other benefits, such as interference mitigation and spoofing detection for improved positioning robustness, multipath mitigation, and more powerful sensor fusion.

MILES WARE, Vice President, Marketing & Global Customer Care, Hemisphere GNSS

Much like the constantly evolving world of smartphones, tablets, and computers, the improvements in multi-constellation GNSS receiver performance have been significant, even over just the past few years.

Many legacy rovers, bases and reference stations that are older than four years cannot track some of the newest signals, such as from BeiDou Phase 3 satellites. This means some of the highest performing signals available are now accessible to many users. As fewer BeiDou Phase 2 satellites continue to transmit, many legacy receivers will no longer have the performance they once did.

With upcoming services such as OSNMA (the Galileo GNSS data authentication service) and global PPP signals, many receivers from a few years ago do not have the CPU capacity to employ them. Today’s GNSS engines track more satellites, more signals per satellite, and have more CPU to perform advanced operations, all while consuming the same or less power than previous generations.

The latest GNSS RTK rover technology evolutions are based on the maturity and enhancement of satellite navigation systems, as well as the integration of IMU sensors into the receivers.

The most recent generation of our GNSS rovers, such as the CHCNAV i83, is based on the sophisticated iStar algorithm that significantly improves the efficiency of GNSS satellite signals tracking for unmatched performance in GPS, GLONASS, BeiDou, Galileo and QZSS constellations, utilizing all available frequencies, including BeiDou 3.

Moreover, the fusion of GNSS and IMU technologies enables centimeter-level positioning, maintains fixed and reliable RTK accuracy, and collects points faster than ever before, even in challenging conditions. GNSS survey productivity is increased by up to 30%, and the user base expands from experienced users to new users such as construction site foremen.

New Players

A “roll your own” example is Tersus GNSS, which has designed and manufactured in-house GNSS boards and RTK engines since its inception in 2014. I asked Winston Wen, founder and CEO of Tersus, why they chose this strategy.

“I’m a hardware guy; electronics, computer science, signal processing, etc.,” Wen said. “In 2014, I took a look at the price and portfolios for high-precision, and for equipment for surveyors — the price point looked exceptionally high. From my point of view, it looked like there was room for a new player, and I felt we could do better. There are also growing markets for applications for high-precision GNSS, such as the internet of things (IoT) and autonomy.”

Tersus has experienced solid reception for its products globally. I asked Wen if he felt GNSS for surveying has reached a new level of performance. “Yes, nowadays with 50 satellites, that is huge. Surveyors will be very happy with performance, especially in environments with limited sky view. At this time, there don’t appear to be any new signals announced, so rovers bought today should be top performers to, say, 2025 and beyond.”

GAVIN SCHROCK, PLS, is a practicing land surveyor, the operator of a cooperative real-time GNSS network in Washington state, and a technology writer.