RTN-­101 (Part 16): A Decade of RTN

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"I seldom end up where I wanted to go, but almost always end up where I need to be."
—Douglas Adams

Has it really been ten years? Did RTNs really catch on? Does this RTN thing really work? In answer to all three questions, yes! Network corrected real-time high precision GNSS for surveying (and a great many other uses) has endured for its first full decade. Did RTNs revolutionize surveying and real-time GNSS? Perhaps not as much as how it took the fruits of the real-time kinematic (RTK) revolution and turned it into a reliable and consistent wide area "utility" that has undeniably changed substantial segments of surveying, asset inventory, precision agriculture, construction, and geophysical sciences. Indeed, the term "GPS as a utility" has been attributed to a number of the GNSS pioneers, like Charlie Trimble­—there was even a 1989 book GPS: A Guide to the Next Utility, by Jeff Horn. But who would have envisioned where the technology of RTNs is now, and how widespread RTNs have become worldwide? While this decade has been one of great expansion and refinement of RTNs, there were some folks working the promise of an RTN future in the early 90s.

RTNs have been up and running in the United States for about a decade, and for a few years more in Europe and parts of Asia. It is generally accepted that the first functional network-RTK instances developed were developed by a team from the company Geo++ under the leadership of Dr. Gerhard Wubbena and Andreas Bagge. Around the mid 90s a number of network RTK approaches (like FKP, also known as "area" or "tilt" corrections) were proposed and demonstrated by the team, and many installations have grown from these under the Geo++ name or marketed by third parties. Arguably the most widespread approach to network-RTK has been the non-physical (or virtual) base; most commonly implemented as Trimble’s VRSTM. This was developed by Dr. Herbert Landau of Terrasat (now part of Trimble) in the late 90s with the first installation launched in Germany at the end of the millennium.

The early implementers of RTNs in 2000-2001 included individual states of Germany (which would later form a national network under the cooperative body of SAPOS), Denmark, Switzerland, Scandinavian countries, and the huge Japanese network which was built on a backbone of 1,200 stations originally deployed for plate tectonics studies. Key enabling technologies of the budding RTNs were the availability of cellular-based data streaming for live field connections, and the ever important international data transfer standard called NTRIP, developed by the team of Dr. Georg Weber of the government agency BKG of Germany. NTRIP was developed specifically as a protocol for streaming GPS/GNSS RTCM corrections via the Internet. During the same period of early adopters, an additional network-RTK approach was under development­—master-auxiliary—­which was first productized a few years later by a team developing for Leica led by Dr. Hans-Jürgen Euler. There have been so many dedicated and innovative scientists and engineers involved in developing the engines now utilized by RTNs it would take an entire separate series to acknowledge them all. By 2003, the core approaches and platforms utilized by most of the world’s RTNs were successfully productized, stable, and reliable­but not without significant further improvements along the way.

After a few short years of some brand-driven bickering and posturing over touted advantages and disadvantages of respective approaches, it became evident that none had a magical technological edge over another. Most of the commercial RTN suites used to operate these networks have chosen to provide variations on multiple approaches: non-physical (virtual), master-auxiliary, and even single base if desired. Initial concerns, or even fear, that RTNs or any specific approach may or may not be "legal" never did bear any actually case law and some have concluded that there may have partially been some marketing motivations behind the spread of those fears. The dark days of RTNs appear to be over, and the healthy competition has yielded several great RTN software suites that when operated optimally provide excellent results. Now the focus of the manufacturers is on smooth, robust operations, geodetic management tools, communities of peer operators, and features to accommodate broadening markets—­not just surveying.

RTNs hit North America in early 2002 with a network by the Minnesota Department of Transportation (later to go statewide), and in the fall of the same year in Seattle with what would later become the statewide Washington State Reference Network. The boom continued rapidly with a statewide network in Ohio, and many more, both public and private, mainly in major metropolitan areas around the country. The big developments to come in the years of 2002-2006 were in business and operations models, and RTN-ready base and rover units. As RTNs spread, the manufacturers now offered base units with design features to make them Internet ready, added NTRIP to their data collector software packages, and added communications options for rovers in addition to the traditional radios—like WiFi and Bluetooth­to link through cell modems/phones and peripherals, even built-in modems on some models. The limitations of cellular coverage were met with the development of separate relaying and bridging devices; those that could take corrections from the Internet at the edge of mobile-data coverage and relay a few more miles via radio.

It was no surprise that the early RTNs were mostly developed and driven by surveying interests. Surveyors, who were already used to realizing tremendous cost-benefits from base-rover RTK, could take those savings much further while working more freely without the degradation-over-distance inherent in single-base RTK, plus saving on the equipment and "babysitting" costs of a base unit. Surveying uses for RTNs still yield some of the best immediate returns on investment, depending on the type of work. RTN surveying users have reported savings ranging from 10%-70% over conventional methods for some of the same tasks. But as the use of RTNs has grown among the surveying community where RTNs have been established, the numbers of surveying users can only grow so far. A dilemma many RTN operators have faced is how to grow the market to provide for operations, support, upgrades, and profit (where applicable).

It has become apparent to many involved that RTNs may not necessarily be a cash cow for the network owners/ operators. The surveyor in the field may find the technology quite beneficial as a competitive edge, with clients increasingly demanding more for less. With narrow margins on just how much the user can charge a client, the RTN operator may be limited in just how much they can charge the individual subscriber. This has prompted many to more deeply examine the questions: Who really benefits from the use of an RTN? And how does this drive the various RTN business models? Mostly it is the end client that actually realizes the most savings; they can get a project done faster and with tremendous cost savings for individual elements of the job (such as machine control, some types of staking, topo, grade checking, as-builting). The client gets a lower cost project, but does the surveyor or RTN operator get to keep the difference? Not usually. The cost-benefit model might be different for a larger firm, or a design-build firm, but the challenge for the RTN is how to pass on the cost to those who actually realize the most benefit. In part, this is why some department of transportation,
mining, agriculture, and large utility-run RTN models have been especially successful; they can realize the benefit directly as they are the operator and client. But there has been enough of a growing market for some private and for-profit RTNs to have done quite well in densely populated areas where there are sufficient numbers of surveying/construction interests and with growth or stability in applicable projects. Successful private networks also include those that are offered as an adjunct to equipments sales­"buy a rover and get corrections in the deal"-type models.

Covering a large geographic area like a state or country can prove to be a challenge for a private enterprise unless there is a profitable market across the entire region. Denmark was one whole country that had sufficiently populated "not-so-remote" areas to support an early and rapidly developed nationwide network. In very remote regions, entities like a highway department, a geographic service, or a utility may have the only real stake in putting up bases there. That is why a lot of statewide or nationwide RTNs were often funded public entities. Another model that has been successful are cooperatives, often public/private. In a cooperative model, various entities may be willing to put up bases that other partners would not have even considered. You might see private bases in the cities, and highway/ science/agriculture bases in the rural/ remote areas; but all contributing to a single RTN.

The challenges facing RTNs of various business model types have not stopped RTNs from rapidly filling nearly every cost-effective patch of country; there are fewer and fewer patches left. By 2010 there were about 100 RTNs in the U.S., with about 350 worldwide; there are more than 50 RTNs in China of one brand alone. While there are huge areas of the U.S. without RTN coverage, there is coverage for the areas where a substantial majority of people live and work. The focus on potential markets of the more densely populated areas resulted in some cases of overlapping and competing networks. At one point in time there were as many as five networks on top of each other in the Atlanta area. The numbers of redundant networks have thinned somewhat as different business models were tested.

Why haven’t RTNs completely covered the country? It would not be cost effective as yet. There were several models researched that explored ideas like `piggybacking’ on cellular and broadband communications networks where comms and power would be readily available; that would make sense at first glance. But as specifics were thought through, there were a few impracticalities inherent in such models. Wishful thinkers soon discovered what RTN operators had learned by experience. Designing and building an RTN site is not as simple as sticking an antenna on a tower­—the towers sway too much to maintain the strict relative integrity RTNs require, or present multipath hazards if co-located­—these are just a few of the many RTN design considerations. Those building RTNs around the world have come to very similar conclusions in how to design sites, maintain the geodesy of, and operate networks. An RTN either works well, or it does not meet the standards and precision thresholds end users demand. RTN operators have likened their pool of clients to canaries in a mine—­if the slightest thing goes wrong with the RTN they will hear about it immediately!

There were two schools of thought concerning the design of RTNs and the pace at which an RTN was to be deployed. The first was the "get it done" school—­rapidly deployed, field-fit design, common sense approach, few guidelines; the other school was a more meticulous design with an eye to more uniformity. In practice, there were drawbacks to both; the former would find a few stations that needed redesign after testing, and sometimes the latter approach would crawl or stall. There are situations where anxieties over technical specifications and business models have left some parts of the country without an RTN because the potential infrastructure sponsors or advisors have spent many years analyzing (or in some cases over-analyzing). Towards the latter half of the decade, many RTNs were built or expanded rapidly under the philosophy "Get it built quickly, get people using it, and realize return on investment as soon as possible."

RTN Operators Gather

An overview of the current state of RTNs can be seen by the meetings of RTN operators; a recent gathering was for operators from the Americas was held in Denver in October of 2011. The two-day meeting saw 60+ RTN operators, developers, and support staff share network tips, usage statistics, support issues, and new market ideas and success stories. These types of meetings are held regularly and often by world region, with a recent China-only meeting drawing several hundred attendees. Past meetings, like three regional events held in the summer of 2007, focused mainly on operational training and education; more recent meetings are focusing on new markets and lateral developments like precision agriculture, geophysical sciences, and structural integrity monitoring.

Highlights included a detailed look at usage statistics and market shares of various end use segments from Cansel, operating the 250+ station Can-net RTNs across regions of Canada, and developments in real-time plate tectonics studies by Dr. Tim Melbourne of Central Washington University. Using stunning time-lapse data from the recent Japan quakes, Dr. Melbourne demonstrated how GNSS can provide actual displacements, something that traditional seismic devices cannot. Now, GNSS is viewed as an essential complement for seismology. Precision agriculture interests, while running many clusters of RTK stations and utilizing several satellite-based augmentation systems, are rapidly turning to RTNs. Another rapid rise in usage has come from the asset/resource management/inventory folks (I hesitate to say "GIS" without evoking fears of non-surveyors mapping) but it has not gone unnoticed by these folks in terms of the benefits of higher precision measurements. Perhaps the dreams of "infecting GIS with accuracy" may be partially realized (if managed correctly). High precision structural integrity monitoring, while nothing new, is given a new set of tools for tying to hierarchical external references, something the purely relative, or conventional structural health devices could not really do.

Another recent RTN track at the June 2011 Hexagon Conference in Orlando highlighted the growing model of "hosted" RTNs. Vendors like Leica, with its Smartnet networks, Trimble with its VRS Now, and a similar model underway from Topcon, offer alternatives for developing and accessing RTNs. An entity or group of interested parties may have an array of GNSS stations that could become the backbone of an RTN, or wish to develop such an array, but may not want the overhead of actually running the RTN; the respective vendor can do that for them. Often this involves the vendor hosting the centralized servers, dealing with the customers directly, and collecting the subscriber revenue. There are various ways for the station owners to recover investments, and to use the services themselves. This is an appealing model for many, but there are still many practical, structural, technical, and bureaucratic reasons why many choose to operate standalone RTN.

But how does the end user deal with the many varied RTN models? This is often not an issue for most users as their activities may be limited to one specific geographic area and RTN, but there are potential issues of performance and geodesy across adjoining or overlapping RTNs. The semigovernmental entity of SAPOS in Germany is one model for RTN operator-developed standards and practices exercised across an amalgam of RTNs. In the U.S., the National Geodetic Survey now has RTN guidelines out in draft, and new developments
like OPUS Project are seen as a great tool for RTN operators to keep RTN stations registered to the National Spatial Reference Framework. As the NGS is moving to a purely CORS-based reference framework and a future purely gravity-based vertical datum, the geodetic needs of RTNs and the tools being developed are headed for synchronicity.

But what next for RTNs? Despite the anxieties about crowded spectrum and the jubilation over new constellations and signals, there are not expected to be major changes in the nature of RTNs, and the usage should steadily grow at least for the next decade. That is not to say that new developments might bring centimeter-precision positioning to wider areas, because this idea has been theorized and researched for as long as RTNs have been around. Solutions like PPP (Precise Point Positioning), the darling of the academic positioning crowd, and SSR (States Space Representation, soon to have an RTCM standard), are taking the advances in clock and orbit to new heights. Together with new constellations and signals, PPP and SSR may very well yield instantaneous centimeter positions without a base or network, or at the very least fewer stations needed.

The book on RTNs is not closing anytime soon, and we have only begun to see the full spectrum of RTN-related end uses and innovation. This will be the last entry in the RTN101 series, but far from the end of the RTN story. RTNs have grown and so have the users. Now on to RTN201, RTN301, and …

A 1.445Mb PDF of this article as it appeared in the magazine—complete with images—is available by clicking HERE