Real-Time Networks – Laying the Fallacies to Rest
By Jesse Kozlowski, PLS, article from Professional Surveyor Magazine • June 2008
 Whether taken by Gunter's chain or the latest RTN technology (shown here by a standard radome often used to cover a network antenna), a surveyor can stand behind his or her measurement. Despite being a relatively new sub-genre of space-based positioning, RTNs are now almost unanimously considered a solid amenity, a new utility, and a reliable tool in the surveyor's kit. They are also ubiquitous—their spread around the globe over the last few years could almost be described as infectious. However, it wasn't always so.
Early implementers of RTN solutions faced considerable opposition for various reasons, including a general lack of understanding of the technology. It took ordinary field surveyors—the best test subjects—to turn negative opinion around. The concept of network-corrected RTK (real-time kinematic) surveying came under fire from the outset. The first academic white papers were met with skepticism, and the developers of early practical implementations and software solutions were criticized by both suspicious late adopters and potential competitors. So, in the late 1990s—the period following initial RTN introduction but before widespread adoption—little authoritative reference material was available to new practitioners, while misinformation abounded. Of the few white papers that were published, and that cited results based on controlled-testing conditions, results seemed too good to be true and/or appeared far out of reach. Sadly, while such published results were oftentimes accurate, it would be several years before RTNs were spread widely enough for independent verification. This combination of lack of information, misinformation, and misunderstanding spawned a number of fallacies about RTNs, fallacies that should be laid to rest once and for all so that they can no longer hamper broader adoption of this valuable new RTK tool.
Which Solution: RTK or RTN?
In the early days of RTNs, many in the industry insisted that a long-baseline RTK solution was the answer, and that RTNs either used "bad math" or were simply unnecessary. However, despite the undeniable value of the iono-free solution, the RTK-only technique remains hampered by its limitations over distance. One will always hear anecdotal evidence of initializations at 20 km, 30 km, or even 200 km, but these achievements are certainly not the rule. The RTN solution is the one that offers greater success over areas encompassing cities, counties, states, or entire countries.
Virtual Reference Stations and Virtual Measurements
Much of the criticism received by early pioneers in RTNs, such as the developers at Trimble Terrasat in Munich, was almost understandable; after all, the results from RTNs did seem too good to be true. At Trimble Terrasat, the Trimble Virtual Reference Station (VRS) solution, which is now the most widely used network correction solution, was introduced to much skepticism due to the term "virtual" in its name. Critics wrongly asserted that the corrections were, in some way, also virtual, and were, in fact, not real.All RTN or RTK solutions model corrections in some manner, either from one or many stations; ultimately the resultant positions are relative to those stations. The term "virtual," in Virtual Reference Station, simply alludes to the development of a network correction customized to the immediate vicinity of the rover, as if there were a base station right next to the user, a solution that is no less real than any other RTN solution.
Triangles and Dubious Mathematics
An unfortunate misconception about the math behind RTNs further stalled their initial adoption. This error arose from the appearance of the RTN operator interface itself.In the software applications used to run RTNs, stations were shown onscreen connected by lines indicating the shortest vectors between them. This onscreen display, which looked like a series of connected triangles, enabled operators to determine the distance between stations, and whether or not each station was part of the RTN solution. However, it led to the mistaken belief that the math behind RTNs simply comprised solutions for the "triangles," and was therefore inaccurate. This belief was profoundly incorrect, but persisted for some time. The actual math has been presented in white papers and at public forums such as The Institute of Navigation (ION). These presentations show that network modeling isn't limited to just three stations; most network models take advantage of many more stations to create wide area coverage.
The Defensibility of RTNs
Surveying history offers many instances of anxiety over nearly every new tool. For example, the use of solar instruments in the laying out of the Public Lands Survey System led to much heated debate in the early 1800s. As recently as the 1960s, when the new tool was the Electronic Distance Meter (EDM), there were many surveyors who refused to "believe" the distances being displayed until they convinced themselves by physically measuring the length with a steel tape. They had to develop their own comfort level with this new technology by "checking" it with an already tried-and-true method. Later on in the early 1990s, as the usage of GPS began to spread, the  Taylor Wiseman &Taylor surveyor Rex Bohn, PLS, using the North Carolina Geodetic Survey RTN to position an aerial control target at Duke University in Raleigh, NC. The full question of how RTN may properly be used for certain tasks, particularly within the realm of cadastral work, has not yet been answered for many, and may never be answered for some. So, the greatest expression of anxiety in regards to RTNs typically comes in the form of the age-old question: Literally, could one defend an RTN solution in court?A surveyor must be able to stand behind his or her measurement, whether that measurement is taken by Gunter's chain, total station, or RTN. And it is the strengths or weaknesses of any tool that dictate the proper procedure for proving its product. A key strength of an RTN is the speed of observation, which enables users to make multiple observations to prove repeatability, and hence defend their measurements and solution.Discussions regarding the defensibility of RTNs typically hold two camps: Those who require documentation of each observation to an exceptional degree, including every element of the RTN and processes used (even the ground and space segments of each observation), and those who use RTN like any other surveying instrument—as a tool to prove positional relativity. The documentation of one's procedures is essential, but there are those who are drafting guidelines or seeking to legislate procedures that would have RTN users documenting volumes of data for each observation, thus negating the cost and time-saving benefits of the tool.
The Geodetic Premium
There are some who believe RTNs could not be properly implemented unless the user has had formal geodesy training. On the contrary, RTNs are predominantly used in non-geodetic applications. However, RTNs do offer significant potential in this area.The geodetic issue can be addressed from a number of angles. Firstly, users of RTNs are typically more concerned with the inverse between two coordinates, or the angle between three, than the absolute position of a point. Of course, they may wish or need to express results relative to a reference framework, or some published values for control, and so to address these requirements users can apply localization. They can then calibrate or adjust measurements to those values. This method follows much the same principle as closing on known marks for traverses or level runs. So, an RTN is more than sufficient for typical applications.Secondly, unlike users, who, as stated, may often not be concerned with absolute values, RTN operators must be very cognizant of the underlying geodesy, especially in areas of tectonic movement, and must constantly monitor the relative positional integrity of the reference stations.Finally, the U.S. National Geodetic Survey (NGS) organization, acknowledging the strength and potential of RTNs, currently has a task group working on guidelines for proper implementation and use in geodesy. This NGS involvement has done much to diffuse the controversy over geodesy and RTN. Similar activities have been taking place around the world for some time, typically wherever RTNs are already fully implemented.
White Papers - Publishing Real Research
White papers are usually published by academia or the scientific community  Photo from the 1960s showing Taylor Wiseman &Taylor surveyors Bob Ballard, instrument
Is an RTN Solution the Only Tool You Need?
The short answer is, no. RTNs are an excellent tool, saving an enormous amount of time, and, of course, cost. However, other tools in the surveyor's kit may occasionally be more appropriate in a given job. For example, RTNs will not replace total stations and will not make monuments obsolete. Additionally, they will not relieve surveyors of the responsibility of following solid surveying practices and independently verifying evidence.Some users have de-scribed RTNs as "magic tape," enabling them to relate two or more positions with great speed, repeatability, and precision, but only if proper procedures are used to "close" on those sets of observations to verify the measurement. However, even with this additional step, RTNs save more than sufficient time to offset the cost of additional gear and independent verification.
Brand Loyalty
Brand loyalty is not necessarily a bad thing. It is inevitable, and fostering loyalty is a good business practice for manufacturers. But, in the case of RTN, such loyalties were sometimes exploited in ways that did great disservice to the subject. Customers who have good success with their gear will very likely choose the same brand in the future. However, RTN is more of a solution than a traditional piece of hardware and software. Forward-thinking manufacturers are moving into more holistic approaches to work processes.The dialogue sometimes became a little too "noisy" and we have just examined several examples of this. Posturing over perceived advantages or disadvantages in particular solutions sounded more like comparisons of hardware features, not as whole solutions. Claims and counterclaims were usually not backed up by any empirical data; head-to-head tests have been few, with fewer still meeting any criteria that would be considered truly controlled conditions. Promoters of particular solutions sometimes spent far more time denigrating a competitor's solution than clearly demonstrating the value of their own. Ironically, most networks provide multiple solutions, including those that may have previously been considered competing solutions.Why have some solutions become more widespread than others? The answer is in proven track records, excellent support, and wide communities of supportive peer networks, i.e., the quality of the whole solution rather than individual features.One operator of a successful RTN in its sixth year of operations put it like this: "At times it seemed like the old Beta-VHS war," alluding to the VCR-tape format battle of the 1980s. "Did it really matter if it was Beta or VHS, or was what really mattered the quality of the movie you watched on it?" What really mattered was the quality of the movie—and where you could get the movie. So too with RTN.
Tried and Tested
Over the last decade, despite many hindrances, RTN technology has proven its worth, and today hundreds of successful networks are installed around the world. Slowly but surely, the noise of doubt and debate is dying down, enabling users to determine, with greater clarity, what employing or operating an RTN has the potential to offer them, and their business. JESSE KOZLOWSKI, PLS, is director of surveying technology at Taylor Wiseman & Taylor in Mount Laurel, NJ. With offices throughout NJ, PA, MD, and NC, Taylor Wiseman & Taylor operates in all surrounding areas. 
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