GPS steering and guidance equipment companies and their dealers have been on a building spree of real-time kinematic (RTK) networks in recent years.

State transportation departments also have built statewide RTK networks. Although designed primarily to assist with surveying, these networks can be used to provide RTK signal corrections to mobile users, including those in agriculture.

Both trends significantly reduce the cost of adopting RTK steering. Private RTK networks typically charge a $1,200 to $1,500 annual fee, or a one-time charge of $3,500 to $4,000.

The statewide Department of Transportation (DOT) networks have an even more attractive price. Corrections are free via the Internet, at least at this point. However, users must pay the cost of receiving corrections through commercial cellular communications networks.

If you farm in a sweet spot that has a public or private RTK network, you can take the leap to sub-inch-accuracy RTK steering for far less money than paid by early RTK adopters. Typically, they faced costs of $30,000 or more for a basic system, including a single base station. Today, your out-of-pocket cost could be about half that amount, or possibly less, if an RTK network exists in your area.

Expanded dealer networks

Over the past few years, the three main RTK network systems — which support guidance systems from AutoFarm, John Deere and Trimble — each have expanded to cover 100 to 150 million acres across the U.S., the companies say. Many of those acres are in the heart of the Corn Belt, and in some areas, the companies compete with each other for RTK customers.

Because the radios used by the various networks use unique communications protocols, each of the networks stands alone, even though they share the same towers, in some instances. Although it is technically possible in some cases to marry a radio from RTK Network X to drive a steering system from Company Y, it's rarely done.

Deere and its dealers may have been on the biggest network building binge over the past couple of years. Starting from practically zilch across the Corn Belt two years ago, the Deere network now encompasses 45 million acres in Iowa, Illinois, Indiana, southern Minnesota and northern Ohio, says Jason Beuligmann, John Deere Ag Management Solutions RTK network specialist.

Across the Cotton Belt, Deere networks cover another 50 million acres, with another 35 million acres of coverage in California and other geographies where specialty crops are important.

“Many of our customers in the past few years have started asking for RTK,” Beuligmann explains. “They need the higher accuracy for new cropping practices that help reduce input costs, such as controlled traffic and strip tillage.”

Trimble and AutoFarm also report major growth in their networks in recent years. “Worldwide, we have gone from networks covering 20 million acres to 130 million acres in the past three years,” says John Bressler, Trimble's senior product manager for RTK networks and base stations. All but 10 to 15 million acres of network coverage are in the U.S.

“Trimble networks cover a lot of Iowa, Illinois, Nebraska and Kansas,” he continues. “Networks in Illinois, Indiana and Iowa are growing fast. In Iowa, we have a good portion of the state covered already. Our dealers have plans to cover the entire state.”

Across the U.S., AutoFarm networks now cover 125 million acres, according to Wade Stewart, RTK field marketing manager for AutoFarm. “Interest in RTK is expanding at a phenomenal rate,” he says. “In the last year, we have doubled the number of acres covered.”

AutoFarm and its dealer network have set up and expanded RTK networks in several Midwest states. A large network in Illinois and Indiana, for example, now includes 160 towers and is expanding at a rate of 50 towers or more a year.

Given the gusto of network expansion in recent years, growth is likely to slow in the future, RTK company officials say. “I think we will see some additions to networks to fill in gaps,” Beuligmann says. “I don't think it will be at the same pace as the past year and a half.”

DOT networks level the field

Although the proliferation of private RTK networks has brought down the out-of-pocket cost of adopting guidance systems with sub-inch accuracy, it also has given the major network providers a leg up on competitive guidance companies that don't have a network available in a specific geography.

Even companies that have extensive RTK networks feel an extra challenge in areas where competitors dominate. “Going into areas where Deere or Trimble have tremendous market share, it's hard to compete there,” says Stewart of AutoFarm. “If I don't have a network there today, it is hard to get started.”

However, RTK networks operated by state transportation departments could level the playing field, says John Hill, global business director for Leica Geosystems.

Leica, an international guidance systems powerhouse, joined the competitive U.S. ag guidance fray in 2007 when it introduced its mojoRTK system. The company also is supplying the technology being installed in the Iowa DOT's new statewide RTK network. (Trimble and Topcon Positioning Systems also manufacture survey-grade RTK equipment used in state and regional RTK networks.)

“We are rapidly building out RTK networks, but not the same way the competition is,” Hill says. “These DOT networks are highly funded, mission-critical networks. Most of the DOTs [with RTK networks] in the U.S. offer the service for free. My question is, How will the [proprietary] networks compete with free?”

DOT networks free

Despite being free, the DOT networks have been largely under the radar among mobile users, including those in agriculture. Private surveyors have quickly latched on to the new tool as the networks have been built out. The DOTs themselves use the networks heavily for the surveying of transportation systems.

In the Midwest, statewide DOT networks are currently in place in Michigan, Minnesota and Ohio. Iowa will join the list by the end of 2008. Other statewide networks are in the works, including one in Indiana.

Farmers' interest in using existing systems has been modest, according to system administrators in Michigan, Minnesota and Ohio, who note that they have not aggressively sought users outside their traditional surveyor base. For example, in Michigan, only one farmer has inquired about using the > system, which the state began expanding in 2000, says system administrator Andrew Semenchuk.

“We would like to get the news out to farmers,” he says. “It is a public utility that is free. It is theirs for the using.”

In Iowa, where the RTK network has been publicized, interest among farmers has been higher. “We have been getting a lot of e-mails from farmers and agricultural suppliers,” notes Steve Milligan, coordinator of the Iowa DOT RTK network.

Up to the task?

State DOTs across the U.S. began constructing regional and statewide RTK networks in 2000. The primary goal was to improve surveying accuracy and efficiency as they managed road and other transportation construction projects.

The technologies and processes that the networks use to generate corrections vary, depending on whose equipment they use. Corrections typically provide accuracy to a radius of an inch or less, comparable to accuracies of dedicated agricultural RTK networks.

In general, they rely upon fixed RTK base stations, which are placed at relatively wide intervals of about every 30 miles. That compares to the six-mile grid typical of dedicated agricultural networks. The DOT base stations feed positional data into central computers, which use software to compute refined corrections before data are streamed to the Internet. This differs from dedicated ag RTK networks, where RTK base stations broadcast correction data directly to users and base stations typically are not linked through a computer network.

Some experts question whether the technologies used by some DOT networks are capable of providing correction signals reliably 24 hours a day, seven days a week.

“When you are controlling a machine, you are affected by latency [delays] in the Internet, as well as questions about cellular coverage,” says Bressler of Trimble, whose equipment is used in the Minnesota and Ohio DOT networks. “It is very effective for surveying but not as effective for machine control.”

But Leica's Hill says technologies used in newer DOT networks have eliminated latency as a practical concern. “This has been proven in 24/7 machine autosteer by our testing, as well as others,” he says.

Another concern is that DOT networks generally do not provide 24/7 network support, raising questions about downtime in off hours. The Minnesota system, for example, has technical support available only during normal working hours. However, the administrators say their system has a strong track record of being up and running more than 99% of the time.

In general, the systems have redundant backup server computers to reduce the chance of shutting down.

Proven in the field

After testing the Minnesota DOT RTK network last year, Dave Lagerstedt of GPS Services in Adams, MN, now works with 15 ag customers. “Our customers are very pleased with it,” he says. “If we have any issues at all, it is with the cell phone providers.”

Even cell phone problems have been relatively minor. In most instances, customers have required only external antennas to get a reliable cell signal, even in bluff terrain.

“We use an external antenna most of the time,” Lagerstedt says. “In some areas, we also use a booster [amplifier]” to improve the signal. Data transmission often continues even where voice calls tend to drop. (For more information about improving cellular communications signals with antennas and amplifiers, see “Wireless farm,” August 2008, page 31.)

Customers access corrections with a “smart” cell phone (the HTC 6800 is the company's preferred model). The cell phone relays signals to GPS controllers via Bluetooth wireless and software from InTime (www.gointime.com) for a package price of $4,400, excluding the phone.

Accessing DOT networks

Not all RTK guidance systems can use DOT RTK corrections, but most can, Lagerstedt says. Deere systems currently cannot use DOT RTK corrections because the company uses a proprietary communications protocol, says Beuligmann of Deere. But the company is looking into adding that capability.

Leica plans to add, to its mojoRTK product line, the ability to access DOT RTK corrections without an external modem or cell phone. Current survey-grade RTK receivers from Leica, Trimble and others typically have this capability.

For information about RTK networks in Michigan, visit www.mdotcors.org and click on RTK User Agreement. In Minnesota, go to www.olmweb.dot.state.mn.us/CORS.GPS/cors.html. In Ohio, send an e-mail to aerial@dot.state.oh.us or call the survey operations manager at aaaaaaaaaaaa614/275-1359a. Information about the Iowa DOT network is available at www.dot.state.ia.us/rtn.

Additional regional public and private surveying-based RTK networks also have been built in the Midwest. Individual locations and operators of these RTK base stations are listed on a Web site of the National Geodetic Survey (NGS), an arm of the National Oceanic and Atmospheric Administration (www.ngs.noaa.gov/CORS/sort_sites).

NGS coordinates a cooperative network of these stations, which it calls Continuously Operating Reference Stations (CORS). Additional information can be found by searching for “CORS RTK” with a Web search engine.