Sep 4, 2012
Growers are getting more choices in ag GPS

Most farmers have a basic familiarity with global positioning systems (GPS) technology. In agriculture, GPS is used to plant and harvest crops and increase efficiency. Picking the right system depends on how accurate you want to be.

RTK

The current standard system used by agriculture, land surveying and hydrographic surveying is Real Time Kinematic (RTK), also referred to as carrier-wave enhanced GPS. Using base stations and receivers, RTK is common in planting and harvest machinery because the accuracy levels are sub-inch. There are several manufacturers with systems that work off RTK signals.

“For specialty crops, RTK is the way to go to get that sub-inch accuracy,” said Mike Martinez, solutions market manager for Trimble Navigation Limited’s agriculture division. “The auto-steering options allow growers to plant and harvest without worrying about ruining crops or missing anything.”

One issue with RTK systems has always been price, Martinez said. RTK has been around for 15 years. Back in 2007, it would have cost more than $50,000 to outfit one machine to run off an RTK platform. Now, systems are available in the $15,000 or less range – and they are more reliable, Martinez said.

Specialty crop growers should consider an RTK system for planting and harvest for optimum efficiency, Martinez said. The systems are geared for specialty planting and have trigger systems that tell you the exact moment when to plant a tree or seed.

‘Free’ RTK

There are many states with “built-in” RTK networks already. The technical term for these networks is continuously operating reference stations (CORS). What these networks provide is a free RTK GPS signal. It allows growers to avoid buying expensive base station receivers, which saves them thousands of dollars, Martinez said.

These services are typically “free” except for the cost of the equipment – including modem and cellular data plans, depending on the equipment and the manufacturer. Minnesota runs a full network. For more information about the Minnesota CORS system, click here.

These state-run systems were designed for state governments, but the technology is the same and is there to be used, Martinez said. In all cases, there is no charge for the service, and registration is simple and online. A user still needs hardware to receive the RTK data, which generally happens over the Internet with a modem. In most cases, systems cover the entire state, with the same level of RTK accuracy.

Other states that offer a similar service include Indiana, Wisconsin, West Virginia, Kentucky, Missouri, Ohio, Michigan, North Carolina, Alabama and Iowa. Their CORS systems are offered as a public service for construction contractors and surveyors, also serving as positioning services for both state and local governments. Other uses include zoning and planning, emergency management, asset management, education and engineering.

Going fully cellular

RTK systems require line-of-sight to be accurate and the use of a base station receiver, or CORS access, to obtain the signal. Trimble’s RTX platform uses a cellular-based system that requires less hardware, but doesn’t offer the exact accuracy of RTK, Martinez said.

It used to be that the line-of-sight issue could be overcome with markers and additional base stations, but buying additional markers and base stations adds significantly to the cost of the system, said Brian Stark, a marketing specialist with Trimble. RTX systems operate on cellular and satellite systems. This eliminates issues with distance, trees, hilly areas or other potential obstacles, he said.

The RTX correction service delivers GPS-repeatable navigation that is accurate to 1.5 inches. The signals are fed via satellite, and cellular signals directly to a receiver. It works with the built-in receiver in select Trimble integrated displays, eliminating the need to purchase additional radio hardware or cellular data plans, Stark said.

The key thing with RTX is that growers can use it for activities that don’t require the extreme accuracy of RTK, Martinez said.

By Derrek Sigler, Assistant Editor




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