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January 13, 2005
Geospatial Applications: RTK GPS Differential Correction Services
Global Positioning System (GPS) applications that require consistent accuracy of less than 6 inches in mobile equipment need a commercial connection service. Normal civilian GPS positions are accurate to about 30 feet, and free differential correction services are accurate to approximately 3 feet. To get consistent GPS positions within a few inches, users must subscribe to a commercial GPS differential correction service. Farmers and others who use accurate GPS correction signals use the term RTK when referring to the most accurate GPS correction signals. Real-time Kinematic (RTK) differential correction refers to Global Positioning System (GPS) locations that are accurate to within a few inches. Commercial companies that supply GPS differential correction services often use the terms of centimeter and decimeter (10 centimeters) accuracies. These precise GPS differential correction services are used for agricultural equipment auto-steering systems and can be used for most other GPS applications in agriculture. The highly accurate GPS differential correction services use base stations with known locations to measure GPS position errors and geosynchronous satellites to deliver the corrections to receivers in mobile agriculture equipment. Several nationwide commercial companies sell differential correction services, including Omnistar and John Deere. Both Omnistar and John Deere provide two accuracy levels of GPS differential correction services. Other agricultural equipment companies also provide GPS differential correction services, but they cooperate with Omnistar to supply their services. Omnistar offers OmniSTAR VBS and OmniSTAR HP. OmniSTAR VBS, available for an annual subscription cost of $800, is a “submeter” level of service. OmniSTAR HP service is available for an annual subscription cost of $1,500. It will usually have a horizontal error of less than 15 centimeters. It operates without the need for local base stations. John Deere offers two levels of accuracy available with its StarFire™ GPS system: Starfire 1 and Starfire 2. Starfire 1, available without additional subscription cost to John Deere customers, has an accuracy of 13 inches. Starfire 2, available for an annual subscription cost of $800, is accurate to plus or minus 4 inches. StarFire RTK is designed for use with John Deere GPS equipment. The StarFire RTK system consists of a local base station that transmits corrections to the vehicle StarFire receiver using radios. The StarFire receiver on the RTK-equipped vehicle must have a direct line of sight with the base station to receive the RTK signal. At distances beyond six miles, accuracy and reliability of the signal will be degraded. A repeater is available from John Deere that will extend the base station signal around obstructions such as hills or tree lines. The Rural Tower Network, a regional GPS differential correction service, is available in the Red River Valley area of North Dakota and Minnesota. The Rural Tower Network differential connection service is available for an annul subscription cost of $1,500, plus a one-time fee of $2,500. This service uses a series of local base stations and is accurate to plus or minus 4 inches. ### Source: John
Nowatzki, (701) 231-8213, jnowatzk@ndsuext.nodak.edu |
Market Advisor: |
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North Dakota State University |
