 |
|
|
|||||
|
|
January 27, 2005
Geospatial Applications: Choosing a GPS Receiver for Mobile Agricultural Applications
How do you decide which Global Positioning System (GPS) receiver to buy for agricultural GPS applications? There are several companies selling GPS receivers and most have several models. One way to help sort through the many selections is to keep in mind the intended uses for the system. The most common farm use is equipment guidance, but there are other GPS applications, such as yield monitoring, variable rate crop input applications, marking field boundaries and identifying soil test locations. Each application requires certain features, so if you intend to use a GPS receiver for more than one purpose, it is important to consider the requirements for each application. GPS is used as a guidance system on tractors and other farm equipment in two ways. One system requires the operator to monitor a position display and manually steer the vehicle, the second system, often called auto-steer, is connected directly to the steerage mechanism and automatically steers the equipment. Both systems require frequent position updates because the vehicle is moving. How often the GPS position is re-calculated is referred to as frequency. A standard measure of frequency is hertz, which means "cycles per second." If the GPS receiver is listed as 5 hertz, it re-calculates its position five times per second. Guidance systems require GPS receivers with at least 5 hertz. If the equipment is used for row-crop planting or cultivation, the GPS receiver may need a higher frequency. The other relevant frequency feature is single verses dual frequency. GPS satellites, called NAVSTAR satellites, continually broadcast on two frequencies. The standard positioning service (SPS) is the standard level of positioning and timing broadcast on one frequency (L1) and is available continuously to any user worldwide. The precise positioning service (PPS) is the most accurate level of positioning and timing broadcast on a second frequency (L2), and also is available continuously, but only to authorized U.S. and foreign governments and eligible civil users. Dual-frequency GPS receivers are more accurate than single-frequency receivers and more suitable to mobile GPS applications. The frequency of position update is not as critical for the other common GPS applications in agriculture, such as yield monitoring and variable rate application. Another factor to consider is the differential correction signal the GPS receiver is capable of receiving. There are several correction signals available, including WAAS, U.S. Coast Guard Beacon, Omnistar and Starfire. GPS receivers capable of receiving more types of correction signals are more versatile. John Deere only makes their Starfire signals available to John Deere GPS receivers. GPS receivers should be capable of connecting to portable computers for real-time geographic information system (GIS) use. GPS receivers connect to portable handheld (PDA) and tablet computers with serial or universal serial bus (USB) connections. Real-time GIS is used for marking field boundaries and other locations. For more information about geospatial technology, go to the North Dakota State University Geospatial Technology Education Web site at http://134.129.78.3/geospatial/default.htm. ### Source: John
Nowatzki, (701) 231-8213, jnowatzk@ndsuext.nodak.edu |
Market Advisor: |
|
North Dakota State University |
