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, says John Nowatzki, an extension geospatial specialist at
North Dakota State University.
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
autosteer, is connected directly to the steerage mechanism and automatically
steers the rig. 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 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 vs. 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 world-wide.
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
