Accuracy Versus Cost

When purchasing a GPS receiver, one of the most important requirements you'll need to consider is accuracy. The accuracy of the receiver has the greatest impact on its cost. There are fundamental differences—both in cost and design—between a GPS receiver that's accurate to a few feet, and a GPS receiver that's accurate to a few inches.

Differential Corrections

The next thing to think about is the source of differential corrections. The intentional random error that the Department of Defense (DoD) had introduced into the GPS system, called Selective Availability (SA) was removed on 1st May 2000. Without correction, GPS positions are accurate to approximately 30 feet (10 meters). This may be accurate enough for some applications but not for others (e.g., precision guidance). Fortunately, there are a number of ways to obtain differential corrections that will improve receiver accuracy to meet your needs. These sources include DGPS radiobeacons, commercial satellite differential service providers (Omnistar and Racal), and the Wide Area Augmentation System (WAAS) (becoming fully operational in the U.S. in the year 2002). Many receivers are designed to use only one correction option. Others, such as Trimble's AgGPS® 132, allow you to choose the source of differential corrections. Make sure the receiver you choose can provide the accuracy you need and use the correction sources available in your area.

Compatibility

System compatibility with other precision agriculture equipment is also very important. Two questions you should ask are:

1. Does the receiver have enough ports to connect to your equipment?
2. Can the GPS receiver output data in a format that your other equipment can use?

Some receivers have only one port, while others have two. Most receivers use the NMEA format to communicate with other equipment. Data output from Trimble AgGPS receivers is easy to configure for communication with almost any system.

Reliability

Another important consideration when choosing a GPS receiver is its ability to withstand the rigors of agriculture. Field work is rough on electronic equipment. So, you'll want to make sure the receiver you choose is field reliable and won't break in harsh conditions—like high vibration, extreme heat or cold, dust or moisture. Trimble AgGPS receivers are designed for the extremes of field work. They are rugged and won't break when the going gets tough.

Conclusion

Obviously, there's a lot more than this to think about when buying a GPS receiver. But hopefully, the information here will help you choose the best GPS receiver for your agribusiness.