How to choose farm GPS receiver?

Don’t overspend on a GPS receiver with accuracy you don’t need

If you are considering to purchase a farm GPS system, you will confront with the notion of accuracy. There is a clear relationship between the precision of GPS receiver and how expensive it is. What level of GPS accuracy is sufficient for you? Do you need to pay extra for a very precise antenna? These are the questions we try to answer in this article.

I have 10-year experience in agricultural technologies. Our mobile app – eFarmer has been downloaded by more than 85,000 farmers from around the world. I love to meet and communicate with our customers. Asking how they use the app. Therefore, all the following information and recommendations are based on my experience as a technical engineer and the experience of our community of eFarmers.

What does “accuracy” mean

First, let’s deal with the very concept of “accuracy”. It can be absolute and relative.

accuracy_precisionen

Absolute accuracy means that if you specify your location, you will be able to return to this point in a day, month, year, with the level of accuracy that is listed in the technical characteristics of the receiver, for example – 4cm – 50cm – 1m. This is why absolute accuracy characteristics explain the applicability of a GPS receiver for geodesy work.

Relative or pass-2-pass accuracy shows how position deviates from a specific location if one comes back to it in 10, 20, 40min. This is what we need in farming when accuracy is important within one day and allows you to make parallel rows.

Why does it Vary?

Now when we have clarified the concept of the accuracy itself, let’s look at what does it depend upon:

  • Receiver type: GPS of your smartphone, outdoor GPS tracker, an external smart antenna, RTK external antenna.
  • Signal quality: obstacles, accessibility of corrections (DGPS), proper installation of the antenna.

Types of GPS

GPS of Your Smartphone or Tablet

  • Absolute accuracy: 2-20 m
  • Pass-2-pass accuracy: 1-3 m
  • Popular models: Samsung Galaxy S, Samsung Tab.
ark5_framedSmartphone with internal GPS

For area measurement. It is suitable for measuring the area of a field. If you hold a tablet or a smartphone in your arms in open air you can achieve the optimal level of reception of satellite signal.

For parallel driving. It is not suitable for reliable driving, our customers use it when driving in Skip and Fill driving pattern and tracking covered area.

For field notes. Suitable for soil sampling, to mark places of loading and unloading of materials, points of entry into the field.

External GPS Tracker

  • Absolute accuracy: 2-20 m
  • Pass-2-pass accuracy: 50cm to 2 meters
  • Popular models: Garmin GLO, Quartz 818
garminGPS Tracker

This unit has the same accuracy as the built-in receiver of your smartphone/tablet. But it benefits from the fact that you can install it in a more suitable location and get better reception. For example, on tractor roof, hood or on a mast.

For area measurement. With a tracker, you measure field area more accurately. It is important to understand that this type of measurement can be used for mapping fields, but can’t be used for exact calculation or map position because of low absolute accuracy. (eg your field boundary may be shifted to a road).

For parallel driving. You can use it for spraying operations with implement width of 11 meters and more. Work at night and fog is now possible.

For field notes. To indicate the position of a stop / pause of work,  points of entry into the field, mark obstacles.

Transport operations. The tracker is suitable for tracking routes such as field – warehouse.

Smart Antenna

  • Absolute accuracy: 1.5 m
  • Pass-2-pass accuracy: 20-50 cm
  • Popular models: Novatel AG Star, Novatel Smart 6, Hemisphere, Trimble, StarFire and a new antenna from eFarmer
360-smart-ag-1GPS Smart Antenna

These instruments deliver relatively high accuracy of 20 cm, which will enable you to perform precise operations and measurements.

Measurement of field boundaries. Due to the high relative accuracy, you can measure the area of the field with high precision, but because of the low absolute accuracy, you cannot use it for compliance with government regulations and resolving issues with your neighbours.

For parallel driving. Particularly comfortable to work on spraying operations without tramlines, because it is possible to achieve minimal overlap between passes.You could work in fog and at night.

For field notes. To mark places, such as end/start points, to add location to your scouting photos, obstacles, entry to the field and storage, obstacles, garage, home and etc. It can help to find bearings in the field, particularly if you do not know where your next assignment is, or if the orientation is obstructed by the crop.

Transport operations. Suitable for route tracking. eg. Field-Warehouse-Elevator

RTK external antenna

  • Absolute accuracy: 1 cm
  • Pass-2-pass accuracy: 1 cm
  • Popular models: Novatel Smart 6L RTK option, Hemisphere and a new antenna from eFarmer
tractor_rtk_RTK Base Station

Measurement of field boundaries. With this antenna, you will be able to measure areas with 1 cm accuracy. Due to high absolute accuracy, these antennae can be used for the construction work, or very precise measurement of boundaries, eg. for rented fields.

For parallel driving. High-precision antenna can help you with precise sowing, weeding, harvesting and other operations in narrow rows.

This level of precision enables GPS receiver to be used with the auto steer and autopilots. With such accuracy there are, of course, additional sources of error, such as the shaking and slope of the cabin may result in a deviation of 10-50 cm.

For field notes. To mark places, such as end/start points, to add location to your scouting photos, obstacles, entry to the field and storage, obstacles, garage, home and etc. It can help to find bearings in the field, particularly if you do not know where your next assignment is, or if the orientation is obstructed by the crop.

Transportation. This accuracy enables you to track the route with centimetre precision. However,  it is unlikely such precision is needed on the road, it’s like a microscope to hammer nails. But it can be suitable for truck and tractor operations performed near combine.

Signal Quality

We have look at the various types of receivers and their projected accuracy. Now it is very important to understand that the GPS receiver is alike FM radio receiver. But unlike sound, GPS receiver converts radio signal to location coordinates.

The noise in a radio receiver is the same as the scattering of location points in determining GPS position. Therefore, the quality of signal can significantly affect the accuracy of the GPS system. And it depends upon:

  • Proper antenna installation;
  • Obstacles and weather conditions.

To achieve high-quality signal, GPS antenna should be installed on the roof of the cabin in open air. The best position is the intersection of the rear axis of the wheels and the axis of movement.

Also, the following factors can lower the accuracy of the signal: – bad weather conditions, trees, buildings, high-voltage lines and other obstacles. Receivers that support multiple positioning systems (Galileo, GPS, GLONASS and BieDou) are more stable.

tractorgps-_page_3
The best possible mounting position

This overview should help you understand that all receivers can be used for certain types of operations. Your choice will depend on your goals, what exactly you want: to save materials,  to carry out a professional job or to increase your comfort.

One of the biggest advantages of eFarmer’ equipment, is that it is modular. You can start with a simple antenna with 20-50 cm, to see how it works in your field and what precision it gives in your specific conditions. And if you are not satisfied with the result, you can purchase a base station, and get the super accuracy of 0-4 cm. Further, you can equip tractor with the auto-steer system that uses the same antenna.

If you read our blogs – please let us know. We will be very glad to see your comments under this post. What questions do you still have about GPS systems?
We will be glad to share our knowledge with you.

Yours faithfully,

Alexey Bogatyrev

CTO eFarmer

4 Response Comments

  • Peter HolscherDecember 6, 2016 at 6:20 pm

    Hi Alexey.
    Can I connect the gps smart antenna to a smart phone or tablet or does it work via bluetooth?
    What will the smart antenna cost?

    Regards
    Peter (South Africa)

    Reply
  • MarkDecember 6, 2016 at 8:44 pm

    Hi Alexei, when will your new antenna be avaliable to buy?

    Reply
  • OscarFebruary 1, 2017 at 11:47 pm

    Hi any auto-steer system can work with your antenna. Let me know the price.
    Thank’s

    Reply
  • JackMarch 13, 2017 at 11:41 am

    Hi
    I must buy the atenna and the base station for best results

    Reply

Leave A Comment

Please enter your name. Please enter an valid email address. Please enter message.