Earlier on this week I accepted the challenge of comparing my driving judgement, against the GPS guidance on the tractor.

John Arrell from Progressive Agriculture Solutions provided the GPS kit. The base level GPS unit was fitted to a Case Puma CVX 160. The job of fitting the GPS receiver and display unit was very easy – just locate the power supply and attach the magnetic receiver to the roof. Most tractor roofs are made from composite fibreglass material, so a steel plate must be attached to hold the receiver in place.

The display inside the cab was fixed to the windscreen using a suction cup in the driver’s eye line. The GPS unit is very similar to a standard car system in size and weight. This makes it very easy for the suction to hold it firmly in place while driving. The touchscreen menu is easy to navigate, with just two options on the screen when powered up – option one enter a new field, or option two resume position in the previous field.

Obtaining a signal from just the Egnos satellites was difficult enough near the sheds and trees. Turning on the Glonas satellites increased the number available and a signal was obtained. This is the most annoying aspect – dropping signal and losing coverage. When deciding to invest, try to get a demo from the supplier and really check that the coverage is adequate.

Any GPS system is worthless with poor satellite coverage. Some units will use a patch antenna or a full receiver on the roof. There is no problem with either as long as they can obtain signal.

The result

The task we set out to do was simulating a fertilizer application in a typical grass paddock of about 4 acres. For the test I drove the tractor at 15-metre width and 24-metre width, with and without GPS guidance. The initial drive was made to simulate spreading fertilizer at 15 metres without GPS. After finishing the field, I turned on the GPS and entered the working width at 15 metres. On the first run from the headland along the fence, my judgment was almost the same as the line the GPS was taking me on. That is where the similarities ended, as the further away from the fence I moved the less accurate the driving was. Losing the reference point of the last run in the short grass, I was unable to judge as effectively the working width. This resulted in the errors being compounded as I drove across the field. In one run in the middle of the paddock I was out by 3.5 metres, which is a 23% driving error.

The day was wet and cloudy and the cab was misting up and these are my excuses. The other aspect is that when you enter a field that is unfamiliar to you, it is often quite hard to establish the best way to travel the field. Making out a map with the GPS creating an AB line can often result in fewer passes.

The map data exported using Google Earth overlays my route around the field with no guidance. The areas missed are clear and the areas overlapped are highlighted also.

Not being familiar driving with the GPS guidance, I was a little slow to get going, and followed the LED lights on the display very closely, reacting to every twitch or blink. Driving this way it ends up being a little squiggly down to the end of the field.

As I got used to the guidance in my eye line, the driving became a little less erratic. The light bar will move with the sway on the tractor cab on this entry-level model. More expensive systems will react for the roll of the machine. John Arrell pointed out that if this was a severe problem in a very bumpy field, locating the receiver on the bonnet could reduce the effect of the sway on the receiver. Overall, I was happy that the short test showed I could drive accurately when I could see the reference point. The further away and the wider the spreading width the less accurate I was.

The other advantages of using the GPS was it allowed us to generate a field map, showing the area and coverage. Some systems will allow this data to be exported via an SD card to a computer. This data can then be overlaid on Google Maps or Google Earth to show the field and the coverage.

Also, for simple jobs such as fencing, a straight A and B line could help to keep the fence moving in the right direction.