GPS accuracy

[ghand2]

Have been using Oziexplorer on my note book with a with a magnetic base receiver (BU-353) for my touring. I recently used it to make a route around my farm for crop spraying with my tractor & boom spray. Plotted a blank map with parallel lines 12meters apart. After a bit of practise I managed to keep on track reasonably well when spraying.
Does anyone know of a way of increasing the accuracy of this set up.
Geoff.

[windsock]

Have been using Oziexplorer on my note book with a with a magnetic base receiver (BU-353) for my touring. I recently used it to make a route around my farm for crop spraying with my tractor & boom spray. Plotted a blank map with parallel lines 12meters apart. After a bit of practise I managed to keep on track reasonably well when spraying.
Does anyone know of a way of increasing the accuracy of this set up.
Geoff.

I don't know of any direct answer to this relating to GPS but colleagues of mine are involved in university research on Precision Farming. I guess if you google "precision Farming" this may show some pages with inf you are looking for. My understanding is that it involves spraying but also fertiliser application etc. Just a quick search of the uni website revealed these links (http://www.massey.ac.nz/massey/sitemap/search_massey.cfm?q=precision%20farming&cx=007028990505551826392:mqdofac7ule&cof=FORID:9&ie=UTF-8#1102).

On another non-GPS track... I have seen sprayers over here (in NZ) use a foaming tip on the ends of their booms. The foam builds up on the tip over 6-10 metres of distance and then drops to the ground, this leaves blobs of foam on the ground on the outside of the sprayed area. They can then turn around and come back seeing where they have been.

[Bushie]

Pretty sure that any 'precision' work will need the use of an additional GPS signal from a fixed (known location) ground station operating along the lines of differential GPS.


Martyn

[Tombie]

Pretty sure that any 'precision' work will need the use of an additional GPS signal from a fixed (known location) ground station operating along the lines of differential GPS.


Martyn

Exactly what Survey use at the mine.

[KarlB]

We have a few fancy Trimbles at work and the accuracy is under 30 cm but you are talking expensive gear (see GeoXH handheld computers from Trimble Australia (http://www.ferret.com.au/c/Trimble-Australia/GeoXH-handheld-computers-from-Trimble-Australia-n900511) and Hand-held Ranger field computers from Trimble Australia (http://www.ferret.com.au/c/Trimble-Australia/Hand-held-Ranger-field-computers-from-Trimble-Australia-n901818)). Most 'ordinary 'GPS' including those in your iPhone and the like, are reliable to about 10 m. Couple critical issues are repeatability (does the GPS give the same coordinates for the same location every time you use it); and how 'accurate' the ground control, map or plan to which you are cross referencing it to, is. Added to that, obviously the more satellites you pick up the more accurate the output. However, tied with this is that GPSs like Trimbles pick up additional satellites that your normal GPS cannot. Also, the algorithms (programs if you like) that a Trimble would use would be far more complex and require significant addition 'computing power' to undertake the 'calculations'. But back to the original question, rather than a GPS jerry built approach, have a look at this Trimble approach: Spray control systems from Trimble Australia (http://www.ferret.com.au/c/Trimble-Australia/Spray-control-systems-from-Trimble-Australia-n900517) . Would not be cheap, but may achieve what you are seeking.

Cheers
KarlB
:)

[tastrax]

Here is another option and its good for both on the street and in the paddock!

Leica mojoMINI (http://www.ja-gps.com.au/Leica/mojomini-field-street-navigation/)

[LOVEMYRANGIE]

My Garmin Colorado will get 3m radius in standalone or down to 1.5 - 2m with an external antenna.

Try installing the antenna on the roof of the sprayer, will get better reception than being in the cab or on the dash.

[DeanoH]

Pretty sure that any 'precision' work will need the use of an additional GPS signal from a fixed (known location) ground station operating along the lines of differential GPS.


Martyn

I thought differential GPS became obsolete when the Yanks removed the built in inacuracy from the system.

Deano:)

[JDNSW]

I thought differential GPS became obsolete when the Yanks removed the built in inacuracy from the system.

Deano:)

Depends on what you are using it for. For mobile positioning, an accuracy of 6m is routinely achievable without differential positioning, but better than this requires a differential signal. For fixed positions, centimetre accuracy is achievable by recording signals over several hours and post processing without differential GPS. Both these figures assume good satellite geometry and adequate processing power not to have too many shortcuts in the algorithms used.

These are more accurate than most maps.

John

[ghand2]

So greatful for all the useful feedback. Since my original post, I have made a Google satelite map of my farm & callibrated it. The scaling of the map now gives me about 3cm on the screen between my 12 metre rows. After repeated passes on my experimental patch I'm supprised to find the accuracy to be within 1/2 a metre, plenty good enough for my intended use. The advertised accuracy for both the BU353 magnetic base receiver and my NAV 7" GPS is 5 metres. Possibly the fact that I'm driving continuously along a straight route allows the accuracy to average to a higher degree.
The other factor I was considering, the NAV is receiving 11 satelites & my BU353, 10 satelites. Is this the norm? I thought it was a lot less. Love to hear more of your ideas on this, Geoff:)

[Bushwanderer]

Hi Geoff,
I hope that I'm not "teaching my grandmother to suck eggs" with this.

To have any chance of an accurate lat/long & alt. your gps needs to be seeing AT LEAST 4 satellites. Accuracy, in this case will be optimised by having the satellites distributed fairly evenly throughout your sky.

Accuracy is also increased the more satellites the gps "sees".

In your case being able to "see" 10, or more, satellites is great. I suspect that this is partly due to your terrain, which is probably reasonably flat, and with few, if any, trees.

HTH,
Peter

[theresanothersteve]

I think there is a misconception here...

GPS recievers can return a fix from 3 satelitites, but 'guess' the elevation.

To give an accurate fix they require 4.

Ideally the satelites need to be evenly scattered in the sky, the closer the satelites are together, the less accurate the positioning.

More satelites does not mean a more accurate positioning, the GPS unit only uses 4. More satelites increases the likelihood of a more accurate position as it gives the receiver a wider choice of satelites!

GPS units that receive a correction from a ground station broadcasting from a known location are great, except the further you are from the ground station, the less reliable the correction. After a couple of hundred kilometres they are no more accurate than a normal commercial unit.

You either have to spend up big, or put up with accuracy of about +- 10 metres. I reckon I can see what I'm looking for from 10 metres away, so I'm very happy with commercial GPS!

[Bushwanderer]

I think there is a misconception here...

GPS recievers can return a fix from 3 satelitites, but 'guess' the elevation.

In guessing the elevation, they are also, to a certain extent, guessing the lat/long.

To give an accurate fix they require 4.

Isn't that what I said?

Ideally the satelites need to be evenly scattered in the sky, the closer the satelites are together, the less accurate the positioning.

Isn't that what I said?

More satelites does not mean a more accurate positioning, the GPS unit only uses 4. More satelites increases the likelihood of a more accurate position as it gives the receiver a wider choice of satelites!

So, the GPS receiver is using more satellites in order to decide which ones to use at each update.

GPS units that receive a correction from a ground station broadcasting from a known location are great, except the further you are from the ground station, the less reliable the correction. After a couple of hundred kilometres they are no more accurate than a normal commercial unit.

I didn't mention DGPS! It isn't available with his gps receiver.

You either have to spend up big, or put up with accuracy of about +- 10 metres. I reckon I can see what I'm looking for from 10 metres away, so I'm very happy with commercial GPS!

That is the quoted figure, but with increasing Nos. of satellites, it is somewhat less in practice.

...

[theresanothersteve]

I'm sorry you have taken exception to my post and consider me an instant expert.

I have a backgroung in IT training, including the delivery of training courses in GPS to emergency services personnel.

I at no stage refuted what you said, I am trying to point out that GPS only uses 4 satelites, irrespective of howm many the unit can detect. If you read the thread there is a ambiguity about the more satelites the GPS can 'see', the more accurate it is. The inference is that the reciever is using all the satelites.

I like to clear up misconceptions so that everyone is well informed. Information should be shared.

If I have caused you offence, I apologise.

[Aaron IIA]

I have been reading a few of the magazines from the Kondonin Group (farming association). In there, I read of a direct drill seader that was accurately seeding between the previous year's stubble. This was achieving accuracy of around 2~3 cm, although this was with auto steer and using a transponder in the field. Accuracy this great is not needed for spraying. It would be much cheaper to use the foam dollop method described before.

Aaron.

[miky]

...
This was achieving accuracy of around 2~3 cm, although this was with auto steer and using a transponder in the field.
...
Aaron.


Using a transmitter which is transmitting it's know position combined with the data received from the GPS satellite system gives extremely accurate positioning.
This sort of system is readily available for anyone to buy and use.


.

[stuman92]

if you want a good setup for spraying or general navigation, get one of the garmin bluetooth units a laptop, download the latest google earth, sync the gps and conect it on Google earth and walah u have a gps system thats acurate to 1m when your moving, and you have it on a nice map. im a surveyor and we do this at work when mapping out crosscountry piplines its as acurate as you need to be and for $100 is great value for money.