Verify GPS accuracy


I have been trying to import a spotspray map in an amazone sprayer. It wouldn’t load the typical prescription map. So I tried a different approach where I export the file as an annotation and load it in the sprayer a a field boundary. so it 'only sprays within the field boundary’s. its not the way to go but it works. But when we tried to use spot spray today for the first real test we found out it has an offset somehow. The spray does turn the sections on and off at the right time. but not In the right place. it turns off the nozzles 1 meter besides the place its supposed to. Is there any way to confirm the gps coordinates from the annotation. I want to see if there’s a problem with the sprayer or the annotation.


Hi Dennis,

can you tell us the exact configuration of your tractor, terminal and sprayer? Not all terminals are capable of reading prescription maps, and some only work with boundary files as you described.

Did you fly the mission to create your spot spraying map with RTK? Did the tractor use the same RTK as the mapping drone?


The field was flown with mavic 3 multispectral with dji d-rtk stick. The sprayer is an amazone with amapad1 that gets its signal from an external gps system. The gps is an rtk enabled sbg geostar 200 screen which sends its signal to the amapad. I will check if the gps on the sprayer is incorrect. But I would like to also check if the prescription coordinates are correct. I thought maybe there is a way to use the rtk stick to import a certain coordinate to check.

Thats where I see the problem the drone and the tractor have different RTK corrections. Its better to use the same for both system, for example like the SAPOS (Germany) mobile RTK correction signal.

To check the accurcay of the map you would need an external rover, and measure in some GCPs with with the Coordinate Reference System (CRS) the Tractor is working in. So even if you map is accurate, if you tractor assumes a different CRS there will be an offset.

For example in agriculture most systems assume coordinates to be in WGS84. But in reality RTK corrections and surveys are done in ETRS89 (European Terrestrial Reference System 1989) in Germany/Europe. Between WGS84 and ETRS89 there is a slight shift. This not a problem when all system are working with the same RTK corrections, as than the error cancles out. But if the drone is using WGS84 and the tractor something different or vice versa it can become a problem.

Also I am sceptical of the DJI D-RTK Station, as this provides relative accuracy towards the station but not absolute global accuracy in my perspective ( I may be wrong though).

To mak eit short, best would be the use of mobile RTK like SAPOS on both systems drone and tractor.

Hey Julius, do you know if I can configure my John Deere RTK beacon to any base station I choose? They run on John Deere base stations here in Australia and while it would be much better to have my DJI drone run off the John Deere station which our tractors do, I don’t think Mr Deere would give me the login credentials even if I asked nicely. At the very least they would want more money on top of what we already pay for RTK capability’s.
I have been going fine with hitting my intended weed targets but if I can do something better I will.

Yes, you are right! Best would be if Deere would allow the drones to access thier corrections, but thats not on the horizon so far.

You can configure your Starfire/Greenstar Display to use a mobile NTRIP correction signal, if you have a mobile MTG I think.

I only found a video in german where that is shown.

Thanks Julius, I don’t have that menu on my screen. I’m thinking it may require a paid activation to be able to do this after some research. Not surprised, John Deere love to empty our pockets every way they can

How big is the delay/accuracy for you, hitting your targets currently?

It’s hard to tell how accurate it is precisely. I’m hitting the weeds and have seen high kill rates in paddocks I’ve spayed a few weeks ago now. Once you guys create the buffer zone around the grid cells it won’t be much of an issue. Centimetres off won’t be an issue it’s really when you get into feet I see it being a problem personally.

I have the same problem, my maps can be out by up to 2 meters when I load them onto our Deere sprayer. And we don’t have access to Deere’s Mobile RTK in Australia unfortunately so that’s not an option here. The only solution I have found it to use QGIS to move the entire map to line up with a known point in the field. It’s time consuming and takes a bit of trial and error but it works.

Hi Micheal your known point on the map is measured how, because I assume that for the reference of that point you also had no access to the JD RTK. So I don’t understand how this could be a solution it rather indicates to me that your data is of in the first place. Can you share more details?

By known point I mean I placed a marker in the paddock before I map it. I line the sprayer up with the marker later on to check the map is accurate.

So I place a marker, map the paddock using PPK, send the ortho + operations map to QGIS, draw a cross where the marker is on the ortho and merge this with the operations map. If the cross lines up with the marker in the field then I know for sure it’s going to work.

In the past I have checked the accuracy of the maps using checkpoints and they are always fine or close enough. The problem occurs when I load the maps onto the Deere sprayer. It’s always off by a certain amount.