Accuracy agopen gps without correction with a base

We are looking for a agricultural GPS guidance with a minimal accuracy of 15cm. It would be use in Guinea, so the cellphone network is not really stable and good. it’s why at this time, it’s diificult for us to imagine using RTK correction with a base in a farm at this time.

Do you an idea of the accuracy without base gps correction on the farm?


Well, accuracy from minute to minute is fine, but sattelites move which causes drift.
You should consider a radiobased basestation.
But as you see in this thread it is possible to seed without RTK, as long as you keep an eye on the drift.

Thankts Larvest,

As you say in this post above, you have used ag open GPS without rtk at first, i 'm right?

Because, for us, we are not trying to seed with gps at this time, we just want fertilizing and spraying , so it’s why we don’t really need rtk.

What did you observe in your use regarding the accuracy without rtk? 20 cm precise? 50cm precise? 100cm precise?

Why would you need 15 cm accuracy for fertilizing and spraying? We used to have GPS with EGNOS for those tasks and it was fine for section control etc. Pass-to-pass accuracy about 20 to 30 cm with Egnos (within 15 minutes). F9P with all 4 constellations probably gives similar accuracy.

How large are the fields, maximum distance from base if you had radio RTK as suggested?

Depends on how long time.
5 mins would be 2 to 3 cm
1 hour perhaps 50 to 100 cm
All depends on the drift at your place.
An A B line made an hour or a day ago wil never be same place now.
You then must recenter line before proceeding.

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Remember that EGNOS covers Europe only. It may be possible to see EGNOS statellites from Guinea, but given the distance to the nearest ground reference station (Guinea is sligthly below the equator), you likely won’t get a differential GPS fix. So you’re stuck with just regular 3D GPS fixes. Some have mentioned on this forum that with the ZED-F9P using GPS, Glonass, Galileo and Beidou, the accuracy of a normal 3D GPS fix is almost as good as a GPS fix with WAAS or EGNOS. But you’re still talking about an accuracy (repeatability) of about 2 metres and a pass-to-pass accuracy of at least 30 cm.

Eventually satellite-delivered PPP correction service will be available for Africa, but that is some years away.

If you really need 12 cm, an RTK base station with a radio transmitter is the best choice. Of course this means line of sight to the tractors in the field, or the use of radio systems that employs repeaters.


Well, about the accuracy, it was just an example. What we want is sufficient accuracy for making good spraying and fertilizing (if it’s 20-30 cm, it would be ok i think so). For the rtk by radio, we will see, it depend of the relief and distance.

For the field, i will tell you later about size, lenght

I think you can get 20-30 cm pass-to-pass accuracy with the ZED-F9P using all the constellations and just 3D fix. Worth trying.

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Could also make a mobile base station with a radio transmitter and a battery you put at the edge of the field


Hello everyone,

Thank you to all of you for yours anwers. We will try to build one with also an option for RTK with a radio transmitter.

I will let you know how it work in field

Galileo E6_HAS in theory horizontal acc below 20cm

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Interesting that the service is free globally. I interpret the satellite broadcast corrections are not yet available when they say “internet based corrections have been available since 2023”?

When do we have E6 HAS capable receivers at less than F9P rover and base?

Yes it is

The Galileo High Accuracy Service (HAS) provides free of charge high accuracy Precise Point Positioning (PPP) corrections through the Galileo signal (E6-B) (no internet needed)

As far as I know F9P does not support E6-HAS.

I list some modules that supports and much cheaper than F9P:

1.Unicore Communications’ UM982 GPS Module

Upresise command for using E6-HAS:


2.### ComNav’s K8 series GNSS modules

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Thanks. So the EGNOS E6b signal is alive as of today, also confirmed by your second document. Price info for the K803 would have been interesting.

The UM982 is a low cost device (at least the versions not supporting HAS) but the specs lack details. Does it really support HAS or does it only support E6 signal tracking (which as such is useful)?

Interesting technology but is this valuable for farmers? I consider RTK accuracy a must for many tasks. SBAS is sufficient for some tasks like spraying and fertilizer spreading. 10 cm accuracy is an improvement over SBAS but does it enable farming tasks that could not be handled with SBAS (or F9P standalone accuracy)?

um982 new firmware for sure support it do not worry about that, for real usage I am not able to test it, have to be reviewed in the real situation

UM982 Supports E6 HAS. I think HAS has advantage to single that it will not drift over short time, you can converge to cm level in static conditions but at time frame of few hours to a day it will get to ±20cm Which is still better than single. When looked at in short term its close to deviation reported by PPPNAVA, we see from longer log that actual position vary even if PPPNAVA reports smaller deviation. Max deviation reported from PPPNAVA Lat, Lon, Height in entire log is 0.0423m, 0.0325m, 0.0778m).

Hire is 12h+ static E6-HAS survey log. (After about 1h of converging)


That is professional

need firmware for um980 with e6-has support