Emlid day-to-day variability of the RTK-GPS pass over the same line


We have EMLID reach RS+. We have been using it successfully for some months. It gets a correction from NTRIP source which is only about 5 kilometers away and works fine for the Topcon system on the Massey Ferguson.
We use it to collect data here in Tifton, Ga (The University of Georgia Experiment Station). We used it to collect waypoints for our robot to navigate over the cotton rows. However, recently, we have observed changes in the position of the GPS location compared to the waypoints. The coordinates reported by the GPS on the same spot tend to change every time while the GPS has a “fixed” signal. So we tried to collect waypoints of the cotton row on three occasions, Nov 6, Nov 11 and Nov 19. The image attached represents the waypoints; orange, ocean blue, and purple represent the days consecutively. The distance between the lines is more than 1.5 metres

So now, we always record the waypoints almost every two days to keep the system up to date.

What could be a problem?


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what’s the variation? cm o m level?

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The distance is more than 1.5 metres between the lines…

It sounds like your NTRIP-source has changed their base location coordinates.
You should contact them and ask.

Sorry but 1.5m seems like the width of a cotton row? What’s the width of the row?

As @wizprod mentioned, maybe your point changed the coordinates

You have the raw data? Have you tried to post process?

More than that… it is the same row.

I second that.

Also you can upload raw logs from your rover and the reference station to a cloud storage and share the link here. We’ll look into them to confirm that it’s not the issue of RTK performance

Thanks Dmitriy. Here is the link to google drive https://drive.google.com/drive/folders/1I7jiNo6gJNzNnuBooW-_f3l35iwjG3cE?usp=sharing

Is your NTRIP source using stable coords? I can imagine seeing this variance if the NTRIP base was restarted each day, and just coordinated using Average Single (ie. so it’s coordinates were determined by averaging it’s own uncorrected observations), rather than having the base coordinates manually entered over a known mark.


Hi @kadefue,

Sorry for the delayed response!

I’ve looked into your logs. From what I can see, everything is okay with them.

I’d recommend reaching out to your NTRIP provider. It seems like, as our users have already mentioned above, the NTRIP service sends you a different base position every time and that causes such difference in the results.

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