Point inaccuracy between sessions

I am using two RS2+ units to do topographic surveys. When these jobs require more than one day of work, i set the base on the same point (hub and tack at assumed random location). Every time i have done this, my points between sessions do not check. On average, they are off by around 5 feet or so horizontally and 10 feet vertically.

I am using the average single method each time and have not changed the horizontal or vertical datum. This is most likely user error but have not been able to figure out how to fix it. Any help would be appreciated.

1 Like

Hi there! You will always have that margin of error if you average single every time. You must do a average single the first time, and always use that same coordinates for the following jobs.


Average Single 1st day.

Record those coords and elevation Height. Screenshot, notes, etc.

2nd day:

Set up over same point.

Enter those SAME coordinates from Day 1 MANUALLY, NOT SINGLE AGAIN!


If you want repeatablility you need to do as rsurveyor1 and timd1971 mentioned, by only using the single average on the first survey. Any time you need to revisit the site, set the base up on the same control point and use manual and key in lat/long/elev you used on the first day.

Key thing to remember though, is if you are only using a single average solution, then that solution is not going to be an accurate position. You can get repeatable results with the above instructions, but if a real surveyor came out and checked your control point then he may find it off 5, 10 feet, or more horizontally and most like worse vertically.

If you need survey quality precision, then you’ll need to stay away from only using a Single Average Solution as a way of getting the final position of a control point.


Thank you all for the information. I will try that procedure next time.


I agree with the points above.

With the Average Single base position, you’ll obtain only relative accuracy. It means that the rover positions will be accurate to each other but not to global coordinates. And this can only give you an absolute accuracy of several meters.

As @rsurveyor1, @snillor999, and @timd1971 mentioned, to ensure consistency, use the average single from the first survey and set up the base on the same control point for subsequent surveys. Manually enter the latitude, longitude, and elevation from the first day on subsequent surveys.

To tie your results to global coordinates, you’ll need to use an accurate base position. There are 2 ways to do it:

  • Connect the base to a local NTRIP service and average its position with a Fix solution
  • Enter the accurate base coordinates manually. If you don’t have a known point nearby, you can find Reach RS2+ coordinates with the PPP technique.

Is there a way to press a button and save that Single Average Solution for subsequent use without hand entering the position?

1 Like

It’s been requested in another thread. Seems it won’t be pursued, but would be helpful though. I.e. SAVE BASE POINT and designated if AVERAGE SINGLE, FLOAT, FIX etc.

Take screenshot or note manually… i don’t even think you can copy paste it which is a bummer too? Not sure.

Thanks for the reply - it’s kind of disappointing. It just adds an unneeded opportunity for error.

Assuming at some point you save your base point, you can choose it from your project without having to manually enter in all the data (you just adjust the the antenna height each day).


Hey Mike.

This comes up from time to time. You probably have a project set up. Simply go to that project and add a point. In the add dialog, set up how you want to obtain the point, e.g. average single. Then, in the future, from within the base settings, select the option to use a point from a project. Select that point. No manual input of coordinates.

Some folks think there should be an easy “save to base point” setting from the base tab without the step of adding the point through a project. In this case, where do you suppose it should be saved for later use? Isn’t a project the logical place?

If you only need to average a point for a one-off use without any other data on that site, then don’t bother with the extra 45 - 120 seconds to set up a project. If you are going to use it in the future, then invest the 45 seconds. If you are collecting more than 1 point, you will already be setting up a project, so you are investing 0 more time.


Hi Jknodel. When you have to work in two or more sesions. In the first sesion your base must be in average single, because you dont know the point. In the next sesions, your base must be in manual, whit the coordinates from the first sesion.


1 Like

Hi guys,

Actually, Emlid Flow has an option to save the position from Averaging to Manual. To use it, you need to wait till the averaging is finished, tap on Configure, and select Manual. The app will autofill the Latitude, Longitude, and Ellipsoidal height fields with averaged coordinates.

P.S. This feature is only available on the 30 firmware version or higher. So please make sure that your receiver is up-to-date to use it.

P.P.S. I agree that collecting the base position in the project is a good workaround. It’ll help you save it to a CSV file with the survey, which can come in handy.