Range Fixed

We are a user with very few requirements.
So an accuracy of 10cm would be enough for us.
Can the range for the Fixed status be entered manually?

Greetings Andre

Do you require absolute accuracy or relative precision?

Hi @Boess_Infra,

The solution is not considered fixed when accuracy reaches the specified limit. It’s more an effect than a cause.

The solution becomes fixed when all the calculations ambiguities are resolved. So, there is no way to enter the range manually. But you can still rely on RMS values.

I noticed that when I go to Status in the receiver, the accuracy displayed is different from the RMS values ​​that are stored in the points.
Is RMS the possible inaccuracy?

What is the specified limit?

Some food for thought:
I can get a fix on 200 km distance (I would not recommend more than 30 km, just for the reference), but the solution will drift up to 0.5m over 3 hours. That leads to question, when is a fix a real fix, or what does fix mean in the eyes of a common user?

Some other vendors have 2 kinda of fix-“engines”: an optimistic and a trustworthy. Some even have multiple engines and cross reference these to guarantee that a fix indeed is within a few cm, and if not, no fix is given.


Hi there,

Hmm, it seems my words caused confusion. Sorry for that! I was just about to say that there is no such accuracy value a Fix depends on. Fix becomes Fix when all the ambiguities are resolved, not because RMS is 1/6/10/any other number centimeters.

That’s why you still can obtain a Fix on the 200 km baseline. The algorithm works as expected, but the atmosphere differs too much to obtain a Fix within a few cm.

But I understand you from the user’s point of view. So thanks for food for thought. I’ll think about that :slightly_smiling_face:

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These are just two different values. When the point is already collected, you have a dataset to calculate RMS from. On the Status tab, the accuracy value is calculated another way.

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sorry, I don’t understand that now.
FIX has nothing to do with accurac

Fix solution status means your coordinates are centimeter-accurate. But you can’t configure Reach to change solution status to Fix when accuracy is 10 cm, for instance.

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The two displays of precision (not accuracy) are made from different timeframes.
The one in the status of RV2 is a continuously running calculation over some time (I guess @svetlana.nikolenko can help with the timeframe). The calculation of the surveyed point is done over the recording-period of that particular point.

But to get the the real indication of the absolute accuracy, given that your base reference is correct, you have to look at the specification of the GNSS unit, and do the calculation that takes into account the baseline.


You’re absolutely right!

It depends on the update rate. For example, if you set 1 Hz, the position is updated each second.

By the way, you mean RV3, right?

Hello Svetlana
You write at FIX, I have centimeter accuracy.
so + - 1cm?
or how many centimeters?
Sorry, I’m not a specialist, just a user.
So maybe I ask a little bit stupidly
greeting Andre

Nop, actually meant RV2, in the Status window (where all sat bars and map is also displayed). Here there is a running stddev calculation.

Hmm, but on the reach gear, as the engine works currently, this isn’t true, as you have said yourself earlier, it is

Hence I can get a fix over a 200 km baseline, with 0.5 m deviation, and everything is still within “spec” so to speak (ppm etc taken into account).

Hi guys,

I feel like we need to start from scratch because I’ve already confused myself😅 The topic isn’t even about Reach devices exactly, but about RTK algorithm in general.

So, we say that the RTK technique provides us with centimeter-level coordinates. This “centimeter-level” various for different GNSS receivers and depends on the baseline. For example, Reach RS2 positioning accuracy is 7mm + 1ppm horizontally.

RTK has three solution statuses, including the Fix one, which means all ambiguities are resolved. You can achieve a Fix as long as the base and the rover track the same satellites. However, RTK still has a baseline limitation. We consider it 60 km. Why?

Roughly speaking, a standalone device can’t calculate its position precisely because of atmospheric errors. But two devices can because we consider that within 60 km, the atmosphere is the same, which means the atmospheric errors are the same too.

Of course, they can be the same on the baseline over 60 km, but we can’t guarantee that. Call it a statistic. We don’t have tools to define if the atmosphere differs or not, so the RTK algorithm always considers the atmosphere the same. And this is the main thing that causes errors on large baselines: the algorithm thinks the atmospheric errors are the same, but they are not.

So, everything we say about accuracy is valid only if we work on a baseline up to 60 km.


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