Not getting any accuracy with RTK

ArduCopter Copter 4.5
1

I am using Here 3+ GPS + RTK setup, Upon injecting the RTK data, the GPS status shows RTK-Float, it switches between Float and Fix. According to the documentation, We can expect around 20-30cm of accuracy with RTK-Float, However, I am not observing any improvements.

I am reading LOCAL_POSITION_NED mavlink msg, the position is inaccurate by 5-6m and keeps on drifting everywhere.

The test environment in an open field with clear sky.

I’d really appreciate it if someone could help me solve this issue.

@rmackay9

2

1)Firstly to get down to cm tolerance you need to layout your base station to collect data for at least 24 hours. Or you can buy the differential data from providers. And it takes time for your client gps to get it’s own position accurately as well.

  1. there are a large arrays of issue with gps not getting precision. Mainly to do with environment. Especially urban environment. I won’t go into details you can Google them yourself.

  2. did you set up the position of your gps in your parameters?

  3. the antenna is extreme sensitive, you need to place it on the drone with almost no Interference.

  4. Distance between your base and client needs to be within few km for precision

3

In practice, an RTK Float status is not particularly useful over a simple 3D fix.

Unfortunately, the Here 3 series use an older M8P module that tends to need a fairly ideal environment to achieve and hold onto an RTK Fixed status.

This isn’t a developer issue, it’s a hardware choice issue.

3 Likes
4

I very much agree with what @Yuri_Rage says. I’ve only tried to use the Here3+ with RTK once and it struggled to get RTK Fixed. The UBlox F9 (which is in the Here4) seems much better than the M8 although again, I don’t use RTK very often

2 Likes
5

Exactly my experience, along with the experience shown in the linked post above.

The Zed-F9P is among the most capable modules in the price range of the Here-series modules. The Here4 uses a slightly less capable Neo-F9P inside, but that is mostly inconsequential for the discussion - the Here4 has plenty of capability for most users (and CubePilot has done a very good job of curating the Here4 firmware to make the differences between the Zed and Neo models almost transparent to the user). The Neo-F9P also offers L5 band reception, though that remains a “pre-operational” feature of the product. It does appear that CubePilot leverages L5 reception in the Here4, which is a nice addition and could be considered “better” than the Zed-F9P, depending on the environment and exact use case.

As for other alternatives: Holybro makes a Zed-F9P module, as does CUAV, and both of those manufacturers also offer some UM982-based dual antenna modules that will get you moving baseline capabilities along with fairly reliable RTK Fixed status assuming a good correction source and sky view.

2 Likes
6

1.) I am talking about relative accuracy with base. I don’t neet GPS accuracy to be cm level.

2.) I am testing things in a open field, in a rural environment.

3.) Which params?

4.) I’ve made sure that there is interference.

5.) The distance is less than 500m.

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I’ve got repeatable positioning of 300mm with the rover using Here 3 in RTK Float. I get 100mm with the ZED-F9P which always gets rtk fixed.

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Could you please explain what steps you took.

I config the GPS as usual.

I connected the rtk base, got valid positions, saved and used the position

Is there anything else needed to be done apart from this?

And did you get the accuracy in NED positions received through mavlink?

9

Your steps are correct. Default telemetry settings should transmit the data you want.

But I explained why your hardware choice is likely less than ideal.

1 Like
10

but as @tboyle mentioned, he got accuracy of 300mm, in my case, I am getting errors of around 5m.

Also, what hardware do you suggest?

11

Accuracy and repeatability are 2 different things. Repeatibility can be measured by does the drone land close to where it took off from in RTL. Accuracy refers to does the GPS coordinates match the actual.

You may have purchased a dodgy knock off that is not RTK at all? Something wrong with 5m accuracy - that is the accuracy of the M8N (non-rtk)

12

The m8p is useless for RTK its intermittent at best. If you need RTK then you need to get another GPS.

1 Like
13

I have the original Here 3+ GPS and RTK