RTK setup - Hardware & Software

[Bmoradi93]

Issue details

Hi friends, I'm trying to use RTK in my application to increase my localization accuracy. My hardware:

• Drone Kit: HolyBro X500 PX4 V2
• GPS and RTK: UBLOX FP9 - base station and robot.
• I have radio telemetry on both my ground computer and and on the robot.
• Ground computer is connected to the base station using USB and I'm able to read the base station GPS.

My software:

• QGroundControl is used and I used it to test the robot.
• RTK is also tested in QGroundControl and it works fine!

Now, I'm going to use MAVSDK and MAVROS in my autonomy software and I need to have RTK as well. When I use MAVROS, I'm not able to get any RTK data for gps/rtk topics. I'm able to read gps/raw though. But no RTK.

Please instruct me how to do my Hardware/Software configuration to enable RTK in MAVROS so I can use it in my application.

MAVROS version and platform

Mavros: latest ROS: Noetic Ubuntu: 20.04

Autopilot type and version

I'm using PX4 autopilot.

Version: latest

[vooon]

Hi,

MAVROS just feeds RTCM data to FCU. You should map your base station's feed to gps_rtk plugin.

See also: https://github.com/mavlink/mavros/blob/master/mavros_extras/src/plugins/gps_rtk.cpp#L39

[Bmoradi93]

My base and rover are UBLOX F9P. I used UCenter to configure RTCM3 output from the base station.

The base station is connected to the ground computer through the ttyACM0 USB port.

The ROS driver does not read the RTCM message.

Can you please explain how to read the RTCM data from this GPS? Is there an API for this?

[gitsr-sys]

@vooon I am having the similar setting and the same issue. My GPS RTK base station module is SparkFun GPS-RTK-SMA Kit - KIT-18292.

In short, I can confirmed RTK GPS streaming in QGC. The output of gps status in mavlink terminal is GPS_FIX_TYPE = 6 (RTK Fixed, 3D position). But, when I run mavros, no outputs from gps/rtk topics: mavros/gps_rtk/rtk_baseline, mavros/gps_rtk/send_rtcm, and /mavros/gpsstatus/gps1/rtk.

I do not understand map your base station's feed to gps_rtk plugin.... In the px4_config.yaml and px4_pluginlists.yaml, I cannot find any rtk setting. Could you please help me get /mavros/gpsstatus/gps1/rtk data?

Thank you in advance.

[diablo1281]

I would also appreciate some clarification.

I am working on injecting Mavlink messages from RTK station which is streaming RTCM to the network.

Is it also possible to stream from UAS to multiple GCSes?

[gitsr-sys]

@vooon any thought?

[vooon]

@diablo1281 https://mavlink.io/en/messages/common.html#GPS_RTCM_DATA as you can see, message doesn't have target, so it's broadcast one. Just make other nodes to hear it with something like mavlink-router (or built-in router on ros2).

@gitsr-sys mavros is not a driver for your GPS device. It doesn't understand serial protocol of your receiver, like QGC does. Instead there must be a ros node which talks to the device and provide gps fix and rtcm stream. If it's not already done by existing driver i suggest that you should white your own. That's must be easy as there plenty of libraries to talk to Ublox, i almost sure that it'll be about 100 LOC of python.

[Bmoradi93]

Yes. MAVROS RTK plugin is able to send RTCM data to FCU. The problem here is getting the correct RTCM3 message from UBLOX F9P Base Station. UBLOX has a ROS package and I tested it. However, it does not provide RTCM3 data.