ublox_driver

ublox_driver

Authors/Maintainers: CAO Shaozu (shaozu.cao AT gmail.com)

The ublox_driver provides essential functionalities for u-blox GNSS receivers. This package is originally designed for u-blox ZED-F9P module according to the specification UBX-18010854, but should also be compatible to other 8-series or 9-series u-blox receivers as long as the interface is the same.

The following diagram shows all possible input and output options supported by ublox_driver.

1. Prerequisites

1.1 C++11 Compiler

This package requires some features of C++11.

1.2 ROS

This package is developed under ROS Kinetic environment.

1.3 Eigen

We use Eigen 3.3.3 for matrix manipulation.

1.4 Boost

Our software utilizes Boost library for serial and socket manipulation. Using command sudo apt-get install libboost-all-dev to install Boost.

1.5 gnss_comm

This package also requires gnss_comm for ROS message definitions and some utility functions. Follow those instructions to build the gnss_comm package.

2. Build ublox_driver

Clone the repository to your catkin workspace (for example ~/catkin_ws/):

cd ~/catkin_ws/src/
git clone https://github.com/HKUST-Aerial-Robotics/ublox_driver.git

Then build the package with:

cd ~/catkin_ws/
catkin_make
source ~/catkin_ws/devel/setup.bash

3. Run with your u-blox receiver

Our software can take the serial stream from the u-blox receiver as an input source. Before running the package, you need to configure your receiver using u-center to output at least UBX-RXM-RAWX, UBX-RXM-SFRBX and UBX-NAV-PVT messages to a specific serial port (a sample config used in our system can be found at config/ucenter_config_f9p_gvins.txt). Then connecting your computer(Linux) with the receiver, make sure the serial port appears as a file in the /dev/ directory. Then add your account to dialout group to obtain permission on serial r/w operation via (no need to substitute $USER):

sudo usermod -aG dialout $USER

Open config/driver_config.yaml, set online and to_ros to 1, and adjust input_serial_port and serial_baud_rate according to your setting. Run the package with:

roslaunch ublox_driver ublox_driver.launch

Open another terminal, echo the ROS message by:

rostopic echo /ublox_driver/receiver_lla

If everything goes smoothly, there should be some ROS messages coming out. Note that some ROS topics remain inactive until the receiver gets GNSS signals.

Besides the ROS message, you can record the serial stream to a file(to_file option) or forward the stream to another serial port(to_serial option). All output options can be turned on simultaneously.

Obtain RTK Solution (Optional)

If your receiver owns an internal RTK engine (for example, ZED-F9P), you can input RTCM messages from the GNSS base station to the receiver in order to obtain the cm-level accurate RTK localization result. Our software can forward the RTCM stream from a local socket to the receiver’s serial port. Nowadays many GNSS stations distribute their RTCM streams via NTRIP protocol and you can easily fetch the NTRIP data and map it to a local socket via RTKLIB. Following those commands to build RTKLIB and setup the RTCM stream:

git clone https://github.com/tomojitakasu/RTKLIB.git
cd RTKLIB/
git checkout rtklib_2.4.3
cd app/consapp/str2str/gcc/
make
./str2str -in ntrip://${NTRIP_SITE}:${NTRIP_PORT}/${MOUNT_POINT} -out tcpsvr://:3503

Then set the input_rtcm option to 1 in config/driver_config.yaml and launch the ros node with:

roslaunch ublox_driver ublox_driver.launch

If the field carr_soln in /ublox_driver/receiver_pvt message becomes 2, the RTK is in fix status. If you find the location of the GNSS base station reported in the RTCM message is somehow biased, you can apply correction via the variable rtk_correction_ecef in the config file.

4. Playback Log Files

Our package can also take an log file as the input. The log file can be recorded via u-center, RTKLIB or our package itself. To playback the log file, you need to set online to 0 and point ubx_filepath to your log file in the config file. Then launch the ros node with:

roslaunch ublox_driver ublox_driver.launch

Similar to the online receiver manner, all three output options are also supported in the playback mode. Note that the playback speed is controlled by the serial_baud_rate variable in the config file.

5. Synchronize System Time

In addition to message parsing and delivery, ublox_driver can also synchronize the local system time to the global time without the need of internet connection. Note that such synchronization is only in a coarse level and the accuracy is not guaranteed. To perform such synchronization, you need to set UTC_OFFSET macro in src/sync_system_time.cpp according to your timezone. Recompile and launch the driver with:

roslaunch ublox_driver ublox_driver.launch

Then open another terminal and run commands:

sudo su
source /opt/ros/kinetic/setup.bash
source ${YOUR_CATKIN_WORKSPACE}/devel/setup.bash
rosrun ublox_driver sync_system_time

The system time will be synchronized to the global time when the receiver gets a valid PVT solution.

6. Todo List

• Config u-blox receiver when the driver gets launched
• Infer timezone from geodetic location when sync time
• Optimize time-sync function to improve precision

7. Acknowledgements

Many of the ephemeris parsing functions in our package are adapted from RTKLIB. We use mini-yaml for config parsing.

8. License

The source code is released under GPLv3 license.