gnss_converter

An Open-source ROS Package for GNSS Preprocessing

This ROS package contains a simple RINEX-to-Rosbag converter written in C++. It decodes observations from a multi-constellation GNSS receiver and augments them with ephemeris, atmospheric corrections and the individual satellite clock bias.

The package is used to generate a Rosbag file containing raw GNSS pseudoranges for further research. In addition, it contains a rover position-fix, base position-fix, and doppler velocity data calculated by the RTKLIB. A Matlab script can ultimately be used to convert the Rosbag file to a .mat file.

Please not that this repository holds just a stripped-down version GraphGNSSLib, which provides a full factor graph back-end. We created this fork for a simpler maintainability of the GNSS preprocessor.

1. Install ROS

Install ROS on a Ubuntu machine. The package is tested under Ubuntu 20.04 and ROS noetic.

2. Build gnss_converter

Clone the repository to a desired folder and build the package:

mkdir -p gnss_converter/src
cd gnss_converter/src
git clone https://github.com/TUC-ProAut/gnss_converter.git
cd ..
catkin_make

Add the setup.bash to your ~.bashrc:

source ~/gnss_converter/devel/setup.bash

3. Configuration

Yaml files are used for the configuration of the gnss preprocessor. Many preconfigured examples are given, but new configurations can also be created.

3.1 Preconfigured

Example configurations of many different datasets can be found here.

3.2 Custom

The following parameters have to be adapted to fit to the considered dataset. They are internally used by the RTKLIB and GraphGNSSLib scripts:

• mode: GNSS positioning mode (0: single, 1: DGPS/DGNSS, 2: kinematic)
• frequency: all used frequencies of the GNSS receiver (1: L1, 2: L1+L2, 3: L1+L2+L5)
• soltype: type of the solution (0: forward, 1: backward, 2: combined)
• satellites: list of all GNSS-systems to be used (GPS, GLONASS, Galileo, BeiDou, QZSS, SBAS)
• shared_ephemeris: use only one RINEX file for the broadcast ephemeris (true/false) --> please see Getting GNSS relates files
• precise_ephemeris: use the precise satellite orbit solution (true/false) --> please see Getting GNSS relates files
• ionex_correction: use a IONEX TEC correction file for ionosphere correction
• custom_atx: use a custom antenna model file --> please see Getting GNSS relates files
• elevationmask: minimal elevation angle of satellites to be used in degrees

Please see the documentation of the RTKLIB for further explanations regarding some parameters.

3.3 Launchfiles

ROS launchfiles are used to start the gnss preprocessor. The paths to the config file and all the other GNSS-related files have to be specified here.

Many examples are given inside the launch folder.

4. Getting GNSS related files

All information about downloading the GNSS-related files is separated to "Getting GNSS relates files".

5. Usage

5.1 Run GNSS preprocessor with your own RINEX file

Run the desired launchfile:

roslaunch gnss_preprocessor <datasetname>.launch

While running you can see the number of satellites used for each system:

[ INFO] [1647857601.020952311]: GPS_cnt [1]   9
[ INFO] [1647857601.020979743]: SBS_cnt [2]   0
[ INFO] [1647857601.020996915]: GLO_cnt [4]   7
[ INFO] [1647857601.021008216]: GAL_cnt [8]   0
[ INFO] [1647857601.021029226]: QZS_cnt [16]  0
[ INFO] [1647857601.021037431]: CMP_cnt [32]  0

The processed data is saved in a rosbag file inside the folder dataset/processed.

5.2 Messages

Different messages are published while the package is running:

• gnss_raw (gnss_msgs::GNSS_Raw_Array): custom message containing the raw GNSS information (pseudoranges and additional information regarding the satellites)
• gnss_fix (sensor_msgs::NavSatFix): receiver position fix calculated by the RTKLIB (reference frame: WGS 84)
• gnss_vel (geometry_msgs::TwistStamped): receiver velocity information calculated by the RTKLIB from doppler data
• gnss_raw_base (gnss_msgs::GNSS_Raw_Array): base GNSS information (only used with relative positioning modes)

5.3 Conversion to a Matlab-file

The file convertRosbags.m can be used to convert the generated Rosbag file to a .mat file for further evaluation. Please note that currently only a few specific datasets can be directly used. For own datasets, the filenames have to be manually entered.

6. Acknowledgments

Since this package is just a stripped-down version of the GraphGNSSLib from Weisong Wen, all credits for creating this helpful converter belong to him. The RTKLIB is used internally for GNSS data decoding and atmospheric corrections.

7. License

The source code is released under GPLv3 license.