sbg_driver

Overview

ROS package for SBG Systems IMU.
The driver allows the user to configure the IMU (if possible, according to the device), to receive messages from the Sbg message protocol, publish ROS standard messages , and to calibrate the magnetometers.

Initial work has been done by ENSTA Bretagne.

Author : SBG Systems
Maintainer : SBG Systems, support@sbg-systems.com

Installation

Installation from Packages

User can install the sbg_ros_driver through the standard ROS installation system.

• Melodic sudo apt-get install ros-melodic-sbg-driver
• Noetic sudo apt-get install ros-noetic-sbg-driver

Building from sources

Dependencies

• Robot Operating System (ROS)
• SBG communication protocol sbgECom, v1.11.920-stable (full compatible with firmwares from 1.7.x).

Building

1. Clone the repository (use a Release version)
2. Build using the normal ROS catkin build system

cd catkin_ws/src
git clone https://github.com/SBG-Systems/sbg_ros_driver.git
cd ../
catkin_make

Usage

To run the default Ros node with the default configuration

roslaunch sbg_driver sbg_device.launch

To run the magnetic calibration node

roslaunch sbg_driver sbg_device_mag_calibration.launch

Config files

Default config files

Every configuration file is defined according to the same structure.

• sbg_device_uart_default.yaml
  This config file is the default one for Uart connection with the device.
  It does not configure the device through the ROS node, so it has to be previously configured (manually or with the ROS node).
  It defines a few outputs for the device :

  • /sbg/imu_data, /sbg/ekf_quat at 25Hz
  • ROS standard outputs /imu/data, /imu/velocity, /imu/temp at 25Hz
  • /sbg/status, /sbg/utc_time and /imu/utc_ref at 1Hz.

• sbg_device_udp_default.yaml
  This config file is the default one for an Udp connection with the device.
  It does not configure the device through the ROS node, so it has to be previously configured (manually or with the ROS node).
  It defines a few outputs for the device :

  • /sbg/imu_data, /sbg/ekf_quat at 25Hz
  • ROS standard outputs /imu/data, /imu/velocity, /imu/temp at 25Hz
  • /sbg/status, /sbg/utc_time and /imu/utc_ref at 1Hz.

Example config files

• ellipse_A_default.yaml
  Default config file for an Ellipse-A.

• ellipse_E_default.yaml
  Default config file for an Ellipse-E with an external antenna and external Gnss.

• ellipse_N_default.yaml
  Default config file for an Ellipse-N with an external antenna and internal Gnss.

• ellipse_D_default.yaml
  Default config file for an Ellipse-D.

Launch files

Default launch files

• sbg_device.launch
  Launch the sbg_device node to handle the receivde data, and load the sbg_device_uart_default.yaml configuration.

• sbg_device_mag_calibration.launch
  Launch the sbg_device_mag node to calibrate the magnetometers, and load the ellipse_E_default.yaml configuration.

Nodes

sbg_device

The sbg_device node handles the communication with the connected device, and publishes the SBG output to the Ros environment.

Published Topics

SBG specific topics

• /sbg/status sbg_driver/SbgStatus

  Provides informations about the general status (Communication, Aiding, etc..).

• /sbg/utc_time sbg_driver/SbgUtcTime

  Provides UTC time reference.

• /sbg/imu_data sbg_driver/SbgImuData

  IMU status, and sensors values.

• /sbg/ekf_euler sbg_driver/SbgEkfEuler

  Computed orientation using Euler angles.

• /sbg/ekf_quat sbg_driver/SbgEkfQuat

  Computed orientation using Quaternion.

• /sbg/ekf_nav sbg_driver/SbgEkfNav

  Computed navigation data.

• /sbg/mag sbg_driver/SbgMag

  Magnetic data.

• /sbg/mag_calib sbg_driver/SbgMagCalib

  Magnetometer calibration data.

• /sbg/ship_motion sbg_driver/SbgShipMotion

  Heave, surge and sway data.

• /sbg/gps_vel sbg_driver/SbgGpsVel

  GPS velocities from GPS receiver.

• /sbg/gps_pos sbg_driver/SbgGpsPos

  GPS positions from GPS receiver.

• /sbg/gps_hdt sbg_driver/SbgGpsHdt

  GPS true heading from dual antenna system.

• /sbg/gps_raw sbg_driver/SbgGpsRaw

  GPS raw data for post processing.

• /sbg/odo_vel sbg_driver/SbgOdoVel

  Odometer velocity.

• /sbg/event[ABCDE] sbg_driver/SbgEvent

  Event on sync in the corresponding pin.

• /sbg/pressure sbg_driver/SbgPressure

  Pressure data.

ROS standard topics

In order to define ROS standard topics, it requires sometimes several SBG messages, to be merged. For each ROS standard, you have to activate the needed SBG outputs.

• /imu/data sensor_msgs/Imu

  IMU data. Requires /sbg/imu_data and /sbg/ekf_quat.

• /imu/temp sensor_msgs/Temperature

  IMU temperature data. Requires /sbg/imu_data.

• /imu/velocity geometry_msgs/TwistStamped

  IMU velocity data. Requires /sbg/imu_data and /sbg/ekf_nav and either /sbg/ekf_euler or /sbg/ekf_quat.

• /imu/mag sensor_msgs/MagneticField

  IMU magnetic field. Requires /sbg/mag.

• /imu/pres sensor_msgs/FluidPressure

  IMU pressure data. Requires /sbg/pressure.

• /imu/pos_ecef geometry_msgs/PointStamped

  Earth-Centered Earth-Fixed position. Requires /sbg/ekf_nav.

• /imu/utc_ref sensor_msgs/TimeReference

  UTC time reference. Requires /sbg/utc_time.

• /imu/nav_sat_fix sensor_msgs/NavSatFix

  Navigation satellite fix for any Global Navigation Satellite System. Requires /sbg/gps_pos.

• /imu/odometry nav_msgs/Odometry

  UTM projected position relative to the first valid INS position. Requires /sbg/imu_data and /sbg/ekv_nav and either /sbg/ekf_euler or /sbg/ekf_quat. Disabled by default, set odometry.enable in configuration file.

sbg_device_mag

The sbg_device_mag node handles the magnetic calibration for suitable devices.

Services

• /sbg/mag_calibration std_srvs/Trigger

  Service to start/stop the magnetic calibration.

• /sbg/mag_calibration_save std_srvs/Trigger

  Service to save the magnetic calibration to the connected device.

How To

Configure the SBG device

The SBG Ros driver allows the user to configure the device before starting the data handling.
To do so, set the corresponding parameter in the used config file.

# Configuration of the device with ROS.
confWithRos: true

Then, modify the desired parameters in the config file, using the SBG Firmware Manual, to see which features are configurable, and which parameter values are available.

Calibrate the magnetometers

Ellipse-A/E/N use magnemoter to provide heading. A calibration is then required to compensate soft and hard iron distortions due to the environmenent (motors, batteries, ...). The magnetic calibration procedure should be held in a non magnetic area (outside of buildings).

roslaunch sbg_driver sbg_device_mag_calibration.launch
rosservice call /sbg/mag_calibration

success: True
message: "Magnetometer calibration process started."

Proceed rotations of the IMU (every orientation if possible).

rosservice call /sbg/mag_calibration

success: True
message: "Magnetometer calibration is finished. See the output console to get calibration informations."

If the magnetic calibration is satisfaying (Quality, Confidence), it could be uploaded/saved to the device.

rosservice call /sbg/mag_calibration_save

success: True
message: "Magnetometer calibration has been uploaded to the device."

Enable communication with the SBG device

To be able to communicate with the device, be sure that your user is part of the dialout group.
Once added, restart your machine to save and apply the changes.

sudo adduser $USER dialout

Create udev rules

Udev rules can be defined for communication port, in order to avoid modifying the port in configuration if it has changed. Udev documentation

A symlink can be configured and defined to uniquely identify the connected device.
Once it is done, configuration file could be updated portName: "/dev/sbg".

See the docs folder, to see an example of rules with the corresponding screenshot using the udev functions.

Time source & reference

ROS uses an internal system time to time stamp messages. This time stamp is generally gathered when the message is processed and published. As a result, the message is not time stamped accurately due to transmission and processing delays.

SBG Systems INS however provides a very accurate timing based on GNSS time if available. The following conditions have to be met to get absolute accurate timing information:

• The ELLIPSE-N or D should have a connected GNSS antenna with internal GNSS enabled
• The ELLIPSE-E should be connected to an external GNSS receiver with a PPS signal
• A valid GNSS position has to be available to get UTC data
• The ELLIPSE internal clock should be aligned to PPS signal (clock status)
• The ELLIPSE should be setup to send SBG_ECOM_LOG_UTC message

You can select which time source to use with the parameter time_reference to time stamp messages published by this driver:

• ros: The header.stamp member contains the current ROS system time when the message has been processed.
• ins_unix: The header.stamp member contains an absolute and accurate time referenced to UNIX epoch (00:00:00 UTC on 1 January 1970)

Configuration example to use an absolute and accurate time reference to UNIX epoch:

# Time reference:
time_reference: "ins_unix"

Change frame parameters

Frame ID

The frame_id of the header can be set with this parameter:

# Frame convention
frame_id: "imu_link_ned"

Frame convention

The frame convention can be set to NED or ENU

• In NED convention axises are the same as device axises.
• In ENU convention (x = X, y = -Y, z = -Z).

  # Frame convention:
  use_enu: true

Troubleshooting

If you experience higher latency than expected and have connected the IMU via an USB interface, you can enable the serial driver low latency mode:

/bin/setserial /dev/<device> low_latency

Contributing

Bugs and issues

Please report bugs and/or issues using the Issue Tracker

Features requests or additions

In order to contribute to the code, please use Pull requests to the devel branch.
If you have some feature requests, use the Issue Tracker as well.