sbg_driver

ROS driver package for SBG Systems IMU, AHRS and INS.
This driver package uses the sbgECom binary protocol to read data and configure SBG Systems devices.

Initial work has been done by ENSTA Bretagne.

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

Features

The driver supports the following features:

• Configure ELLIPSE products using yaml files (see note below)
• Parse IMU/AHRS/INS/GNSS using the sbgECom protocol
• Publish standard ROS messages and more detailed specific SBG Systems topics
• Subscribe and forward RTCM data to support DGPS/RTK mode with centimeters-level accuracy
• Calibrate 2D/3D magnetic field using the on-board ELLIPSE algorithms

[!NOTE] Only ELLIPSE devices can be configured from the ROS driver. For High Performance INS such as EKINOX, APOGEE and QUANTA, please use the sbgInsRestApi

Installation

Installation from Packages

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

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

Building from sources

Dependencies

• Robot Operating System (ROS)
• sbgECom C Library (embeds v1.11.920-stable - compatible with ELLIPSE firmware above 1.7)
• Boost C++ Library

Building

1. Clone the repository (use a Release version)

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

2. Install dependencies

   cd ..
   rosdep install --from-paths src --ignore-src -r -y

3. Build using the normal ROS catkin build system

source /opt/ros/${ROS_DISTRO}/setup.bash
catkin_make

Usage

Source the generated setup environment

source devel/setup.bash

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 NMEA GNSS.

• ellipse_N_default.yaml Default config file for an Ellipse-N using internal GNSS.

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

Launch files

Default launch files

• sbg_device_launch.py Launch the sbg_device node to handle the received data, and load the sbg_device_uart_default.yaml configuration.

• sbg_device_mag_calibration_launch.py Launch the sbg_device_mag node to calibrate the magnetometers, and load the ellipse_E_default.yaml configuration.

Nodes

sbg_device node

The sbg_device node handles the communication with the connected device, publishes the SBG output to the ROS environment and subscribes to useful topics such as RTCM data streams.

Published Topics

SBG Systems specific topics

SBG Systems has defined proprietary ROS messages to report more detailed information from the AHRS/INS.
These messages try to match as much as possible the sbgECom logs as they are output by the device.

• /sbg/status sbg_driver/SbgStatus

  Provides information 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

  Calibrated magnetic field measurement.

• /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/air_data sbg_driver/SbgAirData

  Air data.

ROS standard topics

[!NOTE] Please update the driver configuration to enable standard ROS messages publication output.ros_standard. Also, the driver only publish standard ROS messages if the driver is setup to use ENU frame convention output.use_enu.

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.

• /imu/mag sensor_msgs/MagneticField

  IMU magnetic field. Requires /sbg/mag.

• /imu/pres sensor_msgs/FluidPressure

  IMU pressure data. Requires /sbg/air_data.

• /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.

NMEA topics

The driver can publish NMEA GGA messages from the internal GNSS receiver. It can be used with third party NTRIP client modules to support VRS networks providers.

Disabled by default, set nmea.publish to true in .yaml config file to use this feature.

• /ntrip_client/nmea nmea_msgs/Sentence

  Data from /sbg/gps_pos serialized into NMEA GGA format. Requires /sbg/gps_pos.
  Namespace ntrip_client and topic_name nmea can be customized in .yaml config files.

Subscribed Topics

RTCM topics

The sbg_device node can subscribe to RTCM topics published by third party ROS modules.
Incoming RTCM data are forwarded to the INS internal GNSS receiver to enable DGPS/RTK solutions.

Disabled by default, set rtcm.subscribe to true in .yaml config file to use this feature.

• /ntrip_client/rtcm rtcm_msgs/Message

  RTCM data from /ntrip_client/rtcm will be forwarded to the internal INS GNSS receiver.
  Namespace ntrip_client and topic_name rtcm can be customized in .yaml config files.

sbg_device_mag node

The sbg_device_mag node is used to execute on board in-situ 2D or 3D magnetic field calibration.
If you are planning to use magnetic based heading, it is mandatory to perform a magnetic field calibration in a clean magnetic environnement.

Only ELLIPSE products support magnetic based heading and feature the on-board magnetic field calibration process.

Services

• /sbg/mag_calibration std_srvs/Trigger

  Service to start/stop the magnetic calibration.

• /sbg/mag_calibration_save std_srvs/Trigger

  Service to save in FLASH memory the latest computed magnetic field calibration.

HowTo

Configure the SBG device

The SBG Ros driver allows the user to configure the device before starting data parsing.
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 Firmware Reference Manual, to see which features are configurable, and which parameter values are available.

Configure for RTK/DGPS

The sbg_device node can subscribe to rtcm_msgs/Message topics to forward differential corrections to the INS internal GNSS receiver.

The RTCM data stream is sent through the serial/ethernet interface used by ROS to communicate with the INS.
This enables simple and efficient RTK operations without requiring additional hardware or wiring.

When combined with a third party NTRIP client, it offers a turnkey solution to access local VRS providers and get centimeter-level accuracy solutions.

The driver and the device should be properly setup:

• Configure the INS to accept RTCM corrections on the interface used by the ROS driver:
  • For ELLIPSE, simply use the sbgCenter and in Assignment panel, RTCM should be set to Port A.
  • For High Performance INS, either use the configuration web interface or the sbgInsRestApi.
• Install and configure a third party node that broadcast RTCM corrections such as a NTRIP client
• Update the node config yaml file to set rtcm.subscribe and nmea.publish to true
• If you use a different node to broadcast RTCM topics, you might have to update the config yaml file to update topics and namespaces.

Calibrate the magnetometers

ELLIPSE products can use magnetometers to determine the heading. A calibration is then required to compensate for soft and hard iron distortions due to the vehicle the product is installed on. The magnetic calibration procedure should be held in a clean magnetic environnement (outside of buildings).

You can read more information about magnetic field calibration procedure from the SBG Systems Support Center.

The ROS driver provides a dedicated node to easily use ELLIPSE on board magnetic field calibration algorithms.
The ELLIPSE offers both a 2D and 3D magnetic field calibration mode.

1) Make sure you have selected the desired 2D or 3D magnetic field calibration mode (calibration.mode in the configuration yaml file). 2) Start a new magnetic calibration session once you are ready to map the magnetic field:

roslaunch sbg_driver sbg_device_mag_calibration.launch
rosservice call /sbg/mag_calibration

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

3) Rotate as much as possible the unit to map the surrounding magnetic field (ideally, perform a 360° with X then Y then Z axis pointing downward). 4) Once you believe you have covered enough orientations, compute a magnetic field calibration:

rosservice call /sbg/mag_calibration

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

5) If you are happy with the results (Quality, Confidence), apply and save the new magnetic calibration parameters.
If not, you can continue to rotate the product and try to perform a new computation (and repeat step 4)

rosservice call /sbg/mag_calibration_save

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

6) Reset/Power Cycle the device and you should now get an accurate magnetic based heading.

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"

Frame parameters & conventions

Frame ID

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

# Frame name
frame_id: "imu_link_ned"

Frame convention

The frame convention can be set to NED or ENU:

• The NED convention is SBG Systems native convention so no transformation is applied
• The ENU convention follows ROS standard REP-103

Please read the SBG Systems Support Center article for more details.

You can select the frame convention to use with the following parameter:

# Frame convention
use_enu: true

[!NOTE] The driver only publish standard ROS messages if the driver is setup to use ENU frame convention.

Body/Vehicle Frame:

The X axis should point the vehicle forward direction for both NED and ENU frame conventions. The table below summarizes the body/vehicle axis frame definitions for each convention:

NED Convention	ENU Convention
X Forward	X Forward
Y Right	Y Left
Z Downward	Z Upward

Navigation Frame:

The navigation frame also referred by ROS as the cartesian representation is defined as follow:

NED Convention	ENU Convention
X North	X East
Y East	Y North
Z Down	Z Up

Heading Example:

Based on the definitions above, when using a NED frame, if the vehicle X axis is pointing North, the INS should return a zero heading. When using a ENU frame, the INS should return a zero heading when the vehicle X axis is pointing East.

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.