ROSaic Parameters

The following is a list of ROSaic parameters found in the config/rover.yaml file.

• Parameters Configuring Communication Ports and Processing of GNSS and INS Data

  • device: location of device connection
    • serial:xxx format for serial connections, where xxx is the device node, e.g. serial:/dev/ttyUSB0
    • file_name:path/to/file.sbf format for publishing from an SBF log
    • file_name:path/to/file.pcap format for publishing from PCAP capture.
      • Regarding the file path, ROS_HOME=`pwd` in front of roslaunch septentrio... might be useful to specify that the node should be started using the executable's directory as its working-directory.
    • tcp://host:port format for TCP/IP connections
      • 28784 should be used as the default (command) port for TCP/IP connections. If another port is specified, the receiver needs to be (re-)configured via the Web Interface before ROSaic can be used.
    • default: empty
  • serial: specifications for serial communication
    • serial/baudrate: serial baud rate to be used in a serial connection
    • serial/rx_serial_port: determines to which (virtual) serial port of the Rx we want to get connected to, e.g. USB1 or COM1
    • hw_flow_control: specifies whether the serial (the Rx's COM ports, not USB1 or USB2) connection to the Rx should have UART HW flow control enabled or not
      • off to disable UART HW flow control, RTS|CTS to enable it
    • default: 115200, USB1, off
  • receiver_type: This parameter is to select the type of Septentrio receiver
    • GNSS: If the receiver_type: GNSS then ROS can only output data related to GNSS receivers.
    • INS: If the receiver_type: INS then ROS can only output data related to INS receivers.
  • frame_id: name of the ROS tf frame for the Rx, placed in the header of all published messages
    • In ROS, the tf package lets you keep track of multiple coordinate frames over time. The frame ID will be resolved by tf_prefix if defined. If a ROS message has a header (all of those we publish do), the frame ID can be found via rostopic echo /topic, where /topic is the topic into which the message is being published.
    • default: gnss
  • datum: datum that (ellipsoidal) height should be referenced to in all published ROS messages
    • Since the standardized GGA message does only provide the orthometric height (= MSL height = distance from Earth's surface to geoid) and the geoid undulation (distance from geoid to ellipsoid) for which non-WGS84 datums cannot be specified, it does not affect the GGA message.
    • default: ETRS89
  • marker_to_arp: offsets of the antenna reference point (ARP) with respect to the marker
    • The parameters delta_e, delta_n and delta_u are the offsets in the East, North and Up (ENU) directions respectively, expressed in meters.
    • All absolute positions reported by the receiver are marker positions, obtained by subtracting this offset from the ARP. The purpose is to take into account the fact that the antenna may not be located directly on the surveying point of interest.
    • default: 0.0, 0.0 and 0.0
  • ant_type: type of your antenna
    • For best positional accuracy, it is recommended to select a type from the list returned by the command lstAntennaInfo, Overview. This is the list of antennas for which the receiver can compensate for phase center variation.
    • By default and if ant_type does not match any entry in the list returned by lstAntennaInfo, Overview, the receiver will assume that the phase center variation is zero at all elevations and frequency bands, and the position will not be as accurate.
    • default: Unknown
  • ant_serial_nr: serial number of your antenna
  • leap_seconds: number of leap seconds that have been inserted up until the point of ROSaic usage
    • At the time of writing the code (2020), the GPS time, which is unaffected by leap seconds, was ahead of UTC time by 18 leap seconds. Adapt the leap_seconds parameter accordingly as soon as the next leap second is inserted into the UTC time or in case you are using ROSaic for the purpose of simulations. In the latter case, in addition please set the parameter use_GNSS_time to true and uncomment a paragraph in the UTCtoUnix() function definition found in the file septentrio_gnss_driver/src/septentrio_gnss_driver/parsers/parsing_utilities.cpp and enter the year, month and date to be simulated.
  • polling_period/pvt: desired period in milliseconds between the polling of two consecutive PVTGeodetic, PosCovGeodetic, PVTCartesian and PosCovCartesian blocks and - if published - between the publishing of two of the corresponding ROS messages (e.g. septentrio_gnss_driver/PVTGeodetic.msg)
    • Clearly, the publishing of composite ROS messages such as sensor_msgs/NavSatFix.msg or gps_common/GPSFix.msg is triggered by the SBF block that arrives last among the blocks of the current epoch.
    • default: 500 (2 Hz)
  • polling_period/rest: desired period in milliseconds between the polling of all other SBF blocks and NMEA sentences not addressed by the previous parameter, and - if published - between the publishing of all other ROS messages
    • default: 500 (2 Hz)
  • reconnect_delay_s: delay in seconds between reconnection attempts to the connection specified in the parameter device
    • default: 2
  • use_GNSS_time: true if the ROS message headers' unix epoch time field shall be constructed from the TOW (in the SBF case) and UTC (in the NMEA case) data, false if those times shall be constructed by the driver via the time(NULL) function found in the ctime library
    • default: true
  • ntrip_settings: determines NTRIP connection parameters
    • The two implemented use cases are
      • a) The Rx has internet access, set rx_has_internet to true, and
      • b) The Rx has no internet access, set rx_has_internet to false, but Data Link from Septentrio's RxTools is installed on the computer.
    • The first nested ROS parameter, ntrip_settings/mode, specifies the type of the NTRIP connection and must be one of Client, Client-Sapcorda or off. In Client mode, the receiver receives data from the NTRIP caster. When selecting the Client-Sapcorda mode, the receiver receives data from the Sapcorda NTRIP service and no further settings are required, i.e. all other nested parameters are ignored. Note that the latter mode only works in Europe and North America. Set mode to off to disable all correction services.
    • Next, ntrip_settings/caster is the hostname or IP address of the NTRIP caster to connect to. To send data to the built-in NTRIP caster, use "localhost" for this parameter.
    • Note that ntrip_settings/port, ntrip_settings/username, ntrip_settings/password and ntrip_settings/mountpoint are the IP port number, the user name, the password and the mount point, respectively, to be used when connecting to the NTRIP caster. The receiver encrypts the password so that it cannot be read back with the command "getNtripSettings". The ntrip_settings/version argument specifies which version of the NTRIP protocol to use (v1 or v2).
    • Further, send_gga specifies whether or not to send NMEA GGA messages to the NTRIP caster, and at which rate. It must be one of auto, off, sec1, sec5, sec10 or sec60. In auto mode, the receiver automatically sends GGA messages if requested by the caster.
    • The boolean parameter rx_has_internet specifies whether the Rx has internet access or not. Note that an Ethernet cable is the only way to enable internet access on mosaic receivers (and most others) at the moment. In case internet is available, NTRIP will be configured with a simple command snts, ... that ROSaic sends to the receiver.
    • The parameter rtcm_version specifies the type of RTCM data transmitted to ROSaic by the NTRIP caster, either RTCMv2 or RTCMv3. It depends on the mountpoint.
    • In case the connection to the receiver is via TCP, rx_input_corrections_tcp specifies the port number of the IP server (IPS1) connection that ROSaic establishes on the receiver. Note that ROSaic will send GGA messages on this connection, such that in the Data Link application of RxTools one just needs to set up a TCP client to the host name as found in the ROSaic parameter device with the port as found in rx_input_corrections_tcp. If the latter connection were connection 1 on Data Link, then connection 2 would set up an NTRIP client connecting to the NTRIP caster as specified in the above parameters in order to forward the corrections from connection 2 to connection 1.
    • Finally, in case we are facing a serial connection (COM or USB), the parameter rx_input_corrections_serial analogously determines the port on which corrections could be serially forwarded to the Rx via Data Link.
    • default: off, empty, empty, empty, empty, empty, v2, auto, false, RTCMv2, 6666, USB2

  Inertial Navigation System (INS)

  • Inertial Navigation System (INS) is a device which measures rotation and acceleration and uses this information from Inertial Measurement Unit (IMU) to calculate its position relative to the starting point and provides continuous positioning even during short GNSS outages.

  • The IMU is typically made up of a 3-axis accelerometer, a 3-axiss gyroscope and sometimes a 3-axis magnetometer and measures the system's angular rate and acceleration. The computational unit used to determine the attitude, position, and velocity of the system based on the raw measurements from the IMU given an initial starting position and attitude.

    Measure and Compensate for Antenna Lever arm

    • The antenna lever-arm is the relative position between the IMU reference point and the GNSS Antenna Reference Point (ARP), measured in the vehicle frame.

    • In case of AsteRx SBi3, the IMU reference point is clearly marked on the top panel of the receiver. It is important to compensate for the effect of the lever arm, otherwise the receiver may not be able to calculate an accurate INS position.

    • The IMU/antenna position can be changed by specifying the lever arm x,yand z in the config.yaml file under the ins_ant_lever_arm parameter

      

    Compensate for IMU/Receiver Orientations

    • It is important to take into consideration the mounting direction of the receiver, therefore the IMU, in the body frame of the vehicle. For e.g. when the receiver is installed horizontally with the front panel facing the direction of travel, it will be necessary to compensate for the IMU’s orientation to make sure the IMU reference frame is aligned with the vehicle reference frame.
    • The IMU’s orientation can be changed by specifying the orientation anglestheta_x,theta_yand theta_z in the config.yaml file under the imu_orientation/angles
    • The below image illustrates the orientation of the IMU reference frame with the associated IMU orientation for the depicted installation

    

  • These Steps should be followed to configure the receiver in INS integration mode:

    • Specify the receiver_type:INS
    • Specify the orientation of the IMU sensor with respect to your vehicle, using the imu_orientation parameter
    • Specify the antenna lever arm in the vehicle reference frame. This is the vector starting from the IMU reference point to the ARP of the main GNSS antenna This can be done by ins_ant_lever_arm parameter
    • If the point of interest is not the IMU, the vector between the IMU and the point of interest can be provided with the ins_point_of_interest parameter
    • Make sure that the INS/GNSS integration filter is enabled :ins_output_type

  ROSaic INS parameters

  • The following is a list of ROSaic INS parameters found in the config/rover.yaml file.

  • Tested with the AsteRx-SBi3 Pro receiver

    attitude_offset

    • attitude_offset: Angular offset between two antenna (Main and Aux) and vehicle heading
      • heading:The perpendicular axis can be compensated for by adjusting the heading parameter
      • pitch: Vertical offset can be compensated for by adjusting the pitch parameter
    imu_orientation

    • imu_orientation: IMU sensor orientation
      • If orientation is set to sensor_default to true, the receiver assumes that the IMU is attached to the vehicle in the nominal orientation, i.e. horizontally, upside up and with the X axis marked on the receiver pointing to the front of the vehicle. In this case the value of theta_x, theta_y and theta_z under angles param should be equal to zero
      • If orientation is set to manual: true , the receiver will use parameters theta_x, theta_y and theta_z under angles param to determine the sensor orientation with respect to the vehicle frame. Positive angles correspond to a right-handed (clockwise) rotation of the IMU with respect to its nominal orientation. The order of the rotations is as follows: theta_z first, then theta_y, then theta_x. (The value should be in degrees)
    ins_poi_of_interest

    • ins_point_of_interest: The lever arm from the IMU reference point to a user-defined point of interest in the vehicle

      • The parameters poi_x,poi_y and poi_z refers to the vehicle reference frame (The value should be in meter)
      • The reference point of the navigation output in the insnavcart and insnavgeod of ROS /topic is either the main GNSS antenna, or POI. By default, POI is colocated with the IMU reference point (lever arm is zero by default)
    ins_ant_lever_arm

    • ins_ant_lever_arm: The lever arm from the IMU reference point to the main GNSS antenna
      • The parameters x,y and z refers to the vehicle reference frame (The value should be in meter)
    ins_vel_sensor_lever_arm

    • ins_vel_sensor_lever_arm: The lever arm from the IMU reference point to the velocity sensor
    • The parameters vsm_x,vsm_y and vsm_z refers to the vehicle reference frame (The value should be in meter)
    ins_initial_heading

    • ins_initial_heading: This parameter enables the use of last computed headings when unit is power cycled
      • auto: This mode will store the vehicle heading,whenever the vehicle is in static
      • stored: This mode is used to store the last heading alignment when the vehicle stopped before switching of the receiver.
    ins_std_dev_mask

    • ins_std_dev_mask: This parameter represent the maximum accepted accuracy. By providing the parameter value will let the receiver compansate for the offset before calculating the attitude by sbstracting them from the measured attitude angles. If standard deviation exceed then INS position and INS attitude won't be available in the output.
      • att_std_dev: This parameter configures an output limit on standard deviation of the attitude angles (max accuracy accepted: 5 degree)
      • pos_std_dev: This parameter configures an output limit on standard deviation of the position (max accuracy range between -100m to 100m)
    ins_output_type

    • ins_output_type: The INS navigation filter
      • output_location: This parameter either refer to the main GNSS antenna ARP or to a user-defined point of interest (POI) on the vehicle. The user can either use lever arms from the IMU to main antenna as output_location: MainAnt or to user defined point of interest as output_location: POI1
      • The ins_output_type parameter enables or disables the computation of INS attitude or velocity and the associated standard deviations, and publish the following INS related data. For e.g. if pos_std_dev: false then the value of position standard deviation block in the topic /insnavcart and /insnavgeod will be NaN and even these parameters will affect the ROS standard messages, so make sure to set all these param to true.
      • pos_std_dev: true
      • att: true
      • att_std_dev: true
      • vel: true
      • vel_std_dev: true

• For further more information about receiver and their parameters, visit ins_user_manual reference_guide

Parameters Configuring (Non-)Publishing of ROS Messages

• publish/gpgga: true to publish septentrio_gnss_driver/GPGGA.msg messages into the topic /gpgga
• publish/gprmc: true to publish septentrio_gnss_driver/GPRMC.msg messages into the topic /gprmc
• publish/gpgsa: true to publish septentrio_gnss_driver/GPGSA.msg messages into the topic /gpgsa
• publish/gpgsv: true to publish septentrio_gnss_driver/GPGSV.msg messages into the topic /gpgsv
• publish/pvtcartesian: true to publish septentrio_gnss_driver/PVTCartesian.msg messages into the topic /pvtcartesian
• publish/pvtgeodetic: true to publish septentrio_gnss_driver/PVTGeodetic.msg messages into the topic /pvtgeodetic
• publish/poscovcartesian: true to publish septentrio_gnss_driver/PosCovCartesian.msg messages into the topic /poscovcartesian
• publish/poscovgeodetic: true to publish septentrio_gnss_driver/PosCovGeodetic.msg messages into the topic /poscovgeodetic
• publish/atteuler: true to publish septentrio_gnss_driver/AttEuler.msg messages into the topic /atteuler
• publish/attcoveuler: true to publish septentrio_gnss_driver/AttCovEuler.msg messages into the topic /attcoveuler
• publish/gpst: true to publish sensor_msgs/TimeReference.msg messages into the topic /gpst
• publish/navsatfix: true to publish sensor_msgs/NavSatFix.msg messages into the topic /navsatfix
• publish/gpsfix: true to publish gps_common/GPSFix.msg messages into the topic /gpsfix
• publish/pose: true to publish geometry_msgs/PoseWithCovarianceStamped.msg messages into the topic /pose
• publish/diagnostics: true to publish diagnostic_msgs/DiagnosticArray.msg messages into the topic /diagnostics
• publish/insnavcart: true to publish septentrio_gnss_driver/INSNavCart.msg message into the topic/insnavcart
• publish/insnavgeod: true to publish septentrio_gnss_driver/INSNavGeod.msg message into the topic/insnavgeod
• publish/extsensormeas: true to publish septentrio_gnss_driver/ExtSensorMeas.msg message into the topic/extsensormeas
• publish/imusetup: true to publish septentrio_gnss_driver/IMUSetup.msg message into the topic/imusetup
• publish/velsensorsetup: true to publish septentrio_gnss_driver/VelSensorSetup.msgs message into the topic/velsensorsetup
• publish/exteventinsnavcart: true to publish septentrio_gnss_driver/ExtEventINSNavCart.msgs message into the topic/exteventinsnavcart
• publish/exteventinsnavgeod: true to publish septentrio_gnss_driver/ExtEventINSNavGeod.msgs message into the topic/exteventinsnavgeod

ROS Topic Publications

A selection of NMEA sentences, the majority being standardized sentences, and proprietary SBF blocks is translated into ROS messages, partly generic and partly custom, and can be published at the discretion of the user into the following ROS topics. All published ROS messages, even custom ones, start with a ROS generic header std_msgs/Header.msg, which includes the receiver time stamp as well as the frame ID, the latter being specified in the ROS parameter frame_id.

• /gpgga: publishes custom ROS message septentrio_gnss_driver/Gpgga.msg - equivalent to nmea_msgs/Gpgga.msg - converted from the NMEA sentence GGA
• /gprmc: publishes custom ROS message septentrio_gnss_driver/Gprmc.msg - equivalent to nmea_msgs/Gprmc.msg - converted from the NMEA sentence RMC
• /gpgsa: publishes custom ROS message septentrio_gnss_driver/Gpgsa.msg - equivalent to nmea_msgs/Gpgsa.msg - converted from the NMEA sentence GSA
• /gpgsv: publishes custom ROS message septentrio_gnss_driver/Gpgsv.msg - equivalent to nmea_msgs/Gpgsv.msg - converted from the NMEA sentence GSV
• /pvtcartesian: publishes custom ROS message septentrio_gnss_driver/PVTCartesian.msg, corresponding to the SBF block PVTCartesian
• /pvtgeodetic: publishes custom ROS message septentrio_gnss_driver/PVTGeodetic.msg, corresponding to the SBF block PVTGeodetic
• /poscovcartesian: publishes custom ROS message septentrio_gnss_driver/PosCovCartesian.msg, corresponding to SBF block PosCovCartesian
• /poscovgeodetic: publishes custom ROS message septentrio_gnss_driver/PosCovGeodetic.msg, corresponding to SBF block PosCovGeodetic
• /atteuler: publishes custom ROS message septentrio_gnss_driver/AttEuler.msg, corresponding to SBF block AttEuler
• /attcoveuler: publishes custom ROS message septentrio_gnss_driver/AttCovEuler.msg, corresponding to the SBF block AttCovEuler
• /gpst (for GPS Time): publishes generic ROS message sensor_msgs/TimeReference.msg, converted from the PVTGeodetic block's GPS time information, stored in its header, or - if use_gnss_time is set to false - from the systems's wall-clock time
• /navsatfix: publishes generic ROS message sensor_msgs/NavSatFix.msg, converted from the SBF blocks PVTGeodetic,PosCovGeodetic and INSNavGeod
  • The ROS message sensor_msgs/NavSatFix.msg can be fed directly into the navsat_transform_node of the ROS navigation stack.
• /gpsfix: publishes generic ROS message gps_common/GPSFix.msg, which is much more detailed than sensor_msgs/NavSatFix.msg, converted from the SBF blocks PVTGeodetic, PosCovGeodetic, ChannelStatus, MeasEpoch, AttEuler, AttCovEuler, VelCovGeodetic, INSNavGeod and DOP
• /pose: publishes generic ROS message geometry_msgs/PoseWithCovarianceStamped.msg, converted from the SBF blocks PVTGeodetic, PosCovGeodetic, AttEuler, AttCovEuler and INSNavGeod
• /insnavcart: publish custom ROS message septentrio_gnss_driver/INSNavCart.msg, corresponding to SBF block INSNavCart
• /insnavgeod: publish custom ROS message septentrio_gnss_driver/INSNavGeod.msg, corresponding to SBF block INSNavGeod
• /extsensormeas: publish custom ROS message septentrio_gnss_driver/ExtSensorMeas.msg, corresponding to SBF block ExtSensorMeas
• /imusetup: publish custom ROS message septentrio_gnss_driver/IMUSetup.msg, corresponding to SBF block IMUSetup
• /velsensorsetup: publish custom ROS message septentrio_gnss_driver/VelSensorSetup.msg corresponding to SBF block VelSensorSetup
• /exteventinsnavcart: publish custom ROS message septentrio_gnss_driver/ExtEventINSNavCart.msg, corresponding to SBF block ExtEventINSNavCart
• /exteventinsnavgeod: publish custom ROS message septentrio_gnss_driver/ExtEventINSNavGeod.msg, corresponding to SBF block ExtEventINSNavGeod
  • Note that GNSS provides absolute positioning, while robots are often localized within a local level frame. The pose field of this ROS message contains position with respect to the absolute ENU frame (longitude, latitude, height), while the orientation is with respect to a vehicle-fixed (e.g. for mosaic-x5 in moving base mode via the command setAntennaLocation, ...) !local! NED frame. Thus the orientation is !not! given with respect to the same frame as the position is given in. The cross-covariances are hence set to 0.
  • In ROS, all state estimation nodes in the robot_localization package can accept the ROS message geometry_msgs/PoseWithCovarianceStamped.msg.
• /diagnostics: accepts generic ROS message diagnostic_msgs/DiagnosticArray.msg, converted from the SBF blocks QualityInd, ReceiverStatus and ReceiverSetup