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Overview

Interface (driver) software, including ROS node, for Microstrain 3DM-GX5-45.

The interface makes use of the MIP SDK Version 1.1 from Microstrain to communicate with the device. Includes the following applications:

Supported Devices

• LORD/Microstrain 3DM-GX5-45: This driver has been mainly tested using the LORD/Microstrain 3DM-GX5-45 sensor. We have done limited testing on the 3DM-GX4-45, and the interface seems to be the same. We have not tested this with the 3DM-GX3-45, but the interface (MIP) should be the same. Please let us know if you find issues.

• Limited testing has been done using the 3DM-GX4-25 (AHRS-only) device. See the microstrain_25.launch file for an example of how to configure the driver for use with the -25.

ROS Nodes

microstrain_3dm_gx5_45

ROS node reports the GPS data, AHRS data and Nav Filter estimate

Published Topics

gps/fix (sensor_msgs/NavSatFix)

• See [[#navsatmsg]Nav Sat Fix message description] below.

imu/data (sensor_msgs/Imu)

• IMU (AHRS) data is provided

nav/odom (nav_msgs/Odometry)

• See Odometry message description below

nav/status (std_msgs/Int16MultiArray)

• See Filter status message description below

Services

reset_kf (std_srvs/Empty)

• Resets the Kalman filter on the device

Parameters

port (string, default: /dev/ttyACM0)

• Serial port - Linux only

baud_rate (int, default: 115200)

• Baud rate of serial connection

device_setup (bool, default: true)

• If true, puts device in idle mode and configures the device.If false, skips configuration. Important: the configuration parameters below are not effective unless this flag is true.

readback_settings (bool, default: true)

• coming soon

auto-init (bool, default: true)

• tbd

dynamics_mode (int, default: 1)

• Vehicle dynamics mode 0x01=Portable, 0x02=Automotive, 0x03=Airborne

declination_source (int, default: 2)

• Possible declination sources: 0x01=Node, device reports magnetic north, 0x02=Internal World Magnetic Model, 0x03=Manual (see declination parameter)

gps_frame_id (string, default: wgs84)

• Value for the frame_id field in the header of the NavSatFix message published on the gps/fix topic

imu_frame_id (string, default: base_link)

• Value of the frame_id field in the header of the Imu message publised in the imu/data topic

odom_frame_id (string, default: wgs84)

• Value of the frame_id field in the header of the Odometry message published on the nav/odom topic

odom_child_frame_id (string, default: base_link)

• Value of the child_frame_id field in the Odometry message published on the nav/odom topic.

publish_gps (bool, default: true)

• Sets if ~gps/fix should be advertised/published or not. Note - to maximize performance you may want to only publish the Odometry messages

publish_imu (bool, default: true)

• Sets if ~imu/data should be advertised/published or not.

publish_gps (bool, default: true)

• Sets if ~nav/odom should be advertised/published or not.

gps_rate (int, default: 1)

• Target update (publishing) rate for gps/fix messages. See update [[#rates] Update Rates] below.

imu_rate (int, default: 10)

• Target update (publishing) rate for imu/data messages. See update [[#rates] Update Rates] below.

odom_rate (int, default: 10)

• Target update (publishing) rate for nav/odom messages. See update [[#rates] Update Rates] below.

Update Rates

The rates are set as a target value in Hz. The device accepts a decimation value for each output; the packet rate is base_rate/decimation, where decimation is an integer. The program calculates the decimation to get close the the desired rate, based on polling the sensor for its base rate.

For the 3DM-GX4-45 and 3DM-GX5-45 devices tested the base rates were...

• GPS - base rate = 4 Hz
• IMU - base rate = 500 Hz
• Filter - base rate = 500 Hz

Odometry message information

• Currently the pose.position is the longitude (x), latitude (y) and ellipsoid height (z)
• pose.covariance and twist.covariance include diagonal elements for position and attitude

Nav Status message description

• Includes three values - see communication protocol for full documentation.
  • filter_state
    • 0x00 – Startup
    • 0x01 – Initialization (see status flags)
    • 0x02 – Running, Solution Valid
    • 0x03 – Running, Solution Error (see status flags)
  • dynamics mode
    • 0x01 – Portable (device default)
    • 0x02 – Automotive
    • 0x03 – Airborne
  • status_flags
    • See device documentation

Nav Sat Fix message description

Position covariance is populated with diagonals based on reported horizontal and vertical accuracy. The status.status field is the LLH position data "valid flag"-1. The valid flag mapping from the 3DM protocol is

• 0x0001 – Latitude and Longitude Valid
• 0x0002 – Ellipsoid Height Valid
• 0x0004 – MSL Height Valid
• 0x0008 – Horizontal Accuracy Valid
• 0x0010 – Vertical Accuracy Valid
• E.g., if all valid, then the status.status field should be 30.

Build Instructions

Building from source

DISTRO={hydro|indigo}
cd ~/catkin_ws
rosdep update
rosdep check --from-paths src/microstrain_3dm_gx5_45/ --rosdistro=$DISRO
rosdep install --from-paths src/microstrain_3dm_gx5_45/ --ignore-src --rosdistro=$DISTRO --simulate
rosdep install --from-paths src/microstrain_3dm_gx5_45/ --ignore-src --rosdistro=$DISTRO
catkin_make
source devel/setup.bash

Dev Notes

• The mip_sdk_user_functions are C functions that need to be called by various parts of the SDK. The main purpose of these functions is to implement the platform-specific serial (RS232) port elements. The prototype serial port open function takes the COM number as an integer input - which is clunky for Linux serial ports. Changed this to take a string defining the port (e.g., /dev/ttyS0), but this necessitated also modifying the mip_sdk_interface.[ch] files, since this is what is called by the application - changed the mip_interface_init function to accept a string argument for specifying the port.

TODO

• Verify order of quaternions

Launch File Examples

There are launch files in the /launch directory to illustrate use of the node.