ENU NED frames

By default, the sensors that the microstrain_inertial_driver supports output data in the NED frame. The ROS standard is for position data to be in ENU. Additionally, the vehicle frame definition for microstrain sensors is different than the ROS definition. use_enu_frame will cause the driver to either publish data using ROS's standards, or microstrain standards.

When use_enu_frame: False, the driver will output all globally referenced data in the NED frame. Additionally, any local frame data will be output in the microstrain vehicle frame. See Different Frames for more information.

When use_enu_frame: True, the driver will output all globally referenced data in the ENU frame. Additionally, any local frame data will be output in the ROS vehicle frame. See Different Frames for more information.

Behavior

The list below breaks down how different components of the driver will behave depending on the value of use_enu_frame.

Publishers

• /imu/data:
  • orientation: Reported in device body frame with respect to the NED/ENU frame.
  • angular_velocity: Reported in the microstrain/ROS vehicle frame.
  • linear_acceleration: Reported in the microstrain/ROS vehicle frame.
• /imu/mag:
  • magnetic_field: Reported in the microstrain/ROS vehicle frame.
• /gnss_1/velocity:
  • twist: Reported in the NED/ENU frame.
• /gnss_2/velocity:
  • twist: Reported in the NED/ENU frame.
• /ekf/imu/data:
  • orientation: Reported in device body frame with respect to the NED/ENU frame.
  • orientation_covariance: Reported in the NED/ENU frame.
  • angular_velocity: Reported in the microstrain/ROS vehicle frame.
  • linear_acceleration: Reported in the microstrain/ROS vehicle frame.
• /ekf/llh_position:
  • position_covariance: Reported in the NED/ENU frame.
• /ekf/velocity:
  • twist: Reported in the NED/ENU frame.
• /ekf/odomtery_map:
  • twist: Reported in the microstrain/ROS vehicle frame.
  • pose: Reported in the NED/ENU frame.
• /ekf/dual_antenna_heading:
  • pose: Reported in device body frame with respect to the NED/ENU frame.

Transforms

Note

See Frame IDs for more information on what these Frame IDs represent.

• frame_id -> gnss1_frame_id:
  • Will be published in the microstrain/ROS vehicle frame.
• frame_id -> gnss2_frame_id:
  • Will be published in the microstrain/ROS vehicle frame.
• frame_id -> odometer_frame_id:
  • Will be published in the microstrain/ROS vehicle frame.
• earth_frame_id -> map_frame_id:
  • Will be interpreted or published in the NED/ENU frame.

Subscribers

The following topics accept external aiding measurements. If use_enu_frame: True, they will expect that the frame_id of the message is in the ROS vehicle frame. If use_enu_frame: False, they will expect that the frame_id of the message is in the microstrain vehicle frame.

• ext/llh_position
• ext/velocity_ned
• ext/velocity_enu
• ext/velocity_ecef
• ext/velocity_body
• ext/heading_ned
• ext/heading_enu

Different Frames

NED Frame

The NED frame is outlined in the NED Frame page of the microstrain documentation, and is described as:

• X North
• Y East
• Z Down

ENU Frame

The ENU frame is outlined in REP 103, and is described as:

• X East
• Y North
• Z Up

MicroStrain Vehicle Frame

The microstrain vehicle frame is outlined in the Vehicle Frame page of the microstrain documentation. It is described as:

• X Forward
• Y Right
• Z Down

And can be visualized as:

ROS Vehicle Frame

The ROS vehicle frame is outlined in REP 103. It is described as:

• X Forward
• Y Left
• Z up

And can be visualized as: