ROS - Usage

I provide an online node component, a standalone online node, and an offline node.

The offline node provides a way to directly read data from a rosbag, instead of the usual pattern of playing the bag with ros2 bag play.

Both nodes can be launched via the odometry.launch.py launch file, specifying the mode argument (default: online).

To see all possible configuration options:

ros2 launch rko_lio odometry.launch.py -s

That will also provide additional documentation about the different parameters.

For some additional details regarding the odometry parameters and data itself, please refer to Configuring the odometry and The sensor data. ROS-specific parameters are covered here.

At minimum, you’ll need to specify the lidar_topic, imu_topic and base_frame parameters.

You can define all parameters in a config file and pass it with the launch argument config_file:=/path. Please note that we don’t modify the path you provide in any way.

If your TF tree is well defined, i.e., it exists and the message frame ids match the frame ids in the TF tree (I’ve seen both conditions fail), then the sensor frame ids are picked up from the topics and the extrinsics via TF lookup.

Otherwise you’ll need to either specify just the frame ids (if there’s a mismatch), or specify the extrinsics via extrinsic_lidar2base_quat_xyzw_xyz written as quaternion (xyzw) and translation (xyz) in a list (only supported via a config file). Similarly for the IMU to base as extrinsic_imu2base_quat_xyzw_xyz.

But really, if you have a TF problem, just fix it instead.

config/default.yaml specifies the default set of parameters explicitly, and also leaves some placeholders you can modify to pass the lidar_topic and similar.

Please note that the parameter definitions from the CLI will override those provided in a config file.

You can enable RViz visualization by passing rviz:=true which launches an RViz window simultaneously using the default RViz config file in config/default.rviz.

An example full invocation with RViz can look like this:

ros2 launch rko_lio odometry.launch.py \
    config_file:=/path/to/config/file \
    rviz:=true

Published topics

• /rko_lio/odometry: Odometry topic, the name can be modified using the odom_topic parameter.

  This also includes the twist of the base_frame expressed in base_frame coordinates. This twist is estimated from the LiDAR scan registration.

  A TF is also simultaneously published from the base_frame to the odom_frame. Please note the parameter invert_odom_tf in case your TF configuration requires this (you’re running multiple odometries or some other complicated setup).

• /rko_lio/frame: The input LiDAR scan deskewed using the IMU data.

  Only published if publish_deskewed_scan:=true.

• /rko_lio/local_map: The local map the odometry maintains is published at a set frequency given by publish_map_after (seconds), and only if publish_local_map:=true.

• /rko_lio/linear_acceleration: Linear acceleration of the base_frame expressed in base_frame coordinates.

  Note that this acceleration can be quite noisy, as it is essentially a double time derivative of the pose update from the LiDAR scan registration (similar to the twist/velocity).

  Only published if publish_lidar_acceleration:=true.

Offline node

As mentioned before, you can use the offline node to read a bag directly and run the odometry on it at the same time.

Specify mode:=offline as the default is online.

Pass the bag_path:= parameter to the launch file, which should be a folder containing the .db3 or .mcap or other ROS-supported formats (you probably need the respective plugins).

The offline node additionally publishes a convenient topic /rko_lio/bag_progress which you can use to monitor bag playing progress. It has two values, a percentage completion and an ETA.

An example invocation would then look like:

ros2 launch rko_lio odometry.launch.py \
    config_file:=/path/to/config/file \
    rviz:=true \
    mode:=offline \
    bag_path:=/path/to/rosbag/directory