launch的参数

前文实现的launch较简单,对比ROS1的launch确实了参数传入的功能

<launch>
    <arg name="baudrate" default="$(env PIBOT_DRIVER_BAUDRATE)"  doc="pibot driver baudrate"/>
    <arg name="publish_odom_tf" default="true"  doc="pub tf"/>
    <arg name="use_imu" default="true"  doc="use imu"/>
    <arg name="use_accelerometer" default="true"  doc="use acce"/>
    <arg name="use_gyroscope" default="true"  doc="use gyro"/>
    <arg name="use_magnetometer" default="true"  doc="use mag"/>
    <arg name="cali_imu_startup" default="true"  doc="use mag"/>

    <!-- PIBOT DRIVER -->
    <node name="pibot_driver" pkg="pibot_bringup" type="pibot_driver" output="screen">
        <param name="base_frame" value="base_link" />
        <param name="baudrate" value="$(arg baudrate)" />
        <param name="cmd_vel_topic" value="cmd_vel" />
        <param name="odom_frame" value="odom" />
        <param name="odom_topic" value="odom" if="$(arg publish_odom_tf)"/>
        <param name="odom_topic" value="wheel_odom" unless="$(arg publish_odom_tf)" /> 
        <param name="out_pid_debug_enable" value="false" />
        <param name="port" value="/dev/pibot" />
        <param name="publish_odom_tf" value="$(arg publish_odom_tf)" />
        <param name="freq" value="100" />
        <rosparam if="$(arg use_imu)">
            imu/accelerometer_bias: {x: 0.005436, y: 0.014684, z: -0.395418}
            imu/gyroscope_bias: {x: -0.035592, y: 0.080670, z: 0.001216}
        </rosparam>
        <param name="imu/use_accelerometer" value="$(arg use_accelerometer)" if="$(arg use_imu)"/>
        <param name="imu/use_gyroscope" value="$(arg use_gyroscope)" if="$(arg use_imu)"/>
        <param name="imu/use_magnetometer" value="$(arg use_magnetometer)" if="$(arg use_imu)"/>
        <param name="imu/perform_calibration" value="$(arg cali_imu_startup)" if="$(arg use_imu)"/>
    </node>
</launch>

ROS1中我们可以执行roslaunch时传入相应的参数，例如

roslaunch pibot_bringup bringup.launch use_imu:=false

我们中的ROS1中的launch文件是xml格式的，http://wiki.ros.org/roslaunch/XML这里我们可以看到其定义

参考这里https://docs.ros.org/en/galactic/Tutorials/Launch/Using-ROS2-Launch-For-Large-Projects.html#id7我们添加对应的参数

    baudrate_arg = DeclareLaunchArgument(
        "baudrate", default_value=TextSubstitution(text="115200")
    )

    use_imu_arg = DeclareLaunchArgument(
        "use_imu", default_value=TextSubstitution(text="true")
    )
...
    return LaunchDescription([
        baudrate_arg,
        Node(
            package="pibot_bringup",
            executable="pibot_driver",
            name="pibot_driver",
            output="screen",
            emulate_tty=True,
            parameters=[
                ...
                {"imu/use_accelerometer": LaunchConfiguration('use_imu')},
                {"imu/use_gyroscope": LaunchConfiguration('use_imu')},
                {"imu/use_magnetometer": LaunchConfiguration('use_imu')},
                ...
            ]
        )
...

对比ROS1中我们是从环境变量PIBOT_DRIVER_BAUDRATE读取波特率, 稍作修改, 因launch文件是python对比之前xml我们就可以更大发挥空间了

    import os
...
    default_baudrate = os.getenv('PIBOT_DRIVER_BAUDRATE')
    if default_baudrate is None:
        default_baudrate = "115200"

    baudrate_arg = DeclareLaunchArgument(
        "baudrate", default_value=TextSubstitution(text=default_baudrate)
    )

测试

环境变量

export PIBOT_DRIVER_BAUDRATE=921600
ros2 launch  pibot_bringup bringup_launch.py use_imu:=true

指定参数

ros2 launch  pibot_bringup bringup_launch.py baudrate:=921600 use_imu:=false

本文代码https://gitee.com/pibot/pibot_bringup/tree/278aaab26a3b51425496de26dc6a885d0b240cc4