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来源: ros2与Python入门教程-使用参数 - 创客智造

说明：

• 介绍如何在ros2中使用参数

步骤：

• 创建包

cd ~/dev_ws/src
ros2 pkg create --build-type ament_python python_parameters --dependencies rclpy

• --dependencies参数会自动把相关依赖增加到package.xml和CMakeLists.txt文件
• 更改package.xml
• 按实际变更如下几行

<description>Python parameter tutorial</description>
<maintainer email="you@email.com">Your Name</maintainer>
<license>Apache License 2.0</license>

• 在dev_ws/src/python_parameters/python_parameters目录下
• 新增python_parameters_node.py文件，内容如下：

import rclpy
import rclpy.node
from rclpy.exceptions import ParameterNotDeclaredException
from rcl_interfaces.msg import ParameterType
 
class MinimalParam(rclpy.node.Node):
    def __init__(self):
        super().__init__('minimal_param_node')
        timer_period = 2  # seconds
        self.timer = self.create_timer(timer_period, self.timer_callback)
 
        self.declare_parameter("my_parameter")
 
    def timer_callback(self):
        # First get the value parameter "my_parameter" and get its string value
        my_param = self.get_parameter("my_parameter").get_parameter_value().string_value
 
        # Send back a hello with the name
        self.get_logger().info('Hello %s!' % my_param)
 
        # Then set the parameter "my_parameter" back to string value "world"
        my_new_param = rclpy.parameter.Parameter(
            "my_parameter",
            rclpy.Parameter.Type.STRING,
            "world"
        )
        all_new_parameters = [my_new_param]
        self.set_parameters(all_new_parameters)
 
def main():
    rclpy.init()
    node = MinimalParam()
    rclpy.spin(node)
 
if __name__ == '__main__':
    main()

• 变更setup.py,增加入口
• 修改配置，内容与package.xml保持一致

maintainer='YourName',
maintainer_email='you@email.com',
description='Python parameter tutorial',
license='Apache License 2.0',

• 修改entry_points

entry_points={
    'console_scripts': [
        'param_talker = python_parameters.python_parameters_node:main',
    ],
},

• 安装依赖

cd ~/dev_ws
rosdep install -i --from-path src --rosdistro foxy -y

• 编译包

colcon build --packages-select python_parameters

• 新开终端，执行

. install/setup.bash
ros2 run python_parameters param_talker

• 效果：

[INFO] [parameter_node]: Hello world!

• 列出所有参数

ros2 param list

• 终端下更改参数值

ros2 param set /minimal_param_node my_parameter earth

• 通过launch文件来修改参数值
• 在dev_ws/src/python_parameters/launch目录下
• 新增python_parameters_launch.py，内容如下：

from launch import LaunchDescription
from launch_ros.actions import Node
 
def generate_launch_description():
    return LaunchDescription([
        Node(
            package="python_parameters",
            executable="param_talker",
            name="custom_parameter_node",
            output="screen",
            emulate_tty=True,
            parameters=[
                {"my_parameter": "earth"}
            ]
        )
    ])

• 打开setup.py, 增加如下内容

import os
from glob import glob
# ...
 
setup(
  # ...
  data_files=[
      # ...
      (os.path.join('share', package_name), glob('launch/*_launch.py')),
    ]
  )

• 重新编译

colcon build --packages-select python_parameters

• 新开终端，运行

. install/setup.bash
ros2 launch python_parameters python_parameters_launch.py

• 效果如下：

[parameter_node-1] [INFO] [custom_parameter_node]: Hello earth!