1 param介绍

类似C++编程中的全局变量，可以便于在多个程序中共享某些数据，参数是ROS机器人系统中的全局字典，可以运行多个节点中共享数据。

• 全局字典
  在ROS系统中，参数是以全局字典的形态存在的，什么叫字典？就像真实的字典一样，由名称和数值组成，也叫做键和值，合成键值。或者我们也可以理解为，就像编程中的参数一样，有一个参数名 ，然后跟一个等号，后边就是参数值了，在使用的时候，访问这个参数名即可。

• 可动态监控
  在ROS2中，参数的特性非常丰富，比如某一个节点共享了一个参数，其他节点都可以访问，如果某一个节点对参数进行了修改，其他节点也有办法立刻知道，从而获取最新的数值。这在参数的高级编程中，大家都可能会用到。

2 param编码示例

这里创建功能包名为，learning05_param

2.1 parameter.cpp

/*** @file parameters.cpp** @brief A node to declare and get parameters*        Here the parameters are the message data for two publisher*        It's possible to change them at run time using the commad line*        "ros2 param set /set_parameter_node vehicle_speed 100"*        "ros2 param set /set_parameter_node vehicle_type car"*        or using a launch file** @author Antonio Mauro Galiano* Contact: https://www.linkedin.com/in/antoniomaurogaliano/**/#include <chrono>
#include <string>
#include "rclcpp/rclcpp.hpp"
#include "std_msgs/msg/string.hpp"
#include "std_msgs/msg/int16.hpp"using namespace std::chrono_literals;class MySetParameterClass: public rclcpp::Node
{
private:int velocityParam_;std::string typeVehicleParam_;rclcpp::TimerBase::SharedPtr timer_;rclcpp::Publisher<std_msgs::msg::String>::SharedPtr pubString_;rclcpp::Publisher<std_msgs::msg::Int16>::SharedPtr pubInt_;void TimerCallback();public:MySetParameterClass(): Node("set_parameter_node"){// here are declared the parameters and their default valuesthis->declare_parameter<std::string>("vehicle_type", "bike");this->declare_parameter<int>("vehicle_speed", 10);pubString_ = this->create_publisher<std_msgs::msg::String>("/vehicle_type", 10);pubInt_ = this->create_publisher<std_msgs::msg::Int16>("/vehicle_speed", 10);timer_ = this->create_wall_timer(1000ms, std::bind(&MySetParameterClass::TimerCallback, this));}
};void MySetParameterClass::TimerCallback()
{// here the params get their value from outside// such as a set command or a launch filethis->get_parameter("vehicle_type", typeVehicleParam_);this->get_parameter("vehicle_speed", velocityParam_);std_msgs::msg::String messageString;messageString.data=typeVehicleParam_;std_msgs::msg::Int16 messageInt;messageInt.data=velocityParam_;RCLCPP_INFO(this->get_logger(), "Publishing two messages -> vehicle type %s\tVehicle speed %d",typeVehicleParam_.c_str(), velocityParam_);pubInt_->publish(messageInt);pubString_->publish(messageString);
}int main(int argc, char** argv)
{rclcpp::init(argc, argv);auto node = std::make_shared<MySetParameterClass>();rclcpp::spin(node);rclcpp::shutdown();return 0;
}

2.2 CMakeLists.txt

cmake_minimum_required(VERSION 3.5)
project(learning05_param)# Default to C99
if(NOT CMAKE_C_STANDARD)set(CMAKE_C_STANDARD 99)
endif()# Default to C++14
if(NOT CMAKE_CXX_STANDARD)set(CMAKE_CXX_STANDARD 14)
endif()if(CMAKE_COMPILER_IS_GNUCXX OR CMAKE_CXX_COMPILER_ID MATCHES "Clang")add_compile_options(-Wall -Wextra -Wpedantic)
endif()# find dependencies
find_package(ament_cmake REQUIRED)
find_package(rclcpp REQUIRED)
find_package(std_msgs REQUIRED)if(BUILD_TESTING)find_package(ament_lint_auto REQUIRED)# the following line skips the linter which checks for copyrights# uncomment the line when a copyright and license is not present in all source files#set(ament_cmake_copyright_FOUND TRUE)# the following line skips cpplint (only works in a git repo)# uncomment the line when this package is not in a git repo#set(ament_cmake_cpplint_FOUND TRUE)ament_lint_auto_find_test_dependencies()
endif()add_executable(parameters src/parameters.cpp)
ament_target_dependencies(parameters rclcpp std_msgs)install(TARGETSparametersDESTINATION lib/${PROJECT_NAME})ament_package()

2.3 package.xml

<?xml version="1.0"?>
<?xml-model href="http://download.ros.org/schema/package_format3.xsd" schematypens="http://www.w3.org/2001/XMLSchema"?>
<package format="3"><name>learning05_param</name><version>0.0.0</version><description>Example node to handle parameters</description><maintainer email="foo@foo.foo">Antonio Mauro Galiano</maintainer><license>TODO: License declaration</license><buildtool_depend>ament_cmake</buildtool_depend><depend>rclcpp</depend><test_depend>ament_lint_auto</test_depend><test_depend>ament_lint_common</test_depend><export><build_type>ament_cmake</build_type></export>
</package>

3 编译运行

# 编译
colcon build# source环境变量
source install/setup.sh# 运行parameters节点
ros2 run learning05_param parameters

可以看到

再开一个终端，

这里set了vehicle_speed值为12，可以看到运行的程序中vehicle_speed的值从10 变为了12

4 param常用指令

查看列表参数
ros2 param list

ros2 param list
/set_parameter_node:
use_sim_time
vehicle_speed
vehicle_type

查看描述
ros2 param describe /set_parameter_node use_sim_time

ros2 param describe /set_parameter_node use_sim_time
Parameter name: use_sim_time
Type: boolean
Constraints:

获取参数值
ros2 param get /set_parameter_node use_sim_time
Boolean value is: False设置参数值
ros2 param set /set_parameter_node use_sim_time true
Set parameter successful将一个节点所有的param写在一个yaml文件中
ros2 param dump /set_parameter_node
Saving to:  ./set_parameter_node.yaml修改上面的yaml文件，通过下面指令直接生效
ros2 param load /set_parameter_node set_parameter_node.yaml 
Set parameter use_sim_time successful
Set parameter vehicle_speed successful
Set parameter vehicle_type successful