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 values this->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 file this->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(TARGETS parameters DESTINATION 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
