系统学习ROS第二章 :ROS通讯机制

机器人是一种高度复杂的通讯机制在机器人上可以继承多种传感器。例如雷达、相机 GPS等。为了解耦合在ROS中每一个功能点都是一个单独的进程每一个进程都是独立运行的。ROS进程是分布式的框架这些进行还可以分布于不同主机不同主机协调工作从而分散计算压力。ROS中的基本通讯机制主要有如下三种策略话题通讯发布订阅模式服务通讯请求响应模式参数服务器参数共享模式ROS 话题通讯比如一个常见场景机器人在执行导航功能使用的传感器是激光雷达机器人会采集激光雷达感知到的信息进行计算然后生成运动控制信息驱动机器人底盘运动。以激光雷达信息的采集处理为例在ROS中有一个节点需要实时发布当前雷达采集到的数据导航模块中也会有节点订阅和解析雷达数据。再以运动消息发布为例导航木块会根据传感器的数据实时计算出运动控制信息并发布给底盘底盘中有一个节点订阅运动控制信息并最终转换成控制电机的脉冲信号。概念以发布订阅的方式实现不同节点之间数据交互的通讯模式。作用用于不断更新的、少逻辑处理的数据传输场景。#includeros/ros.h #includestd_msgs/String.h #includesstream /* 发布方实现 1. 包含头文件 ROS中文本类型 ----- std_msgs/String 2. 初始化ros节点 3. 创建节点句柄 4. 创建发布者对象 5. 编写发布逻辑并发布消息 */ int main(int argc, char* argv[]) { //初始化ROS节点 ros::init(argc, argv, pub_node); //创建节点句柄 ros::NodeHandle nh; //创建发布者对象 ros::Publisher pubnh.advertisestd_msgs::String(fang, 10); //这里的10是消息队里的长随度 //编写发布逻辑并发布消息 //先创建要发布的消息 //要求以10HZ的频率发布数据并且文本后添加编号 std_msgs::String msg; ros::Rate rate(10); int count0; ros::Duration(3).sleep(); //注册后休眠3s //编写循环逻辑循环中发布数据 while(ros::ok()) //只要ROS节点没有被关闭就继续发布数据 { count; // msg.datahello world; std::stringstream ss; sshello ---count; msg.datass.str(); pub.publish(msg); //添加日志 ROS_INFO(send msg is %s,ss.str().c_str()); rate.sleep(); ros::spinOnce(); //官方建议的写法用于处理回调函数 } return 0; }#includeros/ros.h #includestd_msgs/String.h /* 订阅方实现 1.包含头文件 2.初始化ros节点 3.创建节点句柄 4.创建订阅者对象 5.订阅消息 6.设置循环调用函数spin() */ void Msgcallback(const std_msgs::String::ConstPtr msg) { ROS_INFO(订阅到的消息是%s, msg-data.c_str()); } int main(int argc, char **argv) { setlocale(LC_ALL,); ros::init(argc, argv, sub_node); ros::NodeHandle nh; ros::Subscriber subnh.subscribe(fang, 10, Msgcallback); ros::spin(); return 0; }cmake_minimum_required(VERSION 3.0.2) project(plumbing_pubsub) ## Compile as C11, supported in ROS Kinetic and newer # add_compile_options(-stdc11) ## Find catkin macros and libraries ## if COMPONENTS list like find_package(catkin REQUIRED COMPONENTS xyz) ## is used, also find other catkin packages find_package(catkin REQUIRED COMPONENTS roscpp rospy std_msgs ) ## System dependencies are found with CMakes conventions # find_package(Boost REQUIRED COMPONENTS system) ## Uncomment this if the package has a setup.py. This macro ensures ## modules and global scripts declared therein get installed ## See http://ros.org/doc/api/catkin/html/user_guide/setup_dot_py.html # catkin_python_setup() ################################################ ## Declare ROS messages, services and actions ## ################################################ ## To declare and build messages, services or actions from within this ## package, follow these steps: ## * Let MSG_DEP_SET be the set of packages whose message types you use in ## your messages/services/actions (e.g. std_msgs, actionlib_msgs, ...). ## * In the file package.xml: ## * add a build_depend tag for message_generation ## * add a build_depend and a exec_depend tag for each package in MSG_DEP_SET ## * If MSG_DEP_SET isnt empty the following dependency has been pulled in ## but can be declared for certainty nonetheless: ## * add a exec_depend tag for message_runtime ## * In this file (CMakeLists.txt): ## * add message_generation and every package in MSG_DEP_SET to ## find_package(catkin REQUIRED COMPONENTS ...) ## * add message_runtime and every package in MSG_DEP_SET to ## catkin_package(CATKIN_DEPENDS ...) ## * uncomment the add_*_files sections below as needed ## and list every .msg/.srv/.action file to be processed ## * uncomment the generate_messages entry below ## * add every package in MSG_DEP_SET to generate_messages(DEPENDENCIES ...) ## Generate messages in the msg folder # add_message_files( # FILES # Message1.msg # Message2.msg # ) ## Generate services in the srv folder # add_service_files( # FILES # Service1.srv # Service2.srv # ) ## Generate actions in the action folder # add_action_files( # FILES # Action1.action # Action2.action # ) ## Generate added messages and services with any dependencies listed here # generate_messages( # DEPENDENCIES # std_msgs # Or other packages containing msgs # ) ################################################ ## Declare ROS dynamic reconfigure parameters ## ################################################ ## To declare and build dynamic reconfigure parameters within this ## package, follow these steps: ## * In the file package.xml: ## * add a build_depend and a exec_depend tag for dynamic_reconfigure ## * In this file (CMakeLists.txt): ## * add dynamic_reconfigure to ## find_package(catkin REQUIRED COMPONENTS ...) ## * uncomment the generate_dynamic_reconfigure_options section below ## and list every .cfg file to be processed ## Generate dynamic reconfigure parameters in the cfg folder # generate_dynamic_reconfigure_options( # cfg/DynReconf1.cfg # cfg/DynReconf2.cfg # ) ################################### ## catkin specific configuration ## ################################### ## The catkin_package macro generates cmake config files for your package ## Declare things to be passed to dependent projects ## INCLUDE_DIRS: uncomment this if your package contains header files ## LIBRARIES: libraries you create in this project that dependent projects also need ## CATKIN_DEPENDS: catkin_packages dependent projects also need ## DEPENDS: system dependencies of this project that dependent projects also need catkin_package( # INCLUDE_DIRS include # LIBRARIES plumbing_pubsub # CATKIN_DEPENDS roscpp rospy stdmsgs # DEPENDS system_lib ) ########### ## Build ## ########### ## Specify additional locations of header files ## Your package locations should be listed before other locations include_directories( # include ${catkin_INCLUDE_DIRS} ) ## Declare a C library # add_library(${PROJECT_NAME} # src/${PROJECT_NAME}/plumbing_pubsub.cpp # ) ## Add cmake target dependencies of the library ## as an example, code may need to be generated before libraries ## either from message generation or dynamic reconfigure # add_dependencies(${PROJECT_NAME} ${${PROJECT_NAME}_EXPORTED_TARGETS} ${catkin_EXPORTED_TARGETS}) ## Declare a C executable ## With catkin_make all packages are built within a single CMake context ## The recommended prefix ensures that target names across packages dont collide add_executable(demo01_pub src/demo01.cpp) add_executable(demo02_sub src/demo02.cpp) ## Rename C execu_able without prefix ## The above recommended prefix causes long target names, the following renames the ## target back to the shorter version for ease of user use ## e.g. rosrun someones_pkg node instead of rosrun someones_pkg someones_pkg_node # set_target_properties(${PROJECT_NAME}_node PROPERTIES OUTPUT_NAME node PREFIX ) ## Rename C executable without prefix ## The above recommended prefix causes long target names, the following renames the ## target back to the shorter version for ease of user use ## e.g. rosrun someones_pkg node instead of rosrun someones_pkg someones_pkg_node # set_target_properties(${PROJECT_NAME}_node PROPERTIES OUTPUT_NAME node PREFIX ) ## Add cmake target dependencies of the executable ## same as for the library above # add_dependencies(${PROJECT_NAME}_node ${${PROJECT_NAME}_EXPORTED_TARGETS} ${catkin_EXPORTED_TARGETS}) ## Specify libraries to link a library or executable target against target_link_libraries(demo01_pub ${catkin_LIBRARIES} ) target_link_libraries(demo02_sub ${catkin_LIBRARIES} ) ############# ## Install ## ############# # all install targets should use catkin DESTINATION variables # See http://ros.org/doc/api/catkin/html/adv_user_guide/variables.html ## Mark executable scripts (Python etc.) for installation ## in contrast to setup.py, you can choose the destination # catkin_install_python(PROGRAMS # scripts/my_python_script # DESTINATION ${CATKIN_PACKAGE_BIN_DESTINATION} # ) ## Mark executables for installation ## See http://docs.ros.org/melodic/api/catkin/html/howto/format1/building_executables.html # install(TARGETS ${PROJECT_NAME}_node # RUNTIME DESTINATION ${CATKIN_PACKAGE_BIN_DESTINATION} # ) ## Mark libraries for installation ## See http://docs.ros.org/melodic/api/catkin/html/howto/format1/building_libraries.html # install(TARGETS ${PROJECT_NAME} # ARCHIVE DESTINATION ${CATKIN_PACKAGE_LIB_DESTINATION} # LIBRARY DESTINATION ${CATKIN_PACKAGE_LIB_DESTINATION} # RUNTIME DESTINATION ${CATKIN_GLOBAL_BIN_DESTINATION} # ) ## Mark cpp header files for installation # install(DIRECTORY include/${PROJECT_NAME}/ # DESTINATION ${CATKIN_PACKAGE_INCLUDE_DESTINATION} # FILES_MATCHING PATTERN *.h # PATTERN .svn EXCLUDE # ) ## Mark other files for installation (e.g. launch and bag files, etc.) # install(FILES # # myfile1 # # myfile2 # DESTINATION ${CATKIN_PACKAGE_SHARE_DESTINATION} # ) ############# ## Testing ## ############# ## Add gtest based cpp test target and link libraries # catkin_add_gtest(${PROJECT_NAME}-test test/test_plumbing_pubsub.cpp) # if(TARGET ${PROJECT_NAME}-test) # target_link_libraries(${PROJECT_NAME}-test ${PROJECT_NAME}) # endif() ## Add folders to be run by python nosetests # catkin_add_nosetests(test)ROS 服务通信服务通信也是ROS种一种及其常用的通信模式服务通新是基于请求响应模式的是一种应答机制。也即一个节点A向另一个节点B发送请求B接收处理请求并产生响应结果返回给A。比如机器人巡逻过程中控制系统分析传感器数据发现可疑物或人此时需要排查照片并留存。在上述场景中就是用到了服务通讯。一个节点需要像相机节点发送拍照请求相机节点处理请求并返回处理结果。概念以请求响应的方式实现不同节点之间的数据交互的通信模式。作用用于偶然的、对实时性有要求有一定逻辑处理需求的数据传输场景角色ROS Master 管理者 ROS核心Server 服务端Client 客户端流程master会根据话题实现 Server和Client的链接举例说明0 保洁公司在114平台注册自身信息疏通下水道1我我需要访问114 平台注册自己所需要的服务疏通下水道2114平台匹配话题并将服务端的电话响应给我4我向保洁公司拨打电话5保洁公司回复我参数服务器参数服务器在ROS中主要用于实现不同参数之间的数据共享参数服务器相当于是独立所有节点的一个公共容器可以将数据存储在该容器中被不同节点调用当然不同的节点也可以往其中存储数据关于参数服务器的典型应用场景如下导航实现时会进行路径规划比如全局路径规划设计一个从出发点到目标点的大致路径。本地路径规划会根据当前路况生成实时的行进路径。上述场景中全局路径规划和本地路径规划时就会使用参数服务器路径规划时需要参考车辆的尺寸我们可以将这些尺寸信息存储到参数服务器全局路径规划节点与本地路径规划节点都可以从参数服务器中调用这些参数参数服务器一般适用于一些数据共享的一些应用场景。概念以共享的方式实现不同节点之间数据交互的通讯模式作用存储一些多节点共享的数据类似于全局变量参数服务器实现时最为简单的该模型如下图所示该模型中涉及三个角色ROS Master管理者Talker参数设置者Listener参数调用者