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。
#include"ros/ros.h" #include"std_msgs/String.h" #include<sstream> /* 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 pub=nh.advertise<std_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 count=0; 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.data="hello world"; std::stringstream ss; ss<<"hello --->"<<count; msg.data=ss.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; }#include"ros/ros.h" #include"std_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 sub=nh.subscribe("fang", 10, &Msgcallback); ros::spin(); return 0; }cmake_minimum_required(VERSION 3.0.2) project(plumbing_pubsub) ## Compile as C++11, supported in ROS Kinetic and newer # add_compile_options(-std=c++11) ## 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 CMake's 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 isn't 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} ${catkin_EXPORTED_TARGETS}) ## Declare a C++ executable ## With catkin_make all packages are built within a single CMake context ## The recommended prefix ensures that target names across packages don't collide add_executable(demo01_pub src/demo01.cpp) add_executable(demo02_sub src/demo02.cpp) ## Rename C++ execu_able without prefix ## The above recommended prefix causes long target names, the following renames the ## target back to the shorter version for ease of user use ## e.g. "rosrun someones_pkg node" instead of "rosrun someones_pkg someones_pkg_node" # set_target_properties(${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）
2：114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
