• ROS 消息订阅 节点发布 通信方式

     

    1、节点（node）


        节点是进行运算任务的进程。一个系统可以由很多节点组成，节点也可以称为软件模块。

        ROS是以节点的形式开发的，节点是根据其目的，可以细分的可执行程序的最小单位。节点使基于ROS的系统在运行时更加形象化，当许多节点同时进行时，

        可以将不同节点的通讯绘制成下图。

     

     

    3、 话题（topic）

            话题本质是对套接字的一种封装，一个节点可以向一个给定的话题发布消息，另一个节点可以订阅给定话题中特定消息类型的消息。在实现上，消息是序列化的

           消息通过一个GlobalCallbackQueue和一个TopicManager管理

          需要注意的是，在ROS中，话题必须是唯一的，否则消息路由就会产生错误。

          查看工具 ： 可视化工具rqt_graph、命令行工具rostopic。

    4、服务（service）


          基于主题 发布/订阅 的通信方法是一种异步方法，该 发布/订阅 模型是一种很灵活的通讯模式。但在某些情况下，需要一种同时使用请求和响应的同步消息交换方案，ROS提供了叫做服务的消息同步方法，是一种一对一的机制。

          一个服务被分成服务服务器和服务客户端，其中服务服务器只在有请求（request）的时候才响应（response），而服务客户端会在发送请求后接收响应。与话题不同，服务是一次性消息通信。

           因此，当服务的请求和响应完成时，两个连接的节点将被断开。

           服务通常被用作请求机器人执行特定操作时使用的命令，或者用于根据特定条件需要产生事件的节点。

          由于它是一次性的通信方式，在网络上的负载很小，所以它也被用作代替 基于主题 发布/订阅 的通信手段。
     

    PS：查看列表topic列表

    rostopic常用命令  topic的名字全局唯一

     查看话题 rostopic info [话题名]

     获得话题列表 rostopic list

     获得话题列表 rostopic list -v

     发布数据 rostopic pub [话题名] [消息类型] [参数]

    三、发布模式：rostopic的发布模式有：

    闩锁模式(latch mode)、速率模式(rate mode)、单次模式(once mode)、文件模式（file mode）。

     闩锁模式(latch mode) 默认模式，只发布一次，确保收到,选项为-l。

     速率模式(rate mode) 以特定速率发布消息，默认10Hz，选项为-r。

     单次模式(once mode) 以闩锁模式发布消息，执行3秒，然后结束发布，选项为-1。

     文件模式（file mode） 从YAML文件中读取消息，文件模式的发布速度也为10Hz，选项为-f。

    1. 示例
    2.  
    3. rostopic pub /turtle1/cmd_vel geometry_msgs/Twist -r 1 -- '[2.0, 0.0, 0.0]' '[0.0, 0.0, -1.8]'
    4.  
    5. “-”短划线代表参数是可选参数， “-- ”代表参数是非可选参数

    5、消息（message）


        节点之间通过传送消息进行通讯。每一个消息都是一种数据结构。

        ROS的消息支持标准的数据类型（整型、浮点型、布尔型等），

        还包括数组、结构体、自定义的数据类型等等。

    四、查看消息：

     查看消息类型 rosmsg info [消息类型]

     消息列表 rosmsg list

     程序包消息 rosmsg package [程序包名] 查看消息常用用法

    五、消息的组织：

    消息类型的命名方式为：程序包名/消息名

    消息类型每行的声明必须包含两部分：域、常量，域定义了消息的数据类型，

    常量定义了域的名称。域可以是独立域也可以是复合域。

    特别的消息类型Header来提供一些通用信息如时间戳、序列号、帧ID等

    std_msgs/Header中的消息头内容如下：

    #序列号 uint32 seq #时间戳 time stamp #坐标系ID string frame_id

    六、常见消息类型：

    std_msgs支持字符串、布尔、整型、浮点型、数组等多种数据类型。


     标准消息

    std_msgs/Char char data

     几何消息

    1. geometry_msgs/Twist geometry_msgs/Vector3 linear
    2. float64 x
    3. float64 y
    4. float64 z
    5.  
    6.  
    7.  
    8. geometry_msgs/Vector3 angular
    9. float64 x
    10. float64 y
    11. float64 z

     传感消息senser_msgs/PointCloud(复合域)

    1. std_msgs/Header header
    2. uint32 seq
    3. time stamp
    4. string frame_id
    5.  
    6.  
    7. geometry_msgs/Point32[] points
    8. float32 x
    9. float32 y
    10. float32 z
    11.  
    12.  
    13. sensor_msgs/ChannelFloat32[] channelsstring name
    14. float32[] values

    示例 查看小海龟的话题、消息。

     启动小海龟 启动节点rosrun turtlesim turtlesim_node

     启动键盘控制rosrun turtlesim turtle_teleop_key

     查看消息 rosrun rqt_console rqt_console

      过滤消息 rosrun rqt_logger_level rqt_logger_level

     查看网络拓扑 rosrun rqt_graph rqt_graph

     

    创建发布订阅

     发布消息 //配置话题、队列大小、发布模式

    template Publisher advertise(const std::string& topic, uint32_t queue_size, bool latch=false)

    //发布消息

    1. template void publish(const boost::shared_ptr& message) const{
    2.  ...... 
    3. SerializedMessage m;
    4.  m.type_info = &typeid(M);
    5.  m.message = message; 
    6. publish(boost::bind(serializeMessage, boost::ref(*message)), m); 
    7. }

    监听消息回调

    spinOnce(监听到后继续往下运行，用于设置发布频率)

    spin(监听到后调回调函数执行，继续循环监听)

    自定义消息步骤

     步骤1：创建自定义消息.msg 文件

    1. Header header
    2. string first_name
    3. string last_name
    4. uint8 age
    5. uint32 score

     步骤2编写消息发布文件   talker

    1. #include "ros/ros.h"
    2. #include "std_msgs/String.h"
    3. #include "example_3/Info.h"
    4. #include 
    5. #include 
    6.  
    7. int main(int argc, char **argv)
    8. {
    9.   ros::init(argc, argv, "talker");      //talk  节点
    10.   ros::NodeHandle nh;
    11.   rosbag::Bag bag;
    12.  
    13.   ros::Publisher chatter_pub = nh.advertise("chatter", 1000);  // 队列长度1000
    14.   bag.open("/home/miaozl/catkin_ws/bagfiles/test.bag",rosbag::bagmode::Write);
    15.   bag.setCompression(rosbag::CompressionType::LZ4);
    16.   ros::Rate loop_rate(10);
    17.   while (ros::ok())
    18.   {
    19.     example_3::Info msg;
    20.     msg.header.stamp=ros::Time::now();
    21.     msg.header.frame_id="info_msg";
    22.     msg.first_name = "Fabio";
    23.     msg.last_name = "Miao";
    24.     msg.age =36;
    25.     msg.score = 100;
    26.  
    27.     chatter_pub.publish(msg);              // 发布消息
    28.     ROS_INFO("publish message");
    29.     bag.write("chatter",msg.header.stamp,msg);
    30.     ros::spinOnce();                      // 监听回调
    31.  
    32.     loop_rate.sleep();
    33.   }
    34.   bag.close();
    35.   return 0;
    36. }

     

    步骤3 编写消息订阅文件 listener

    1. #include "ros/ros.h"
    2. #include "std_msgs/String.h"
    3. #include "example_3/Info.h"
    4.  
    5. void chatterCallback(const example_3::Info::ConstPtr& msg)
    6. {
    7.   //ROS_INFO("I heard: [%s]", msg->data.c_str());
    8.   //ROS_INFO("I heard: %s %s,his age is %d,his score is %d",msg->first_name.c_str(),msg->last_name.c_str(),msg->age,msg->score);
    9.   ROS_INFO("I heard: header frame id is %s, %s %s,his age is %d,his score is %d",msg->header.frame_id.c_str(),
    10.   msg->first_name.c_str(),msg->last_name.c_str(),msg->age,msg->score);
    11. }
    12.  
    13. int main(int argc, char **argv)
    14. {
    15.   ros::init(argc, argv, "listener");
    16.   ros::NodeHandle nh;
    17.  
    18.   ros::Subscriber sub = nh.subscribe("chatter", 1000, chatterCallback);  
    19.  
    20.   ros::spin();
    21.  
    22.   return 0;
    23. }

    步骤3 package.xml、CMakeLists.txt配置

    1. cmake_minimum_required(VERSION 3.0.2)
    2. project(example_3)
    3.  
    4. ## Compile as C++11, supported in ROS Kinetic and newer
    5. # add_compile_options(-std=c++11)
    6.  
    7. ## Find catkin macros and libraries
    8. ## if COMPONENTS list like find_package(catkin REQUIRED COMPONENTS xyz)
    9. ## is used, also find other catkin packages
    10. find_package(catkin REQUIRED COMPONENTS
    11.   roscpp
    12.   rospy
    13.   rosbag
    14.   std_msgs
    15.   message_generation
    16. )
    17.  
    18. ## System dependencies are found with CMake's conventions
    19. # find_package(Boost REQUIRED COMPONENTS system)
    20.  
    21.  
    22. ## Uncomment this if the package has a setup.py. This macro ensures
    23. ## modules and global scripts declared therein get installed
    24. ## See http://ros.org/doc/api/catkin/html/user_guide/setup_dot_py.html
    25. # catkin_python_setup()
    26.  
    27. ################################################
    28. ## Declare ROS messages, services and actions ##
    29. ################################################
    30.  
    31. ## To declare and build messages, services or actions from within this
    32. ## package, follow these steps:
    33. ## * Let MSG_DEP_SET be the set of packages whose message types you use in
    34. ##   your messages/services/actions (e.g. std_msgs, actionlib_msgs, ...).
    35. ## * In the file package.xml:
    36. ##   * add a build_depend tag for "message_generation"
    37. ##   * add a build_depend and a exec_depend tag for each package in MSG_DEP_SET
    38. ##   * If MSG_DEP_SET isn't empty the following dependency has been pulled in
    39. ##     but can be declared for certainty nonetheless:
    40. ##     * add a exec_depend tag for "message_runtime"
    41. ## * In this file (CMakeLists.txt):
    42. ##   * add "message_generation" and every package in MSG_DEP_SET to
    43. ##     find_package(catkin REQUIRED COMPONENTS ...)
    44. ##   * add "message_runtime" and every package in MSG_DEP_SET to
    45. ##     catkin_package(CATKIN_DEPENDS ...)
    46. ##   * uncomment the add_*_files sections below as needed
    47. ##     and list every .msg/.srv/.action file to be processed
    48. ##   * uncomment the generate_messages entry below
    49. ##   * add every package in MSG_DEP_SET to generate_messages(DEPENDENCIES ...)
    50.  
    51. ## Generate messages in the 'msg' folder
    52.  add_message_files(
    53.    FILES
    54.    Info.msg
    55.  )
    56.  
    57. ## Generate services in the 'srv' folder
    58. # add_service_files(
    59. #   FILES
    60. #   Service1.srv
    61. #   Service2.srv
    62. # )
    63.  
    64. ## Generate actions in the 'action' folder
    65. # add_action_files(
    66. #   FILES
    67. #   Action1.action
    68. #   Action2.action
    69. # )
    70.  
    71. ## Generate added messages and services with any dependencies listed here
    72.  generate_messages(
    73.    DEPENDENCIES
    74.    std_msgs
    75. )
    76.  
    77. ################################################
    78. ## Declare ROS dynamic reconfigure parameters ##
    79. ################################################
    80.  
    81. ## To declare and build dynamic reconfigure parameters within this
    82. ## package, follow these steps:
    83. ## * In the file package.xml:
    84. ##   * add a build_depend and a exec_depend tag for "dynamic_reconfigure"
    85. ## * In this file (CMakeLists.txt):
    86. ##   * add "dynamic_reconfigure" to
    87. ##     find_package(catkin REQUIRED COMPONENTS ...)
    88. ##   * uncomment the "generate_dynamic_reconfigure_options" section below
    89. ##     and list every .cfg file to be processed
    90.  
    91. ## Generate dynamic reconfigure parameters in the 'cfg' folder
    92. # generate_dynamic_reconfigure_options(
    93. #   cfg/DynReconf1.cfg
    94. #   cfg/DynReconf2.cfg
    95. # )
    96.  
    97. ###################################
    98. ## catkin specific configuration ##
    99. ###################################
    100. ## The catkin_package macro generates cmake config files for your package
    101. ## Declare things to be passed to dependent projects
    102. ## INCLUDE_DIRS: uncomment this if your package contains header files
    103. ## LIBRARIES: libraries you create in this project that dependent projects also need
    104. ## CATKIN_DEPENDS: catkin_packages dependent projects also need
    105. ## DEPENDS: system dependencies of this project that dependent projects also need
    106. catkin_package(
    107. #  INCLUDE_DIRS include
    108. #  LIBRARIES example_3
    109.    CATKIN_DEPENDS roscpp rospy std_msgs message_runtime
    110. #  DEPENDS system_lib
    111. )
    112.  
    113. ###########
    114. ## Build ##
    115. ###########
    116.  
    117. ## Specify additional locations of header files
    118. ## Your package locations should be listed before other locations
    119. include_directories(
    120. # include
    121.   ${catkin_INCLUDE_DIRS}
    122. )
    123.  
    124. ## Declare a C++ library
    125. # add_library(${PROJECT_NAME}
    126. #   src/${PROJECT_NAME}/example_3.cpp
    127. # )
    128.  
    129. ## Add cmake target dependencies of the library
    130. ## as an example, code may need to be generated before libraries
    131. ## either from message generation or dynamic reconfigure
    132. # add_dependencies(${PROJECT_NAME} ${${PROJECT_NAME}_EXPORTED_TARGETS} ${catkin_EXPORTED_TARGETS})
    133.  
    134. ## Declare a C++ executable
    135. ## With catkin_make all packages are built within a single CMake context
    136. ## The recommended prefix ensures that target names across packages don't collide
    137. ## Rename C++ executable without prefix
    138. ## The above recommended prefix causes long target names, the following renames the
    139. ## target back to the shorter version for ease of user use
    140. ## e.g. "rosrun someones_pkg node" instead of "rosrun someones_pkg someones_pkg_node"
    141. # set_target_properties(${PROJECT_NAME}_node PROPERTIES OUTPUT_NAME node PREFIX "")
    142.  
    143. ## Add cmake target dependencies of the executable
    144. ## same as for the library above
    145. # add_dependencies(${PROJECT_NAME}_node ${${PROJECT_NAME}_EXPORTED_TARGETS} ${catkin_EXPORTED_TARGETS})
    146.  
    147. ## Specify libraries to link a library or executable target against
    148. if(CMAKE_BUILD_TYPE STREQUAL DEBUG)
    149. add_executable(talker src/talker.cpp)
    150. add_executable(listener src/listener.cpp)
    151. target_link_libraries(talker
    152.    ${catkin_LIBRARIES}
    153. )
    154.  
    155. target_link_libraries(listener
    156.    ${catkin_LIBRARIES}
    157. )
    158. endif()
    159. #############
    160. ## Install ##
    161. #############
    162.  
    163. # all install targets should use catkin DESTINATION variables
    164. # See http://ros.org/doc/api/catkin/html/adv_user_guide/variables.html
    165.  
    166. ## Mark executable scripts (Python etc.) for installation
    167. ## in contrast to setup.py, you can choose the destination
    168. # catkin_install_python(PROGRAMS
    169. #   scripts/my_python_script
    170. #   DESTINATION ${CATKIN_PACKAGE_BIN_DESTINATION}
    171. # )
    172.  
    173. ## Mark executables for installation
    174. ## See http://docs.ros.org/melodic/api/catkin/html/howto/format1/building_executables.html
    175. # install(TARGETS ${PROJECT_NAME}_node
    176. #   RUNTIME DESTINATION ${CATKIN_PACKAGE_BIN_DESTINATION}
    177. # )
    178.  
    179. ## Mark libraries for installation
    180. ## See http://docs.ros.org/melodic/api/catkin/html/howto/format1/building_libraries.html
    181. # install(TARGETS ${PROJECT_NAME}
    182. #   ARCHIVE DESTINATION ${CATKIN_PACKAGE_LIB_DESTINATION}
    183. #   LIBRARY DESTINATION ${CATKIN_PACKAGE_LIB_DESTINATION}
    184. #   RUNTIME DESTINATION ${CATKIN_GLOBAL_BIN_DESTINATION}
    185. # )
    186.  
    187. ## Mark cpp header files for installation
    188. # install(DIRECTORY include/${PROJECT_NAME}/
    189. #   DESTINATION ${CATKIN_PACKAGE_INCLUDE_DESTINATION}
    190. #   FILES_MATCHING PATTERN "*.h"
    191. #   PATTERN ".svn" EXCLUDE
    192. # )
    193.  
    194. ## Mark other files for installation (e.g. launch and bag files, etc.)
    195. # install(FILES
    196. #   # myfile1
    197. #   # myfile2
    198. #   DESTINATION ${CATKIN_PACKAGE_SHARE_DESTINATION}
    199. # )
    200.  
    201. #############
    202. ## Testing ##
    203. #############
    204.  
    205. ## Add gtest based cpp test target and link libraries
    206. # catkin_add_gtest(${PROJECT_NAME}-test test/test_example_3.cpp)
    207. # if(TARGET ${PROJECT_NAME}-test)
    208. #   target_link_libraries(${PROJECT_NAME}-test ${PROJECT_NAME})
    209. # endif()
    210.  
    211. ## Add folders to be run by python nosetests
    212. # catkin_add_nosetests(test)

     步骤4 生成消息文件  编译执行

     

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  • 原文地址：https://blog.csdn.net/weixin_44025389/article/details/126469610