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。

示例

rostopic pub /turtle1/cmd_vel geometry_msgs/Twist -r 1 -- '[2.0, 0.0, 0.0]' '[0.0, 0.0, -1.8]'

“-”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

geometry_msgs/Twist geometry_msgs/Vector3 linear
float64 x
float64 y
float64 z



geometry_msgs/Vector3 angular
float64 x
float64 y
float64 z

 传感消息senser_msgs/PointCloud(复合域)

std_msgs/Header header
uint32 seq
time stamp
string frame_id


geometry_msgs/Point32[] points
float32 x
float32 y
float32 z


sensor_msgs/ChannelFloat32[] channelsstring name
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

template void publish(const boost::shared_ptr& message) const{
 ...... 
SerializedMessage m;
 m.type_info = &typeid(M);
 m.message = message; 
publish(boost::bind(serializeMessage, boost::ref(*message)), m); 
}

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

Header header
string first_name
string last_name
uint8 age
uint32 score

 步骤2编写消息发布文件   talker

#include "ros/ros.h"
#include "std_msgs/String.h"
#include "example_3/Info.h"
#include 
#include 

int main(int argc, char **argv)
{
  ros::init(argc, argv, "talker");      //talk  节点
  ros::NodeHandle nh;
  rosbag::Bag bag;

  ros::Publisher chatter_pub = nh.advertise("chatter", 1000);  // 队列长度1000
  bag.open("/home/miaozl/catkin_ws/bagfiles/test.bag",rosbag::bagmode::Write);
  bag.setCompression(rosbag::CompressionType::LZ4);
  ros::Rate loop_rate(10);
  while (ros::ok())
  {
    example_3::Info msg;
    msg.header.stamp=ros::Time::now();
    msg.header.frame_id="info_msg";
    msg.first_name = "Fabio";
    msg.last_name = "Miao";
    msg.age =36;
    msg.score = 100;

    chatter_pub.publish(msg);              // 发布消息
    ROS_INFO("publish message");
    bag.write("chatter",msg.header.stamp,msg);
    ros::spinOnce();                      // 监听回调

    loop_rate.sleep();
  }
  bag.close();
  return 0;
}

 

步骤3 编写消息订阅文件 listener

#include "ros/ros.h"
#include "std_msgs/String.h"
#include "example_3/Info.h"

void chatterCallback(const example_3::Info::ConstPtr& msg)
{
  //ROS_INFO("I heard: [%s]", msg->data.c_str());
  //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);
  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(),
  msg->first_name.c_str(),msg->last_name.c_str(),msg->age,msg->score);
}

int main(int argc, char **argv)
{
  ros::init(argc, argv, "listener");
  ros::NodeHandle nh;

  ros::Subscriber sub = nh.subscribe("chatter", 1000, chatterCallback);  

  ros::spin();

  return 0;
}

步骤3 package.xml、CMakeLists.txt配置

cmake_minimum_required(VERSION 3.0.2)
project(example_3)

## 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
  rosbag
  std_msgs
  message_generation
)

## 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
   Info.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
)

################################################
## 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 example_3
   CATKIN_DEPENDS roscpp rospy std_msgs message_runtime
#  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}/example_3.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
## 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
if(CMAKE_BUILD_TYPE STREQUAL DEBUG)
add_executable(talker src/talker.cpp)
add_executable(listener src/listener.cpp)
target_link_libraries(talker
   ${catkin_LIBRARIES}
)

target_link_libraries(listener
   ${catkin_LIBRARIES}
)
endif()
#############
## 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_example_3.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)

 步骤4 生成消息文件  编译执行