1.流程

话题通信是ROS中使用频率最高的一种通信模式，话题通信是基于发布订阅模式的，也即:一个节点发布消息，另一个节点订阅该消息。在ROS中，实现话题通信只需要如下几步：

确定要发布的数据类型，一般都需要自定义.msg文件，修改好CMakeLists.txt文件和package.xml文件并重编译
编写发布方和订阅方的cpp文件，修改好CMakeLists.txt文件并重编译
分别启动发布方节点和订阅方节点，顺序无所谓

2.自定义发布数据

在 ROS 通信协议中，数据载体是一个较为重要组成部分，ROS 中通过 std_msgs 封装了一些原生的数据类型。但是，这些数据一般只包含一个 data 字段，结构的单一意味着功能上的局限性，当传输一些复杂的数据， std_msgs 由于描述性较差而显得力不从心，这种场景下必须通过编写.msg文件来自定义消息类型。

2.1 std_msgs内置类型

内置类型与 C++ 和 Python 中的对应关系:

| Primitive Type | C++ | Python |

| -------------- | ------------- | -------------- |

| bool | uint8_t | bool |

| int8 | int8_t | int |

| uint8 | uint8_t | int |

| int16 | int16_t | int |

| uint16 | uint16_t | int |

| int32 | uint32_t | int |

| uint64 | uint64_t | long int |

| float32 | float | float |

| float64 | double | float |

| string | std::string | str bytes |

| time | ros::Time | rospy.Time |

| duration | ros::Duration | rospy.Duration |

内置类型的数组与 C++ 和 Python 中的对应关系:

| Primitive Type | C++ | Python |

| --------------- | -------------------------------------- | ------ |

| variable-length | std::vector | tuple |

| fixed-length | boost::array<T, length>或std::vector | tuple |

2.2 编写.msg文件

示例如下：


#文件名Person.msg

string name

uint16 age

float64 height

2.3 修改package.xml文件

查看是否存在如下编译依赖


<build_depend>message_generation</build_depend>

查看是否存在如下执行依赖


<exec_depend>message_generation</exec_depend>

2.3.1 完整的package.xml文件


<?xml version="1.0"?>

<package  format="2">

<name>chat</name>

<version>0.0.0</version>

<description>The chat package</description>

  

<!-- One maintainer tag required, multiple allowed, one person per tag -->

<!-- Example: -->

<!-- <maintainer email="jane.doe@example.com">Jane Doe</maintainer> -->

<maintainer  email="xu736946693@todo.todo">xu736946693</maintainer>

  
  

<!-- One license tag required, multiple allowed, one license per tag -->

<!-- Commonly used license strings: -->

<!-- BSD, MIT, Boost Software License, GPLv2, GPLv3, LGPLv2.1, LGPLv3 -->

<license>TODO</license>

  
  

<!-- Url tags are optional, but multiple are allowed, one per tag -->

<!-- Optional attribute type can be: website, bugtracker, or repository -->

<!-- Example: -->

<!-- <url type="website">http://wiki.ros.org/chat</url> -->

  
  

<!-- Author tags are optional, multiple are allowed, one per tag -->

<!-- Authors do not have to be maintainers, but could be -->

<!-- Example: -->

<!-- <author email="jane.doe@example.com">Jane Doe</author> -->

  
  

<!-- The *depend tags are used to specify dependencies -->

<!-- Dependencies can be catkin packages or system dependencies -->

<!-- Examples: -->

<!-- Use depend as a shortcut for packages that are both build and exec dependencies -->

<!-- <depend>roscpp</depend> -->

<!-- Note that this is equivalent to the following: -->

<!-- <build_depend>roscpp</build_depend> -->

<!-- <exec_depend>roscpp</exec_depend> -->

<!-- Use build_depend for packages you need at compile time: -->

<!-- <build_depend>message_generation</build_depend> -->

<!-- Use build_export_depend for packages you need in order to build against this package: -->

<!-- <build_export_depend>message_generation</build_export_depend> -->

<!-- Use buildtool_depend for build tool packages: -->

<!-- <buildtool_depend>catkin</buildtool_depend> -->

<!-- Use exec_depend for packages you need at runtime: -->

<!-- <exec_depend>message_runtime</exec_depend> -->

<!-- Use test_depend for packages you need only for testing: -->

<!-- <test_depend>gtest</test_depend> -->

<!-- Use doc_depend for packages you need only for building documentation: -->

<!-- <doc_depend>doxygen</doc_depend> -->

<buildtool_depend>catkin</buildtool_depend>

<build_depend>message_generation</build_depend>

<build_depend>roscpp</build_depend>

<build_depend>rospy</build_depend>

<build_depend>std_msgs</build_depend>

<build_export_depend>roscpp</build_export_depend>

<build_export_depend>rospy</build_export_depend>

<build_export_depend>std_msgs</build_export_depend>

<exec_depend>message_generation</exec_depend>

<exec_depend>roscpp</exec_depend>

<exec_depend>rospy</exec_depend>

<exec_depend>std_msgs</exec_depend>

  
  

<!-- The export tag contains other, unspecified, tags -->

<export>

<!-- Other tools can request additional information be placed here -->

  

</export>

</package>

2.4 修改CMakeLists.txt文件

2.4.1 修改find_package指令


# 需要加入 message_generation,必须有 std_msgs

find_package(catkin REQUIRED COMPONENTS

roscpp

rospy

std_msgs

message_generation

)

2.4.2 添加add_message_files指令


## 配置 msg 源文件

add_message_files(

FILES

Person.msg

)

2.4.3 添加generate_messages指令


generate_messages(

DEPENDENCIES

std_msgs

)

2.4.4 修改catkin_package指令


#执行时依赖

catkin_package(

# INCLUDE_DIRS include

# LIBRARIES demo02_talker_listener

CATKIN_DEPENDS roscpp rospy std_msgs message_runtime

# DEPENDS system_lib

)

其中，add_message_files指令必须要在generate_messages指令的前面，然后在工作空间目录编译即可。

2.5 查看头文件

经过以上几步，在${workspace}/devel/include/${package}/目录下应该会出现一个头文件，如图：


xu736946693@ubuntu:~/Desktop/ROS-exercise/devel/include/chat$  tree

.

└──  Person.h

如果没有出现，是无法进行接下来的步骤的。这时，只需要把${workspace}/目录下的build目录和devel目录全部删除，然后重新编译即可。


rm  -rf  build/

rm  -rf  devel/

catkin_make

3.编写cpp文件

3.1 功能包目录文件树


xu736946693@ubuntu:~/Desktop/ros-test/src/chat$  tree

.

├──  CMakeLists.txt

├──  include

├──  msg

│  └──  Person.msg

├──  package.xml

└──  src

├──  listener.cpp

└──  publisher.cpp

  

3  directories,  5  files

3.2 修改CMakeLists.txt文件

3.2.1 添加add_executable指令


add_executable(publisher

src/publisher.cpp)

add_executable(listener

src/listener.cpp)

3.2.2 添加add_dependencies指令


add_dependencies(publisher ${PROJECT_NAME}_generate_messages_cpp)

add_dependencies(listener ${PROJECT_NAME}_generate_messages_cpp)

3.2.3 添加target_link_libraries指令


target_link_libraries(person_talker

${catkin_LIBRARIES}

)

target_link_libraries(person_listener

${catkin_LIBRARIES}

)

3.2.4 完整的CMakeLists.txt

其中很多语句都是catkin_make自动生成的


cmake_minimum_required(VERSION 3.0.2)

project(chat)

  

## 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

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

Person.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

# 生成消息时依赖于 std_msgs

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

#执行时依赖

catkin_package(

# INCLUDE_DIRS include

# LIBRARIES demo02_talker_listener

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}/pkg1.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(${PROJECT_NAME}_node src/pkg1_node.cpp)

add_executable(publisher

src/publisher.cpp)

add_executable(listener

src/listener.cpp)

  

## 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})

add_dependencies(publisher ${PROJECT_NAME}_generate_messages_cpp)

add_dependencies(listener ${PROJECT_NAME}_generate_messages_cpp)

  

## Specify libraries to link a library or executable target against

# target_link_libraries(${PROJECT_NAME}_node

# ${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_pkg1.cpp)

# if(TARGET ${PROJECT_NAME}-test)

# target_link_libraries(${PROJECT_NAME}-test ${PROJECT_NAME})

# endif()

target_link_libraries(publisher

${catkin_LIBRARIES}

)

  

target_link_libraries(listener

${catkin_LIBRARIES}

)

  

## Add folders to be run by python nosetests

# catkin_add_nosetests(test)

3.3 发布方cpp

示例如下：


/*

需求: 实现基本的话题通信，一方发布数据，一方接收数据，

实现的关键点:

1.发送方

2.接收方

3.数据

  

PS: 二者需要设置相同的话题

  
  

消息发布方:

循环发布信息:HelloWorld 后缀数字编号

  

实现流程:

1.包含头文件

2.初始化 ROS 节点:命名(唯一)

3.实例化 ROS 句柄

4.实例化 发布者 对象

5.组织被发布的数据，并编写逻辑发布数据

  

*/

// 1.包含头文件

#include  "ros/ros.h"

#include  "chat/Person.h"

  

int  main(int  argc, char *argv[])

{

//设置编码

setlocale(LC_ALL,"");

  

//2.初始化 ROS 节点:命名(唯一)

// 参数1和参数2 后期为节点传值会使用

// 参数3 是节点名称，是一个标识符，需要保证运行后，在 ROS 网络拓扑中唯一

ros::init(argc,argv,"talker");

//3.实例化 ROS 句柄

ros::NodeHandle nh;//该类封装了 ROS 中的一些常用功能

  

//4.实例化 发布者 对象

//泛型: 发布的消息类型

//参数1: 要发布到的话题

//参数2: 队列中最大保存的消息数，超出此阀值时，先进的先销毁(时间早的先销毁)

ros::Publisher pub = nh.advertise<chat::Person>("chatter",10);

  

//5.组织被发布的数据，并编写逻辑发布数据

//数据(动态组织)

chat::Person p;

p.name = "sunwukong";

p.age = 2000;

p.height = 1.45;

  

//逻辑(一秒1次)

ros::Rate r(1);

  

//节点不死

while (ros::ok())

{

//发布消息

pub.publish(p);

//加入调试，打印发送的消息

ROS_INFO("我叫:%s,今年%d岁,高%.2f米", p.name.c_str(), p.age, p.height);p.age++;

//根据前面制定的发送贫频率自动休眠 休眠时间 = 1/频率；

r.sleep();

//暂无应用

ros::spinOnce();

}

  
  

return  0;

}

3.4 订阅方cpp

示例如下：


/*

需求: 实现基本的话题通信，一方发布数据，一方接收数据，

实现的关键点:

1.发送方

2.接收方

3.数据

  
  

消息订阅方:

订阅话题并打印接收到的消息

  

实现流程:

1.包含头文件

2.初始化 ROS 节点:命名(唯一)

3.实例化 ROS 句柄

4.实例化 订阅者 对象

5.处理订阅的消息(回调函数)

6.设置循环调用回调函数

  

*/

// 1.包含头文件

#include  "ros/ros.h"

#include  "chat/Person.h"

  

void  doMsg(const chat::Person::ConstPtr& person_p){

ROS_INFO("订阅的人信息:%s, %d, %.2f", person_p->name.c_str(), person_p->age, person_p->height);

}

int  main(int  argc, char *argv[])

{

//设置编码

setlocale(LC_ALL,"");

//2.初始化 ROS 节点:命名(唯一)

ros::init(argc,argv,"listener");

//3.实例化 ROS 句柄

ros::NodeHandle nh;

  

//4.实例化 订阅者 对象

ros::Subscriber sub = nh.subscribe<chat::Person>("chatter",10,doMsg);

//5.处理订阅的消息(回调函数)

  

// 6.设置循环调用回调函数

ros::spin();//循环读取接收的数据，并调用回调函数处理

  

return  0;

}

4.效果

如果找不到可执行文件，就把工作目录下的build文件夹和devel文件夹删了重新编译。

【ROS教程】话题通信

1.流程

2.自定义发布数据

2.1 std_msgs内置类型

2.2 编写.msg文件

2.3 修改package.xml文件

2.3.1 完整的package.xml文件

2.4 修改CMakeLists.txt文件

2.4.1 修改find_package指令

2.4.2 添加add_message_files指令

2.4.3 添加generate_messages指令

2.4.4 修改catkin_package指令

2.5 查看头文件

3.编写cpp文件

3.1 功能包目录文件树

3.2 修改CMakeLists.txt文件

3.2.1 添加add_executable指令

3.2.2 添加add_dependencies指令

3.2.3 添加target_link_libraries指令

3.2.4 完整的CMakeLists.txt

3.3 发布方cpp

3.4 订阅方cpp

4.效果