1. 工作空间 workspace
1.1 Create Workspace
$ mkdir -p ~/catkin_ws/src
$ cd ~/catkin_ws/src
$ catkin_init_workspace
1.2 Build Workspace
$ cd ~/catkin_ws
$ catkin_make
// 查看目录结构
$ tree -L 1 ~/catkin_ws
catkin_ws
├── build
├── devel
└── src
1.3 Init Workspace Env
$ source ~/catkin_ws/devel/setup.bash
// 查看工作空间环境变量（一层一层嵌套式的）
$ echo $ROS_PACKAGE_PATH
/home/pi/catkin_ws/src:/opt/ros/melodic/share
2. 自定义功能包 Package
catkin_create_pkg <package_name> [depend1] [depend2] [depend3]
// Create
$ cd ~/catkin_ws/src
$ catkin_create_pkg learning_communication std_msgs rospy roscpp
// Build
$ cd ~/catkin_w
$ catkin_make
// Env
$ source ~/catkin_ws/devel/setup.bash
创建自定义功能包 learning_communication 之后，可以查看一下里边的
package.xml
实际上rospack find、rosdep等命令之所以能快速定位和分析出package的依赖项信息，就是直接读取了每一个pacakge中的package.xml文件
package.xml 包含标签
3. 实现 Topic Demo
发布 / 订阅 publish / subscribe 通信模型
3.1 Create Publisher 发布者
源码：learning_communication/src/talker.cpp
#include <sstream>
#include "ros/ros.h"
#include "std_msgs/String.h"
int main(int argc, char **argv)
{
ros::init(argc, argv, "talker");
ros::NodeHandle nh;
ros::Publisher chatter_pub = nh.advertise<std_msgs::String>("chatter", 1000);
ros::Rate loop_rate(10);
int count = 0;
while (ros::ok())
{
std_msgs::String msg;
std::stringstream ss;
ss << "hello world" << count;
msg.data = ss.str();
ROS_INFO("%s", msg.data.c_str());
chatter_pub.publish(msg);
ros::spinOnce();
loop_rate.sleep();
++count;
}
return 0;
}
3.2 Create Subscriber 订阅者
源码：learning_communication/src/listener.cpp
#include "ros/ros.h"
#include "std_msgs/String.h"
void chaterCallback(const std_msgs::String::ConstPtr& msg)
{
ROS_INFO("I heard: [%s]", msg->data.c_str());
}
int main(int argc, char *argv[])
{
ros::init(argc, argv, "listener");
ros::NodeHandle nh;
ros::Subscriber sub = nh.subscribe("chatter", 1000, chaterCallback);
ros::spin();
return 0;
}
3.3 编译
对于ROS这样大体量的平台来说，就采用的是CMake，并且ROS对CMake进行了扩展，于是便有了Catkin编译系统
3.3.1 编辑功能包里的 CMakeList.txt
如果使用了如 RoboWare Studio 支持ROS的IDE开发工具，会自动修改CMakeList.txt，可以跳过此步骤。
vi ~/catkin_ws/src/learning_communication/CMakeList.txt
include_directories(include ${catkin_INCLUDE_DIRS})
add_executable(talker src/talker.cpp)
add_dependencies(talker ${${PROJECT_NAME}_EXPORTED_TARGETS} ${catkin_EXPORTED_TARGETS})
target_link_libraries(talker ${catkin_LIBRARIES})add_executable(listener src/listener.cpp) add_dependencies(listener ${${PROJECT_NAME}_EXPORTED_TARGETS} ${catkin_EXPORTED_TARGETS})
target_link_libraries(listener ${catkin_LIBRARIES})
3.3.2 编译 catkin_make
$ cd ~/catkin_ws
$ catkin_make
3.3.3 运行 Publisher 与 Subscriber
1) 初始化 Workspace 环境变量
$ source ~/catkin_ws/devel/setup.bash
2) 启动 roscore
$ roscore
3) 启动 roscore
$ rosrun learning_communication talker
[ INFO] [1613488268.472365199]: hello world0
[ INFO] [1613488268.572595116]: hello world1
[ INFO] [1613488268.672710021]: hello world2
[ INFO] [1613488268.772716550]: hello world3
[ INFO] [1613488268.872738656]: hello world4
[ INFO] [1613488268.972714741]: hello world5
[ INFO] [1613488269.072722907]: hello world6
...
4) 启动 roscore
$ rosrun learning_communication listener
[ INFO] [1613488311.557644751]: I heard: [hello world3]
[ INFO] [1613488311.657438007]: I heard: [hello world4]
[ INFO] [1613488311.757441799]: I heard: [hello world5]
[ INFO] [1613488311.857386007]: I heard: [hello world6]
[ INFO] [1613488311.957357331]: I heard: [hello world7]
[ INFO] [1613488312.057212225]: I heard: [hello world8]
[ INFO] [1613488312.157438854]: I heard: [hello world9]
[ INFO] [1613488312.257411530]: I heard: [hello world10]
...
4 实现 Service Demo
4.1 自定义服务数据
创建srv文件：learning_communication/srv/AddTowInts.srv
该文件包含 请求与应答两个数据域，数据中的内容与话题消息数据类型相同，只是在请求与应答的描述之间，用“---”进行分割。
int64 a
int64 b
---
int64 sum
如果使用了如 RoboWare Studio 支持ROS的IDE开发工具，会自动修改 package.xml、CMakeList.txt，可以跳过此步骤。
package.xml
<build_depend>message_generation</build_depend>
<build_export_depend>message_generation</build_export_depend>
<exec_depend>message_runtime</exec_depend>
CMakeLists.txt
find_package(catkin REQUIRED COMPONENTS geometry_msgs message_generation std_msgs rospy roscpp)
add_service_files(FILES AddTowInts.srv)
4.2 创建 server
源文件：learning_communication/src/server.cpp
#include "ros/ros.h"
#include "learning_communication/AddTowInts.h"
bool add(learning_communication::AddTowInts::Request &req,
learning_communication::AddTowInts::Response &res)
{
res.sum = req.a + req.b;
ROS_INFO("request: x=%ld, y=%ld", (long int)req.a, (long int)req.b);
ROS_INFO("sending back response: [%ld]", (long int)res.sum);
return true;
}
int main(int argc, char *argv[])
{
/* code for main function */
ros::init(argc, argv, "add_two_ints_server");
ros::NodeHandle nh;
ros::ServiceServer service = nh.advertiseService("add_two_ints", add);
ROS_INFO("Ready to add_two_ints.");
ros::spin();
return 0;
}
4.3 创建 Client
源码：learning_communimation/src/client.cpp
#include <cstdlib>
#include "ros/ros.h"
#include "learning_communication/AddTowInts.h"
int main(int argc, char *argv[])
{
ros::init(argc, argv, "add_two_ints_client");
if (argc != 3)
{
ROS_INFO("usage: add_two_ints_client X Y");
return 1;
}
ros::NodeHandle nh;
ros::ServiceClient client = nh.serviceClient<learning_communication::AddTowInts>("add_two_ints");
learning_communication::AddTowInts srv;
srv.request.a = atoll(argv[1]);
srv.request.b = atoll(argv[2]);
if (client.call(srv))
{
ROS_INFO("Sum: %ld", (long int)srv.response.sum);
}
else
{
ROS_ERROR("Failed to call service add_two_ints");
return 1;
}
return 0;
}
4.4 编译功能包
如果使用了如 RoboWare Studio 支持ROS的IDE开发工具，会自动修改CMakeList.txt，可以跳过此步骤。
vi ~/catkin_ws/src/learning_communication/CMakeList.txt
add_executable(server src/server.cpp)
add_dependencies(server ${${PROJECT_NAME}_EXPORTED_TARGETS} ${catkin_EXPORTED_TARGETS})
target_link_libraries(server ${catkin_LIBRARIES})add_executable(client src/client.cpp)
add_dependencies(client ${${PROJECT_NAME}_EXPORTED_TARGETS} ${catkin_EXPORTED_TARGETS})
target_link_libraries(client ${catkin_LIBRARIES})
现在就可以用 catkin_make 编译了
$ cd ~/catkin_wd
$ catkin_make
4.5 运行 Server 和 Client
启动 rescore
$ rescore
运行 Server
$ rosrun learning_communication server
[ INFO] [1613489902.213953459]: Ready to add_two_ints.
// 等clint运行之后，输出
[ INFO] [1613489983.113582239]: request: x=3, y=5
[ INFO] [1613489983.113607501]: sending back response: [8]
运行 Client
$ rosrun learning_communication client 3 5
[ INFO] [1613489943.361253908]: Sum: 8
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