请你提取出：编写一个控制节点，发布消息，控制小海龟运动，例如按照矩形走，或者按照其他预定轨 迹走。编写一个服务节点，在指定位置参数一只新的海龟。根据小海龟节点提供的消息或者服务，创新性的编写一个节点，完成某种功能。相关的完整代码

根据您提出的需求，这里为您总结了几个任务的关键步骤和示例代码，详情您可以参考原链接 [CSDN博客](https://blog.csdn.net/weixin_64179065/article/details/136421093) 获取更多细节。

### 编写控制节点，发布消息，控制小海龟按预定轨迹行走

#### 示例：控制小海龟画方形

1. **创建功能包**

   cd ~/catkin_ws/src
   catkin_create_pkg learning_topic std_msgs rospy roscpp geometry_msgs

2. **编写C++代码**

在 `~/catkin_ws/src/learning_topic/src` 目录下创建 `square_publisher.cpp` 文件：

   #include "ros/ros.h"
   #include "geometry_msgs/Twist.h"

   int main(int argc, char **argv)
   {
     ros::init(argc, argv, "square_publisher");
     ros::NodeHandle n;
     ros::Publisher pub = n.advertise<geometry_msgs::Twist>("/turtle1/cmd_vel", 1000);
     ros::Rate loop_rate(1);

     // 停留时间和速度
     double duration = 2.0; // 秒
     double speed = 2.0;    // 单位距离/秒

     while (ros::ok())
     {
       for (int i = 0; i < 4; ++i)
       {
         geometry_msgs::Twist move_cmd;
         move_cmd.linear.x = speed;
         move_cmd.angular.z = 0;

         // 发布直线前进指令
         pub.publish(move_cmd);
         ros::Duration(duration).sleep();

         move_cmd.linear.x = 0;
         move_cmd.angular.z = M_PI / 2; // 90度转弯

         // 发布转动指令
         pub.publish(move_cmd);
         ros::Duration(1.0).sleep();
       }
     }

     return 0;
   }

3. **编译并运行**

修改 `CMakeLists.txt` 文件，添加如下内容：

   add_executable(square_publisher src/square_publisher.cpp)
   target_link_libraries(square_publisher ${catkin_LIBRARIES})

编译并运行：

   cd ~/catkin_ws
   catkin_make
   source devel/setup.bash
   roscore

打开新终端：

   rosrun turtlesim turtlesim_node

再打开一个新终端：

   rosrun learning_topic square_publisher

### 编写服务节点，创建新海龟

1. **创建服务文件**

在 `~/catkin_ws/src/learning_topic/srv` 目录下创建 `Spawn.srv` 文件：

   float32 x
   float32 y
   float32 theta
   string name
   ---
   string name

2. **编写服务端代码**

在 `~/catkin_ws/src/learning_topic/src` 目录下创建 `spawn_server.cpp` 文件：

   #include "ros/ros.h"
   #include "learning_topic/Spawn.h"
   #include "turtlesim/Spawn.h"
   #include "turtlesim/Kill.h"

   bool spawn_cb(learning_topic::Spawn::Request &req, learning_topic::Spawn::Response &res)
   {
     ros::NodeHandle n;
     ros::ServiceClient client = n.serviceClient<turtlesim::Spawn>("spawn");

     turtlesim::Spawn srv;
     srv.request.x = req.x;
     srv.request.y = req.y;
     srv.request.theta = req.theta;
     srv.request.name = req.name;

     if (client.call(srv))
     {
       res.name = srv.response.name;
       ROS_INFO("Spawned new turtle named %s at (%f, %f)", res.name.c_str(), req.x, req.y);
     }
     else
     {
       ROS_ERROR("Failed to call service spawn");
       return false;
     }

     return true;
   }

   int main(int argc, char **argv)
   {
     ros::init(argc, argv, "spawn_server");
     ros::NodeHandle n;
     ros::ServiceServer service = n.advertiseService("spawn_turtle", spawn_cb);
     ROS_INFO("Ready to spawn a new turtle.");
     ros::spin();

     return 0;
   }

3. **编译并运行**

修改 `CMakeLists.txt` 文件，添加如下内容：

   find_package(catkin REQUIRED COMPONENTS
     roscpp
     std_msgs
     geometry_msgs
     turtlesim
     message_generation
   )

   add_service_files(
     FILES
     Spawn.srv
   )

   generate_messages(
     DEPENDENCIES
     std_msgs
     geometry_msgs
   )

   add_executable(spawn_server src/spawn_server.cpp)
   target_link_libraries(spawn_server ${catkin_LIBRARIES})

编译并运行：

   cd ~/catkin_ws
   catkin_make
   source devel/setup.bash
   roscore

打开新终端：

   rosrun turtlesim turtlesim_node

再打开一个新终端：

   rosrun learning_topic spawn_server

4. **客户端调用服务**

在另一个终端中调用服务：

   rosservice call /spawn_turtle "{x: 1.0, y: 1.0, theta: 0.0, name: 'turtle2'}"

希望这些代码和说明能帮助您更好地理解和实现您的需求。如果您有任何疑问，欢迎随时提问！