17、 Solutions to duplicate names of ROS function packages and nodes

1、ROS Different workspace function packages have the same name

1. Definition

The so-called workspace coverage , It means in different workspaces , There are function packages with duplicate names . stay ROS In development , In the same workspace , The function package will not have the same name . however , In different workspaces , There may be the phenomenon of duplicate function package names .

2. Call rules when the function package has the same name

• 1. In the root directory .bashrc Add... To the file ROS Function package retrieval path ：

  source /opt/ros/noetic/setup.bash
  source /media/d102/EPAN/Desktop/code_study_ubuntu/rosdemo_05/devel/setup.bash
  source /media/d102/EPAN/Desktop/code_study_ubuntu/rosdemo_04/devel/setup.bash
  

• 2. Update the search path
     In the root directory :

  source .bashrc
  

• 3. Print ROS Function package retrieval path
  • command ：echo $ROS_PACKAGE_PATH

echo $ROS_PACKAGE_PATH 
/media/d102/EPAN/Desktop/code_study_ubuntu/rosdemo_04/src:/media/d102/EPAN/Desktop/code_study_ubuntu/rosdemo_05/src:/opt/ros/noetic/share

so , The path is farther back , The higher the priority , When the function package has the same name , Will search according to priority , Those with high priority are executed first

• 4. roscd Function pack
     Will enter the workspace containing the corresponding function package , By viewing the workspace path , You can know which workspace function package is called

3. Safe hidden trouble

When there is a function package with the same name , Execution exceptions may occur . such as ,C When the function package is executed , rely on A Medium turtle Function pack , But it did B Medium turtle Function pack , Because the two function packs have the same name , Different functions , This leads to execution exceptions

4.BUG explain

In the root directory .bashrc In file , meanwhile source Multiple files , It might show up in ROS_PACKAGE_PATH Contains only two workspaces bug, The solution is as follows ：（ This BUG It's very metaphysical , At present, we have not found 100% Effective methods , The following methods are for reference ）

 Delete... In the workspace build and devel Folder recompile , And then reload .bashrc file 

• Be careful ：
  When recompiling , It may appear as follows BUG：

  -- Using PYTHON_EXECUTABLE: /home/matthew/anaconda3/envs/torch/bin/python3
  -- Using Debian Python package layout
  -- Could NOT find PY_em (missing: PY_EM) 
  CMake Error at /opt/ros/noetic/share/catkin/cmake/empy.cmake:30 (message):
  Unable to find either executable 'empy' or Python module 'em'...  try
  installing the package 'python3-empy'
  Call Stack (most recent call first):
  /opt/ros/noetic/share/catkin/cmake/all.cmake:164 (include)
  /opt/ros/noetic/share/catkin/cmake/catkinConfig.cmake:20 (include)
  CMakeLists.txt:58 (find_package)
  

This is because catkin Looking for python Version is anaconda The following version , So you need to specify the following command instead :

catkin_make -DPYTHON_EXECUTABLE=/usr/bin/python3

2. ROS Duplicate node name

2.1 background

Sometimes , You need to start the same node , If you start directly , Because the node names are the same , The node that starts first will be shut down due to the duplicate name , To solve this problem , The following three methods can be used ：

2.2 terms of settlement

2.2.1 rosrun Set namespace and remap

2.2.1.1 rosrun Set namespace

• Format ：rosrun package_name node_name __ns:=ns_name
• Code implementation ：

  # bash1
  rosrun turtlesim turtlesim_node __ns:=ns1
  # bash2
  rosrun turtlesim turtlesim_node __ns:=ns2
  

• Running results ：

  rosnode list
  /ns1/turtlesim
  /ns2/turtlesim
  /rosout
  /turtlesim
  

2.2.1.2 rosrun Name remapping

• Format ：rosrun package_name node_name __name:=new_name( Do not apply to Python)
• Code implementation ：

  # bash1
  rosrun turtlesim turtlesim_node __name:=t1
  # bash2
  rosrun turtlesim turtlesim_node __name:=t2
  

• Running results ：

  rosnode list
  /t1
  /t2
  /turtlesim
  

2.2.1.3 rosrun Superposition of namespace and name remapping

• Format 1：rosrun package_name node_name __ns:=ns_name __name:=new_name
• Format 2：rosrun package_name node_name __name:=new_name __ns:=ns_name
• Code implementation ：

  # bash1
  rosrun turtlesim turtlesim_node __ns:=ns1 __name:=t1
  # bash2
  rosrun turtlesim turtlesim_node __name:=t2 __ns:=ns2
  

• Running results ：

  /ns1/t1
  /ns2/t2
  

2.2.1.4 Setting environment variables can also set namespaces

• Format ：export ROS_NAMESPACE=ns_name
• Code implementation ：

  # bash1
  [email protected]:~$ export ROS_NAMESPACE=ns3
  [email protected]:~$ rosrun turtlesim turtlesim_node  
  # bash2
  [email protected]:~$ export ROS_NAMESPACE=ns4
  [email protected]:~$ rosrun turtlesim turtlesim_node 
  

• Running results ：

  /ns3/turtlesim
  /ns4/turtlesim
  

2.2.2 launch File set namespace and remap

• Code implementation ：

  <launch>
      <!--  Reference nodes  -->
      <node pkg="turtlesim" type="turtlesim_node" name="turtlesim" />
      <!--  Name remapping  -->
      <node pkg="turtlesim" type="turtlesim_node" name="turtlesim_01" />
      <!--  Namespace  -->
      <node pkg="turtlesim" type="turtlesim_node" name="turtlesim" ns="ns_01"/>
      <!--  Namespace + Name remapping  -->
      <node pkg="turtlesim" type="turtlesim_node" name="turtlesim_02" ns="ns_02"/>
  </launch>
  

• Running results ：

  rosnode list
  /ns3/ns_01/turtlesim
  /ns3/ns_02/turtlesim_02
  /ns3/turtlesim_01
  /turtlesim
  

2.2.3 Code set namespace and remap

2.2.3.1 C++ Implement remapping

• Code implementation ：

  ros::init(argc,argv,"server",ros::init_options::AnonymousName);// Add a timestamp after the node 
  

• Running results ：

  # bash1
  rosrun server_client server
  # bash2
  rosnode list 
  /server_1656775703891563446
  

2.2.3.2 C++ Implementation namespace

• Code implementation ：

  std::map<std::string, std::string> map;
  map["__ns"] = "namespace_01";
  ros::init(map,"server",ros::init_options::AnonymousName);//server Name the node 
  

• Running results ：

  # bash1 
  rosrun server_client server
  # bash2
  rosnode list 
  /namespace_01/server_1656776071871347181
  

2.2.3.3 Python Implement remapping （ Cannot implement namespace ）

• Code implementation ：

  rospy.init_node("server_p",anonymous=True) # The timestamp will be added after the node 
  

• Running results ：

  # bash1
  rosrun server_client server_p.py 
  # bash2
  rosnode list
  /server_p_188947_1656776369182