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• starts with "/" are global

• starts with "~"
• define in ros::NodeHandle nh1("~") or ros::NodeHandle nh2("~my_private_ns")
  • Namespace of nh1: /[node_name] or nh2: /[node_name]/[my_private_ns]

• rostopic pub [topic]
• rostopic echo [topic]
• rostopic info [topic]

• Structure
  • catkin_ws/src/[package directory]/msg/[file].msg file
• [field_type] [field_name]
• 4 Field types
  1. Built-in type
     • http://wiki.ros.org/msg#Fields (check out 2.1.1)
  2. Names of self-defined Message descriptions (Q: message of message?) ?
  3. Arrays (E.g.: float32[] ranges)
  4. Header type, which maps to std_msgs/Header

• Under [msg_package_name] directory
  • Under package.xml
    • change the depend

      <!-- use at build time --> 
      <build_depend>message_generation</build_depend>
      <!-- use at runtime -->
      <exec_depend>message_runtime</exec_depend>
      

  • Under CMakeLists.txt
    • Under find_package(catkin REQUIRED COMPONENTS
      • Add package component: message_generation

        find_package(catkin REQUIRED COMPONENTS
            roscpp
            std_msgs
            message_generation  # add this
        )
        

    • Under add_message_files(
      • Include the .msg file name

        add_message_files(
            FILES
            Num.msg # add this
        )
        

    • Under generate_messages(
      • Include the dependencies required by the added messages (and services) above

        generate_messages(
            DEPENDENCIES
            std_msgs
        )
        

• Under [directory] where the user-defined msg is used
  • Under CMakeLists.txt
    • Under find_package(catkin REQUIRED COMPONENTS
      • Add package component: [msg_package_name]

        find_package(catkin REQUIRED COMPONENTS
            roscpp
            std_msgs
            lab_msg  // add this
        )
        

      • Add dependency for the node which uses the message

        add_dependencies(talker [msg_package_name]_generate_messages_cpp)
        

• Under the [node_src_file]
  • #include "[msg_package_name]/[msg_filename].h"
    • msg header file will be generated under devel/include/[package name], include the header file when we use those messages.
  • Declare a msg object and assign values

    # Num.msg file
    int32 val
    

    // node file
    lab_msg::Num num;
    num.val = 0;
    

• rostopic type [topic]
  • Will output the message type of that topic
• rosmsg show [message_type]
  • Look up the fields of the msg_type

• Structure
  • catkin_ws/src/[package directory]/srv/[service_type].srv file
• Fields
  • request field (update by client)
  • response field (update by server)
  • separated by "------"
• The corresponding modifications are very similar to those for messages.
  • But in CMakeLists.txt, instead of changing "add_message_files(", modify the "add_service_files(" block.

• rossrv show [service_type]
  • E.g.: rossrv show AddTwoInts
  • Display the details of the .srv file
• rosservice list
  • Display all the currently active services that where launched after you started the ROS master

• Shall be instantiated at the Client (Q: any situation to instantiate at the Server) ?
• 2 members
  • request and response
• 2 class definitions
  • Request and Response

• Information about request and reponse are logged
  • Instances involved as function parameter
    • [package_name]::[service_type]::Request &req
    • [package_name]::[service_type]::Response &res
• ros::ServiceServer service = n.advertiseService("add_two_ints", add)
  • advertiseService() create a service and advertise over ROS
    • First parameter: service name (E.g.: add_two_ints)
    • Second parameter: service function (E.g.: add)
    • Return value: ros::ServiceServer object (E.g.: service)

• ros::ServiceClient client = n.serviceClient<lab_msg::AddTwoInts>("add_two_ints")
  • serviceClient<>() creates a ros::ServiceClient object
    • The object will be used to call the service
    • Will "subscribe" to the [service_name]: add_two_ints
    • Return value: ros::ServiceClient object (E.g.: client)
• lab_msg::AddTwoInts srv
  • Instantiate a autogenerated service class ?
• srv.request.a = atoll(argv[1]);
  • Assign value into the class's request member
• if (client.call(srv)) calls the service
  • client.call()
  • Q: Can I change how frequent service is tried to be called? ?

• Node enables us to: publish/subscribe topic, and advertise/subscribe service
• Node: info exchange, Service: under node, acts just like a function

• Structure
  • catkin_ws/src/[package directory]/launch/[file].launch xml file
• Tags
  • - `pkg=" "` - `type=" "` - Node type, name that matches the executable - `name=" "` - Node name, defined at ros::init() - `ns="my_private_ns"(optional)` - Node name in "my_private_ns" namespace - `output="screen"` to show ROSINFO output
  • • <rosparam file="$(find [package_name])/param/[file].yaml" />
    • <remap from="chatter" to="/talker_node/chatter"/>
• Under [bringup_package_name]/CMakeLists.txt
  • Modify "find_package(catkin REQUIRED COMPONENTS" according to package needs

• roslaunch [package_name] [file].launch
  • Initializes the robot
• http://wiki.ros.org/roslaunch

• Structure
  • catkin_ws/src/[package directory]/param/[file].yaml file
• Commands
  • rosparam list
    • List all parameter names
  • rosparam get /
    • Display contents of the entire Parameter Server
  • rosparam set my_param "hello world"
  • rosparam load lab/param/val.yaml
    • Q: how to control which node the parameter loads to? ?
  • rosparam delete my_param
• std::string s;
• n.getParam("my_param", s);
  • n: instance of NodeHandle
  • Return value: boolean
• n.setParam("my_param", "hello world");
• n.hasParam("my_param")
  • Return value: boolean
  • Check for parameter existence
• Q: Apart from using terminal commands and in .launch file, anyways to load the parameter inside a node? ?

• topic name
• node name

• https://hackmd.io/@st9540808/ByAVGsa1S?type=view
• http://wiki.ros.org/roscpp_tutorials/Tutorials/AccessingPrivateNamesWithNodeHandle
• http://wiki.ros.org/roscpp_tutorials/Tutorials/WritingServiceClient
• http://wiki.ros.org/roslaunch/XML/node
• http://wiki.ros.org/roscpp_tutorials/Tutorials/Parameters