至此,我们初步学习了ROS的基本工具,接下来一步步理解ROS的各个工作部件的创建和工作原理。

本文的详细文档:http://wenku.baidu.com/view/623f41b3376baf1ffd4fad7a

  1. Creating a ROS msg and srv

    This tutorial covers how to create and build msg and srv files as well as therosmsg, rossrv and roscp commandline tools.

1. msg & srv 文件介绍

    msg 文件 就是用来让不同语言能产生message的一个指导性文本文件。

    srv file describes a service. It is composed of two parts: a request and a response.



2. msg & srv 文件存储位置:

    <workspace>/packagename/msg/

    &

    <workspace>/packagename/srv/

   
==== msg file 说明 ====

3. msgfile 的格式和生成

    生成:

         $ cd ~/catkin_ws/src/beginner_tutorials

         $ mkdir msg

         $ echo "int64 num" > msg/Num.msg



    格式:

         string first_name

         string last_name

         uint8 age

         uint32 score



4. msgfile 添加到package.xml的dependency中

      <build_depend>message_generation</build_depend>

      <run_depend>message_runtime</run_depend>



5. 对CMakeLists.txt文件的修改:



  5.1 添加message_generation dependency到CMakeLists.txt中:

      message_generation before the closing parenthesis

        find_package(catkin REQUIRED COMPONENTS

        roscpp

        rospy

        std_msgs

        message_generation  // add ’message_generation’

        )



  5.2 export the message runtime dependency.

      catkin_package(

      ...

      CATKIN_DEPENDS message_runtime ...

      ...)



  5.3 添加msg文件

      add_message_files(

      FILES

      Num.msg

      )

    添加了.msg文件在CMake里,我们保证在你添加其他.msg文件时,CMake知道何时它需要reconfigure重新配置项目。



  5.4 确保generate_messages 函数被调用

      generate_messages(

      DEPENDENCIES

      std_msgs

      )



6. rosmsg 工具的使用

    make sure that ROS can see it using the rosmsg show command.

    Usage:

      $ rosmsg show [message type]

    Example:

      $ rosmsg show beginner_tutorials/Num

      $ rosmsg show Num

===================
      === srv file 说明 ===

 1. srv的路径和生成

      $ roscd beginner_tutorials

      $ mkdir srv

    Instead of creating a new srv definition by hand, we will copy an existing one from another package.

For that, roscp is a useful commandline tool for copying files from one package to another.

    使用roscp工具从一个package拷贝文件到另一个。

    Usage:

      $ roscp [package_name] [file_to_copy_path] [copy_path]

    Now we can copy a service from the rospy_tutorials package:

      $ roscp rospy_tutorials AddTwoInts.srv srv/AddTwoInts.srv



 2. 保证package.xml里有dependency配置(可能独立修改了srv,确保一下)

      <build_depend>message_generation</build_depend>

      <run_depend>message_runtime</run_depend>



 3.1 add the message_generation dependency to generate messages in CMakeLists.txt:

# Do not just add this line to your CMakeLists.txt, modify the existing line

       find_package(catkin REQUIRED COMPONENTS

         roscpp

         rospy

         std_msgs

         message_generation

       )



  3.2 添加 srvice 文件

    add_service_files(

      FILES

      AddTwoInts.srv

    )



  3.3 确保generate_messages 函数被调用

      generate_messages(

      DEPENDENCIES

      std_msgs

      )



4. 使用rossrv工具

    添加以后,确保ROS can see it using the rossrv show command.

    Usage:

    $ rossrv show <service type>

    Example:

    $ rossrv show beginner_tutorials/AddTwoInts

    You will see:

    int64 a

    int64 b

    ---

    int64 sum

    Similar to rosmsg, you can find service files like this without specifying package name:

    $ rossrv show AddTwoInts

    [beginner_tutorials/AddTwoInts]:

    int64 a

    int64 b

    ---

    int64 sum



    [rospy_tutorials/AddTwoInts]:

    int64 a

    int64 b

    ---

    int64 sum

无论是修改了msg还是srv,都需要做的步骤:

CMakeLists.txt文件的修改

  1.

        find_package(catkin REQUIRED COMPONENTS

        roscpp

        rospy

        std_msgs

        message_generation  // add ’message_generation’

        )



  2. add any packages you depend on which contain .msg files that your messages use (in this case std_msgs), such that it looks like this:

        generate_messages(

          DEPENDENCIES

          std_msgs

        )

终于到了catkin_make出手的时候:

Now that we have made some new messages we need to make our package again:

# In your catkin workspace (by default:~/catkin_ws$)

$ cd ../..
$ catkin_make
$ cd -

至此,我们就编译完成了一套ROS 的 msg & srv

Any .msg file in the msg directory will generate code for use in all supportedlanguages.

The C++ message header file will be generated in ~/catkin_ws/devel/include/beginner_tutorials/.

The Python script will be created in ~/catkin_ws/devel/lib/python2.7/dist-packages/beginner_tutorials/msg.

The lisp file appears in ~/catkin_ws/devel/share/common-lisp/ros/beginner_tutorials/msg/.

The full specification for the message format is available at theMessage Description Language page.

Getting Help

We've seen quite a few ROS tools already. It can be difficult to keeptrack of what arguments each command requires. Luckily, most ROS tools providetheir own help.

Try:

$ rosmsg -h

You should see a list of different rosmsg subcommands.

Commands:

  •   rosmsgshow Show message description
  •   rosmsgusers  Find files that use message
  •   rosmsgmd5  Display message md5sum
  •   rosmsgpackage  List messages in a package
  •   rosmsgpackages List packages that contain messages

You can also get help for subcommands

$ rosmsg show -h

  • This shows the arguments that are needed for rosmsg show:

·       Usage: rosmsg show[options] <message type>

·

·       Options:

·         -h, --help show this help message and exit
  -r, --raw   show raw message text, including comments

Review

Lets just list some of the commands we've used so far:

  • rospack = ros+pack(age) : provides information related to ROS packages
  • roscd = ros+cd : changes directory to a ROS package or stack
  • rosls = ros+ls : lists files in a ROS package
  • roscp = ros+cp : copies files from/to a ROS package
  • rosmsg = ros+msg : provides information related to ROS message definitions
  • rossrv = ros+srv : provides information related to ROS service definitions
  • catkin_make : makes (compiles) a ROS package
    • rosmake = ros+make : makes (compiles) a ROS package (if you're not using a catkin workspace)

Next Tutorial

Now that you've made a new ROS msg and srv, let's look at writing a simplepublisher and subscriber(python)(c++).

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