ROS学习手记 - 7 创建ROS msg & srv

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

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++).