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

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++).