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++).