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Creating a ROS msg and srv (plain cmake)
Description: This tutorial covers how to create and build msg and srv files using plain cmake (i.e., not catkin).Tutorial Level: BEGINNER
Contents
Note: Be sure that you have already installed ROS and remember that you must source the appropriate setup file in every shell you create.
Making a directory in which to work
To help keep yourself organized, make a directory in which to work. You can use any name; we'll just call it msgsrv:
mkdir -p msgsrv cd msgsrv
Introduction to msg and srv
msgs are just simple text files with a field type and field name per line. The field types you can use are:
- int8, int16, int32, int64 (plus uint*)
- float32, float64
- string
- time, duration
- other msg files
- variable-length array[] and fixed-length array[C]
There is also a special type in ROS: Header, the header contains a timestamp and coordinate frame information that are commonly used in ROS. You will frequently see the first line in a msg file have Header header.
Here is an example of a msg that uses a Header, a string primitive, and two other msgs :
Header header string child_frame_id geometry_msgs/PoseWithCovariance pose geometry_msgs/TwistWithCovariance twist
srv files are just like msg files, except they contain two parts: a request and a response. The two parts are separated by a '---' line. Here is an example of a srv file:
int64 A int64 B --- int64 Sum
In the above example, A and B are the request, and Sum is the response.
Using msg
Creating a msg
Let's define a couple of new messages. Create a file named Foo.msg and put the following in it:
https://raw.githubusercontent.com/gerkey/ros1_external_use/master/ros1_msgs/Foo.msg
1 int16 foo
Create a file named Bar.msg and put the following in it:
https://raw.githubusercontent.com/gerkey/ros1_external_use/master/ros1_msgs/Bar.msg
1 uint16 bar
2 # Use messages from other packages
3 geometry_msgs/Pose pose
4 map_msgs/ProjectedMap map
Using an existing msg (C++)
To have a simple C++ example of using an existing ROS message in code, create a file named use_existing_msg.cpp and put the following in it:
https://raw.githubusercontent.com/gerkey/ros1_external_use/master/ros1_msgs/use_existing_msg.cpp
#include <sensor_msgs/LaserScan.h>
#include <stdio.h>
int
main(void)
{
sensor_msgs::LaserScan scan;
for(int i=0; i<100; i++)
scan.ranges.push_back(42.0*i);
for(std::vector<float>::const_iterator it = scan.ranges.begin();
it != scan.ranges.end();
++it)
printf("%f\n", *it);
}
Using the new message in code (C++)
To have a simple C++ example of how to use custom messages from code, create a file named use_custom_msg.cpp and put the following in it:
https://raw.githubusercontent.com/gerkey/ros1_external_use/master/ros1_msgs/use_custom_msg.cpp
#include <myproject/Foo.h>
#include <myproject/Bar.h>
#include <stdio.h>
int
main(void)
{
myproject::Foo foo;
foo.foo = 42;
printf("%d\n", foo.foo);
myproject::Bar bar;
}
Using existing and new messages in code (Python)
To have a simple Python example of using both existing and new messages in code, create a file named use_msgs.py and put the following in it:
https://raw.githubusercontent.com/gerkey/ros1_external_use/master/ros1_msgs/use_msgs.py
#!/usr/bin/env python from sensor_msgs.msg import LaserScan from myproject.msg import Foo f = Foo(42) print(f.foo) s = LaserScan()
Building messages and code
To use custom messages, we need to run the code generators provided by ROS to process .msg files into code for use in C++, Python, and other languages. Create a file named CMakeLists.txt and put the following in it:
https://raw.githubusercontent.com/gerkey/ros1_external_use/master/ros1_msgs/CMakeLists.txt
1 cmake_minimum_required(VERSION 2.8.3)
2 project(myproject)
3
4 # Build an executable that uses an existing ROS msg: find_package() the ROS
5 # package that contains the message, then use its reported include directories.
6 find_package(sensor_msgs REQUIRED)
7 include_directories(${sensor_msgs_INCLUDE_DIRS})
8 add_executable(use_existing_msg use_existing_msg.cpp)
9
10 # Generate code from our own custom messages
11 # find_package catkin and genmsg, required for message generation macros
12 find_package(catkin REQUIRED)
13 find_package(genmsg REQUIRED)
14 # find_package the other message packages that our custom messages use
15 find_package(geometry_msgs REQUIRED)
16 find_package(map_msgs REQUIRED)
17 # Enumerate our custom messages files
18 add_message_files(DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR} FILES Foo.msg Bar.msg)
19 # Do code generation, specifying which other message packages we depend on.
20 generate_messages(DEPENDENCIES geometry_msgs map_msgs)
21
22 # Build an executable that uses our messages, making it depend on the
23 # message-generation step.
24 add_executable(use_custom_msg use_custom_msg.cpp)
25 add_dependencies(use_custom_msg ${PROJECT_NAME}_generate_messages)
26
27 # (optional) Install the executables. The generated code will also
28 # automatically be installed.
29 install(TARGETS use_existing_msg use_custom_msg
30 DESTINATION bin)
31 install(PROGRAMS use_msgs.py
32 DESTINATION bin)
Process your messages and build your (C++) code in a subdirectory of msgsrv named build using the standard cmake sequence:
mkdir -p build cd build cmake .. make
Running the code
To confirm that everything is working properly, run each of the programs (they won't do anything terribly interesting):
./build/use_existing_msg
./build/use_custom_msg
python use_msgs.py
Using srv
TODO: fill out this section with analogous examples
