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Migration guide from ROS 1

There are two different kinds of package migrations:

• Migrating the source code of an existing package from ROS 1 to ROS 2 with the intent that a significant part of the source code will stay the same or at least similar. An example for this could be pluginlib where the source code is maintained in different branches within the same repository and commonly patches can be ported between those branches when necessary.

• Implementing the same or similar functionality of a ROS 1 package for ROS 2 but with the assumption that the source code will be significantly different. An example for this could be roscpp in ROS 1 and rclcpp in ROS 2 which are separate repositories and don’t share any code.

This article focuses on the former case and describes the high-level steps to migrate a ROS 1 package to ROS 2. It does not aim to be a step-by-step migration instruction and is not considered the final “solution”. Future versions will aim to make migration smoother and less effort up to the point of maintaining a single package from the same branch for ROS 1 as well as ROS 2.

Prerequisites

Before being able to migrate a ROS 1 package to ROS 2 all of its dependencies must be available in ROS 2.

Migration steps

Package manifests

ROS 2 doesn’t support format 1 of the package specification but only newer format versions (2 and higher). Therefore the package.xml file must be updated to at least format 2 if it uses format 1. Since ROS 1 supports all formats it is safe to perform that conversion in the ROS 1 package.

Some packages might have different names in ROS 2 so the dependencies might need to be updated accordingly.

Metapackages

ROS 2 doesn’t have a special package type for metapackages. Metapackages can still exist as regular packages that only contain runtime dependencies. When migrating metapackages from ROS 1, simply remove the <metapackage /> tag in your package manifest.

Message, service, and action definitions

Message files must end in .msg and must be located in the subfolder msg. Service files must end in .srv and must be located in the subfolder srv. Actions files must end in .action and must be located in the subfolder action.

These files might need to be updated to comply with the ROS Interface definition. Some primitive types have been removed and the types duration and time which were builtin types in ROS 1 have been replaced with normal message definitions and must be used from the builtin_interfaces package. Also some naming conventions are stricter than in ROS 1.

In your package.xml:

• Add <buildtool_depend>rosidl_default_generators</buildtool_depend>.

• Add <exec_depend>rosidl_default_runtime</exec_depend>.

• For each dependent message package, add <depend>message_package</depend>.

In your CMakeLists.txt:

• Start by enabling C++14

set(CMAKE_CXX_STANDARD 14)

• Add find_package(rosidl_default_generators REQUIRED)

• For each dependent message package, add find_package(message_package REQUIRED) and replace the CMake function call to generate_messages with rosidl_generate_interfaces.

This will replace add_message_files and add_service_files listing of all the message and service files, which can be removed.

Build system

The build system in ROS 2 is called ament and the build tool is colcon. Ament is built on CMake: ament_cmake provides CMake functions to make writing CMakeLists.txt files easier.

Build tool

Instead of using catkin_make, catkin_make_isolated or catkin build ROS 2 uses the command line tool colcon to build and install a set of packages.

Pure Python package

If the ROS 1 package uses CMake only to invoke the setup.py file and does not contain anything beside Python code (e.g. also no messages, services, etc.) it should be converted into a pure Python package in ROS 2:

• Update or add the build type in the package.xml file:

  <export>
    <build_type>ament_python</build_type>
  </export>
  

• Remove the CMakeLists.txt file

• Update the setup.py file to be a standard Python setup script

ROS 2 supports Python 3 only. While each package can choose to also support Python 2 it must invoke executables with Python 3 if it uses any API provided by other ROS 2 packages.

Update the CMakeLists.txt to use ament_cmake

Apply the following changes to use ament_cmake instead of catkin:

• Set the build type in the package.xml file export section:

  <export>
    <build_type>ament_cmake</build_type>
  </export>
  

• Replace the find_package invocation with catkin and the COMPONENTS with:

  find_package(ament_cmake REQUIRED)
  find_package(component1 REQUIRED)
  # ...
  find_package(componentN REQUIRED)
  

• Move and update the catkin_package invocation with:

  • Invoke ament_package instead but after all targets have been registered.

  • The only valid argument for ament_package is CONFIG_EXTRAS. All other arguments are covered by separate functions which all need to be invoked before ament_package:

    • Instead of passing CATKIN_DEPENDS ... call ament_export_dependencies(...) before.

    • Instead of passing INCLUDE_DIRS ... call ament_export_include_directories(...) before.

    • Instead of passing LIBRARIES ... call ament_export_libraries(...) before.

  • TODO document ament_export_targets (``ament_export_interfaces`` in Eloquent and older)?

• Replace the invocation of add_message_files, add_service_files and generate_messages with rosidl_generate_interfaces.

  • The first argument is the target_name. If you’re building just one library it’s ${PROJECT_NAME}

  • Followed by the list of message filenames, relative to the package root.

    • If you will be using the list of filenames multiple times, it is recommended to compose a list of message files and pass the list to the function for clarity.

  • The final multi-value-keyword argument fpr generate_messages is DEPENDENCIES which requires the list of dependent message packages.

    rosidl_generate_interfaces(${PROJECT_NAME}
      ${msg_files}
      DEPENDENCIES std_msgs
    )
    

• Remove any occurrences of the devel space. Related CMake variables like CATKIN_DEVEL_PREFIX do not exist anymore.

  • The CATKIN_DEPENDS and DEPENDS arguments are passed to the new function ament_export_dependencies.

  • CATKIN_GLOBAL_BIN_DESTINATION: bin

  • CATKIN_GLOBAL_INCLUDE_DESTINATION: include

  • CATKIN_GLOBAL_LIB_DESTINATION: lib

  • CATKIN_GLOBAL_LIBEXEC_DESTINATION: lib

  • CATKIN_GLOBAL_SHARE_DESTINATION: share

  • CATKIN_PACKAGE_BIN_DESTINATION: lib/${PROJECT_NAME}

  • CATKIN_PACKAGE_INCLUDE_DESTINATION: include/${PROJECT_NAME}

  • CATKIN_PACKAGE_LIB_DESTINATION: lib

  • CATKIN_PACKAGE_SHARE_DESTINATION: share/${PROJECT_NAME}

Unit tests

If you are using gtest:

Replace CATKIN_ENABLE_TESTING with BUILD_TESTING. Replace catkin_add_gtest with ament_add_gtest.

-   if (CATKIN_ENABLE_TESTING)
-     find_package(GTest REQUIRED)  # or rostest
-     include_directories(${GTEST_INCLUDE_DIRS})
-     catkin_add_gtest(${PROJECT_NAME}-some-test src/test/some_test.cpp)
-     target_link_libraries(${PROJECT_NAME}-some-test
-       ${PROJECT_NAME}_some_dependency
-       ${catkin_LIBRARIES}
-       ${GTEST_LIBRARIES})
-   endif()
+   if (BUILD_TESTING)
+     find_package(ament_cmake_gtest REQUIRED)
+     ament_add_gtest(${PROJECT_NAME}-some-test src/test/test_something.cpp)
+     ament_target_dependencies(${PROJECT_NAME)-some-test
+       "rclcpp"
+       "std_msgs")
+     target_link_libraries(${PROJECT_NAME}-some-test
+       ${PROJECT_NAME}_some_dependency)
+   endif()

Add <test_depend>ament_cmake_gtest</test_depend> to your package.xml.

-   <test_depend>rostest</test_depend>
+   <test_depend>ament_cmake_gtest</test_depend>

Linters

In ROS 2 we are working to maintain clean code using linters. The styles for different languages are defined in our Developer Guide.

If you are starting a project from scratch it is recommended to follow the style guide and turn on the automatic linter unit tests by adding these lines just below if(BUILD_TESTING) (until alpha 5 this was AMENT_ENABLE_TESTING).

find_package(ament_lint_auto REQUIRED)
ament_lint_auto_find_test_dependencies()

You will also need to add the following dependencies to your package.xml:

<test_depend>ament_lint_auto</test_depend>
<test_depend>ament_lint_common</test_depend>

Continue to use catkin in CMake

ROS 2 uses ament as the build system but for backward compatibility ROS 2 has a package called catkin which provides almost the same API as catkin in ROS 1. In order to use this backward compatibility API the CMakeLists.txt must only be updated to call the function catkin_ament_package() after all targets.

NOTE: This has not been implemented yet and is only an idea at the moment. Due to the number of changes related to dependencies it has not yet been decided if this compatibility API is useful enough to justify the effort.

Update source code

Messages, services, and actions

The namespace of ROS 2 messages, services, and actions use a subnamespace (msg, srv, or action, respectively) after the package name. Therefore an include looks like: #include <my_interfaces/msg/my_message.hpp>. The C++ type is then named: my_interfaces::msg::MyMessage.

Shared pointer types are provided as typedefs within the message structs: my_interfaces::msg::MyMessage::SharedPtr as well as my_interfaces::msg::MyMessage::ConstSharedPtr.

For more details please see the article about the generated C++ interfaces.

The migration requires includes to change by:

• inserting the subfolder msg between the package name and message datatype

• changing the included filename from CamelCase to underscore separation

• changing from *.h to *.hpp

// ROS 1 style is in comments, ROS 2 follows, uncommented.
// # include <geometry_msgs/PointStamped.h>
#include <geometry_msgs/msg/point_stamped.hpp>

// geometry_msgs::PointStamped point_stamped;
geometry_msgs::msg::PointStamped point_stamped;

The migration requires code to insert the msg namespace into all instances.

Use of service objects

Service callbacks in ROS 2 do not have boolean return values. Instead of returning false on failures, throwing exceptions is recommended.

// ROS 1 style is in comments, ROS 2 follows, uncommented.
// #include "nav_msgs/GetMap.h"
#include "nav_msgs/srv/get_map.hpp"

// bool service_callback(
//   nav_msgs::GetMap::Request & request,
//   nav_msgs::GetMap::Response & response)
void service_callback(
  const std::shared_ptr<nav_msgs::srv::GetMap::Request> request,
  std::shared_ptr<nav_msgs::srv::GetMap::Response> response)
{
  // ...
  // return true;  // or false for failure
}

Usages of ros::Time

For usages of ros::Time:

• Replace all instances of ros::Time with rclcpp::Time

• If your messages or code makes use of std_msgs::Time:

  • Convert all instances of std_msgs::Time to builtin_interfaces::msg::Time

  • Convert all #include "std_msgs/time.h to #include "builtin_interfaces/msg/time.hpp"

  • Convert all instances using the std_msgs::Time field nsec to the builtin_interfaces::msg::Time field nanosec

Usages of ros::Rate

There is an equivalent type rclcpp::Rate object which is basically a drop in replacement for ros::Rate.

ROS client library

• Python migration guide from ROS 1

NOTE: Others to be written

Boost

Much of the functionality previously provided by Boost has been integrated into the C++ standard library. As such we would like to take advantage of the new core features and avoid the dependency on boost where possible.

Shared Pointers

To switch shared pointers from boost to standard C++ replace instances of:

• #include <boost/shared_ptr.hpp> with #include <memory>

• boost::shared_ptr with std::shared_ptr

There may also be variants such as weak_ptr which you want to convert as well.

Also it is recommended practice to use using instead of typedef. using has the ability to work better in templated logic. For details see here

Thread/Mutexes

Another common part of boost used in ROS codebases are mutexes in boost::thread.

• Replace boost::mutex::scoped_lock with std::unique_lock<std::mutex>

• Replace boost::mutex with std::mutex

• Replace #include <boost/thread/mutex.hpp> with #include <mutex>

Unordered Map

Replace:

• #include <boost/unordered_map.hpp> with #include <unordered_map>

• boost::unordered_map with std::unordered_map

function

Replace:

• #include <boost/function.hpp> with #include <functional>

• boost::function with std::function

Parameters

In ROS 1, parameters are associated with a central server that allowed retrieving parameters at runtime through the use of the network APIs. In ROS 2, parameters are associated per node and are configurable at runtime with ROS services.

• See ROS 2 Parameter design document for more details about the system model.

• See ROS 2 CLI usage for a better understanding of how the CLI tools work and its differences with ROS 1 tooling.

• See Migrating YAML parameter files from ROS 1 to ROS 2 to see how YAML parameter files are parsed in ROS 2 and their differences with ROS implementation.

Launch files

While launch files in ROS 1 are always specified using .xml files, ROS 2 supports Python scripts to enable more flexibility (see launch package) as well as XML and YAML files. See separate tutorial on migrating launch files from ROS 1 to ROS 2.

Example: Converting an existing ROS 1 package to use ROS 2

Let’s say that we have simple ROS 1 package called talker that uses roscpp in one node, called talker. This package is in a catkin workspace, located at ~/ros1_talker.

The ROS 1 code

Here’s the directory layout of our catkin workspace:

$ cd ~/ros1_talker
$ find .
.
./src
./src/talker
./src/talker/package.xml
./src/talker/CMakeLists.txt
./src/talker/talker.cpp

Here is the content of those three files:

src/talker/package.xml:

<package>
  <name>talker</name>
  <version>0.0.0</version>
  <description>talker</description>
  <maintainer email="gerkey@osrfoundation.org">Brian Gerkey</maintainer>
  <license>Apache 2.0</license>
  <buildtool_depend>catkin</buildtool_depend>
  <build_depend>roscpp</build_depend>
  <build_depend>std_msgs</build_depend>
  <run_depend>roscpp</run_depend>
  <run_depend>std_msgs</run_depend>
</package>

src/talker/CMakeLists.txt:

cmake_minimum_required(VERSION 2.8.3)
project(talker)
find_package(catkin REQUIRED COMPONENTS roscpp std_msgs)
catkin_package()
include_directories(${catkin_INCLUDE_DIRS})
add_executable(talker talker.cpp)
target_link_libraries(talker ${catkin_LIBRARIES})
install(TARGETS talker
  RUNTIME DESTINATION ${CATKIN_PACKAGE_BIN_DESTINATION})

src/talker/talker.cpp:

#include <sstream>
#include "ros/ros.h"
#include "std_msgs/String.h"
int main(int argc, char **argv)
{
  ros::init(argc, argv, "talker");
  ros::NodeHandle n;
  ros::Publisher chatter_pub = n.advertise<std_msgs::String>("chatter", 1000);
  ros::Rate loop_rate(10);
  int count = 0;
  std_msgs::String msg;
  while (ros::ok())
  {
    std::stringstream ss;
    ss << "hello world " << count++;
    msg.data = ss.str();
    ROS_INFO("%s", msg.data.c_str());
    chatter_pub.publish(msg);
    ros::spinOnce();
    loop_rate.sleep();
  }
  return 0;
}

Building the ROS 1 code

We source an environment setup file (in this case for Jade using bash), then we build our package using catkin_make install:

. /opt/ros/jade/setup.bash
cd ~/ros1_talker
catkin_make install

Running the ROS 1 node

If there’s not already one running, we start a roscore, first sourcing the setup file from our catkin install tree (the system setup file at /opt/ros/jade/setup.bash would also work here):

. ~/ros1_talker/install/setup.bash
roscore

In another shell, we run the node from the catkin install space using rosrun, again sourcing the setup file first (in this case it must be the one from our workspace):

. ~/ros1_talker/install/setup.bash
rosrun talker talker

Migrating to ROS 2

Let’s start by creating a new workspace in which to work:

mkdir ~/ros2_talker
cd ~/ros2_talker

We’ll copy the source tree from our ROS 1 package into that workspace, where we can modify it:

mkdir src
cp -a ~/ros1_talker/src/talker src

Now we’ll modify the C++ code in the node. The ROS 2 C++ library, called rclcpp, provides a different API from that provided by roscpp. The concepts are very similar between the two libraries, which makes the changes reasonably straightforward to make.

Included headers

In place of ros/ros.h, which gave us access to the roscpp library API, we need to include rclcpp/rclcpp.hpp, which gives us access to the rclcpp library API:

//#include "ros/ros.h"
#include "rclcpp/rclcpp.hpp"

To get the std_msgs/String message definition, in place of std_msgs/String.h, we need to include std_msgs/msg/string.hpp:

//#include "std_msgs/String.h"
#include "std_msgs/msg/string.hpp"

Changing C++ library calls

Instead of passing the node’s name to the library initialization call, we do the initialization, then pass the node name to the creation of the node object (we can use the auto keyword because now we’re requiring a C++14 compiler):

//  ros::init(argc, argv, "talker");
//  ros::NodeHandle n;
    rclcpp::init(argc, argv);
    auto node = rclcpp::Node::make_shared("talker");

The creation of the publisher and rate objects looks pretty similar, with some changes to the names of namespace and methods.

//  ros::Publisher chatter_pub = n.advertise<std_msgs::String>("chatter", 1000);
//  ros::Rate loop_rate(10);
  auto chatter_pub = node->create_publisher<std_msgs::msg::String>("chatter",
    1000);
  rclcpp::Rate loop_rate(10);

To further control how message delivery is handled, a quality of service (QoS) profile could be passed in. The default profile is rmw_qos_profile_default. For more details, see the design document and concept overview.

The creation of the outgoing message is different in the namespace:

//  std_msgs::String msg;
  std_msgs::msg::String msg;

In place of ros::ok(), we call rclcpp::ok():

//  while (ros::ok())
  while (rclcpp::ok())

Inside the publishing loop, we access the data field as before:

msg.data = ss.str();

To print a console message, instead of using ROS_INFO(), we use RCLCPP_INFO() and its various cousins. The key difference is that RCLCPP_INFO() takes a Logger object as the first argument.

//    ROS_INFO("%s", msg.data.c_str());
    RCLCPP_INFO(node->get_logger(), "%s\n", msg.data.c_str());

Publishing the message is the same as before:

chatter_pub->publish(msg);

Spinning (i.e., letting the communications system process any pending incoming/outgoing messages) is different in that the call now takes the node as an argument:

//    ros::spinOnce();
    rclcpp::spin_some(node);

Sleeping using the rate object is unchanged.

Putting it all together, the new talker.cpp looks like this:

#include <sstream>
// #include "ros/ros.h"
#include "rclcpp/rclcpp.hpp"
// #include "std_msgs/String.h"
#include "std_msgs/msg/string.hpp"
int main(int argc, char **argv)
{
//  ros::init(argc, argv, "talker");
//  ros::NodeHandle n;
  rclcpp::init(argc, argv);
  auto node = rclcpp::Node::make_shared("talker");
//  ros::Publisher chatter_pub = n.advertise<std_msgs::String>("chatter", 1000);
//  ros::Rate loop_rate(10);
  auto chatter_pub = node->create_publisher<std_msgs::msg::String>("chatter", 1000);
  rclcpp::Rate loop_rate(10);
  int count = 0;
//  std_msgs::String msg;
  std_msgs::msg::String msg;
//  while (ros::ok())
  while (rclcpp::ok())
  {
    std::stringstream ss;
    ss << "hello world " << count++;
    msg.data = ss.str();
//    ROS_INFO("%s", msg.data.c_str());
    RCLCPP_INFO(node->get_logger(), "%s\n", msg.data.c_str());
    chatter_pub->publish(msg);
//    ros::spinOnce();
    rclcpp::spin_some(node);
    loop_rate.sleep();
  }
  return 0;
}

Changing the package.xml

ROS 2 doesn’t support format 1 of the package specification but only newer format versions (2 and higher). We start by specifying the format version in the package tag:

<!-- <package> -->
<package format="2">

ROS 2 uses a newer version of catkin, called ament_cmake, which we specify in the buildtool_depend tag:

<!--  <buildtool_depend>catkin</buildtool_depend> -->
  <buildtool_depend>ament_cmake</buildtool_depend>

In our build dependencies, instead of roscpp we use rclcpp, which provides the C++ API that we use.

<!--  <build_depend>roscpp</build_depend> -->
  <build_depend>rclcpp</build_depend>

We make the same addition in the run dependencies and also update from the run_depend tag to the exec_depend tag (part of the upgrade to version 2 of the package format):

<!--  <run_depend>roscpp</run_depend> -->
  <exec_depend>rclcpp</exec_depend>
<!--  <run_depend>std_msgs</run_depend> -->
  <exec_depend>std_msgs</exec_depend>

In ROS 1, we use <depend> to simplify specifying dependencies for both compile-time and runtime. We can do the same in ROS 2:

<depend>rclcpp</depend>
<depend>std_msgs</depend>

We also need to tell the build tool what kind of package we are, so that it knows how to build us. Because we’re using ament and CMake, we add the following lines to declare our build type to be ament_cmake:

<export>
  <build_type>ament_cmake</build_type>
</export>

Putting it all together, our package.xml now looks like this:

<!-- <package> -->
<package format="2">
  <name>talker</name>
  <version>0.0.0</version>
  <description>talker</description>
  <maintainer email="gerkey@osrfoundation.org">Brian Gerkey</maintainer>
  <license>Apache License 2.0</license>
<!--  <buildtool_depend>catkin</buildtool_depend> -->
  <buildtool_depend>ament_cmake</buildtool_depend>
<!--  <build_depend>roscpp</build_depend> -->
<!--  <run_depend>roscpp</run_depend> -->
<!--  <run_depend>std_msgs</run_depend> -->
  <depend>rclcpp</depend>
  <depend>std_msgs</depend>
  <export>
    <build_type>ament_cmake</build_type>
  </export>
</package>

TODO: show simpler version of this file just using the ``<depend>`` tag, which is enabled by version 2 of the package format (also supported in ``catkin`` so, strictly speaking, orthogonal to ROS 2).

Changing the CMake code

ROS 2 relies on a higher version of CMake:

#cmake_minimum_required(VERSION 2.8.3)
cmake_minimum_required(VERSION 3.5)

ROS 2 relies on the C++14 standard. Depending on what compiler you’re using, support for C++14 might not be enabled by default. Using gcc 5.3 (which is what is used on Ubuntu Xenial), we need to enable it explicitly, which we do by adding this line near the top of the file:

set(CMAKE_CXX_STANDARD 14)

The preferred way to work on all platforms is this:

if(NOT CMAKE_CXX_STANDARD)
  set(CMAKE_CXX_STANDARD 14)
endif()
if(CMAKE_COMPILER_IS_GNUCXX OR CMAKE_CXX_COMPILER_ID MATCHES "Clang")
  add_compile_options(-Wall -Wextra -Wpedantic)
endif()

Using catkin, we specify the packages we want to build against by passing them as COMPONENTS arguments when initially finding catkin itself. With ament_cmake, we find each package individually, starting with ament_cmake:

#find_package(catkin REQUIRED COMPONENTS roscpp std_msgs)
find_package(ament_cmake REQUIRED)
find_package(rclcpp REQUIRED)
find_package(std_msgs REQUIRED)

System dependencies can be found as before:

find_package(Boost REQUIRED COMPONENTS system filesystem thread)

We call catkin_package() to auto-generate things like CMake configuration files for other packages that use our package. Whereas that call happens before specifying targets to build, we now call the analogous ament_package() after the targets:

# catkin_package()
# At the bottom of the file:
ament_package()

The only directories that need to be manually included are local directories and dependencies that are not ament packages:

#include_directories(${catkin_INCLUDE_DIRS})
include_directories(include ${Boost_INCLUDE_DIRS})

A better alternative is to specify include directories for each target individually, rather than including all the directories for all targets:

target_include_directories(target include ${Boost_INCLUDE_DIRS})

Similar to how we found each dependent package separately, we need to link each one to the build target. To link with dependent packages that are ament packages, instead of using target_link_libraries(), ament_target_dependencies() is a more concise and more thorough way of handling build flags. It automatically handles both the include directories defined in _INCLUDE_DIRS and linking libraries defined in _LIBRARIES.

#target_link_libraries(talker ${catkin_LIBRARIES})
ament_target_dependencies(talker
  rclcpp
  std_msgs)

To link with packages that are not ament packages, such as system dependencies like Boost, or a library being built in the same CMakeLists.txt, use target_link_libraries():

target_link_libraries(target ${Boost_LIBRARIES})

For installation, catkin defines variables like CATKIN_PACKAGE_BIN_DESTINATION. With ament_cmake, we just give a path relative to the installation root, like bin for executables:

#install(TARGETS talker
#  RUNTIME DESTINATION ${CATKIN_PACKAGE_BIN_DESTINATION})
install(TARGETS talker
  DESTINATION lib/${PROJECT_NAME})

Optionally, we can install and export the included directories for downstream packages:

install(DIRECTORY include/
  DESTINATION include)
ament_export_include_directories(include)

Optionally, we can export dependencies for downstream packages:

ament_export_dependencies(std_msgs)

Putting it all together, the new CMakeLists.txt looks like this:

#cmake_minimum_required(VERSION 2.8.3)
cmake_minimum_required(VERSION 3.5)
project(talker)
if(NOT CMAKE_CXX_STANDARD)
  set(CMAKE_CXX_STANDARD 14)
endif()
if(CMAKE_COMPILER_IS_GNUCXX OR CMAKE_CXX_COMPILER_ID MATCHES "Clang")
  add_compile_options(-Wall -Wextra -Wpedantic)
endif()
#find_package(catkin REQUIRED COMPONENTS roscpp std_msgs)
find_package(ament_cmake REQUIRED)
find_package(rclcpp REQUIRED)
find_package(std_msgs REQUIRED)
#catkin_package()
#include_directories(${catkin_INCLUDE_DIRS})
include_directories(include)
add_executable(talker talker.cpp)
#target_link_libraries(talker ${catkin_LIBRARIES})
ament_target_dependencies(talker
  rclcpp
  std_msgs)
#install(TARGETS talker
#  RUNTIME DESTINATION ${CATKIN_PACKAGE_BIN_DESTINATION})
install(TARGETS talker
  DESTINATION lib/${PROJECT_NAME})
install(DIRECTORY include/
  DESTINATION include)
ament_export_include_directories(include)
ament_export_dependencies(std_msgs)
ament_package()

TODO: Show what this would look like with ``ament_auto``.

Building the ROS 2 code

We source an environment setup file (in this case the one generated by following the ROS 2 installation tutorial, which builds in ~/ros2_ws, then we build our package using colcon build:

. ~/ros2_ws/install/setup.bash
cd ~/ros2_talker
colcon build

Running the ROS 2 node

Because we installed the talker executable into bin, after sourcing the setup file, from our install tree, we can invoke it by name directly (also, there is not yet a ROS 2 equivalent for rosrun):

. ~/ros2_ws/install/setup.bash
talker

Update scripts

ROS CLI arguments

Since ROS Eloquent, ROS arguments should be scoped with --ros-args and a trailing -- (the trailing double dash may be elided if no arguments follow it).

Remapping names is similar to ROS 1, taking on the form from:=to, except that it must be preceded by a --remap (or -r) flag. For example:

ros2 run some_package some_ros_executable --ros-args -r foo:=bar

We use a similar syntax for parameters, using the --param (or -p) flag:

ros2 run some_package some_ros_executable --ros-args -p my_param:=value

Note, this is different than using a leading underscore in ROS 1.

To change a node name use __node (the ROS 1 equivalent is __name):

ros2 run some_package some_ros_executable --ros-args -r __node:=new_node_name

Note the use of the -r flag. The same remap flag is needed for changing the namespace __ns:

ros2 run some_package some_ros_executable --ros-args -r __ns:=/new/namespace

There is no equivalent in ROS 2 for the following ROS 1 keys:

• __log (but --log-config-file can be used to provide a logger configuration file)

• __ip

• __hostname

• __master

For more information, see the design document.

Quick reference

Feature	ROS 1	ROS 2
remapping	foo:=bar	-r foo:=bar
parameters	_foo:=bar	-p foo:=bar
node name	__name:=foo	-r __node:=foo
namespace	__ns:=foo	-r __ns:=foo

Licensing

In ROS 2 our recommended license is the Apache 2.0 License. In ROS 1 our recommended license was the 3-Clause BSD License.

For any new project we recommend using the Apache 2.0 License, whether ROS 1 or ROS 2.

However, when migrating code from ROS 1 to ROS 2 we cannot simply change the license. The existing license must be preserved for any preexisting contributions.

To that end if a package is being migrated we recommend keeping the existing license and continuing to contribute to that package under the existing OSI license, which we expect to be the BSD license for core elements.

This will keep things clear and easy to understand.

Changing the License

It is possible to change the license, however you will need to contact all the contributors and get permission. For most packages this is likely to be a significant effort and not worth considering. If the package has a small set of contributors then this may be feasible.