Tutorial: Ros Plugins

In this tutorial we'll walk through creating a very basic Gazebo plugin that is ROS-aware.

Create a ROS Package

Create a new ROS package in your catkin workspace:

cd ~/catkin_ws/src
catkin_create_pkg gazebo_tutorials gazebo_ros roscpp

Create the Plugin

Create a very simple plugin as described here and save the file as gazebo_tutorials/src/simple_world_plugin.cpp:

#include <gazebo/common/Plugin.hh>
#include <ros/ros.h>

namespace gazebo
{
class WorldPluginTutorial : public WorldPlugin
{
public:
  WorldPluginTutorial() : WorldPlugin()
  {
  }

  void Load(physics::WorldPtr _world, sdf::ElementPtr _sdf)
  {
    // Make sure the ROS node for Gazebo has already been initialized
    if (!ros::isInitialized())
    {
      ROS_FATAL_STREAM("A ROS node for Gazebo has not been initialized, unable to load plugin. "
        << "Load the Gazebo system plugin 'libgazebo_ros_api_plugin.so' in the gazebo_ros package)");
      return;
    }

    ROS_INFO("Hello World!");
  }

};
GZ_REGISTER_WORLD_PLUGIN(WorldPluginTutorial)
}

Update CMakeLists.txt

Open gazebo_tutorials/CMakeLists.txt and replace it with the following:

cmake_minimum_required(VERSION 2.8.3)
project(gazebo_tutorials)

# Check for c++11 / c++0x support
include(CheckCXXCompilerFlag)
CHECK_CXX_COMPILER_FLAG("-std=c++11" COMPILER_SUPPORTS_CXX11)
CHECK_CXX_COMPILER_FLAG("-std=c++0x" COMPILER_SUPPORTS_CXX0X)
if(COMPILER_SUPPORTS_CXX11)
    set(CMAKE_CXX_FLAGS "-std=c++11")
elseif(COMPILER_SUPPORTS_CXX0X)
    set(CMAKE_CXX_FLAGS "-std=c++0x")
else()
    message(FATAL_ERROR "The compiler ${CMAKE_CXX_COMPILER} has no C++11 support. Please use a different C++ compiler.")
endif()

# Load catkin and all dependencies required for this package
find_package(catkin REQUIRED COMPONENTS
  roscpp
  gazebo_ros
)

# Depend on system install of Gazebo
find_package(gazebo REQUIRED)

link_directories(${GAZEBO_LIBRARY_DIRS})
include_directories(${Boost_INCLUDE_DIR} ${catkin_INCLUDE_DIRS} ${GAZEBO_INCLUDE_DIRS})

catkin_package(
  DEPENDS
    roscpp
    gazebo_ros
)

add_library(${PROJECT_NAME} src/simple_world_plugin.cpp)
target_link_libraries(${PROJECT_NAME} ${catkin_LIBRARIES} ${GAZEBO_LIBRARIES})

Update package.xml

Update gazebo_tutorials/package.xml by adding the following line within the <export></export> tags (or add the <export></export> tags also).

  <gazebo_ros plugin_path="${prefix}/../../lib" gazebo_media_path="${prefix}" />

Compiling the Plugin

Build the plugin by going to the base of your work space and running catkin:

cd ~/catkin_ws
catkin_make

Creating a World file

Save the following file as gazebo_tutorials/worlds/hello.world:

<?xml version="1.0" ?>
<sdf version="1.4">
  <world name="default">
    <include>
      <uri>model://ground_plane</uri>
    </include>

    <include>
      <uri>model://sun</uri>
    </include>

    <!-- reference to your plugin -->
    <plugin name="gazebo_tutorials" filename="libgazebo_tutorials.so"/>
  </world>
</sdf>

Create a Launch File

Create the following launch file gazebo_tutorials/launch/hello.launch:

<launch>
  <!-- We resume the logic in empty_world.launch, changing only the name of the world to be launched -->
  <include file="$(find gazebo_ros)/launch/empty_world.launch">
    <arg name="world_name" value="$(find gazebo_tutorials)/worlds/hello.world"/>
    <!-- more default parameters can be changed here -->
  </include>
</launch>

Before continuing source your new setup.*sh file:

source devel/setup.bash

Run the Plugin

roslaunch gazebo_tutorials hello.launch

An empty Gazebo should open and in the terminal you should see it print out something like:

 INFO ros.gazebo_tutorials: Hello World!

Starting from a Template

A template is available to help you quickly get a Gazebo-ROS plugin working:

gazeborostemplate.cpp

Adding Functionality

To make your plugin do something useful with Gazebo and ROS, we suggest you read the ROS-agnostic tutorials on Plugins.

ROS Node Note

All gazebo-ros plugins should check if the ROS node has already been initialized in their Load() function, as discussed in this issue. The initialization of the ROS node is performed automatically when you run

rosrun gazebo_ros gazebo

or use the generic empty.world launch file. The gazebo_ros/src/gazebo_ros_api_plugin.cpp should be the only place in Gazebo that calls ros::init().

Next Steps

For miscellaneous Gazebo-ROS tricks see Advanced ROS integration