[ros2] Port gazebo_ros_path plugin to ROS2

[shiveshkhaitan]

Port gazebo_ros_paths_plugin plugin to ROS2.

To export a model, plugin or media file, a package needs to export them from package.xml e.g.

<export>
    <gazebo_ros gazebo_model_path="${prefix}/models"/>
    <gazebo_ros gazebo_media_path="${prefix}/models"/>
</export>

The directory also needs to be installed from CMakeLists.txt e.g.

install(DIRECTORY models
          DESTINATION share/${PROJECT_NAME})

The plugin is directly included in gazebo.launch.py launch file.

[sloretz]

With a few changes this mostly works for me. I tested with model and world/media path. I did not try adding a plugin path.

[chapulina]

The default value could be an empty string. This way we're sure we're using Gazebo's default value, in case that ever changes.

[chapulina]

@shiveshkhaitan , mind rebasing this and adding a migration guide? Thanks!

[shiveshkhaitan]

Porting gazebo_ros launch scripts might require some changes in this. Can we wait for the scripts before merging this?

[chapulina]

Can we wait for the scripts before merging this?

SGTM

[shiveshkhaitan]

I have removed the gazebo launch part as gazebo_ros_paths was originally supposed to be a plugin. The plugin is now available as a python script which can be used by other launch files gzclient, gzserver

[chapulina]

@shiveshkhaitan , can you rebase against the latest ros2 branch? (And we shouldn't forget to backport to dashing). This branch doesn't currently build:

/home/developer/ros2_ws/src/ros-simulation/gazebo_ros_pkgs/gazebo_ros/src/node.cpp: In static member function 'static gazebo_ros::Node::SharedPtr gazebo_ros::Node::Get(sdf::ElementPtr)':
/home/developer/ros2_ws/src/ros-simulation/gazebo_ros_pkgs/gazebo_ros/src/node.cpp:82:16: error: 'class rclcpp::NodeOptions' has no member named 'initial_parameters'
   node_options.initial_parameters(initial_parameters);
                ^~~~~~~~~~~~~~~~~~

[chapulina]

LGTM.

@shiveshkhaitan , we just need a migration guide and a backport to dashing.