Missing parameter `source_list` when porting from ROS 1 to ROS 2

[adeguet1]

In ROS1, the robot_state_publisher had an option to subscribe to multiple topics to retrieve the joint state (source_list). This can be used with a device (e.g. gripper) attached to another robot (e.g. UR). Then both the gripper and UR controllers push their own joint state. Since the state publisher looks for names in the joint_state, it can pick the joint values from one or more topics. This worked as long as the joint names are unique, including across topics.

Is this supported in ROS 2 and I missed it? If not, is there an alternative approach in ROS? If the answer is still no, is this a feature that could be added? If so, I could try to implement this and create a PR.

[sloretz]

I don't see a source_list parameter in robot_state_publisher in ROS 1 or ROS 2, but I do see one in joint_state_publisher. Is that what you're thinking of? If so, it's also available in ROS 2.

I expect remapping both the gripper's and controller's joint states to the same topic and having robot_state_publisher subscribe to that would work as well.

[adeguet1]

Solution 1:

Using the joint_state_publisher, it works but I'm getting a slightly confusing message:

Waiting for robot_description to be published on the robot_description topic...

It would be nice to get a confirmation message once the joint_state_publisher finally gets the robot_description. Alternatively, maybe the joint_state_publisher could have an option to use a node/parameter for the robot_description.

Solution 2:

Does the topic remapping happen on the publisher's node or on the subscriber node? I tried to modify the launch for the robot_state_publisher using something like:

    robot_state_publisher_node = Node(
        package='robot_state_publisher',
        executable='robot_state_publisher',
        name='robot_state_publisher',
        remappings=[
            ('joint_states', 'PSM1/jaw/measured_js'),
            ('joint_states', 'PSM1/measured_js')],
        parameters=[{'use_sim_time': use_sim_time,
                               'robot_description': ParameterValue(
                                    Command(['xacro ', str(urdf)]), value_type=str),
        }],
        arguments=[urdf]
    )

But that didn't work. I assume the remapping is some kind of map of subscriptions, not a multimap? So the first element of the remapping can't be repeated...