ROS and MORSE tutorial :tag:`ros`
=================================

This is an extension of the current :doc:`tutorial <../beginner_tutorials/tutorial>`
using the ROS as our middleware (instead of raw sockets).

The builder script is the same as the one used in the sockets tutorial.
Except the part on the inteface, which in this case is ROS.
You can find it in ``examples/tutorials/tutorial-1-ros.py``.


Configuring ROS
---------------

.. code-block:: python

    pose.add_stream('ros')
    motion.add_stream('ros')


Running the simulation
----------------------

Run morse with::

    morse run examples/tutorials/tutorial-1-ros.py

In another terminal, use the ``rostopic``, ``rqt_plot`` and ``rqt_graph``
commands to control the robot.


rostopic
--------

First, send a motion command to the robot's MotionVW actuator::

    rostopic pub -1 /atrv/motion geometry_msgs/Twist "{linear: {x: .5}, angular: {z: .5}}"

- ``pub`` stands for publish
- ``-1`` will publish 1 message
- ``/atrv/motion`` correspond to the robots's motion controller topic
- ``geometry_msgs/Twist`` is the message's type
- ``"{linear: {x: .8}, angular: {z: .5}}"`` the message in json

  - 0.8 m/s for the linear speed ``v``
  - 0.5 rad/s for the angular speed ``w``


Second, look at its pose::

    rostopic echo -n10 /atrv/pose

- ``echo`` will subscribe and print
- ``-n10`` will print 10 messages
- ``/atrv/pose`` correspond to the robots's pose sensor topic


rqt_plot
--------

Once you sent a motion command, you can plot the pose in realtime with::

    rqt_plot /atrv/pose/pose/position/x,/atrv/pose/pose/position/y /atrv/pose/pose/orientation/z

.. note:: in former ROS versions, this tool was called ``rxplot``


rqt_grah
--------

It's an alternative to ``rostopic list`` showing a connexion of nodes and topics.


rospy
-----

From a terminal, start an interactive Python session typing ``python``
and paste the following code:

.. code-block:: python

    import rospy
    from geometry_msgs.msg import PoseStamped
    from geometry_msgs.msg import Twist

    cmd = rospy.Publisher("/atrv/motion", Twist)
    motion = Twist()
    def callback(msg):
        position = msg.pose.position
            if position.x < 1:
                motion.linear.x = +0.5
            if position.x > 2:
                motion.linear.x = -0.5
        cmd.publish(motion)

    rospy.init_node("rostuto1")
    rospy.Subscriber("/atrv/pose", PoseStamped, callback)
    rospy.spin() # this will block untill you hit Ctrl+C

You should see the robot move forward then backward after 1m.


etc
---

For more, visit ROS wiki, where you will find many well written
`tutorials <http://ros.org/wiki/ROS/Tutorials>`_