Introduction

The purpose of this programming assignment is to work through all of the steps of creating a ROS package using Python. This project will not require the use of the Turtlebots, so you should be able to complete it outside of the robotics lab.

The goal of your project will be to create a Python node that is able to navigate a simulated 2D turtle to a designated goal location.

Part 1 - Creating the Package

Follow the steps from the ROS Packages Lab to create a repository and package for this assignment. Your package should be named turtle_nav and it should depend on geometry_msgs, turtlesim, rospy and std_msgs.

Part 2 - Navigation

Create a Python file named turtle_nav_node.py that moves the turtle in a smooth trajectory to a designated goal location. Ultimately, the goal location will be provided through the mechanism of ROS services, but to get started you can just hard-code a goal location in your Python code. You should be able to test your node by starting the turtlesim node, then running turtle_nav_node.py.

If your code is correct, and your package is configured correctly, you should be able to type:

rosrun turtle_nav turtle_nav_node.py

and watch your turtle merrily navigate to the goal.

Warning! The logic involved in smoothly moving the turtle to a target location is trickier than you might expect. You may find it helpful to transform the goal location into turtle-centric coordinates. The Python module turtle_pos.py provides code for accomplishing this.

Part 3 - Navigation as a Service

The next step is to provide a mechanism for communicating goal locations to the turtle_nav node. We will accomplish this by converting the node you developed above into a ROS service provider.

Your modified node must meet the following requirements:

• The service name must be move_turtle_to_goal.
• You must use the service type TurtleGoal.srv.
• If the goal location is reachable by the turtle, then your node must navigate to within .01 meters of the goal, and then return a value of True.
• If the goal location is not reachable, then the your node must return a value of False. Locations are unreachable in the turtle simulation if they have x or y coordinates less than zero or greater than 11.0.

The following tutorials will be helpful in completing this portion of the assignment:

• Creating a ROS msg and srv - This tutorial explains the steps necessary to properly build a package that includes a custom service type.
• Writing a Simple Service and Client (Python) - This tutorial explains how to create a ROS service node using Python.

Once your service is running, you should be able to test it by making calls from the terminal:

$ rosservice call /move_turtle_to_goal "goal_x: 3.0
goal_y: 5.0" 
success: True
$ rosservice call /move_turtle_to_goal "goal_x: 3.0
goal_y: 25.0" 
success: False

I've also written a mouse-based ROS service client that you can use for testing: mouse_teleop.py.

Part 4 - Creating a Launch File

Create a launch file named turtle_nav.launch that handles starting the turtlsim node and the navigation service node. I should be able to test your code by typing:

roslaunch turtle_nav turtle_nav.launch

in the terminal, and than making service requests.

Submitting

Submit by tagging the final version of your code as "submit" and pushing the result to stu:

hg tag submit --user YOUR_EID
hg commit . -m 'Tagged as submission.' --user YOUR_EID
hg push

I'll grade your work by cloning this tagged version of the repository. Your submission will be graded on the basis of functionality, code-quality, documentatation, and adherence to ROS packaging standards.