08. AMCL Launch File: Move Base Node

Move Base Node

Two nodes down, one node to go!

You will be working with the move_base package using which you can define a navigation goal position for your robot in the map, and the robot will navigate to that goal position. Note that this step is optional if you choose to use teleop node to control and localize your robot.

The move_base package is a very powerful tool. It utilizes a costmap - where each part of the map is divided into which area is occupied, like walls or obstacles, and which area is unoccupied. As the robot moves around, a local costmap, in relation to the global costmap, keeps getting updated allowing the package to define a continuous path for the robot to move along.

What makes this package more remarkable is that it has some built-in corrective behaviors or maneuvers. Based on specific conditions, like detecting a particular obstacle or if the robot is stuck, it will navigate the robot around the obstacle or rotate the robot till it finds a clear path ahead.

Add ROS move_base Node

Let's add the move_base node to the amcl.launch file: 

<launch>
  <!-- Map Server -->
  ...

  <!-- AMCL Node -->
  ...

  <!-- Move Base -->
  <node name="move_base" pkg="move_base" type="move_base" respawn="false" output="screen">
  </node>

</launch>

Remap scan Topic

Again, we need to remap the scan topic to the correct one. 

  <remap from="scan" to="<YOUR PACKAGE NAME>/laser/scan"/>

Add Parameters to move_base Node

Similar to the amcl node, move_base node requires a set of parameters to move the robot in the world. As we already know , we could use the param tag to specify the parameter. But when there are plenty of parameters, we could use the rosparam tag to include config files to set multiple parameters directly!

Planners

Add the following param tags to the move_base node: 

  <param name="base_global_planner" value="navfn/NavfnROS" />
  <param name="base_local_planner" value="base_local_planner/TrajectoryPlannerROS"/>

Load Config Files

Then we need to create/get the config files and load them in the launch file: 

$ cd ..
$ mkdir config
$ cd config

Download the config files from Udacity S3 bucket and add them to the config folder: 

wget https://s3-us-west-1.amazonaws.com/udacity-robotics/Resource/where_am_i/config.zip
unzip config.zip
rm config.zip

These config files have a preset of parameters defined for you to navigate the robot if you choose to send navigation goal to the robot in testing.

Config Files

Now that we have the config files ready, we will include them in the launch file, in the move_base node: 

  <rosparam file="$(find udacity_bot)/config/costmap_common_params.yaml" command="load" ns="global_costmap" />
  <rosparam file="$(find udacity_bot)/config/costmap_common_params.yaml" command="load" ns="local_costmap" />
  <rosparam file="$(find udacity_bot)/config/local_costmap_params.yaml" command="load" />
  <rosparam file="$(find udacity_bot)/config/global_costmap_params.yaml" command="load" />
  <rosparam file="$(find udacity_bot)/config/base_local_planner_params.yaml" command="load" />

Well done! That was a lot of work. Let us move on!

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