ROS Launch

A quick tutorial into ROS launch.

Please see an example launch file below:
<launch> <rosparam file="$(find glider_kayak_sim)/yaml/sim_params.yaml"/> <param name="package_path" value="$(find glider_kayak_sim)"/> <include file="$(find glider_kayak_sim)/launch/world_launch.launch"/> <node name="wms_server" pkg="glider_kayak_sim" type="" output="screen"/> <node name="ros_web_interface" pkg="glider_kayak_sim" type="" output="log"/> </launch>
Launch files can make your life easier when developing large projects in ROS.
You can use launch files to launch multiple nodes at once and define global parameters.
Note the rosparam tag:
<rosparam file="$(find glider_kayak_sim)/yaml/sim_params.yaml"/>
The rosparam tag loads an entire configuration YAML file and makes the YAML parameters available to the nodes you launch.
Note the param tag:
<param name="package_path" value="$(find glider_kayak_sim)"/>
The param tag allows you to manually specify parameter values.
The include file tag, below, includes an entire launch file, and allows you to establish a hierarchy of launch files and sub-launch files.
<include file="$(find glider_kayak_sim)/launch/world_launch.launch"/>
The node tag, below, launches a specific ROS node, a python script.
<node name="wms_server" pkg="glider_kayak_sim" type="" output="screen"/>
Inside the code of each ROS node, you can access the parameter values using rospy.get_param, as in the examples below:
max_turn = rospy.get_param("/kayak_max_turn", 0.10) max_abs_vel = rospy.get_param("/kayak_max_abs_vel", 0.01) wpt_tol = rospy.get_param("/kayak_wpt_tol", 0.01) control_const = rospy.get_param("/kayak_control_const", 4.00)
Note how the second argument of rospy.get_param is the default value, used in case the parameter is not defined.
Follow this link for the raw script.