ROSlaunch Command-line Arguments
COM2009 Assignment #1 Checkpoint
It helps if you've already completed Assignment #1 Part 1 before working on this.
A lot of the launch files that we have use throughout COM2009 Assignment #1 actually have Command-Line Arguments (CLAs) that can be (optionally) supplied when making the roslaunch
call. Consider the turtlebot3_empty_world.launch
file for instance...
Enter the full command and then press the Space and Tab keys on your keyboard like so:
roslaunch turtlebot3_gazebo turtlebot3_empty_world.launch[SPACE][TAB][TAB]
This will reveal the available command-line arguments for this launch file:
model x_pos y_pos z_pos
We can therefore optionally specify custom values for these parameters in order to change what happens when the launch file is executed. Try this, for example:
When the Gazebo simulation is launched, the robot will be located at coordinates (1, 1)
in the X-Y
plane, rather than (0, 0)
, as would usually be the case.
Note
We assign values to roslaunch
command-line arguments using the :=
operator.
This is all made possible through the use of <arg>
tags at the start of a launch file (just after the opening <launch>
tag):
Within these tags we need to define two attributes:
name
: the name we want to give to the CLA (name="x_pos"
,name="y_pos"
etc...)-
default
: A default value in order to make the CLA optional(In the above example, the robot will be located at coordinates
(0, 0)
by default, unless we specify otherwise.)