Currently I’m using Melodic Morenia.

rosbash

There is tab-completion for almost everything

Load ROS Environment

For Bash:

source /opt/ros/melodic/setup.bash

or Zsh:

source /opt/ros/melodic/setup.zsh

Commands

rospack

Each package is defined by a package directory that contains a manifest file called package.xml.

Package executables are not stored in the package directory. They are placed in a separate standardized directory hierarchy.

The Master (roscore)

• roscore starts the master. There are no command line arguments.

Nodes

Start a node (rosrun)

rosrun <package-name> <executable-name>

• package-name: the name of the node’s package
• executable-name: the executable name in that package

Handle multiple nodes (roslaunch)

Launch File Structure (XML Tags and Arguments)

• <launch>: Root element of launch file
• <node name="listener" pkg="roscpp_tutorials" type="listener" output="screen" />: A ROS node to be launched
  • name: Name of the node (free to choose)
  • pkg: The ROS package name containing the node executable
  • type: Type of the node in the package
  • output: Where to output log messages (screen or log)
• <arg name="arg_name" default="default_value"/>: Define arguments (variables)
  • $(arg arg_name): Reference arguments
  • roslaunch launch_file.launch arg_name:=value: Provide arguments when running a launchfile
• <include file="package_name"/>: Include other launchfile
  • $(find package_name): Find other package in workspace

Notes about how to writ launch files can be found at roslaunch/XML and Roslaunch tips for large projects

Flags:

• -v: Print verbose output
• --screen: Display output for all nodes in launch file

Commands for handling Nodes

Communication and Data Sharing

Topics and Messages

Parameters (rosparam)

Services

A client node sends a request to a server node and waits for a response.

• rosservice: interacting with services that are currently offered by a node
• rossrv: information about service data types

Information about writing services and clients in C++ can be found here Writing a Simple Service and Client (C++).

Topics, Messages and Services

Overview

Bag files

Flags:

• -j: Compress bag files

Workspaces and Packages

All packages belonging to one project should be placed in one workspace.

Creating a Workspaces

mkdir -p <workspace-name>/src    # don't forget the `src` subdirectory
cd  <workspace-name>/
catkin build  # don't use catkin_make
source devel/setup.zsh

Creating a Package

cd  <workspace-name>/src
catkin_create_pkg <package-name> [list of dependencies]

Building a Workspace

cd  <workspace-name>/
catkin build  # don't use catkin_make
source devel/setup.zsh

Configuring build in a Workspace

cd  <workspace-name>/
catkin config
source devel/setup.zsh

Provide Arguments to CMake

catkin config --cmake-args -DCMAKE_BUILD_TYPE=Debug

Running a Node from Workspace

A master is required to run before running any nodes.

cd  <workspace-name>/
source devel/setup.zsh
rosrun <package-name> <executable-name>

Cleaning the Workspace

cd  <workspace-name>/
catkin clean --all

Client Libraries

Node Handles

It’s also possible to use global node handlers. But it is not recomended.

Time Library

It’s recomended to always use the ROS Time APIs (and not the standard library).

This allows to handle simulated time properly.

• ros::Time:

ros::Time begin = ros::Time::now();
double secs = begin.toSec();

• ros::Duration:

duration(0.5); // 0.5s
ros::Duration passed = ros::Time()::now() - begin;

• ros::Rate:

ros::Rate rate(10); // 10Hz

If wall time is required, use ros::WallTime, ros::WallDuration and ros::WallRate

URDF and Xacro

To generate an URFD file from a xacro file:

xacro input.xacro > output.urdf

Checking URDF files:

check_urdf file.urdf

Create graph for URDF:

urdf_to_graphiz file.urdf  # note the missing 'v' in graphiz

Checking for Problems

• roswtf: Perform sanity checks for the running ROS system
• rosnode info: Get information about nodes
• rostopic echo: Show data published on a topic
• rqt_graph: Show nodes and topics as graphs
• rviz: Visualize data
• rqt: Generic GUI with a lot of plugins

References

• A Gentle Introduction to ROS
• ROS Wiki