ROS Notes

Installing and Configuring the Environment

Source Setup Files

source /opt/ros/<distro>/setup.bash

-> written in .bashrc

create workspace

mkdir -p catkin_ws/src
cd catkin_ws
catkin init 

Using Catkin-Tools instead of catkin_make has many advantages including easier package managing

catkin build

will create devel and build folder

source devel/setup.bash 

needs to be run everytime (-> added to .bashrc)

Navigating ROS

rospack find <package_name>

ros + package will the Path to package if found

roscd

ros + cd changes your pwd to package directory

rosls

ros + ls lists contents of that package

building a package

not so important for now Every Package contains build, devel, src Folders

Cmake Workflow:

mkdir build
cd build
cmake ..
make

ROS Nodes

Nodes are the executables inside ROS Packages. Use ROS client library to communicate with other Nodes. Nodes can publish or subscribe to a Topic. Nodes can also provide and use a Service. Client libraries are rospy and roscpp.

roscore

roscore = ros+core : master (provides name service for ROS) + rosout (stdout/stderr) + parameter server must be run at first when using ROS

rosnode

rosnode = ros+node : ROS tool to get information about a node.

rosnode list

lists all nodes

rosnode info /<node_name>

more info about specific node eg.: where it publishes to

rosrun

rosrun = ros+run : runs a node from a given package.

rosrun <node_name>

directly run a node

ROS Topics

2 Nodes communicate over ROS Topics. One Node publishes and the other subscribes to a certain Topic. With rqt_graph (run from a new terminal window) these nodes an Topics are shown.

rostopic

rostopic -h 

... to get a list of sub commands

rostopic echo </topic/name>

listens to one topic

rostopic list -v

prints all available topics

ROS Messages

rostopic type

retuns the type of a topic

publish ROS Messages

rostopic pub [topic] [msg_type] [args]

ROS Services

Services allow nodes to send a request and receive a response.

rosservice

rosservice list         print information about active services
rosservice call         call the service with the provided args
rosservice type         print service type
rosservice find         find services by service type
rosservice uri          print service ROSRPC uri

rosparam

store and manipulate data on the ROS Parameter Server

rosparam set            set parameter
rosparam get            get parameter
rosparam load           load parameters from file
rosparam dump           dump parameters to file
rosparam delete         delete parameter
rosparam list           list parameter names

RQT

rqt provides different visual services eg rqt_graph, rqt_console & logger_level, rqt_plot

Launch a Node

roslaunch

Launches a node as specified in the .launch file. It is good Practice to have a launch dir with the .launch files although not necessary.