ROS Tutorials

Walking through tutorial at http://wiki.ros.org/ROS/Tutorials

Requires

sudo apt-get install ros-indigo-ros-tutorials
sudo apt-get install ros-indigo-rqt ros-indigo-rqt-common-plugins

Basic Info

• Nodes are executables ROS uses to communicate with other nodes by subscriping to topics
  • rosnode to interact with nodes (get info, list, etc)
• Messages are ROS data types used when subscribing or publishing to a topic
• Topics are an ROS element that nodes can publish or subscribe to to receive messages
• Master is the name of the main ROS service which lets nodes find each other
  • roscore is command to run master + rosout + parameter server
  • rosout is a stdout/stderr equivalent
  • rosrun to run nodes within packages

Editor

rosed [package_name] [file_name]
Setup with export EDITOR='emacs -nw'
roscp [package_name] [file_to_copy_path] [copy_path]

Creating a workspace

source /opt/ros/indigo/setup.bash
mkdir -p ~/ros_tutorials/src
cd ~/ros_tutorials/src
catkin_init_workspace
cd ..
catkin_make
source devel/setup.bash

Creating a package

cd ~/ros_tutorials/src
catkin_create_pkg beginner_tutorials std_msgs rospy roscpp
cd beginner_tutorials

Update info in package.xml

Building Packages

cd ~/ros_tutorials
catkin_make

Running Nodes

Must run roscore first (in different terminal)
Running with custom naming:
rosrun turtlesim turtlesim_node __name:=my_turtle
To visualize node diagram:
rqt_graph or rosrun rqt_graph rqt_graph
Use rostopic to get info on ROS topics:
rostopic list
rostopic echo /turtle1/cmd_vel
rostopic type /turtle1/cmd_vel to get name of message type
Use rosmsg for more information on message
rosmsg show geometry_msgs/Twist
To publish data on to a topic:
rostopic pub -1 /turtle1/cmd_vel geometry_msgs/Twist -- '[2.0, 0.0, 0.0]' '[0.0, 0.0, 1.8]'
To graph data over time:
rqt_plot or rosrun rqt_plot rqt_plot

Services

Services allow nodes to send a request and get a response
Use rosservice to list, call, type, find, and uri
rosservice type /clear
rosservice call /clear
rosservice type /spawn| rossrv show
rosservice call /spawn 2 2 0.2 ""

Parameter Server

Use rosparam to store and update data on the ROS Parameter Server
rosparam can set, get, load, dump, delete, and list
rosparam list
rosparam set /background_g 200
rosparam dump params.yaml
rosparam load params.yaml copy
rosparam get /copy/background_g

Debugging with rqt_console

rqt_console attaches to ROS's logging framework to display output from nodes.
rqt_console or rosrun rqt_console rqt_console
rqt_logger_level is used to change verbosity level
rqt_logger_level or rosrun rqt_logger_level rqt_logger_level

Using roslaunch

roslaunch starts nodes as defined in a launch file. This example will launch two turtlesim nodes and mimic actions from turtlesim1 to turtlesim2,
roscd beginner_tutorials
mkdir launch && cd lauch
Take a look at turtlemimic.launch file
roslaunch beginner_tutorials turtlemimic.launch
rostopic pub /turtlesim1/turtle1/cmd_vel geometry_msgs/Twist -r 1 -- '[2.0, 0.0, 0.0]' '[0.0, 0.0, -1.8]'

Basics of Message and Service (msg and srv)

msg files define the fields of ROS messages and are used to generate source code for messages.
srv files define a service's request and response.

Using Message

Example of a msg that uses a Header, a string primitive, and two other msgs:

Header header
  string child_frame_id
  geometry_msgs/PoseWithCovariance pose
  geometry_msgs/TwistWithCovariance twist

Look in beginner_tutorials/msg for a basic msg example.
Remeber to update package.xml and enable the message_generation and message_runtime dependencies.
Also need to add message_generation to the required components in CMakeLists.txt and message_runtime to the CATKIN_DEPENDS section.
Add message file name to the add_message_files section of CMakeLists.txt
Make sure generate_messages is called in CMakeLists.txt
Verify message with rosmsg show beginner_tutorials/Num

Using Service

srv files separate the request and reponse with a --- line:

int64 A
int64 B
---
int64 Sum

Take a look in beginner_tutorials/srv for a basic service example.
Remeber to update package.xml and enable the message_generation and message_runtime dependencies.
Also need to add message_generation to the required components in CMakeLists.txt and message_runtime to the CATKIN_DEPENDS section.
Add service file name to the add_service_files section of CMakeLists.txt
Make sure generate_messages is called in CMakeLists.txt
Verify service with rossrv show beginner_tutorials/AddTwoInts

Publisher Node

The example node at beginner_tutorials/src/talker.cpp will continually broadcast a message.
Node activities:

• Init ROS system
• Advertise publishing std_msgs/String messages on the chatter topic to the master
• Loop while publishing messages to chatter 10 times a second

Subscriber Node

The example node at beginner_tutorials/src/listener.cpp will subscribe to and receive messages from the talker node. Node activities:

• Initialize the ROS system
• Subscribe to the chatter topic
• Spin, waiting for messages to arrive
• When a message arrives, the chatterCallback() function is called

Building Nodes

Based on the above publisher and sucscriber example, add the following to CMakeLists.txt

include_directories(include ${catkin_INCLUDE_DIRS})

add_executable(talker src/talker.cpp)
target_link_libraries(talker ${catkin_LIBRARIES})
add_dependencies(talker beginner_tutorials_generate_messages_cpp)

add_executable(listener src/listener.cpp)
target_link_libraries(listener ${catkin_LIBRARIES})
add_dependencies(listener beginner_tutorials_generate_messages_cpp)

In the catkin workspace run catkin_make, may need --force-cmake option when adding a new pkg.

Running the Publisher and Subscriber

Make sure roscore is running and workspace is sourced.
rosrun beginner_tutorials talker
rosrun begineer_tutorials listener
Investigate with rostopic list and rqt_graph

Using a Service and Client Nodes

Service

The example at beginner_tutorials/src/add_two_ints_server.cpp creates a node which will receive two ints and return the sum.

Client

The example at beginner_tutorials/src/add_two_ints_client.cp creates a node which will send two ints to the server and receive the sum response.

Building

Add the following to CMakeLists.txt

add_executable(add_two_ints_server src/add_two_ints_server.cpp)
target_link_libraries(add_two_ints_server ${catkin_LIBRARIES})
add_dependencies(add_two_ints_server beginner_tutorials_gencpp)

add_executable(add_two_ints_client src/add_two_ints_client.cpp)
target_link_libraries(add_two_ints_client ${catkin_LIBRARIES})
add_dependencies(add_two_ints_client beginner_tutorials_gencpp)

In the catkin workspace run catkin_make, may need --force-cmake option when adding a new pkg.

Running the Client Server Example

Make sure roscore is running.
rosrun beginner_tutorials add_two_ints_server
rosrun beginner_tutorials add_two_ints_client 1 3

Record and Play Back Data

Data from topics can be recorded into a bag file using rosbag.
Record all topics: rosbag record -a
rosbag info <bagfile>
Playback data: rosbag play <bagfile>
Record specific data: rosbag record -O velandpose /turtle1/cmd_vel /turtle1/pose

Troubleshooting with roswtf

roswtf examines the system and tries to find problems.