This repository showcases the tutorials on ROS and is a part of ENPM808X course at University of Maryland.
The dependencies of this repository are:
* Ubuntu 16.04
* ROS Kinetic Kame
Before proceedigng to install ROS, ensure that version of Ubuntu is 16.04. To install ROS follow the steps given below:
$ sudo sh -c 'echo "deb http://packages.ros.org/ros/ubuntu $(lsb_release -sc) main" > /etc/apt/sources.list.d/ros-latest.list'
$ sudo apt-key adv --keyserver hkp://ha.pool.sks-keyservers.net:80 --recv-key 421C365BD9FF1F717815A3895523BAEEB01FA116
$ sudo apt-get update
$ sudo apt-get install ros-kinetic-desktop-full
After installation of ROS, the next step is to initialize and install its dependencies using following commands:
$ rosdep init
$ rosdep update
The next step is to setup ROS environment which can be done using following commands:
$ echo "source /opt/ros/kinetic/setup.bash" >> ~/.bashrc
$ source ~/.bashrc
Following the environment setup, next step is to create the workspace.
$ cd <path where workspace needs to be created>
$ mkdir -p <name of workspace>
$ cd <workspace>
<workspace>$ catkin_make
Just like the path of the ROS was sourced in .bashrc file, same needs to be done for the workspace by writing source <path to workspace>/devel/setup.bash at the end of the .bashrc file.
This avoids the need to source every time one needs to use workspace's packages.
The code can be built by cloning the repository and executing following steps:
<home>$ cd <workspace>/src
<workspace>/src$ git clone https://github.com/nr-parikh/beginner_tutorials.git
<workspace>/src$ cd ..
<workspace>$ catkin_make
This week's tutorials deal with services and launch files. Launch files are very useful in case where multiple nodes needs to be started from within the package. One can also set the arguments of the nodes from within the launch files. The file change_text.launch does that. If the nodes are being launched from the launch file, the messages being published will be different than the messages being published if nodes were started individually using rosrun commands.
Services are also a very useful tool of ROS. While publisher/subscriber communication model is very useful for continuous communication, server/client communication has its own uses. Server/client model is very useful when one has to execute certain process only if the need arises by requesting the service. This code has a service called change_text which can be used whenever one wants to change the message being published. It takes an input the string which needs to be published and responses with a bool value.
Please ensure that rosmaster is running before executing following steps. rosmaster can be started by following command.
<home>$ roscore
To start the publisher node follow the steps given below:
<home>$ rosrun beginner_tutorials pulisher_node
subscriber node can be started by following commands:
<home>$ rosrun beginner_tutorials subscriber_node
Starting the nodes using the steps above, prints out Welcome to ENPM808X, Fall 2017! on the console.
To start both the nodes with a single command, launch file can be created and used to launch both the nodes. To launch both nodes execute following command:
<home>$ roslaunch beginner_tutorials change_text.launch
Please note here that it is not mandatory to start rosmaster node while using launch file. It starts when the file is launched if it is not running. The command above will launch the node with default string in the launch file. To pass the custom string to launch file use the following command:
<home>$ roslaunch beginner_tutorials change_text.launch str:="Passing-parameter-to-launch-file."
Please note that while passing the parameter to launch file the string should be a single cannot contain whitespaces.
Service can be called from the terminal when both the nodes are running. This is necessary because publisher node is the server for service while subscriber node is client of the service. Thus, in order for the service to execute properly both server and client should run properly.
<home>$ rosservice call /change_text <string to be published>
Consider for examply one wants to change the message being published to This is beginner_tutorials. This can be done as follows:
<home>$ rosservice call /change_text "This is beginner_tutorials."
Logger GUI can be used to check the logged messages. To launch logger GUI, run the following lines:
<home>$ rosrun rqt_console rqt_console
TF transforms are the way to define coordinate transforms between various frames. The publisher node now publishes a non-zero transformation between world and publisher frames. The easiest to check if the transforms are being broadcasted between the two frames is using tf_echo. To see the transforms between all the frames and how they are connected, one can use view_frames or rqt_tf_tree.
Ensure that publisher_node is already running. It can be run using the instructions given in the earlier sections. Now to see the transform being broadcasted, execute the following command:
<home>$ rosrun tf tf_echo /world /publiher
Here, the first frame is the parent frame while the second frame is the child frame. The output after executing the above command looks like below:
At time 1510459281.025
- Translation: [1.000, 1.000, 1.000]
- Rotation: in Quaternion [0.000, 0.000, 1.000, 0.001]
in RPY (radian) [0.000, -0.000, 3.140]
in RPY (degree) [0.000, -0.000, 179.909]
At time 1510459282.025
- Translation: [1.000, 1.000, 1.000]
- Rotation: in Quaternion [0.000, 0.000, 1.000, 0.001]
in RPY (radian) [0.000, -0.000, 3.140]
in RPY (degree) [0.000, -0.000, 179.909]
At time 1510459283.025
- Translation: [1.000, 1.000, 1.000]
- Rotation: in Quaternion [0.000, 0.000, 1.000, 0.001]
in RPY (radian) [0.000, -0.000, 3.140]
in RPY (degree) [0.000, -0.000, 179.909]
To generate a PDF containing the connections between various frames assuming publisher node is already running,
<home>$ rosrun rqt_tf_tree rqt_tf_tree
Or use following,
<home>$ rosrun tf view_frames
Integration testing is very important to ensure that the newly created or modified modules does not break the running version of the code. This module has two unit tests which ensure that change_text service is running and that the transform being boradcasted is as expected.
There are two ways to run the tests viz. using catkin_make and rostest. Before running the tests, ensure that catkin_make is invoked to build the units that are not being tested. The tests can be run using either of the following commands:
<home>$ cd <path to directory>/catkin_ws
<workspace>$ catkin_make run_tests_beginner_tutorials
<home>$ rostest beginner_tutorials publisher_test.launch
The output upon executing tests will look as shown below:
testpublisherTest ... ok
[ROSTEST]-----------------------------------------------------------------------
[beginner_tutorials.rosunit-publisherTest/serviceTest][passed]
[beginner_tutorials.rosunit-publisherTest/transformTest][passed]
SUMMARY
* RESULT: SUCCESS
* TESTS: 2
* ERRORS: 0
* FAILURES: 0
rostest log file is in /home/nrparikh/.ros/log/rostest-ubuntu-107385.log
rosbag allows to record all the data that is being published across all the nodes. Bag files are very useful when one wants to debug what is happening on the robot. However, rosbag does not record calls to services as well as responses of the services. It can be recorded from the commandline using rosbag record -a. And the recorded bag file can be played using rosbag play <path to bag file>.
One can check the information of the bag file using rosbag info <filename> command. Sample output looks like below:
nrparikh@ubuntu:~/catkin_ws$ rosbag info src/beginner_tutorials/results/publisher.bag
path: src/beginner_tutorials/results/publisher.bag
version: 2.0
duration: 43.7s
start: Nov 11 2017 19:03:05.44 (1510444985.44)
end: Nov 11 2017 19:03:49.10 (1510445029.10)
size: 544.7 KB
messages: 2614
compression: none [1/1 chunks]
types: rosgraph_msgs/Log [acffd30cd6b6de30f120938c17c593fb]
std_msgs/String [992ce8a1687cec8c8bd883ec73ca41d1]
tf2_msgs/TFMessage [94810edda583a504dfda3829e70d7eec]
topics: /chatter 435 msgs : std_msgs/String
/rosout 874 msgs : rosgraph_msgs/Log (3 connections)
/rosout_agg 870 msgs : rosgraph_msgs/Log
/tf 435 msgs : tf2_msgs/TFMessage
change_text launch file of this package accepts a flag record that can be used to record the bag file which will record all the data that is being published on the chatter topic. It will save the file in results directory. This can be done using following commands:
<home>$ roslaunch beginner_tutorials change_text record:=true
Before proceeding to play the bag file, ensure that subscriber node is running as per the instructions given the earlier sections. To see the data stored in the bag file recorded using the above command:
<home>$ cd catkin_ws/src/beginner_tutorials/results
<results>$ rosbag play publisher.bag
This command will start playing the recorded bag file and the subscriber node which was running previously will be able to listen to the data that is being published. One can check the transform being broadcasted using the instructions given before.