What is ROS?

1. What is ROS? • Robot Operating System • ROS essentially provides two things: • A set of tools that are generally useful for controlling robots • E.g. Interfaces to sensors, general-purpose algorithms, etc. • A communication framework to allow different pieces of your robot brain to talk to one another

2. Intro to ROS Nodes cam_data subscriber cam_data publisher cam_data subscriber

3. ROS $ roscore ... logging to ~/.ros/log/9cf88ce4-b14d-11df-8a75-00251148e8cf/roslaunch-machine_name-13039.log Checking log directory for disk usage. This may take awhile. Press Ctrl-C to interrupt Done checking log file disk usage. Usage is <1GB. … blah blahblah Master rosout

4. ROS $ rosrun package1 first-node Note: run this in a new terminal window Master Advertise topic1 rosout first-node

5. ROS $ rosrun package2 second-node Note: run this in a new terminal window Master Subscribe to topic1 second-node rosout first-node

6. ROS Note: run this in a new terminal window $ rosrun package2 second-node Master Master connects topic1 publisher to topic1 subscriber second-node rosout first-node

7. ROS $ rosnode list /rosout /first-node /second-node Master topic1 second-node rosout first-node

8. ROS $ rostopic list /rosout /rosout_agg /topic1 Master topic1 second-node rosout first-node

9. ROS commands • roscore : Run this first; starts the Master and some other essential ROS stuff • rosrun [package-name] [node-name] : Use this to start a ROS node • rosnode: • rosnode list : List all currently running nodes • rosnode info [node-name] : Get more info about a particular node • rosnode -h : Learn about more things rosnode can do • rostopic : • rostopic list : List all topics currently published • rostopic echo : See the messages being published to a particular topic • rostopic -h : Learn about more things rostopic can do

10. ROS commands • roslaunch[package-name] [launch-file-name] : Reads a .launch file, which contains instructions for running multiple nodes, and doing fancy things like passing parameters to nodes, renaming topics, etc. <launch> <node name="listener-1" pkg="rospy_tutorials" type="listener" /> <node name="listener-2" pkg="rospy_tutorials" type="listener" args="-foo arg2" /> <node name="listener-3" pkg="rospy_tutorials" type="listener" respawn="true" /> <group ns="wg2"> <remap from="chatter" to="hello"/> <node pkg="rospy_tutorials" type="listener" name="listener" args="--test" /> <node pkg="rospy_tutorials" type="talker" name="talker"> <param name="talker_1_param" value="a value" /> <remap from="chatter" to="hello-1"/> <env name="ENV_EXAMPLE" value="some value" /> </node> </group> </launch>

11. ROS Skeleton #include "ros/ros.h" intmain (intargc, char **argv) { ros::init(argc, argv, “name"); ros::NodeHandle n; ros::Rate loop_rate(10); while (ros::ok()) { ros::spinOnce(); loop_rate.sleep(); } return0; } /* Body of event loop goes here */

12. Line-by-Line Breakdown • Include the ROS library #include "ros/ros.h" intmain (intargc, char **argv) { ros::init(argc, argv, “name"); ros::NodeHandle n; ros::Rate loop_rate(10); while (ros::ok()) { ros::spinOnce(); loop_rate.sleep(); } return0; } /* Body of event loop goes here */

13. Line-by-Line Breakdown • Program execution always starts at “main” • main gets passed command line arguments (argc, argv), which you are required to pass into ros::init so it can handle them appropriately #include "ros/ros.h" intmain (intargc, char **argv) { ros::init(argc, argv, “name"); ros::NodeHandle n; ros::Rate loop_rate(10); while (ros::ok()) { ros::spinOnce(); loop_rate.sleep(); } return0; } /* Body of event loop goes here */

14. Line-by-Line Breakdown • ros:: is a namespace; a collection of related functions, data, etc. that are all packaged together • Anything in this namespace has to be accessed by prefixing it with ros:: • ros::init(initialize) must be called before any other ROS functions; it expects to be passed main’s command line arguments (argc, argv) and the name of the current node #include "ros/ros.h" intmain (intargc, char **argv) { ros::init(argc, argv, “name"); ros::NodeHandle n; ros::Rate loop_rate(10); while (ros::ok()) { ros::spinOnce(); loop_rate.sleep(); } return0; } /* Body of event loop goes here */

15. Line-by-Line Breakdown • ros::NodeHandleis a class which allows us to communicate with the ROS system • You must create a NodeHandle object in order to properly initialize and register your ROS node; when the handle goes out of scope at the end of the program, it will automatically cleanup after itself • In the body of your ROS node, a NodeHandle can also be used to advertise or subscribe to topics #include "ros/ros.h" intmain (intargc, char **argv) { ros::init(argc, argv, “name"); ros::NodeHandle n; ros::Rate loop_rate(10); while (ros::ok()) { ros::spinOnce(); loop_rate.sleep(); } return0; } /* Body of event loop goes here */

16. Line-by-Line Breakdown • The main body of a ROS program is a loop • The loop keeps running as long as this ROS node hasn’t been asked to shutdown (i.e. as long as ros::ok() returns true) • At a high level, a typical loop might look like this: • Do some work • Publish results • Handle any incoming messages • Sleep for a little while, then repeat #include "ros/ros.h" intmain (intargc, char **argv) { ros::init(argc, argv, “name"); ros::NodeHandle n; ros::Rate loop_rate(10); while (ros::ok()) { ros::spinOnce(); loop_rate.sleep(); } return0; } /* Body of event loop goes here */

17. Line-by-Line Breakdown • ros::spinOnce() checks to see if there are any new incoming messages from other ROS nodes, and if so, it invokes callbacks to handle them appropriately • We haven’t subscribed to any topics in this example, but we’ll see shortly how this works #include "ros/ros.h" intmain (intargc, char **argv) { ros::init(argc, argv, “name"); ros::NodeHandle n; ros::Rate loop_rate(10); while (ros::ok()) { ros::spinOnce(); loop_rate.sleep(); } return0; } /* Body of event loop goes here */

18. Line-by-Line Breakdown • ros::Rate is essentially a timer class that helps to keep your main loop running at a reasonable frequency • We first declare loop_rate(10), which is a 10Hz timer • At the end of our main loop, we call loop_rate.sleep(); if our loop took less than 0.1s (1/10th of a second), loop_rate.sleep() will wait until the full 0.1s has passed • This way, our main loop always runs at a (roughly) consistent frequency #include "ros/ros.h" intmain (intargc, char **argv) { ros::init(argc, argv, “name"); ros::NodeHandle n; ros::Rate loop_rate(10); while (ros::ok()) { ros::spinOnce(); loop_rate.sleep(); } return0; } /* Body of event loop goes here */

19. Now, let’s subscribe to a topic

20. ROS Subscriber • Recall, `n` is our NodeHandle • Subscribe to a topic using n.subscribe(...) • “topic1” is the name of the topic to subscribe to • 1000 is the number of incoming messages to hold on to before deleting some (so, if we cannot process messages fast enough, and get more than 1000 messages behind, we will start dropping old messages) • callbackFunction is the name of the function to invoke when a new message is received • n.subscribe(…) returns a ros::Subscriber object; as long as we hold on to this object, we will remain subscribed to “topic1” #include "ros/ros.h" intmain (intargc, char **argv) { ros::init(argc, argv, “name"); ros::NodeHandle n; ros::Subscriber sub = n.subscribe(“topic1", 1000, callbackFunction); ros::Rate loop_rate(10); while (ros::ok()) { ros::spinOnce(); loop_rate.sleep(); } return0; }

21. ROS Subscriber // somewhere else in the program … voidcallbackFunction(conststd_msgs::String::ConstPtr& msg) { printf("I heard: [%s]", msg->data.c_str()); } • This function will be invoked whenever a new “topic1” message is processed by ros::spinOnce() • Note the signature of the function: it returns void, and it accepts a single parameter “msg”, which is a pointer to the message received • The type of “msg” will naturally vary, depending on the type of messages that you are subscribed to. In our case, messages published to “topic1” are string messages, and have type std_msgs::String • Note this is not the same thing as a C++ string object; it is a ROS message which contains a C++ string

22. Common std_msgs

23. Let’s publish to a topic

24. ROS Publisher • Advertise a topic using n.advertise(...) • Unlike with subscribers, where the type of the message can be inferred from the callback function, we need to explicitly tell ROS what type of message to expect using <> triangle brackets • “topic1” is the name of the topic to advertise • 1000 is the number of outgoing messages to hold on to before deleting some (so, if we cannot send messages fast enough, and get more than 1000 messages behind, we will start dropping old messages) • n.advertise(…) returns a ros::Publisher object; we send a message by calling its .publish(…) method and passing in a ROS message of the appropriate type #include "ros/ros.h“ intmain (intargc, char **argv) { /* … blah blahblah … */ ros::Publisher pub = n.advertise<std_msgs::String> (“topic1”, 1000); ros::Rate loop_rate(10); while (ros::ok()) { std_msgs::String msg; msg.data= “Foobar”; pub.publish(msg); ros::spinOnce(); loop_rate.sleep(); } return0; }

25. Okay, we’ve got a complete (trivial) program – let’s build it!

26. ROS Package workspace

27. ROS Package art workspace

28. ROS Package localplanner art artsystem imu ucontroller

29. ROS Package src localplanner include bin CMakeLists.txt manifest.xml

30. ROS Package Source files go in here localplanner src include bin CMakeLists.txt manifest.xml

31. ROS Package Header files go in here src include bin localplanner CMakeLists.txt manifest.xml

32. ROS Package Executables will be built here src include bin localplanner CMakeLists.txt manifest.xml

33. ROS Package Build instructions go here src include bin localplanner CMakeLists.txt manifest.xml

34. ROS Package cmake_minimum_required(VERSION 2.4.6) include($ENV{ROS_ROOT}/core/rosbuild/rosbuild.cmake) # This is a comment rosbuild_init() rosbuild_gen_msg() rosbuild_add_executable(localplannersrc/main.cpp) CMakeLists.txt

35. ROS Package You don’t have to worry about most of this junk … But this line is important. ROS doesn’t magically know where your source files are and which ones you want to package into an executable. So you need to say rosbuild_add_executable(executable_namesource.cpp) or rosbuild_add_executable(executable_namesource1.cppsource2.cppsource3.cpp) cmake_minimum_required(VERSION 2.4.6) include($ENV{ROS_ROOT}/core/rosbuild/rosbuild.cmake) # This is a comment rosbuild_init() rosbuild_gen_msg() rosbuild_add_executable(localplannersrc/main.cpp) CMakeLists.txt

36. ROS Package src localplanner include bin CMakeLists.txt manifest.xml

37. ROS Package Package description goes here src include bin localplanner CMakeLists.txt manifest.xml

38. ROS Package <package> <description brief=“localplanner”> Local Planner </description> <author>Your Name Here</author> <license>BSD</license> <review status=“unreviewed” notes=“”/> <url>http://ros.org/wiki/localplanner</url> <depend package=“roscpp”/> <depend package=“artsystem”/> <depend package=“nav_msgs”/> <depend package=“ucontroller”/> </package> manifest.xml

39. ROS Package <package> <description brief=“localplanner”> Local Planner </description> <author>Your Name Here</author> <license>BSD</license> <review status=“unreviewed” notes=“”/> <url>http://ros.org/wiki/localplanner</url> <depend package=“roscpp”/> <depend package=“artsystem”/> <depend package=“nav_msgs”/> <depend package=“ucontroller”/> </package> You need to list your dependencies here! So if you #include something, and ROS is complaining, one of the first things that you should check is whether you need to add another dependency to the manifest. manifest.xml

40. roscd $roscdlocalplanner in general, roscd [package-name] localplanner src include bin ROS will find the specified package and will change your working directory to be the top-level package directory CMakeLists manifest

41. rosmake $rosmakelocalplanner in general, rosmake [package-name] or, when in a package directory, justrosmake ROS will build the specified package

42. Output of rosmake $rosmakelocalplanner [ rosmake ] rosmake starting … [ rosmake ] Packages requested are: [‘localplanner’] [ rosmake ] Logging into directory /home/sandro/.ros/rosmake/rosmake_output-20130921-135115 [ rosmake ] Expanded args [‘localplanner’] to: [‘localplanner’] [ rosmake-0] Starting >>> roslang [ make ] [ rosmake-1] Starting >>> geometry_msgs [ make ] … blah blahblah … [ rosmake-0 ] Finished <<< ucontroller [PASS] [ 1.53 seconds ] [ rosmake-0] Finished <<< localplanner [PASS] [ 1.02 seconds ] [ rosmake ] Results: [ rosmake ] Built 8 packages with 0 failures. [ rosmake ] Summary output to directory [ rosmake ] /home/sandro/.ros/rosmake/rosmake_output-20130921-135115

43. Output of rosmake $rosmakelocalplanner [ rosmake ] rosmake starting … [ rosmake ] Packages requested are: [‘localplanner’] [ rosmake ] Logging into directory /home/sandro/.ros/rosmake/rosmake_output-20130921-135115 [ rosmake ] Expanded args [‘localplanner’] to: [‘localplanner’] [ rosmake-0] Starting >>> roslang [ make ] [ rosmake-1] Starting >>> geometry_msgs [ make ] … blah blahblah … [ rosmake-0 ] Finished <<< ucontroller [PASS] [ 1.53 seconds ] [ rosmake-0] Finished <<< localplanner [PASS] [ 1.02 seconds ] [ rosmake ] Results: [ rosmake ] Built 8 packages with 0 failures. [ rosmake ] Summary output to directory [ rosmake ] /home/sandro/.ros/rosmake/rosmake_output-20130921-135115 You could potentially see a lot of stuff here, because rosmake actually goes and builds all of your package’s dependencies for you.

44. Output of rosmake $rosmakelocalplanner [ rosmake ] rosmake starting … [ rosmake ] Packages requested are: [‘localplanner’] [ rosmake ] Logging into directory /home/sandro/.ros/rosmake/rosmake_output-20130921-135115 [ rosmake ] Expanded args [‘localplanner’] to: [‘localplanner’] [ rosmake-0] Starting >>> roslang [ make ] [ rosmake-1] Starting >>> geometry_msgs [ make ] … blah blahblah … [ rosmake-0 ] Finished <<< ucontroller [PASS] [ 1.53 seconds ] [ rosmake-0] Finished <<< localplanner [PASS] [ 1.02 seconds ] [ rosmake ] Results: [ rosmake ] Built 8 packages with 0 failures. [ rosmake ] Summary output to directory [ rosmake ] /home/sandro/.ros/rosmake/rosmake_output-20130921-135115 [PASS] means that rosmake successfully built a package. [FAIL] means there were errors.

45. Output of rosmake $rosmakelocalplanner [ rosmake ] rosmake starting … [ rosmake ] Packages requested are: [‘localplanner’] [ rosmake ] Logging into directory /home/sandro/.ros/rosmake/rosmake_output-20130921-135115 [ rosmake ] Expanded args [‘localplanner’] to: [‘localplanner’] [ rosmake-0] Starting >>> roslang [ make ] [ rosmake-1] Starting >>> geometry_msgs [ make ] … blah blahblah … [ rosmake-0 ] Finished <<< ucontroller [PASS] [ 1.53 seconds ] [ rosmake-0] Finished <<< localplanner [PASS] [ 1.02 seconds ] [ rosmake ] Results: [ rosmake ] Built 8 packages with 0 failures. [ rosmake ] Summary output to directory [ rosmake ] /home/sandro/.ros/rosmake/rosmake_output-20130921-135115 0 failures is what you’re looking for (obviously). If there were failures, you’ll also see a list of error messages.