<slide_break></slide_break> ### Odometry * `Odometry` message is used for `/odom` topic. 1. The Robot's "belief" of where it is, and what it is doing. 2. Based on sensors in the base, including possibly the motors, a GPS, a magnetometer etc. 3. Odometry is published as topic /odom and the message definition is called nav_msgs/Odometry * nav_msgs/Odometry 1. Header - standard header 2. pose - where does the robot thinks that it is (including Covariance - how sure is it?) 3. twist - how does it think it is moving (also with a covariance) <slide_break></slide_break> ### catkin * catkin is the ROS build system * It's quite complicated and related to CMAKE * Treat it like a black box <slide_break></slide_break> ### Workspaces * A subdirectory in which you will be doing your ROS work * You need only one and it will be called catkin_ws/ * You should already have it on your linux install, but here's how you would create it otherwise: <pre><code class="language-language-bash$ mkdir -p ~/catkin_ws/src"> $ cs $ catkin_init_workspace </code></pre> * From time to time you have to build things, called "doing a build or make" * Use the alias `cm` <slide_break></slide_break> ### .bashrc * A "hidden" file in your home directory * Contains a series of shell commands that are executed each time you start a shell * It is `populated` with lots of useful stuff by the installation of ROS * Any commands you want run each time will be placed there * source `~/.bashrc command` reads the file and executes it as if you typed it into bash * Key environment variables have to be defined in .bashrc <slide_break></slide_break> ### example <pre><code class="language-language-bash"> $ source ~/catkin_ws/devel/setup.bash $ export ROS_MASTER_URI=http://localhost:11311 $ export ROS_HOSTNAME=localhost $ export TB3_MODEL=burger $ export TURTLEBOT3_MODEL=burger </code></pre> <slide_break></slide_break> ### ROS Packages * A complete "application" or "tool", stored as a directory tree in a standard layout * Analogous to a gem in ruby, or a library in Java * Can be created like this: <pre><code class="language-language-bash$ cd catkin_ws/src"> $ catkin_create_pkg my_new_package rospy </code></pre> <slide_break></slide_break> ### Contents of a package directory * `package.xml` # describes all the things that are in the package * `CMakeLists.txt` # describes how to "build" * `./messages` # descriptors of the messages * `./scripts` # contains all the python source files * `./launch` # contains all the .launch files #<slide_break></slide_break> ### Python programs * Most of your python code will implement nodes * You should put them into the ./scripts directory * Name them *.py and give them execution file property: `chmod +x myfile.py` <slide_break></slide_break> ### rosrun and roslaunch <pre><code class="language-language-bash$cd catkin_ws"> # run a certain program from a certain package $ rosrun package program.py # "execute" that launch file $ roslaunch package file.launch </code></pre> <slide_break></slide_break> ### Names, Namespaces and Remapping * Everything in the ros world has a name that looks like a file path * For example: `/cmd_vel` is a topic name * To allow flexibility,m you can remap a name to another name on the command line, e.g. <pre><code class="language-language-bash$ cs"> $ ./image_view image:=right/image </code></pre> <slide_break></slide_break> ### roslaunch * Many real ROS applications have multiple nodes * To save time having to start each one separately * (And for many other reasons) * A .launch file contains instructions on what to launch and in what order * You run it with the `roslaunch` command. It will start `roscore` if necessary <slide_break></slide_break> ### tf: Coordinate Transforms * See [TF Tutorial](http://wiki.ros.org/navigation/Tutorials/RobotSetup/TF) * Coordinate system * There will/can be many * Some of the components might move (an arm for example) * tf system periodically broadcasts the current relationship between coordinate systems * Quaternions <slide_break></slide_break> ### Poses, Positions, and Orientations * Handy and very common term to mean: 3d position and 3d orientation of something * (Not velocity, just the position) * Usually the transform between the robot coordinate frame and the maps coordinate frame <slide_break></slide_break> ### tf * Frames: Essential and complicated concept * Find the change in position and orientation between two coordinate frames * High level: a way to compute relative coordinate systems * `tf` is a central package of ROS which computes transformations for Frames * If I know a position relative to the room, what is that position relative to the robot?