ROS 2 CLI basics

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# ROS 2 CLI BASICS
A quick dive into ROS 2 Command Line Interface

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# AGENDA
1. Installation and sourcing
2. Basic command structure
3. Publishers and Subscribers
4. Services
5. Actions and Parameters
6. Tools

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# 1. Installation and sourcing
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## 1.1 Installing and Sourcing ROS 2
* Two types of installation - [Binary](https://docs.ros.org/en/jazzy/Installation/Ubuntu-Install-Debs.html) (recommended) or [Source](https://docs.ros.org/en/jazzy/Installation/Alternatives/Ubuntu-Development-Setup.html).
* Verify the ROS 2 Jazzy installation:
 `ll /opt/ros/jazzy`.
* Source ROS 2 to use commands, libraries, packages etc..:
`source /opt/ros/jazzy/setup.bash`
* Source your local workspace as needed after sourcing ROS 2:
`source /path/to/ws/install/local_setup.bash`

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## 1.2 Aliasing
* Aliases are custom defined abbreviations for commands.
* Simply type
`source_jazzy` (or any string you wish)
instead of
`source /opt/ros/jazzy/setup.bash`  (or any command you wish)
* See cheat sheet for syntax.

.center[!!ADVICE!!: Source ROS 2 manually everytime on Day 1 to get used to the concept. Use aliases from Day 2.]

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## 1.3 ROS_DOMAIN_ID

* Environment variable
* Unique identifier number for each machine
* Physically separates network
* Stop ROS 2 node interference
* Set and forget : `echo "export ROS_DOMAIN_ID=<your_id>" >> ~/.bashrc`

.center[100% discount sale! - Ask for your very own domain ID today!!]

### Building ROS 2 (Recap)

* `colcon build --symlink-install`

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# 2. Basic command structure

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## 2.1 Basic command structure

We only explore default packages that come with the binary for simplicity.

* All ROS 2 commands follow this syntax :
`ros2 <main_command> <sub_command> <<arguments>>`

* Examples :
`ros2 pkg list`
`ros2 pkg executables`

Use tab completion to either complete a command, or to see a list of available options.
* Example: `ros2 ` *tab* *tab* - List all ROS 2 commands.
* `ros2 pkg ` *tab* *tab* - List of sub-commands for `pkg`.
* `-h` at almost any point to get a brief help description.
`ros2 -h`
`ros2 pkg -h`
`ros2 pkg executable -h`

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# 3. Publishers and Subscribers
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##  3.1 Publisher

The most basic example of ROS - a *Publisher/Subscriber* pair

* Remember to source ROS 2
* Command `run` to run an executable within a package (C++ compiled object/Python script):

`ros2 run <package_name> <executable_name> <<optional_command_line_arguments>>`

* Try the example publisher node packaged with ROS 2.
* We first need to find out what the name of the package is.
* Run the package listing command  with a filter:
`ros2 pkg list | grep demo`
* Next find the available executables we could use by running  :
`ros2 pkg executables demo_nodes_cpp`
* Run one of these executables - the publisher:
`ros2 run demo_nodes_cpp talker`

Observe the state of the ROS 2 runtime system so far...

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## 3.2 Introspection - Publisher

### Nodes
* To look at what nodes are currently running:
`ros2 node list`
* To see more info about a node:
`ros2 node info <node_name>`

### Topics
* To see currently running topics and their message types:
`ros2 topic list -t`
* To get more info about a topic (verbose output):
`ros2 topic info -v <topic_name>`
* To see what is being published on a topic:
`ros2 topic echo <topic_name>`

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## 3.3 Subscriber

* Start a subscriber that listens to this topic:
`ros2 run demo_nodes_cpp listener`

* The subscriber echoes on the terminal what it hears over the topic.

* Check the running nodes and topics again to see the update.

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## 3.4 Introspection - Terminal Publisher

* Publishers can also be created from the terminal.
`ros2 topic pub <topic_nam> <msg_type> "{<field1_key>: <field1_value>,  <field2_key>: <field2_value>, ...}"`
* The message type must be properly understood first.
`ros2 topic list -t`
* The message type of `/topic` is `std_msgs/msg/String`
* For more info: `ros2 interface show std_msgs/msg/String`
* It has only one field - `data` - of the type `string`.
* The message body is a dictionary type, with key-value pairs for the message fields.
* Use `ros2 interface proto std_msgs/msg/String` to get an example of the dictionary to use.
> NOTE THAT SPACING IS VERY IMPORTANT!!
* To spawn a publisher over `/topic` with a rate of 10 Hz:
`ros2 topic pub -r10 /topic std_msgs/msg/String "data: "Hello""`

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## 3.5 Launch files

* A way to start many nodes from a single starting point:

`ros2 launch <package_name> <launch_file_name.launch> <<optional_command_line_arguments>>`

* To run both the Subscriber and Publisher from one point:
`ros2 launch demo_nodes_cpp talker_listener.launch.py`

* Use introspection to verify results and compare.

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# 4. Services

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## 4.1 Introduction - Services

* Useful for making short but guaranteed transfer of messages between nodes.
* It involves two entities - a Server that provides the service and a Client that consumes this service.
* Start these just just like a typical node:
`ros2 run demo_nodes_cpp add_two_ints_server`
`ros2 run demo_nodes_cpp add_two_ints_client`

* A Topic streams data whereas a Service makes one exchange per call.

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## 4.2 Introspection - Services

* List the services offered by servers:
`ros2 service list -t`
* Service offered by the demo server - *add_two_ints*
* We invoked this service by running a client node
* You can also do this via the CLI.

Syntax: `ros2 service call <service_name> <service_type_name> "{<field1_key>: <field1_value>,  <field2_key>: <field2_value>, ...}"`

* To understand the service type:
`ros2 interface list -s`   (-s for services. Also, -m, -a)
`ros2 interface show <service_type_name>`

Example: `ros2 service call /add_two_ints example_interfaces/srv/AddTwoInts "{a: 5, b: 6}"`
> NOTE THAT SPACING IS VERY IMPORTANT!!

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# 5. Actions and Parameters

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## 5.1 Actions

* Useful for longer tasks that need a feedback & involves an action server and an action client.
* Interface has 3 parts - goal, feedback and result.
* Typical sequence - Publish a goal, observe feedback & receive result  when execution is completed/aborted
* Use the `ros2 action [..]` commands to interact. (New in ROS 2)
    * Similar to `ros2 topic [..]`

###### More in workshop

##  5.2 Parameters

* Key-value pairs to store runtime configuration information.
    * Ex: laser scan field, camera calibration, navigation obstacle layer thickness etc...
* Parameters are stored per each node and can be accessed via services
    * As opposed to ROS 1 which had a dedicated parameter server managed by rosmaster.
* Use `ros2 param [..]` commands to interact from the CLI.

###### More in workshop
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# 6. Tools

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## 6.1 Tools - RQT

* QT Based ROS GUI tool.
* Offers plugins for many purposes:
    * Node graph monitor,
    * Service caller/type viewer,
    * Topic publisher/listener/type viewer,
    * Image view,
    * Plot  etc....
* Similar to ROS 1, but few plugins still missing
* `rqt &` to launch default main window (`&` ->detached process)
or
`ros2 run rqt_<plugin> rqt_<plugin>` to launch a specific plugin
* Load a plugin : `Plugins -> <Library> -> <Plugin>`
    * Example to monitor node graph `Plugins -> Introspection -> Node Graph`
* Explore and use all tools as necessary.

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## 6.2 Tools - ros2doctor
##### The doctor is in the house!

* Identify issues in the system (similar to roswtf, can use wtf as an alias)
* Analyse ROS 2 installation as well as running systems, show reports
* `ros2 doctor` - Shows warnings and errors about the current state
    * Dangling topics, incorrect configurations, missing system files etc...
* `ros2 doctor -r` - Full technical report of the installation
* `ros2 doctor hello` - Check network connectivity betwwen multiple hosts

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## 6.3 Tools - ros2bag

* Same function and similar API as rosbag from ROS 1
    * Available through the Jazzy rosbag2 packages
* Record the messages being published on topics for a duration into a file. Replay later with nearly the same time characteristics.
* Stored in a bag directory with *metadata.yaml* and *.mcap* files by default in Jazzy; SQLite3 (*.db3*) is also supported.

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## 6.4 Tools - ros1_bridge

* A "dual homed" package - simultaneously ROS 1 AND ROS 2.
* ROS 1 <=topics/services=> `ros1_bridge` <=topics/services=> ROS 2
* Binary installation supports default msg/srv types, source installation can be extended with custom types.

```
Shell 1 $  Source ROS 1, Run ROS 1 stuff
Shell 2 $  Source ROS 1, Source ROS 2, Run bridge
Shell 3 $  Source ROS 2, Run ROS 2 stuff
```
>                                        MAGIC!

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# QUESTIONS?