What is Rqt and usage examples

RQT is a ROS graphical user interface (GUI) tool for visualizing various aspects of a ROS system, including ROS nodes, topics, services, parameters, etc. It is an important component of ROS and can help users debug and test ROS systems more conveniently.

The following is an example using RQT:

Suppose we have a ROS system that contains a topic named "/turtle1/cmd_vel" for controlling the movement of a small turtle robot. We can use the "Topic Monitor" plugin in RQT to view the messages of this topic.

First, open a terminal and start the ROS system:

roscore

Next, start the little turtle robot node in another terminal:

rosrun turtlesim turtlesim_node

We can then use RQT to monitor the "/turtle1/cmd_vel" topic. Open a terminal and enter the following command:

```

rqt

```

This will open the RQT GUI. In the left panel, select Plugins > Topics > Topic Monitor. In the right panel, select the "/turtle1/cmd_vel" topic. You should now be able to see the topic's messages live in the RQT GUI.

You can control the movement of the little turtle robot by posting messages to this topic. For example, you can publish a message to this topic to make the little turtle robot move forward with the following command:

```
rostopic pub /turtle1/cmd_vel geometry_msgs/Twist "linear:
  x: 2.0
  y: 0.0
  z: 0.0
angular:
  x: 0.0
  y: 0.0
  z: 0.0" -r 1
```

Now, you should be able to see the "/turtle1/cmd_vel" topic's messages changing in the RQT GUI, and the little turtle robot should also move forward.