roscore is command before running all ros command to run.
roscore = master + rosout(stdout + stderr) + parameter service Node node
A node is ros package executable file
rosrun + package name + node name to execute a program.
We opened two nodes: one is above turtlesim_node, the other is the keyboard turtle_teleop_key they are in the package turtlesim.
Rqt_graph and visualized with their relationship.
Topics topic
Contact between the nodes with the topic, a node publish topic Another subscribe
We look at the usage rostopic
Let's use some rostopic order to familiarize yourself
Use rostopic echo the specific content of the message printed. At the same time update rqt_graph
Next we look at the specific usage rostopic list of current topic and print them all
Or to the topic / turtle1 / cmd_vel between the keyboard and the turtle, for example, in the format
topic name 【topic type】
Can be understood as a node is executable train station, topic is train (carrier), it's the type of message that is actually delivered is the train is pulled or someone else or goods.
Then we look at this train (/ turtle1 / cmd_vel) in the end what is
Next, we made a number of parameters to the instruction manual Turtle (instead of the keyboard)
-1 for parameters sent once to exit, topic name + topic type + - (represents the next argument is not an order)
The meaning of the sentence is to let the turtle liner angular 2.0 and 1.8, the result is the turtle will draw an arc.
We then send a command stream to the turtle, it has been movement
-r indicates a command flow, a represents 1hz
In this way, turtle will love going round in circles in a magic place. . .
Topic topic drawing rqt_plot
Dynamically view changes in the data.
rosrun rqt_plot rqt_plot
