How are topics and nodes connected?
I'm pretty new to ROS programming, This question might seem silly but can someone please clear this one for me? It is really bothering me.
simple_publisher = rospy.Publisher('topic_1', String, queue_size = 10)
the line above creates a publisher object which takes string type messages for transfer under the topic_1 name
rospy.init_node('node_1', anonymous = False)
Initialized the node for publisher
topic1_content = "my first ROS topic"
have my content for transfer ready
while not rospy.is_shutdown():
simple_publisher.publish(topic1_content)
In this bit how does the program know that the topic1_content that was published using simple_publisher is from the node_1. How is node_1 getting connected to topic_1?
Can we only make 1 node per program i.e. we can only run rospy.init_node only once?
Yes. A node is a process that performs computation,It is an executable program running inside your application. (Source: ROS Wiki). So yes, strictly speaking a program can only have a node.
Next in your program:
This Line:
rospy.init_node('node_1', anonymous = False)
Specify:
The program is creating and initializing a node call 'node 1'.
This line:
simple_publisher = rospy.Publisher('topic_1', String, queue_size = 10)
Specify:
The program/node will create a communication line known as a topic which is named as 'topic 1'.
this line:
simple_publisher.publish(topic1_content)
Specify:
In the topic there is a message in it. The message is 'topic1_content'.
Hope it clarify a bit.