I do not like to memorize definitions, methods, procedures, etc., but I like to find solutions to help me reach my final goal.
In ROS, the structure of a simple node is repeated almost every time. To write the Publisher nodes as easily as possible, I’ve made a template that you can modify as you needed.
The template below represents a ROS Publisher node written in Python. All you have to do is to copy the template into a ‘. py’ file, delete the extra text and replace the text in capital letters.
|
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
|
#The ROS Node Publisher template
#!usr/bin/env python
#remove or add the library/libraries for ROS
import rospy, time, math, random
#remove or add the message type
from std_msgs.msg import Int32, Float32, String
from basics.msg import TimerAction, TimerGoal, TimeResult
from time import sleep
#you can define functions to provide the required functionality
def body(arg):
    def_body_here
    return the_value
if __name__==‘__main__’:
    #add here the node name. In ROS, nodes are unique named.
    rospy.init_node(‘THE_NAME_OF_THE_NODE’)
    #publish messages to a topic using rospy.Publisher class
    name_pub=rospy.Publisher(‘THE_NAME_OF_THE_TOPIC’, THE_TYPE_OF_THE_MESSAGE, queue_size=1)
    #you can define functions to provide the required functionality
    if var1==var2:
        make_something()
        else:
            make_something()
    #set a publishing rate. Below is a publishing rate of 10 times/second
    rate=rospy.Rate(10)
    while not rospy.is_shutdown():
        #some calculation here
        if a1==a2:
            pub.publish(message1)
            else:
                pub.publish(message2)
rate.sleep()
|
I used the above template to make a ROS node that generates a random number between 0 and 5000.
|
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
|
#!/usr/bin/env python
import rospy
from std_msgs.msg import Int32
from random import randint
#a function to generate the random number
def generate_random_number():
    rnd= randint(0,5000)
    return rnd
if __name__==‘__main__’:
    rospy.init_node(‘random_number’)
    pub=rospy.Publisher(‘rand_no’, Int32, queue_size=10)
    rate= rospy.Rate(5)
    while not rospy.is_shutdown():
        rnd_gen=generate_random_number()
     Â
        if rnd_gen<=2500:
        rospy.loginfo(“The number generated is lower than 2500: %s”, rnd_gen)
        pub.publish(rnd_gen)
        else:
        rospy.loginfo(“The number generated is higher than 2500: %s”, rnd_gen)
        pub.publish(rnd_gen)
rate.sleep()
|
To run the above node, navigate to the .py file and make it executable. The command is:
|
1
|
chmod u+x my_python_file.py
|
After the file is executable, you can run the node.
Step 1: open a new Terminal and run the command:
|
1
|
roscore
|
Step 2: open a new Terminal and run the node with the following command:
|
1
|
rosrun your_package your_ros_node_file.py
|
