Use data from multiple topics in ROS - Python

Question

I'm able to display data from two topics but I can't do use and compute data in real time from these two topics in ROS (written in Python code).

Have you got any idea to stock this data and compute in real time ?

Thanks ;)

#!/usr/bin/env python

import rospy
import string
from std_msgs.msg import String 
from std_msgs.msg import Float64MultiArray
from std_msgs.msg import Float64
import numpy as np


class ListenerVilma:

    def __init__(self):
        self.orientation = rospy.Subscriber('/orientation', Float64MultiArray , self.orientation_callback)
        self.velocidade = rospy.Subscriber('/velocidade', Float64MultiArray, self.velocidade_callback)

    def orientation_callback(self, orientation):
        print orientation

    def velocidade_callback(self, velocidade):
        print velocidade


if __name__ == '__main__':
   rospy.init_node('listener', anonymous=True)
   myVilma = ListenerVilma()
   rospy.spin()

Answer 1

Possible solution:

#!/usr/bin/env python

import rospy
from std_msgs.msg import Float64MultiArray


class Server:
    def __init__(self):
        self.orientation = None
        self.velocity = None

    def orientation_callback(self, msg):
        # "Store" message received.
        self.orientation = msg

    def velocity_callback(self, msg):
        # "Store" the message received.
        self.velocity = msg


if __name__ == '__main__':
    rospy.init_node('listener')

    server = Server()

    rospy.Subscriber('/orientation', Float64MultiArray , server.orientation_callback)
    rospy.Subscriber('/velocity', Float64MultiArray, server.velocity_callback)

    rospy.spin()

Now you have a "stock of data" in the form of self.orientation and self.velocity, and you can use that to "compute in real time".

For example:

#!/usr/bin/env python

import rospy
from std_msgs.msg import Float64MultiArray


class Server:
    def __init__(self):
        self.orientation = None
        self.velocity = None

    def orientation_callback(self, msg):
        # "Store" message received.
        self.orientation = msg

        # Compute stuff.
        self.compute_stuff()

    def velocity_callback(self, msg):
        # "Store" the message received.
        self.velocity = msg

        # Compute stuff.
        self.compute_stuff()

    def compute_stuff(self):
        if self.orientation is not None and self.velocity is not None:
            pass  # Compute something.


if __name__ == '__main__':
    rospy.init_node('listener')

    server = Server()

    rospy.Subscriber('/orientation', Float64MultiArray , server.orientation_callback)
    rospy.Subscriber('/velocity', Float64MultiArray, server.velocity_callback)

    rospy.spin()

Answer 2

you need message_filter to synchronize multiple messages. read this http://wiki.ros.org/message_filters#Example_.28Python.29-1