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using rosbag in callback

asked 2018-12-18 12:28:34 -0500

hsrbrchat gravatar image

For my project I am interested in many frames of reference contained in a list called frame_list, each with Pose messages published to their own topic e.g. 'frame_transform'. I am trying to subscribe to all of these topics and use rosbag to save the Poses as they are published. The code below creates the .bag file, but does not write any data into it even though messages are being published to the topics. Is this a good way to achieve what I want? Can anybody spot where I am going wrong? Thanks.

#!/usr/bin/env python  
import roslib
import rospy
import rosbag
from geometry_msgs.msg import Pose

def callback(data, args):

    bag = rosbag.Bag('data.bag', 'w')
    bag.write(str(args), data)

if __name__ == '__main__':

    if rospy.has_param('init_complete'): #check if initialisation is complete
        rospy.init_node('rosbag_writer') #initiate node
        frame_list = rospy.get_param('frame_list') #import list of frames from rosparam
        for frame in frame_list:
            rospy.Subscriber(str(frame) + '_transform', Pose, callback, frame) #check for frame transforms
        rospy.spin()
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Why are you using the rosbag Python API instead of just using rosbag from the command line?

jayess gravatar imagejayess ( 2018-12-18 15:01:03 -0500 )edit

My project is to create a robot task-learning program which is accessible to those with no knowledge of ros or Python, therefore stuff like this must be done using the Python API to minimise user input.

hsrbrchat gravatar imagehsrbrchat ( 2018-12-18 15:05:51 -0500 )edit

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answered 2018-12-18 15:34:57 -0500

jayess gravatar image

You could use launch files to start rosbag and your other nodes such as in #q175133 and #q52773, for example.

What I'm seeing from your code, however, is that you're not storing your subscribers at all, just instantiating them in a for loop and then spinning. If this is how you want to do it, try storing them in a list. Something like

subscribers = []
for frame in frame_list:
    subscriber = rospy.Subscriber(str(frame) + '_transform', Pose, callback, frame)
    subscribers.append(subscriber)
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Asked: 2018-12-18 12:28:34 -0500

Seen: 155 times

Last updated: Dec 18 '18