Filter out messages from a ros bag

edit

It's a bit easier with python:

import rosbag

with rosbag.Bag('output.bag', 'w') as outbag:
    for topic, msg, t in rosbag.Bag('input.bag').read_messages():
        if topic == "/tf" and msg.transforms:
            outbag.write(topic, msg, msg.transforms[0].header.stamp)
        else:
            outbag.write(topic, msg, msg.header.stamp if msg._has_header else t)

http://wiki.ros.org/rosbag/Cookbook

For anyone searching just how to extract, or read messages out of a bag file, as of the year 2020 you can now use ros_readbagfile, like this:

ros_readbagfile <mybagfile.bag> [topic1] [topic2] [topic3] [...] [topic1000]

I recently wrote this script, and this tutorial here: http://wiki.ros.org/ROS/Tutorials/rea...

See the tutorial for full instructions.

Thanks to this answer for getting me started: https://answers.ros.org/question/2408....

The rosbag:MessageInstance object that you get for each message in the bag file has a getTopic() method. Unfortunately the docs are a bit hard to find now that the message storage has been moved to the rosbag_storage package: http://docs.ros.org/kinetic/api/rosba...