How to extract data from *.bag?

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Make sure you have set the path variable and add these two lines to the top of your main python script to avoid any dependency errors.

import roslib; roslib.load_manifest('your_package_name')

then write your rest of the script. Please keep in mind that this does not need to be in every python script but just in the main entry point.

I followed guide at http://www.ros.org/doc/api/rosbag/html/c++/ when i run the code it tells me "ImportError: No module named rosbag"

Traceback (most recent call last): File "/home/user/ros_workspace/beginner_tutorials/nodes/read_bag.py", line 4, in <module> import rosbag ImportError: No module named rosbag

please tell me how to fix this!

just type the following in the directory of bag file:

rostopic echo -b bagname.bag -p /topicname > filename.csv

the data will save into filename.csv then you can use it in matlab