read single message from bag-file (c++)

asked 2016-02-29 07:30:00 -0500

Duke
1 ●1 ●1 ●1

updated 2016-02-29 07:31:20 -0500

Hi,I'm new to this whole ROS stuff and have a problem which I can't solve on my own.

I want to read a single message from a given bag-file using c++11. To do this I read the short tutorial and cookbook for rosbag. I get the message with iterating over all messages in the bag. But I want to know if there is a way to direct get the specified message (data)? The topic (m.getTopic()), timestamp (m.getTime()) and the structure of the message (m.MessageDefinition()) is known.

Thanks for your help.

answered 2016-02-29 10:26:58 -0500

vaziri
46 ●3

I dont know for sure what the best solution to your problem is. But just to brainstorm things you might try (I have not tried these myself): Perhaps you could use the filter functionality to make a new bag file containing only the messages you care about. Another option would be to use cut.py script from bag_tools ( https://github.com/srv/srv_tools/blob... ). Those would be more "direct" in that you would write fewer lines of codes, but I am not sure that it would be any faster than what you are doing now.

If you need a faster solution the bag file format supports random access. Assuming the bag file is in chronological order you could make a function that does a binary search to find the message you care about.

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thanks for your answer. I think the filter functionality also iterates over the whole bag and looking for one element is already a kind of filter. its working but it feels not right to search the whole file just to get one special element.