How to filterout a type from a rosbag record?

asked 2021-04-22 13:52:09 -0500

I have on my hands a 18GiB rosbag that contains multiple topics of PointCloud2 type. From my experience those are the main contributors to the rosbags' size. After the bag is recorded I can use the following to throw away the PointCloud2 messages: rosbag filter big.bag small.bag "'PointCloud2' not in str(type(m))" but what flag to rosbag record should I use to not record them?

I know rosbag record -x but according to documentation that only works with regexes and my PointCloud2 topics have different names.

By default I use rosbag record -a since the PointCloud2 topics are only a fraction of what I want to record.

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answered 2021-04-23 18:17:12 -0500

Aleksander Bobiński
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Somewhat guided by gvdhoorn's answer I wrote the following shell wrapper around rosbag record.

unwanted_type=PointCloud2
unwanted_topics_as_regex_alternative=$(rostopic list --verbose | grep $unwanted_type | cut -d '[' -f 1 | cut -d '*' -f2- | sed -E 's/^ (.*) $/\1/g' | tr '\n' '|')
rosbag record -a -x "($unwanted_topics_as_regex_alternative)"

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Nice idea to use rostopic in a shell script wrapper. Would rostopic list with rostopic type be less --verbose?

gvdhoorn ( 2021-04-24 02:56:37 -0500 )edit

I think one would have to use a for loop since rostopic type does not accept multiple topic names as arguments. Maybe if rostopic type would accept topic names from stdin this could be done in one line without the cut tricks by piping from rostopic list to rostopic type to grep.

Aleksander Bobiński ( 2021-04-24 03:49:05 -0500 )edit

Maybe if rostopic type would accept topic names from stdin this could be done in one line without the cut tricks by piping from rostopic list to rostopic type to grep.

afaik, it does support that.

gvdhoorn ( 2021-04-24 06:32:56 -0500 )edit

Are you sure? For me echo "/velodyne_points" | rostopic type results in: usage: rostopic type [-h] topic_or_field rostopic type: error: the following arguments are required: topic_or_field

Aleksander Bobiński ( 2021-04-24 07:51:29 -0500 )edit

You can do it with xargs: rostopic list | xargs -i rostopic type {}. But you don't really gain anything doing this I believe.

gvdhoorn ( 2021-04-24 10:55:20 -0500 )edit

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answered 2021-04-23 02:24:37 -0500

gvdhoorn
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I don't believe rosbag supports this directly. -x works with topic names, not types. -a will record everything.

You could take a look at the rosbag API, which would make this not too difficult (ie: retrieve a list of all recorded topics, prune those with a specific type), but that wouldn't prevent them from being recorded first. You'd be post-processing an already recorded .bag.

Another option (which would require some work): write a wrapper which uses the ROS Master API to get a list of all topics, filters them based on type, then spits out a list of topic names which don't carry msgs of that type and then you can pass those to rosbag record. This would prevent topics you're not interestd in from being recorded.

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How to filterout a type from a rosbag record?

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