Contents

ROS/Tutorials/reading msgs from a bag file - learn how to use the ros_readbagfile command-line tool. General format: ros_readbagfile  [topic1] [topic2] [topic3] [...] [topic1000]

The rosbag command-line tool provides functionality for ROS bags.

It can record a bag, republish the messages from one or more bags, summarize the contents of a bag, check a bag's message definitions, filter a bag's messages based on a Python expression, compress and decompress a bag and rebuild a bag's index.

This is the current list of supported rosbag subcommands:

IMPORTANT: This wiki page quickly goes out-of-date. To ensure you are fully aware of all command-line options available in your version of ROS, simply run rosbag -h to see what subcommands are available for the rosbag command, then run rosbag  -h to see what options are available for a given subcommand. Ex: rosbag play -h will show you the most up-to-date list of all options available for your installation for the rosbag play subcommand.

record

info

play

check

fix

filter

compress

decompress

reindex

These are described in greater detail in the following sections.

rosbag record subscribes to topics and writes a bag file with the contents of all messages published on those topics. The file contains interlaced, serialized ROS messages dumped directly to a single file as they come in over the wire. This is the most performance and disk-friendly recording format possible. To further reduce disk usage, you can compress bag files as they are created.

If you are recording messages at a high bandwidth, such as from cameras, it is strongly recommended you run rosbag record on the same machine as the camera, and specify the file destination as being on the local machine disk.

record 

-h, --help

-a, --all

Note that newly published topics are discovered by periodically polling the master. rosbag record -a will likely miss initial messages published on any topic.

-e, --regex

Record all topics that contain sensors in their name:

-p, --publish New in ROS Melodic

Publish a message when the record begin to write a new bag (topic = "begin_write").

-x EXCLUDE_REGEX, --exclude=EXCLUDE=REGEX

Exclude topics matching the given regular expression (subtracts from -a or -e).

-q, --quiet

-d, --duration

-o PREFIX, --output-prefix=PREFIX

-O NAME, --output-name=NAME

--split

--max-splits=MAX_SPLITS New in ROS Kinetic

-b SIZE, --buffsize=SIZE

Use an internal buffer of SIZE MB (Default: 256, 0 = infinite). This is the message queue of the recorder object, before messages are being passed on to the bag. Lowering this value might result in messages being dropped before they reach the recording process.

--chunksize=SIZE

Advanced. Record to chunks of SIZE KB (Default: 768). This is a buffer within the bag file object. Lowering this value will result in more writes to disk.

-l NUM, --limit=NUM

--node=NODE

-j, --bz2

Use BZ2 compression. See compress for details.

--lz4

Use LZ4 compression. See compress for details.

-tcpnodelay

--udp

rosbag info displays a human-readable summary of the contents of the bag files, including start and end times, topics with their types, message counts and median frequency, and compression statistics.

To output a machine-readable representation, use --yaml. See the cookbook for an example of how to load this representation in code.

info 

-h, --help

-y, --yaml

Print information in YAML format.

-k KEY, --key=KEY

Print information only on the given field (requires -y).

Example usage:

rosbag play reads the contents of one or more bag file, and plays them back in a time-synchronized fashion. Time synchronization occurs based on the global timestamps at which messages were received. Playing will begin immediately, and then future messages will be published according to the relative offset times. If two separate bag files are used, they are treated as a single bag with interlaced times according to the timestamps. This means if you record one bag, wait an hour, and record a second bag, when you play them back together you will have an hour-long dead period in the middle of your playback.

If you do not want to observe playback timing, the -i option will playback all messages from the file as fast as possible. Note that for large files this will often lead to exceeding your incoming buffers.

Additionally, during playing, you can pause at any time by pressing space. When paused, you can step through messages by pressing s.

play 

-h, --help

-p PREFIX, --prefix=PREFIX

-q, --quiet

-i, --immediate

--pause

--queue=SIZE

Use an outgoing queue of size SIZE (defaults to 0. As of 1.3.3 defaults to 100).

--clock

--hz=HZ

-d SEC, --delay=SEC

-r FACTOR, --rate=FACTOR

-s SEC, --start=SEC

-u SEC, --duration=SEC

--skip-empty=SEC

-l, --loop

-k, --keep-alive

--try-future-version

--topics

--pause-topics

--bags=BAGS

--wait-for-subscribers

--rate-control-topic=RATE_CONTROL_TOPIC

watch the given topic, and if the last publish was more than ago, wait until the topic publishes again to continue playback

--rate-control-max-delay=RATE_CONTROL_MAX_DELAY

maximum time difference from before pausing

See more instructions and usage examples on the rosbag migration page.

check 

-h, --help

-g RULEFILE, --genrules=RULEFILE

-a, --append

-n, --noplugins

If a bag is currently unplayable and non-migratable, it may be necessary to generate rules to bring the bag up to date. See Migrating Messages for the preferred approaches to doing this.

See more instructions and usage examples on the rosbag migration page.

fix   [rules.bmr]

-h, --help

-n, --noplugins

filter   

The Python expression can access any of the Python builtins plus:

topic

m

t

time of message. The time is represented as a rospy Time object (t.secs, t.nsecs)

-h, --help

--print=PRINT-EXPRESSION

Example output:

To filter based on time, convert the time to a floating point number (use UNIX time, to get this value, use rosbag info):