Throttle recording rate per topic

[dw25628]

Description

This feature was previously proposed in #682, having the ability to throttle the rate of recording on a per topic basis. For example an image being published at a frame rate of 30hz but only wanting to log it at 1hz.

I would be interested in the communities feedback on this feature and my potential proposal for implementation. I would be happy to take an initial stab at implementing it.

Related Issues

Completion Criteria

• Ability to enable throttle from cli
• Check whether or not a msg should be logged within the callback based on the last write time
• Update documentation

Implementation Notes / Suggestions

• Implement a record option for enabling the topic throttle and specifying the rate
  Potential example call, no rate entry or a rate entry less than 0 would not throttle the message
  Rate would be hz
  ros2 bag record --topics_and_rates /tf /gps/fix 5 /image/rgb 0.5 /rosout -1

• Store a vector or map of rates per topic within RecordOptions

• Store the last write time for each topic

• Add function within TopicFilter to compare the current receive time to the last write time for that topic. Return whether the message can be written

• For each subscription callback check if the message should be written

Testing Notes / Suggestions

[MichaelOrlov]

Long story short: You can throttle/decimate the topic first, then record the throttled one.

Here are two ways of how to do it in the ROS 2 ecosystem.

1. Throttle by rate (≈1 Hz)

• Pass through ≤1 msg/sec

ros2 run topic_tools throttle messages /camera/image_raw 1.0 /camera/image_raw_1hz

• Then record only the throttled topic

ros2 bag record /camera/image_raw_1hz

Notes:
topic_tools throttle works for any message type, including images, and keeps the original message contents/stamps. You can set --ros-args -p use_wall_clock:=true if you want throttling against wall time (ignoring /clock).
GitHub. Please see https://github.com/ros-tooling/topic_tools for details.

2. Decimate by dropping N of every M messages (exact 1/30)

Let exactly 1 of every 30 images through (≈1 Hz if source ≈30 Hz)

ros2 run topic_tools drop /camera/image_raw 29 30 /camera/image_raw_decimated
ros2 bag record /camera/image_raw_decimated

I wouldn't go the way of adding this feature inside the Rosbag2 recorder. It already has a pretty complicated logic and a lot of various features. Another one good to have feature which is could be accomplished by using a third-party package, will overcomplicate the logic even more.