Often times an Astrobee recording is in multiple bags, so those need to be merged before further processing. There exist two tools for that: this one, merge_bags, written in C++, and merge_bags.py, written in Python. The C++ tool, which is documented here, is more robust, as apparently the Python one may fail if certain topics are present in the the input bag files.

The merge_bags program is also more versatile. It can filter images by acquisition time range, topic, and can keep only one image for a given time interval (useful if the images are too frequent).

The acquisition time for an image or point cloud message is determined from the timestamp field in the header of that message, which is more reliable than extracting it from the message time itself.

Example:

merge_bags bag1.bag bag2.bag -output_bag merged_bag.bag

Command-line options:

-output_bag <string (default="")> The output bag. -start_time <double (default=-1.0)> If non-negative, start at this time, measured in seconds since epoch. -stop_time <double (default=-1.0)> If non-negative, stop before this time, measured in seconds since epoch. -save_topics <string (default="")> If non-empty, the topics to write. Use quotes and a space as separator. Example: '/hw/cam_nav /hw/cam_sci'. -min_time_spacing <double (default=-1.0)> If non-negative, for each input bag, keep only messages for a given topic which differ by no less than this time amount, in seconds. Assumes that messages in a bag are stored in ascending order of time.