16.56. ROS bag handling tools

ASP provides a couple of Python scripts that can query and extract images and depth clouds from a ROS bag. These are stored in the libexec directory of the ASP distribution, as they use the local system’s Python rather than the Python shipped with ASP. It is assumed that ROS is installed on the local system.

These tools are motivated by the fact that robot Structure-from-Motion datasets often come in ROS bags. For context and examples, see Section 9.2.

16.56.1. list_timestamps

Write the list of timestamps for all data in the bag for given topics. Example usage:

/usr/bin/python                        \
  /path/to/ASP/libexec/list_timestamps \
  --bag bag.bag --list bag_list.txt    \
  --topics "/topic1 /topic2"

The output list will have entries of the form:

1654694879.1690574 /topic1

The first value is a timestamp, in seconds since epoch. It is not the message timestamp, which is the time the message arrived at, but the timestamp saved in the message header, which is assumed to have the creation time of an image or depth cloud.

16.56.2. extract_bag

Extract images and depth clouds from a bag. See Section 9.2.7 for usage.

Command line options:

--bag <string>

Input bag.

--topics <string>

A list of topics, in quotes, having image, compressed image, or point cloud (depth) data.

--dirs <string>

A list of directories, in quotes, one for each topic, in which to save the data for that topic.

--timestamp_list <string>

Extract data for the timestamps in this list. If not set, extract all data. Each line in this file must contain a number of the form <digits>.<digits> (the timestamp) and perhaps other text as well, or it will be ignored. So, a filename containing a timestamp as part of its name will be accepted.

--timestamp_tol <float>

If set, extract the data for each the given topics whose timestamps are closest to the ones in the input list, within this tolerance, in seconds. This should be kept small. It is assumed the bag stores the data for each topic in increasing value of timestamp.


If using --timestamp_tol, change the timestamp of the data being saved (which becomes part of the output filename) to be the closest timestamp in the input list.