bag_helper.py

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"""
Helper functions for bag files and timestamps.
"""

import time

import rospy

def stamp_to_str(t):
    """
    Convert a rospy.Time to a human-readable string.
    
    @param t: time to convert
    @type  t: rospy.Time
    """
    t_sec = t.to_sec()
    if t < rospy.Time.from_sec(60 * 60 * 24 * 365 * 5):
        # Display timestamps earlier than 1975 as seconds
        return '%.3fs' % t_sec
    else:
        return time.strftime('%b %d %Y %H:%M:%S', time.localtime(t_sec)) + '.%03d' % (t.nsecs / 1000000)

def get_topics(bag):
    """
    Get an alphabetical list of all the unique topics in the bag.
    
    @return: sorted list of topics
    @rtype:  list of str
    """
    return sorted(set([c.topic for c in bag._get_connections()]))

def get_start_stamp(bag):
    """
    Get the earliest timestamp in the bag.
    
    @param bag: bag file
    @type  bag: rosbag.Bag
    @return: earliest timestamp
    @rtype:  rospy.Time
    """
    start_stamp = None
    for connection_start_stamp in [index[0].time for index in bag._connection_indexes.values()]:
        if not start_stamp or connection_start_stamp < start_stamp:
            start_stamp = connection_start_stamp
    return start_stamp

def get_end_stamp(bag):
    """
    Get the latest timestamp in the bag.
    
    @param bag: bag file
    @type  bag: rosbag.Bag
    @return: latest timestamp
    @rtype:  rospy.Time
    """
    end_stamp = None
    for connection_end_stamp in [index[-1].time for index in bag._connection_indexes.values()]:
        if not end_stamp or connection_end_stamp > end_stamp:
            end_stamp = connection_end_stamp

    return end_stamp

def get_topics_by_datatype(bag):
    """
    Get all the message types in the bag and their associated topics.
    
    @param bag: bag file
    @type  bag: rosbag.Bag
    @return: mapping from message typename to list of topics
    @rtype:  dict of str to list of str
    """
    topics_by_datatype = {}
    for c in bag._get_connections():
        topics_by_datatype.setdefault(c.datatype, []).append(c.topic)
    
    return topics_by_datatype

def get_datatype(bag, topic):
    """
    Get the datatype of the given topic.
    
    @param bag: bag file
    @type  bag: rosbag.Bag
    @return: message typename
    @rtype:  str
    """
    for c in bag._get_connections(topic):
        return c.datatype

    return None