bag2csv.py

'''
This script saves each topic in a bagfile as a csv.
Accepts a filename as an optional argument. Operates on all bagfiles in current directory if no argument provided

Originally Written by Nick Speal in May 2013 at McGill University's Aerospace Mechatronics Laboratory

Modified by J.Hansen in 2021
'''

import rosbag, sys, csv
import time
import string
import os #for file management make directory
import shutil #for file management, copy file
import numpy as np
from glob import glob

input_name = sys.argv[1]
if os.path.isdir(input_name):
    bag_files = glob(os.path.join(input_name, "*.bag"))
else:
    bag_files = [input_name]

for bag_file in bag_files:
    print('reading %s'%bag_file)
    bag = rosbag.Bag(bag_file)
    bag_contents = bag.read_messages()
    bag_name = bag.filename

    #create a new directory
    folder = bag_name.rstrip('.bag')
    if not os.path.exists(folder):
        os.makedirs(folder)
    # get list of topics from the bag
    list_of_topics = []
    for topic, msg, t in bag_contents:
        if topic not in list_of_topics:
            list_of_topics.append(topic)


    for topic_name in list_of_topics:
        #Create a new CSV file for each topic
        filename = os.path.join(folder, topic_name.replace('/','__')+'.csv')
        with open(filename, 'w+') as csvfile:
            filewriter = csv.writer(csvfile, delimiter = ',')
            first_iteration = True    #allows header row
            for subtopic, msg, t in bag.read_messages(topic_name):    # for each instant in time that has data for topicName
                #parse data from this instant, which is of the form of multiple lines of "Name: value\n"
                #    - put it in the form of a list of 2-element lists
                msg_string = str(msg)
                msg_list = msg_string.split('\n')
                instantaneous_list_of_data = []
                for name_value_pair in msg_list:
                    split_pair = name_value_pair.split(':')
                    for i in range(len(split_pair)):    #should be 0 to 1
                        split_pair[i] = split_pair[i].strip()
                    instantaneous_list_of_data.append(split_pair)
                #write the first row from the first element of each pair
                if first_iteration:    # header
                    headers = ["rosbagTimestamp"]    #first column header
                    for pair in instantaneous_list_of_data:
                        headers.append(pair[0])
                    filewriter.writerow(headers)
                    first_iteration = False
                # write the value from each pair to the file
                values = [str(t)]    #first column will have rosbag timestamp
                for pair in instantaneous_list_of_data:
                    if len(pair) > 1:
                        values.append(pair[1])
                filewriter.writerow(values)
    bag.close()