opencv - (Python) Converting image time series to ROS bag -

i have set of images metadata including time stamps , odometry data data set. want convert time series of images rosbag can plug out of code i'll write , switch in real time data after testing. tutorial, process of programmatically saving data rosbag seems work like:

import rosbag std_msgs.msg import int32, string  bag = rosbag.bag('test.bag', 'w')  try:     str = string()     str.data = 'foo'      = int32()     i.data = 42      bag.write('chatter', str)     bag.write('numbers', i) finally:     bag.close() 

for images, data type different process same. however, when have data supposed associated each other, e.g. each image should paired timestamp , odometry recording. sample code seems write "chatter" , "numbers" disjointly. way publish data each image, paired other pieces of data automatically?

in other words, need commented lines in following code:

import rosbag import cv2 std_msgs.msg import int32, string sensor_msgs.msg import image   bag = rosbag.bag('test.bag', 'w') data in data_list:      (imname, timestamp, speed) = data     ts_str = string()     ts_str.data = timestamp      s = float32()     s.data = speed      image = cv2.imread(imname)      # convert cv2 image rosbag format     # write image, ts_str , s rosbag jointly  bag.close() 

many of standard message types sensor_msgs/image or nav_msgs/odometry have attribute header contains attribute stamp meant used timestamps.

when creating bag file, set same timestamp in headers of messages belong , write them separate topics:

from sensor_msgs.msg import image nav_msgs.msg import odometry  ...  img_msg = image() odo_msg = odometry() img_msg.header.stamp = timestamp odo_msg.header.stamp = timestamp  # set other values of messages...  bag.write("image", img_msg) bag.write("odometry", odo_msg) 

later when subscribing messages, can match messages different topics based on timestamp.

depending on how important exact synchronization of image , odometry application, might enough use last message got on each topic , assume fit together. in case need more precise, there message_filter takes care of synchronizing 2 topics , provides messages of both topics in 1 callback.