Reading a ROS (Robot Operating System) datadump (.rosbag) for Velodyne LIDAR pakets

rosbag_velodyne.py

"""
Installing Rosbag
        - http://wiki.ros.org/lunar/Installation

RosBag Python API
        - http://wiki.ros.org/rosbag/Cookbook
        - http://wiki.ros.org/rosbag/Code%20API

ROS : Velodyne PointCloud
        - to convert velodyne_msgs/VelodyneScan messages to sensor_msgs/PointCloud2
         - https://answers.ros.org/question/278052/reading-velodynescan-from-bagfile-offline/

Useful commands
 - rosbag info --yaml <bagname>.bag

Data
 - https://github.com/udacity/self-driving-car/tree/master/datasets/CHX

"""

import rosbag

"""
bag = rosbag.Bag('data_original.bag')
for (topic, msg, t) in bag.read_messages(topics=['/velodyne_packets']):
    print (topic, msg, t)
    break
"""

"""
with rosbag.Bag('data__velodyne_packets.bag', 'w') as outbag:
     for i, (topic, msg, t) in enumerate(bag.read_messages(topics=['/velodyne_packets'])):
        outbag.write(topic, msg, t)
"""

bag = rosbag.Bag('data__velodyne_packets.bag')
for i, (topic, msg, t) in enumerate(bag.read_messages()):
    # print (topic, msg, t)
    print ('Topic : ', topic, ' || Time : ',t, ' || msg.header.seq : ',msg.header.seq, ' || msg.header.frame_id : ', msg.header.frame_id)
    print ('Packet Count : ', len(msg.packets))
    print ('======')
    for j, packet in enumerate(msg.packets):
        print ('Ts : ', packet.stamp, ' || Len : ', len(packet.data))
        break
    break

bag.close()