Convert a Velodyne PCAP file into a ROS bag file

Normally Velodyne laser sensors record LiDAR data packets in PCAP format (*.pcap) file. If later on you want to process this recorded PCAP file in some SLAM algorithm in ROS e.g. ROS Cartogropher, then it may be necessary to convert it into a ROS bag file.

To convert the PCAP file e.g. HDL32-V2_Monterey_Highway.pcap, perform the following:

1.  Open up a Terminal. Enter the command to record the messages under the ROS topic /velodyne_points to an output bag file.
   
   $ rosbag record -O /path/to/output.bag /velodyne_points
   Note: /velodyne_points is the message to record. Leave blank if you want to record all messages.
   
2. Open up another Terminal. Change directory to the location of the PCAP file, e.g. /path/to/Downloads/.
   
   $ cd /path/to/Downloads
3. Enter the command to playback the Velodyne PCAP file and publish as a point cloud.
   
   $ roslaunch velodyne_pointcloud 32e_points.launch pcap:=$(pwd)/HDL32-V2_Monterey_Highway.pcap readonce:=true
   
   
   Note: this command publishes a HDL-32E PCAP file as a point cloud.
4. Wait until the PCAP file is fully read. You can use the following command in another Terminal to check if anymore data is published.
   
   $ rostopic echo /velodyne_points
   
   A stream of points appear.
   
5. When no more messages appear, the PCAP file is fully read. In the first Terminal, press CTRL-C to interrupt and complete the recording process to the bag file.
   
   The bag file is created.