The KITTI Vision Suite benchmark was introduced in the previous post. In this post we are going to convert to “rosbags”, a format that is designed for development of ROS based autonomous systems.
Rosbag (or bag) is a file format for storing ROS message data. Bags are often created by subscribing to one or more ROS topics on a running system, and storing the received message data. But they can also be created programatically if sensor data is already saved in another format. Once you hava a bag you can replay the messages using the rosbag ROS package to aid testing and troubleshooting your robotics applications as well as developing new functionality.
To make this more concrete lets jump ahead and look at vizualising an example conversion. These videos were captured from RViz configured to subsribe to Pointcloud and Image data that originated as KITTI “raw_data” collected on {datetime} for drive number {drive}.
Pointcloud data from a Velodyne 360 laser scanner
Monochrome image from the left-hand monochrome stereo camera
The messages are contained in the file kitti_date_drive.bag and we would like to know what topics are available to playback. We can do this simply by using the rosbag info command after we have setup the ROS environment for our ROS distro {e.g. melodic, noetic} in the usual way:
source /opt/ros/{distro}/setup.bash
rosbag info kitti_{type}_{date}_{drive}.bag
This will generate output similar to this
path: kitti_raw_2011_10_03_0027.bag
version: 2.0
duration: 1:23s (83s)
start: Oct 03 2011 12:55:34.00 (1317639335.00)
end: Oct 03 2011 12:56:58.19 (1317639418.19)
size: 3.4 GB
messages: 14436
compression: none [3079/3079 chunks]
types: sensor_msgs/CameraInfo [c9a58c1b0b154e0e6da7578cb991d214]
sensor_msgs/Image [060021388200f6f0f447d0fcd9c64743]
sensor_msgs/PointCloud2 [1158d486dd51d683ce2f1be655c3c181]
tf2_msgs/TFMessage [94810edda583a504dfda3829e70d7eec]
topics: /camera/00/camera_info 4544 msgs : sensor_msgs/CameraInfo
/camera/00/image_rect 4544 msgs : sensor_msgs/Image
/tf_static 4544 msgs : tf2_msgs/TFMessage
/velo/pointcloud 804 msgs : sensor_msgs/PointCloud2
Now that we know what topics will be published we can configure coresponding subscriptions in RViz, but first we should ensure that bagfile is correctly indexed.
rosbag reindex kitti_{type}_{date}_{drive}.bag
If you are not using ROS2 we need to start ROS core in a new console (after setting up ROS):
source /opt/ros/{distro}/setup.bash
roscore
which should give you something like this
Press Ctrl-C to interrupt
Done checking log file disk usage. Usage is <1GB.
started roslaunch server http://workstation:45613/
ros_comm version 1.15.13
SUMMARY
========
PARAMETERS
* /rosdistro: noetic
* /rosversion: 1.15.13
NODES
auto-starting new master
process[master]: started with pid [6757]
ROS_MASTER_URI=http://workstation:11311/
setting /run_id to 4f23107c-4780-11ec-a8e7-e7a893b0327d
process[rosout-1]: started with pid [6775]
started core service [/rosout]
Now just hit play and our messages will be streamed just as if they were comming from a live source.
rosbag play kitti_{type}_{date}_{drive}.bag
producing something like this
[ INFO] [1637138257.188600355]: Opening kitti_raw_2011_10_03_0027.bag
Waiting 0.2 seconds after advertising topics... done.
Hit space to toggle paused, or 's' to step.
[RUNNING] Bag Time: 1317639334.934675 Duration: 0.000000 / 470.899880
[RUNNING] Bag Time: 1317639334.934833 Duration: 0.000158 / 470.899880
[RUNNING] Bag Time: 1317639334.998265 Duration: 0.063590 / 470.899880
[RUNNING] Bag Time: 1317639335.038506 Duration: 0.103831 / 470.899880
[RUNNING] Bag Time: 1317639335.098377 Duration: 0.163702 / 470.899880
[RUNNING] Bag Time: 1317639335.142415 Duration: 0.207740 / 470.899880
[RUNNING] Bag Time: 1317639335.198251 Duration: 0.263576 / 470.899880
...