error gen_calibration.py: unable to read 32db.xml

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Most likely ROS cannot find the 32db.xml file, however if you're using a VLP16 you should be using a different calibration file. If I'm not mistaken, the 32db.xml file is for the HDL-32E Velodyne LiDAR. For a VLP16 you'll need the VeloView-VLP-16-HiRes.xml file that came on the USB flash drive or CD that was included with your LiDAR. So if you run this step wherever you place the calibration xml, your command would look like this:

rosrun velodyne_pointcloud gen_calibration.py VeloView-VLP-16-HiRes.xml

When running the next command in the tutorial, you'll also want to use the VLP16_points.launch instead of 32e_points.launch So the next command you should run is:

roslaunch velodyne_pointcloud VLP16_points.launch calibration:={Path to}\VeloView-VLP-16-HiRes.yaml

From there, just run rviz like the tutorial says to see the pointcloud.