This is for using Multi velodyne
You can use multiple veloydne with edited launch file.
( velodyne_pointcloud/launch/VLP16_points_multi.launch)
To use multiple devices, You should edit each device's ip and port before editing launch file.
You can edit on the velodyne configuration screen. For further information, please refer to velodyne maunal.
After edting the configuration, you should also edit on the launch files
Now, you can use multiple velodynes!