How can I use two velodyne(VLP16) together at the same time?

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Hello, I have a question about operating two velodyne laser sensors (VLP 16).

I’m a ROS and Ubuntu beginner. So, even if my question is inexperienced, please understand me and answer as in detail as possible. Thank you in advance.

I use Ubuntu 14.04 and ROS indigo. I’m trying to operate two velodyne laser sensors – VLP 16 simultaneously in one laptop. I designate IP of each sensors as 192.168.1.201 and 192.168.1.202. I fixed my laptop Ethernet IP as 192.168.1.77 to coincide bandwidth(?); I mean the third number of IP address like 192.168.”1”.77. I made two sensors connect to my laptop using hub. I use Velodyne package and modified “VLP16_points.launch” in velodyne_pointcloud folder and “nodelet manager.launch” in velodyne_drvier folder to operate at the same time.

In nodelet_manager.launch of velodyne_driver folder, I attached <arg name=”device_ip” default=”” /> under the source code <arg name=”model” default=”VLP16” /> and <param name=”device_ip” value=”$(arg device_ip)” /> under the source code <arg name=”frame_id” default=”veldyne” />

In VLP16_points.launch of velodyne_pointcloud folder, I made the source code as two group and tried to operate independently. First group is defined <group ns = “ns1”></group> and second group is defined <group ns = “ns2”></group>. The difference of two group’s source code is the only “device_ip”. I defined <arg name = “device_ip” value = “192.168.1.201”/> in first group and <arg name = “device_ip” value = “192.168.1.202”/> in second group. I thought because I designated the IPs differently it had to be implemented independently. But it was not.

I ran VLP16_points.launch and rviz , and topic of Pointcloud2 in rviz was presented /ns1/velodyne_points, /ns2/velodyne_points. As I pick the topic: /ns1/velodyne_points, pointcloud of two VLP16s appear simultaneously with regardless of IP address. I tried changing sensors’ IP and “device_ip” of VLP16_points.launch and nodelet_manager.launch. But regardeless of these change, pointcloud in rviz was appeared at the same time in topic /ns1/velodyne_points which is the topic of first group in VLP16_points.launch. When I pick the topic as /ns2/velodyne_points, no pointcloud appears. The terminal presents “bind: Address already in use” The Notice was not showed when I run only one VLP16. I hope to use the pointcloud independently to apply tf to sensors independently.

There were also other attempts in similar ways like operating two same launches which has “different device_ip”. But it also shows same result.

Thank you for reading this long question.

Have a nice day.