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Online LiDAR - Advanced Topics

1 Introduction

The RoboSense LiDAR may work

  • in unicast/multicast/broadcast mode,
  • with VLAN layer
  • with user layers.
  • Also rslidar_sdk supports multi-LiDARs.

This document illustrates how to configure rslidar_sdk in each case.

Before reading this document, please be sure that you have read:

2 Unicast, Multicast and Broadcast

2.1 Broadcast mode

The Lidar sends MSOP/DIFOP packets to the host machine (rslidar_sdk runs on it). For simplicity, the DIFOP port is ommited here.

  • The Lidar sends to 255.255.255.255 : 6699, and the host binds to port 6699.

Below is how to configure config.yaml.

common:
  msg_source: 1                                       
  send_point_cloud_ros: true                            

lidar:
  - driver:
      lidar_type: RS32           
      msop_port: 6699             
      difop_port: 7788            
    ros:
      ros_frame_id: rslidar           
      ros_send_point_cloud_topic: /rslidar_points

The common part and the lidar-ros part is listed here. They will be ommited in the following examples, since they are not changed.

2.2 Unicast mode

To reduce the network load, the Lidar is suggested to work in unicast mode.

  • The Lidar sends to 192.168.1.102 : 6699, and the host binds to port 6699.

Below is how to configure config.yaml. In fact, it same with the broadcast mode.

lidar:
  - driver:
      lidar_type: RS32           
      msop_port: 6699             
      difop_port: 7788

2.3 Multicast mode

The Lidar may also works in multicast mode.

  • The lidar sends to 224.1.1.1:6699
  • The host binds to port 6699. And it makes local NIC (Network Interface Card) join the multicast group 224.1.1.1. The local NIC's IP is 192.168.1.102.

Below is how to configure config.yaml.

lidar:
  - driver:
      lidar_type: RS32           
      msop_port: 6699             
      difop_port: 7788
      group_address: 224.1.1.1
      host_address: 192.168.1.102

3 Multiple LiDARs

3.1 Different remote ports

If you have two or more Lidars, it is suggested to set different remote ports.

  • First Lidar sends to 192.168.1.102:6699, and the first driver instance binds to 6699.
  • Second Lidar sends to 192.168.1.102:5599, and the second driver instance binds to 5599.

Below is how to configure config.yaml.

lidar:
  - driver:
      lidar_type: RS32           
      msop_port: 6699             
      difop_port: 7788
  - driver:
      lidar_type: RS32           
      msop_port: 5599
      difop_port: 6688

3.2 Different remote IPs

An alternate way is to set different remote IPs.

  • The host has two NICs: 192.168.1.102 and 192.168.1.103.
  • First Lidar sends to 192.168.1.102:6699, and the first driver instance binds to 192.168.1.102:6699.
  • Second Lidar sends to 192.168.1.103:6699, and the second driver instance binds to 192.168.1.103:6699.

Below is how to configure config.yaml.

lidar:
  - driver:
      lidar_type: RS32           
      msop_port: 6699             
      difop_port: 7788
      host_address: 192.168.1.102
  - driver:
      lidar_type: RS32           
      msop_port: 6699
      difop_port: 7788
      host_address: 192.168.1.103

4 VLAN

In some user cases, The Lidar may work on VLAN. Its packets have a VLAN layer.

The driver cannot parse this packet. Instead, it depends on a virtual NIC to strip the VLAN layer.

Below is an example.

  • The Lidar works on VLAN 80. It sends packets to 192.168.1.102 : 6699. The packet has a VLAN layer.
  • Suppose there is a physical NIC eno1 on the host. It receives packets with VLAN layer.

To strip the VLAN layer, create a virtual NIC eno1.80 on eno1, and assign IP 192.168.1.102 to it.

sudo apt-get install vlan -y
sudo modprobe 8021q

sudo vconfig add eno1 80
sudo ifconfig eno1.80 192.168.1.102 up

Now the driver may take eno1.80 as a general NIC, and receives packets without VLAN layer.

lidar:
  - driver:
      lidar_type: RS32           
      msop_port: 6699             
      difop_port: 7788

5 User Layer, Tail Layer

In some user cases, User may add extra layers before or after the MSOP/DIFOP packet.

  • USER_LAYER is before the packet and TAIL_LAYER is after it.

These extra layers are parts of UDP data. The driver can strip them.

To strip them, just give their lengths in bytes.

In the following example, USER_LAYER is 8 bytes, and TAIL_LAYER is 4 bytes.

lidar:
  - driver:
      lidar_type: RS32           
      msop_port: 6699             
      difop_port: 7788
      user_layer_bytes: 8
      tail_layer_bytes: 4