How to use lidar

Note: The baud rate is different between A1/A2<115200>, A3/S1<256000> and S2<1000000>.

Note: The information of the lidar M2M2 and the radar of this course (A1/A2/A3/S1/S2) are different, please view the information according to the corresponding model

Note: "Slan Lidar Course" is based on the use of Transbot crawler vehicles, for reference only! ! !

Lidar technology support Email ：support@slamtec.com

Lidar wiki：http://wiki.ros.org/rplidar

Lidar SDK：https://github.com/Slamtec/rplidar_sdk

Lidar ROS：https://github.com/Slamtec/rplidar_ros

Lidar tutorials：https://github.com/robopeak/rplidar_ros/wiki

Lidar website：http://www.slamtec.com/cn/Support

Test the PC computer：https://www.slamtec.com/cn/RoboStudio

1、Overview

Single-line lidar refers to a single-line laser beam emitted by the laser source. It is divided into triangular ranging and TOF lidar. It is mainly used in the field of robotics.

2、Silan lidar components

Take SLAMTec lidar as an example, which is mainly composed of 4 core components: laser, receiver, signal processing unit and rotating mechanism.

2.1、Laser

The laser is the laser emitting mechanism in the lidar. During work, it will light up in pulses.

The RPLIDAR A3 series lidar of SLAMTec will turn on and off 16000 times per second.

2.2、Receiver

After the laser emitted by the laser hits the obstacle, the reflected light will be converged on the receiver through the lens group through the reflection of the obstacle.

2.3、Signal processing unit

The signal processing unit is responsible for controlling the emission of the laser and processing the signal received by the receiver.

Based on this information, the distance information of the target object is calculated.

2.4、Rotating mechanism

The above three components constitute the core part of the measurement.

The rotating mechanism is responsible for rotating the above-mentioned core components at a stable speed, so as to realize the scanning of the plane and generate real-time plan information.

3、Principle of single-line lidar

The working principle of the radar is shown in the figure below:

3.1、Triangular Ranging Method

3.1.1、Direct shot

3.1.2、Oblique shot

3.2、TOF Ranging Method

4、Lidar parameter comparison

It can be seen from the figure above that parameters such as measurement radius, sampling speed, scanning frequency, and angular resolution are important indicators of radar performance.

5、Application scenarios

Lidar plays an indispensable role in many fields such as autonomous robot positioning and navigation, spatial environment mapping, and security.

6、Run rplidar node

6.1、Build the rplidar ros package

Function download link：https://github.com/Slamtec/rplidar_ros/

Clone this feature pack to your workspace src folder

Run catkin_make to build rplidarNode and rplidarNodeClient

Note: If you do not write the update environment variable to【.bahsrc】, you must update the environment variable before each execution of the running program.

source devel/setup.bash  # Update environment variables

6.2、Remap the USB serial port

Under the path of rplidar_ros function package, install USB port remapping:

xxxxxxxxxx
./scripts/create_udev_rules.sh

Use the following command to modify the remapping:

xxxxxxxxxx
ls -l /dev | grep ttyUSB

After changing the USB port and remapping, change the startup file related to the serial_port value.

6.3、Run rplidar ros package

• Method 1

Run rplidar node, view in rviz

xxxxxxxxxx
roslaunch rplidar_ros view_rplidar.launch    # RPLIDAR A1/A2
roslaunch rplidar_ros view_rplidar_a3.launch # RPLIDAR A3
roslaunch rplidar_ros view_rplidar_s1.launch # RPLIDAR S1
roslaunch rplidar_ros view_rplidar_s2.launch # RPLIDAR S2

You can see rplidar scan results in rviz.

• Method 2

Run rplidar node

xxxxxxxxxx
roslaunch rplidar_ros rplidar.launch    # RPLIDAR A1/A2
roslaunch rplidar_ros rplidar_a3.launch # RPLIDAR A3
roslaunch rplidar_ros rplidar_s1.launch # RPLIDAR S1
roslaunch rplidar_ros rplidar_s2.launch # RPLIDAR S2

Start the test application

xxxxxxxxxx
rosrun rplidar_ros rplidarNodeClient

You should see rplidar scan results in the console

7、RoboStudio test

Test tool download link：https://www.slamtec.com/cn/RoboStudio

Take S1M1 radar as an example, other models are similar.

7.1、Install

Double-click robostudio icon to install, and continue to the next step until the installation is complete. Adjust the radar to the corresponding baud rate [A1/A2: 115200, A3/S1: 256000, S2: 1000000].

Using the original data cable to connect the device (for example: PC).

7.2、View device

由上图可知道，激光雷达的端口是【COM2】。

7.3、Log in

Log in for the first time, you need to register before you can use it. Select [Radar], right-click in the blank area of the radar bar, and select [Manually connect to radar...].

7.4、Connect

Select the corresponding [COM2], and click [Connect].

7.5、Test

Enter the test interface, click the green triangle to start the lidar test.

We can view the basic information of the radar: model [S1M1], sampling frequency [9K], scanning frequency [10.02Hz], etc.

8、frame_grabber

8.1、View device

The operation is the same as in 7.2.

8.2、connect

Select the corresponding port [COM2] and baud rate [256000], and click [OK].

8.3、Start up

Click as shown in the figure below to activate the button.

The effect diagram is as follows.