writing_lidar_tutorial_python.md

WritingLidarTutorial(python)

Description: This tutorial covers how to write a lidar tutorial in Python. Tutorial Level: BEGINNER Next Tutorial: Examining the simple lidar tutorial

Table of Contents

• Writing a Simple lidar tutorial (Python)
  • create beginner_tutorials directories
  • The Code Explained

Writing a Simple lidar tutorial (Python)

Description: This tutorial covers how to write a LiDAR data console program in Python. Tutorial Level: BEGINNER

create beginner_tutorials directories

mkdir beginner_tutorials
cd beginner_tutorials

Create the lidar_tutorial.py file within the beginner_tutorials project and paste the following inside it:

https://github.com/YDLIDAR/ydlidar_tutorials/blob/master/pyhton_tutorials/lidar_tutorial/lidar_tutorial.py

import os
import ydlidar

if __name__ == "__main__":
    ydlidar.os_init();
    laser = ydlidar.CYdLidar();
    ports = ydlidar.lidarPortList();
    port = "/dev/ydlidar";
    for key, value in ports.items():
        port = value;
    laser.setlidaropt(ydlidar.LidarPropSerialPort, port);
    laser.setlidaropt(ydlidar.LidarPropSerialBaudrate, 512000);
    laser.setlidaropt(ydlidar.LidarPropLidarType, ydlidar.TYPE_TOF);
    laser.setlidaropt(ydlidar.LidarPropDeviceType, ydlidar.YDLIDAR_TYPE_SERIAL);
    laser.setlidaropt(ydlidar.LidarPropScanFrequency, 10.0);
    laser.setlidaropt(ydlidar.LidarPropSampleRate, 20);
    laser.setlidaropt(ydlidar.LidarPropSingleChannel, False);

    ret = laser.initialize();
    if ret:
        ret = laser.turnOn();
        scan = ydlidar.LaserScan()
        while ret and ydlidar.os_isOk() :
            r = laser.doProcessSimple(scan);
            if r:
                print("Scan received[",scan.stamp,"]:",scan.points.size(),"ranges is [",1.0/scan.config.scan_time,"]Hz");
            else :
                print("Failed to get Lidar Data.")
        laser.turnOff();
    laser.disconnecting();

The Code Explained

Now, let's break the code down.

import ydlidar

You need to import ydlidar if you are writing a YDLIDAR SDK.

  ydlidar.os_init();

Initialize system signal. install a SIGINT handler which provides Ctrl-C handling

  laser = ydlidar.CYdLidar();

Create a handle to this Lidar.

    ports = ydlidar.lidarPortList();
    port = "/dev/ydlidar";
    for key, value in ports.items():
      port = value;

Query avaliable Lidar ports.

    laser.setlidaropt(ydlidar.LidarPropSerialPort, port);
    laser.setlidaropt(ydlidar.LidarPropSerialBaudrate, 512000);
    laser.setlidaropt(ydlidar.LidarPropLidarType, ydlidar.TYPE_TOF);
    laser.setlidaropt(ydlidar.LidarPropDeviceType, ydlidar.YDLIDAR_TYPE_SERIAL);
    laser.setlidaropt(ydlidar.LidarPropScanFrequency, 10.0);
    laser.setlidaropt(ydlidar.LidarPropSampleRate, 20);
    laser.setlidaropt(ydlidar.LidarPropSingleChannel, False);

Set Lidar property paramters.

  // initialize SDK and LiDAR
  ret = laser.initialize();

Initialize the SDK and LiDAR.

initialize will return false if:

• Serial port does not correspond to the actual Lidar.
• Serial port does not have read and write permissions.
• Lidar baud rate settings error.
• Incorrect Lidar type setting.

      if ret:
        ret = laser.turnOn();

Start the device scanning routine which runs on a separate thread and enable motor.

turnOn will return false if:

• Lidar stall.
• Lidar power suppy is unstable.

  // Turn On success and loop  
  while ret and ydlidar.os_isOk() :

By ydlidar.os_isOk() will install a SIGINT handler which provides Ctrl-C handling which will cause ydlidar.os_isOk() to return false if that happens.

ydlidar.os_isOk() will return false if:

• a SIGINT is received (Ctrl-C)
• ydlidar.os_shutdown() has been called by another part of the application.

Once ydlidar.os_isOk() returns false, Loop exit.

      r = laser.doProcessSimple(scan);
      if r:
        print("Scan received[",scan.stamp,"]:",scan.points.size(),"ranges is [",1.0/scan.config.scan_time,"]Hz");
      else :
        print("Failed to get Lidar Data.")

Get the LiDAR Scan Data.

  // Stop the device scanning thread and disable motor.
  laser.turnOff();

Stop the device scanning thread and disable motor.

  // Uninitialize the SDK and Disconnect the LiDAR.
  laser.disconnecting();

Uninitialize the SDK and Disconnect the LiDAR.

Now that you have written a simple lidar tutorial, let's examine the simple lidar tutorial.