Perception Blog: Technology Comparison -Flash and Scanning LiDAR

 

A blog post by
David Brodie BSc (Eng), Sr. Project Manager of Perception and AI, LeddarTech®

 

My name is David Brodie.  In March 2019 I joined LeddarTech as the Product Manager responsible for Perception and AI.  With this occasional blog, I hope to create a platform to exchange ideas on technology and solution related to perception.  I intend to discuss a selection of topics, some at a high level; some in more technical detail. 


 

To start with let’s consider a high-level analysis of one of the classic problems which every autonomous vehicle faces: detecting debris or small objects.   Especially, I want to compare how scanning and flash lidar perform on this problem.

A scanning lidar that surveys its environment using several scan lines is shown symbolically in the following figure.

Figure 1: a scanning lidar’s view of the world

Theoretically, all four small objects could be detected.  Objects 1 and 3 are detected as they are directly in the path of some scan line.  Although object 2 is nearer than object 3 it is not detected as it falls between scan lines.  Similarly, object 4 is not detected in range as it too falls between scan lines.  As a scanning lidar approaches a small object, the object will be detected and lost with increasing frequency until it is close enough to be hit by a scan line in every frame.

The following figure shows the same scene surveyed by a flash lidar like LeddarTech’s Pixell.

Figure 2: flash lidars view of the world

In this case, the entire field of view of the lidar is illuminated.  Rather than detecting point reflections, the flash lidar detects reflections from a “segment” of the illuminated area.  Once an object becomes detectable it is continuously detected as there are no gaps in the illumination.  There are challenges here too.  Object 4 only fills a small section of the relevant segment.  Object 3 is larger but split across multiple segments and so also only fills a small portion of each segment.  It may not be easy to detect but with good beam steering and signal processing, it is possible.  Once an object becomes detectable; it is reliably detected from then on.

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