LiDAR and Time of Flight

A LiDAR fires short laser pulses and times their return, like sonar with light. Light is fast and its beam is narrow, so a spinning LiDAR gives hundreds of sharp range points per turn. This is the main sensor for indoor robot mapping.

Angular resolution Maximum range Range noise Show the rays Drive the robot

Range from time of flight

Light travels at $c \approx 3\times10^8$ m/s, so a 10 m target returns its pulse in about 67 nanoseconds. The range and the gap between neighboring points at distance $r$ are

$$d = \frac{c\,t}{2} \qquad s = r\,\Delta\theta$$

with $\Delta\theta$ the angular resolution in radians.

What to notice

Points get farther apart with distance, so small or thin objects far away can fall between rays. The light blue wall is glass: most of the laser passes through, so it returns nothing and the wall is invisible. The thick black wall is a dark surface: it absorbs light, so returns drop out far away. Mapping software has to cope with both, and robots often add a bumper or sonar to catch glass.