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Difference between LiDAR and Time of Flight | LiDAR vs ToF sensor

This page compares LiDAR vs ToF (Time of Flight) technologies and mentions difference between LiDAR and Time of Flight (ToF) sensor.

Introduction : There are various depth sensing technologies which include Radar, Ultrasound, LiDAR, 2D camera with NIR illumination, Stereo vision, Structured Light and 3D Time of Flight (ToF). All these technologies are used for various applications based on their performance, accuracy, cost, response time, power consumption and range. The typical applications are Games, 3D movies, 3D scanning, User interface control, Augmented reality, autonomous driving, robotics, gesturing, 3D printing, enemy target detection, Safety of premises by monitoring surroundings etc.

What is LiDAR ?

LiDAR is the short form of Light Detection and Ranging. It is also known as LADAR. LiDAR uses laser diode or LED to emit infrared light. At the receiver LiDAR uses photo-receptor to sense any reflected light rays. The time interval and phase of reflections help in distance calculation of the object. It uses pulsed lasers in order to build "point cloud" of desired surface under measurement. This is used to create 3D image or map.

LIDAR or LADAR Block Diagram

LiDAR is optical sensing technique used to estimate range of target and its other parameters. It uses different laser wavelengths based on target material. It uses NIR (Near Infrared) and VL (Visible Light) frequencies to image the objects under surveillance.
Refer LiDAR basics >> and difference between LiDAR vs RADAR >>, its advantages and disadvantages for more information.

What is Time of Flight Sensor ?

As shown, ToF sensor illuminates scene with modulated light and captures reflected light. It uses phase shift between emitted light and received reflection to determine distance. ToF apps construct depth maps using RGB camera as per reflected light detection from the target object or plane.

It uses solid state laser or LED at near infrared range of about 850nm. Imaging sensor is used to receive the reflected light spectrum. This image sensor converts photonic energy to electric current.

Time of Flight (ToF) measurement

➨ Depth, d = c*ΔT/2;
Where c = Speed of light which is 3 x 108 m/s
ΔT = Time interval between light emission and received light by the camera sensor

There are various methods to measure ΔT. The most common methods are CW method and pulse based method.
CW method : It uses periodic modulated signal source typically a sinusoid or square waveform for active illumination. CW ToF sensors measure the distance at each of the pixels by sampling correlation function of received and demodulating signals.
Pulse based method : In this method, illuminating source emits series of short light pulses. Reflected light pulses are captured in series of short temporal windows using sensor equipped with electronic shutter.

Difference between LiDAR and Time of Flight Sensor

Following table mentions difference between LiDAR and Time of Flight (ToF) sensor technologies.

Comparison parameters LiDAR 3D ToF Sensor
Operating principle It emits laser signals and measures reflection from obstacle to calculate time and consecutively distance. It illuminates scene using modulated light source and observes reflected light. It uses solid state lased or LED for illumination and imaging sensor for reflected light detection. At the receiver, photonic energy is converted into electrical current.
Range Higher Medium
Field of View (FoV) Medium High
Resolution of the sensor Low/medium High
Accuracy of distance measurement Medium High
Performance of object classification Lower Higher
Processing cost to calculate distance Lower Medium

➨Also refer DToF vs IToF >> for difference between Direct ToF sensor and Indirect ToF Sensor.



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