LiDAR: Light Detection and Ranging for 3D Reconstruction

What is LiDAR?

LiDAR, or Light Detection and Ranging, is a system that maps various structures, like height, density, etc, of any object around a region. It is also known as Active Laser Scanning. It can be used in various industries. For instance, it is used in vegetation also. This system can directly measure the height and density of the vegetation on the ground, which helps scientists study vegetation over a huge area.

It uses light in a pulsed laser form (in the form of optical pulses or light flashes), which can measure distance. These light pulses and other data points build precise 3-D information about any object related to the environment. It is faster than the RADAR or camera in detecting objects and calculating distance as it is unparalleled in dimensions and depth.

Working of LiDAR

LiDAR ranges the pulsed light to measure the distance to a target position. It is measured by sending a laser and recording the time taken from the source light pulse, and the reflected light pulse. As it is an active system, it generates energy by itself. In the LiDAR system, the light is released from a rapid-firing laser. Firstly, the light travels from the source, moves to the ground, and then reflects the light from the things to be observed. Then, the reflected light energy returns to the LiDAR sensor.

The Light Detection and Ranging system calculates the time from the source point to the destination. Then, the time calculated is used to calculate the distance between both points, which further calculates the elevation (the distance above the sea level). These measurements are measured with the help of the LiDAR system components consisting of the GPS system used to get the X, Y, and Z coordinates of the light energy and the Inertial Measurement Unit, which is used to determine the directions of the plane in the sky.

The LiDAR system is also used to measure the detailed features of the environment, like the scattering of particles, absorption, or emission in the atmosphere. The systems need specific wavelengths to determine these kinds of features in the environment. The LiDAR system can also measure rain droplets, the amount and intensity of rainfall, and different types of molecules like methane, aerosol, etc.

Many LiDAR systems give three-dimensional surfaces in the object space. It does not need any special spectral for observing the 3-D objects. It can be used to make 3-D structures or models in autonomous scenes. For example, the scenarios in driverless cars can be observed using the LiDAR system. Some scanning processes do this.

Process of the LiDAR System

The LiDAR systems give out laser beams ranging up to 150,000 pulses per second. Generally, the beams emitted out in a circular movement, just like RADAR, along with the up and down motion of the laser.

The LiDAR devices follow a basic process including a few steps:

1. The system emits signals in the form of laser beams.
2. The beam reaches the objects on the ground.
3. The object will reflect the beam.
4. The LiDAR system gets the signal back from the object on the ground.
5. It registers the Laser pulses.
6. The registered pulse gets a location in the LiDAR point cloud.

Some Other Applications of LiDAR

LiDAR is a wide technology and is used in various fields and areas. This includes:

• The most common and widely used application of LiDAR system is autonomous vehicles. The vehicles with the LiDAR system fitted in them gather data from it, including navigation, traffic signs, road obstructions, other vehicles passing by, etc., and observe the 3D vehicles with the help of the sensors and GPS built in the LiDAR system. It warns the vehicles about the moving and stationary objects around them (obstructions or other vehicles passing by).
• The LiDAR system is also used in astronomy to calculate the distance for objects in space, like the distance of the moon or any other planet. It is also used to observe stars for various astronomy applications.
• LiDAR can also be helpful in forests and land management as LiDAR can measure the density of the canopies formed in the forest. It can also be useful for analyzing land management, forest fire awareness, etc.
• LiDAR can also be used in producing renewable energies by calculating the requirements needed for them; as for solar energy, the LiDAR system will calculate the position of the solar panels. For wind energy, it can calculate the wind direction and speed for the formation of turbines.

LiDAR data and Computer Vision

LiDAR data can be useful for computer vision and supervised machine learning. To make it more effective, the LiDAR data must be labeled. It isn't easy to scale the data as it is huge. Scientists and artificial intelligence engineers face challenges while handling this kind of data. Because of the huge size of the data, it isn't easy to convert it into structured data and train the data that can understand the optical world.

Challenges faced by LiDAR

• The laser beam sent by the system is much larger than the output beam reflected by the object. The scientist must take care if the input beam does not reflect or scatter from the object.
• The beam light may get some debris while reflecting from the object.
• It is expensive to operate the LiDAR system. And also, it takes more time.
• The frequency of the laser source can be dangerous to human eyes.
• Differentiating the LiDAR and any other wavelengths nearby can be a task.