LiDAR, or Light Detection and Ranging is a remote sensing technology which uses rapid pulses of a near infrared laser to measure the earth's surface and generate a survey accurate point cloud model.
LiDAR has revolutionised the surveying, mapping and civil engineering industries over the past 25 years. Recent advances in LiDAR technology have further improved the accuracy and quality of LiDAR data and resulted in smaller sensors which can today be mounted onto drones (RPAS/UAV), cars or trains.
How do LiDAR sensors or detectors work?
LiDAR sensors are based on rapid pulses of near infrared laser light. A laser is fired from the sensor towards the target, and the time taken for a return signal to bounce back to the sensor is recorded. This time is known as the time of flight. This system operates in a similar manner to Sonar or Radar.
LiDAR sensors or detectors are capable of a very high frequency operation and it is common for LiDAR data collection acquisition rates of over 1 million points per second.
Aircraft mounted LiDAR systems can be flown at high altitudes and high speeds, allowing enormous swaths of data to be captured in a single flight. Equally LiDAR detectors, such as mobile laser scanners can be mounted on cars and trains, collecting data quickly at speeds of up to 100km/h.
How accurate is a LiDAR scan?
Aerial LiDAR can come in a range of accuracies. Typical accuracies for aerial LiDAR are between +/- 0.1m-0.5m.
The density of the data is also a significant consideration which can greatly impacted on the accuracy of final data model. The higher the density the more accurately a model can be produced, better representing the true site conditions. Typical densities range from 1p/m2, up to 8p/m2 (point/m2).
Understanding LiDAR Benefits
Since it is a remote sensing method of measurement it is not as accurate a data source as direct measurement methods such as a traditional field-based survey method. However it is possible to achieve much greater data density or data resolution, which in some cases can be more valuable than absolute accuracy, especially when working over large areas such as long corridors for road and rail design or entire water catchments for flood analysis.
What is a LiDAR 3D Point Cloud?
A LiDAR 3D point cloud is the resulting data set from a LiDAR survey. The point cloud is a collection of millions of discrete points. The density of these points makes the data set appear as a 3D copy of the real world.
How do you interpret LiDAR data?
There are many ways to work with LiDAR data. Typically the point cloud data will be imported into survey or engineering design software and further modelling will be undertaken to convert the point cloud into a 3D model.
The LiDAR point cloud may be converted into a continuous ‘Mesh’ surface or ‘TIN’ “Triangulated Irregular Network”. These are surface models simulating the natural surface and can be used within design or analysis software depending on the task at hand.
LiDAR and machine vision
LiDAR technology is well established as a foundation of many machine vision systems, with the ability to measure or ‘see’ in front of some of the largest pieces of autonomous machinery around the world, including many of the worlds largest mining trucks and machinery such as stacker/reclaimers.
More recently with the push towards autonomous self-driving vehicles, LiDAR technologies have seen a rapid increase in development and significant reduction in size and cost, with sensor manufacturers such as Velodyne & Luminar seeing rapid uptake in technology and significant growth in the automotive LiDAR market which today is worth an estimated $1.5b (US)
Machine vision and automotive grade LiDAR differs from remote sensing and survey grade systems, in that the accuracies and scale of data captured for remote sensing is many orders of magnitude greater than what is required for machine vision. However, as these new markets emerge and technology continually develops, improvements to both hardware and software are flowing rapidly between the two sectors of the LiDAR market.